Today's Message Index:
----------------------
1. 02:06 AM - Re: Trutrak AP with Garmin GPS 18x 5Hz (D McFadyean)
2. 04:22 AM - Re: Trutrak AP with Garmin GPS 18x 5Hz (David Cripps)
3. 07:55 AM - Re: Trutrak AP with Garmin GPS 18x 5Hz (D McFadyean)
4. 08:48 AM - Re: Trutrak AP with Garmin GPS 18x 5Hz (David Cripps)
5. 09:30 AM - Re: Trutrak AP with Garmin GPS 18x 5Hz (Rowland Carson)
6. 02:30 PM - Re: Trutrak AP with Garmin GPS 18x 5Hz (Dpc)
Message 1
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| Subject: | Re: Trutrak AP with Garmin GPS 18x 5Hz |
I'd not seen before the clip on the servo arm; there was an earlier Factory
'fix' of Loctited replacement screws. Later servos have a stud and pinned
locknut instead (I guess the stud is held in only by Loctite!).
The control column stops should take priority, as the servo stops are proba
bly too light to limit enthusiastic control movements by the pilot, but sho
uld at least contain a runaway servo or some other breakage in the servo. I
might have some spare stops (if I can find them). The stops are half-visib
le and annotated 'F' in the photo at: TruTrak-RV10-Roll-Installation-Guide.
pdf (bendixking.com) https://www.bendixking.com/content/dam/bendixking/en/d
ocuments/document-lists/downloads-and-manuals/TruTrak-RV10-Roll-Installatio
n-Guide.pdf
The shear pin is merely a 6-32 screw with a short part of its length (where
this crosses the interface between the mating arm and hub) necked and poli
shed to the roots of the screw thread.
My own servo is mounted towards the back of the Europa 'tunnel' and connect
s to a horn bolted to the rear end of the roll torque tube. This area used
to get hot under certain situations via heat from the stainless firewall an
d no tunnel ventilation. Subsequently a 'fire blanket' (two thin layers of
woven Kevlar with thin fibreglass loft insulation sandwiched between, rathe
r like Orkotek) placed on the back of the firewall enabled cooler temperatu
res. I've not heard of the standard under-seat servo location getting too h
ot.
Duncan McF.
> On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com> wrote:
>
>
> Thank you for the comprehensive reply, Duncan, and also for the repli
es from Alan and Peter. I really appreciate the feedback.
>
>
>
> It seems that the Skymap III should work OK for us, despite its 0.5Hz
data refresh rate. A bit of =98hunting=99 shouldn=99t re
ally be a problem. We hadn=99t planned to have it fly a full route an
d navigate itself around turning points. I had thought we=99d be manu
ally changing the selected track at each turning point, and then lock the t
racking to the new direction required. However, the Skymap III does have a
=98Turn Anticipation=99 feature if we should in the future want
it to follow a route, and not overshoot a waypoint. Do most people use it
to follow a full track, and make all the waypoint turns?
>
>
>
> Good to know about the shear pin in the arm as a last resort! Do you
have any drawing of the necked stainless pin that you got the LAA to agree
to?
>
>
>
> The servo that I have came out of an old Europa and didn=99t se
em to have any physical stops on the servo arm. It did, however, have the e
xtra alloy =98clip=99 to secure the screw that attaches the arm
to the servo. I=99ve seen that that clip was an LAA requirement too
(see photo). For the physical stops, I did see on another forum something t
hat looked like it would do the job on this servo (may even have been a Tru
trak part). Does the LAA specify what these stops should look like or be ma
de of? Should they be set so that the servo arm touches them at the same ti
me as the control column reaches its full deflection (if not, then which st
op should =98take priority=99 and be hit first)? Does anyone ha
ve a photo of what the stops look like in their setup? I imagine them being
mounted on the bolts that attach the servo motor to its mounting frame.
>
>
>
> My servo would be mounted under the pax seat per Mod 75, so there is
not really any ventilation there. Is it worth adding a little cooling fan t
o the seat locker to keep the air circulating around the servo?
>
>
>
> Many thanks for all the input!
>
> David
>
> i). The Trutrak will work on a Europa at 0.5Hz update frequency (i.e.
every 2 seconds). Sometimes the AP will hunt gently (yesterday was a case
in point, but there were sites yesterday that were GPS-jamming as well, so
that might have been a cause' or possibly I have a too low torque setting t
han optimal in order to limit servo overheating). If too many options of ou
tput data are requested in the GPS NMEA output setup then there won't be en
ough time to output all that data within a faster update period; the GPS se
t will normally tell you if this is going to be the case.
>
> iii). The servo does not care about torque feedback. The servo will p
rovide a force (torque) only up to the maximum value that has been preselec
ted.
>
> iv). The Europa needs quite a high torque setting (10 or 12 from memo
ry, which can on hot days plus a high 'activity' setting result in servo ov
erheating and shutdown if you have a trigear with 'heated'/unventilated fus
elage tunnel and depending where the servo is mounted).
>
> The pilot stick force required to overcome maximum torque will be app
lied without even thinking about it and in any case there is a necked brass
shear pin (comprising a modified 6-32 brass instrument mounting screw) in
the servo arm that can be easily sheared (even without knowing it, and then
you wonder why the AP is not tracking!). I agreed with LAA to replace this
with a (necked) stainless steel pin in order to provide a little more stre
ngth and haven't sheared it since.
>
> I also think that when the servo gets very hot (as above) it's intern
al voltage regulator starts to shut down (as many are designed to do). Agai
n, there is no way of knowing when this happens until realisation that the
AP is not tracking!
>
> v). The LAA will insist upon the stops on the servo, although these s
tops are not particularly robust and the set up would be better adjusted so
that the stops never have to resist the pilot's stick inputs.
>
> Otherwise, the Trutrak system and its dynamics work extremely well an
d can do a much better job than the pilot, especially in turbulent conditio
ns.
>
> Have you found a setting on your Skymap that allows adjustment of the
pre-emptive steering sensitivity (or "turn anticipation")?
>
>
>
> Duncan McF.
>
> > >
> > On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com m
ailto:dpc@knightonweb.com > wrote:
> >
> >
> > So, I've slowly been making some progress on this, having mocke
d up the whole system out of the aircraft. I have now been able to test it
in the workshop and yesterday in a car (it needed to be moving to get a tra
ck signal). See attached photo. However, I now have a couple more questions
/observations!
> >
> > i) It seems that the Skymap III that I used in these tests work
s in terms of making the servo move and display a track on the Trutrak, so
that's progress! However, I note from the Skymap manual that it only gives
its GPS info every 2 seconds, rather than the once every second that the Tr
utrak recommends to avoid 'wandering'. Peter, in your post you mentioned th
at you were using a Skymap III - have you ever had a problem with this (ass
uming your A/P is the Trutrak Digitrak too)? Alan, is the Garmin 196 that y
ou've mentioned as suitable, able to be set to give data at the 'once per s
econd' rates, as from the manual it seems it may too default to once every
2 seconds?
> >
> > ii) I noticed when testing in the car, that when the track that
was displayed in the Trutrak was close to what we were actually tracking (
as read from the Skymap), that the servo was more or less static, and moved
in the correct direction when there was a small deviation between what was
set on the Trutrak and what we were tracking. However, because our roads a
re not straight, there were frequently occasions when the actual track from
the Skymap was miles away from that set on the Trutrak. In that situation
the servo went a bit crazy and rotated its arm by many more degrees than it
could ever do in the plane. Is this to be expected in this rather 'offline
' mode? I can imagine that when the Trutrak senses that its control input i
s not creating the sort of aircraft track change that it had expected, that
it just moves the servo even further in order to try to get aircraft to do
something?
> >
> > iii) Clearly my mock-up does not provide any sort of 'force fee
dback' to the servo control arm (ie the arm is completely free to rotate as
it likes). In an aircraft, would this be taken care of by aerodynamic feed
back via the aileron torque tube? What happens to the servo when it reaches
the full movement that the aileron would allow (the point when the control
column hits its roll stops)?
> >
> > iv) I can imagine that I wouldn't want the servo ever applying
full aileron to create a turn as that would make for a very violent manoeuv
re! I see that there are settings that can be adjusted in the Trutrak set-u
p menus that control activity level and also control maximum torque. What v
alues have people set in theirs? I note that when I have set the recommende
d value of 12 for the torque, it is almost impossible to override the servo
arm when the A/P is engaged (though I appreciate that with no control colu
mn attached the leverage I can apply to the servo arm with my fingers is ve
ry low. I also appreciate that normally if one wanted to override the A/P y
ou would disengage it first).
> >
> > v) Lastly (for now!) has anyone fitted physical 'stops' to the
servo body that the servo arm would hit to ensure that the servo can never
try to move the pushrod beyond the point where full aileron is applied?
> >
> > Apologies for all the questions but I want to make sure it is r
eally working correctly before I contort myself to fit it into the aircraft
itself!
> >
> > Best regards
> >
> > David
> >
> > On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-server@
matronics.com mailto:owner-europa-list-server@matronics.com <mailto:owner-e
uropa-list-server@matronics.com mailto:owner-europa-list-server@matronics.c
om > on behalf of alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk <mailto:alanb@
dpy01.co.uk mailto:alanb@dpy01.co.uk >> wrote:
> >
> >
.uk mailto:alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk mailto:alanb@dpy01.c
o.uk >>
> >
> >
> > Ok I=99ve had a. Ha ce to fly mine with the GPS feed off.
> >
> >
> > As Duncan says below the display drops to show -|=94|- bu
t maintains the track last set or you are holding when you switch it on.
> >
> >
> > The are no heading digits on the display so you will need use y
our compass/DI to show that.
> >
> >
> > If you press the left or right =A4=B5=EF=B8=8F buttons then
you can alter the track the AP is following either left or right and a numb
er appears which if you press the button you can increase or decrease after
the AP locks on the numbers disappear and you have the -|=94|- on th
e display.
> >
> >
> > Useful if you have a GPS failure but wouldn=99t want that
as normal mode of operation so my suggestion is you need a GPS feed with t
he right NEMA message set to get the most out of the AP and the ability for
it to follow a track you have programmed in is a bonus.
> >
> >
> > One word of caution, I have come across some GPS that don
=99t put out any messages, even the position message for driving a Transpon
der ADS-B output, unless there is a track in the GPS. That was how some of
the older version worked, GARMIN 430 and possible the early AVMAP were guil
ty of that.
> >
> >
> > Hope that helps.
> >
> >
> > Alan
> >
> >
> > Sent from my iPad
> >
> >
> > > > >
> > > On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talk
talk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktalk.n
et mailto:ami-mcfadyean@talktalk.net >> wrote:
> > >
yean@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@t
alktalk.net mailto:ami-mcfadyean@talktalk.net >>
> > >
> > > Digitrak only needs basic positional information from the
GPS on a regular basis. It will use this information to fly the track that
has been set on the Digitrak.
> > > If a route is programmed in to the GPS, it will fly that
too (with different commands being set at the Digitrak control head to enab
le this), so long as the GPS is also putting out the crosstrack error signa
l; not all of them do.
> > >
> > > Duncan McF.
> > >
> > > > >
> >
> >
> >
> >
> > s.com/Navigator?Europa-List>
> > ion>
> >
> >
> >
> >
> >
> >
> >
> > >
Message 2
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| Subject: | Re: Trutrak AP with Garmin GPS 18x 5Hz |
Thanks very much for this extra info, Duncan.
If you can find that spare stop that would be great. I had seen a picture s
imilar to the one you sent of the stops in another aircraft application.
Following your comments about the shear pin, I think this is the small bras
s screw located just above the main central cross-head screw that holds the
control arm onto the servo in the photo I=99ve attached here? I looked at mi
ne more closely and saw that the head of that brass screw appeared to be sli
ghtly loose and with some tapping I could get the screw head to drop out of
the arm. If that is the shear pin you=99re referring to then it appears mine
is already sheared! However, the arm doesn=99t show any tendency to rotate
on the hub? I guess the cross-head screw is holding it onto the hub pretty f
irmly, but I can see that the arm could potentially rotate against the hub w
ithout the pin being there (since there is no positive locking mechanism aga
inst rotation), but the cross-head screw would need to be looser than it cur
rently is for rotation of the arm to be possible. Should the arm be free to
rotate against the hub without the pin there? Question also now is how to ge
t the threaded bit out and the pin replaced?!
Best regards
David
I'd not seen before the clip on the servo arm; there was an earlier Factory
'fix' of Loctited replacement screws. Later servos have a stud and pinned l
ocknut instead (I guess the stud is held in only by Loctite!).
The control column stops should take priority, as the servo stops are proba
bly too light to limit enthusiastic control movements by the pilot, but shou
ld at least contain a runaway servo or some other breakage in the servo. I m
ight have some spare stops (if I can find them). The stops are half-visible
and annotated 'F' in the photo at: TruTrak-RV10-Roll-Installation-Guide.pdf
(bendixking.com)
The shear pin is merely a 6-32 screw with a short part of its length (where
this crosses the interface between the mating arm and hub) necked and polis
hed to the roots of the screw thread.
My own servo is mounted towards the back of the Europa 'tunnel' and connect
s to a horn bolted to the rear end of the roll torque tube. This area used t
o get hot under certain situations via heat from the stainless firewall and
no tunnel ventilation. Subsequently a 'fire blanket' (two thin layers of wov
en Kevlar with thin fibreglass loft insulation sandwiched between, rather li
ke Orkotek) placed on the back of the firewall enabled cooler temperatures.
I've not heard of the standard under-seat servo location getting too hot.
Duncan McF.
On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com> wrote:
Thank you for the comprehensive reply, Duncan, and also for the replies fro
m Alan and Peter. I really appreciate the feedback.
It seems that the Skymap III should work OK for us, despite its 0.5Hz data
refresh rate. A bit of =98hunting=99 shouldn=99t really be a problem. We had
n=99t planned to have it fly a full route and navigate itself around turning
points. I had thought we=99d be manually changing the selected track at eac
h turning point, and then lock the tracking to the new direction required. H
owever, the Skymap III does have a =98Turn Anticipation=99 feature if we sho
uld in the future want it to follow a route, and not overshoot a waypoint. D
o most people use it to follow a full track, and make all the waypoint turns
?
Good to know about the shear pin in the arm as a last resort! Do you have a
ny drawing of the necked stainless pin that you got the LAA to agree to?
The servo that I have came out of an old Europa and didn=99t seem to have a
ny physical stops on the servo arm. It did, however, have the extra alloy
=98clip=99 to secure the screw that attaches the arm to the servo. I=99ve seen
that that clip was an LAA requirement too (see photo). For the physical sto
ps, I did see on another forum something that looked like it would do the jo
b on this servo (may even have been a Trutrak part). Does the LAA specify wh
at these stops should look like or be made of? Should they be set so that th
e servo arm touches them at the same time as the control column reaches its
full deflection (if not, then which stop should =98take priority=99 and be h
it first)? Does anyone have a photo of what the stops look like in their set
up? I imagine them being mounted on the bolts that attach the servo motor to
its mounting frame.
My servo would be mounted under the pax seat per Mod 75, so there is not re
ally any ventilation there. Is it worth adding a little cooling fan to the s
eat locker to keep the air circulating around the servo?
Many thanks for all the input!
David
i). The Trutrak will work on a Europa at 0.5Hz update frequency (i.e. every
2 seconds). Sometimes the AP will hunt gently (yesterday was a case in poin
t, but there were sites yesterday that were GPS-jamming as well, so that mig
ht have been a cause' or possibly I have a too low torque setting than optim
al in order to limit servo overheating). If too many options of output data
are requested in the GPS NMEA output setup then there won't be enough time t
o output all that data within a faster update period; the GPS set will norma
lly tell you if this is going to be the case.
iii). The servo does not care about torque feedback. The servo will provide
a force (torque) only up to the maximum value that has been preselected.
iv). The Europa needs quite a high torque setting (10 or 12 from memory, wh
ich can on hot days plus a high 'activity' setting result in servo overheati
ng and shutdown if you have a trigear with 'heated'/unventilated fuselage tu
nnel and depending where the servo is mounted).
The pilot stick force required to overcome maximum torque will be applied w
ithout even thinking about it and in any case there is a necked brass shear
pin (comprising a modified 6-32 brass instrument mounting screw) in the serv
o arm that can be easily sheared (even without knowing it, and then you wond
er why the AP is not tracking!). I agreed with LAA to replace this with a (n
ecked) stainless steel pin in order to provide a little more strength and ha
ven't sheared it since.
I also think that when the servo gets very hot (as above) it's internal vol
tage regulator starts to shut down (as many are designed to do). Again, ther
e is no way of knowing when this happens until realisation that the AP is no
t tracking!
v). The LAA will insist upon the stops on the servo, although these stops a
re not particularly robust and the set up would be better adjusted so that t
he stops never have to resist the pilot's stick inputs.
Otherwise, the Trutrak system and its dynamics work extremely well and can
do a much better job than the pilot, especially in turbulent conditions.
Have you found a setting on your Skymap that allows adjustment of the pre-e
mptive steering sensitivity (or "turn anticipation")?
Duncan McF.
On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com> wrote:
So, I've slowly been making some progress on this, having mocked up the who
le system out of the aircraft. I have now been able to test it in the worksh
op and yesterday in a car (it needed to be moving to get a track signal). Se
e attached photo. However, I now have a couple more questions/observations!
i) It seems that the Skymap III that I used in these tests works in terms o
f making the servo move and display a track on the Trutrak, so that's progre
ss! However, I note from the Skymap manual that it only gives its GPS info e
very 2 seconds, rather than the once every second that the Trutrak recommend
s to avoid 'wandering'. Peter, in your post you mentioned that you were usin
g a Skymap III - have you ever had a problem with this (assuming your A/P is
the Trutrak Digitrak too)? Alan, is the Garmin 196 that you've mentioned as
suitable, able to be set to give data at the 'once per second' rates, as fr
om the manual it seems it may too default to once every 2 seconds?
ii) I noticed when testing in the car, that when the track that was display
ed in the Trutrak was close to what we were actually tracking (as read from
the Skymap), that the servo was more or less static, and moved in the correc
t direction when there was a small deviation between what was set on the Tru
trak and what we were tracking. However, because our roads are not straight,
there were frequently occasions when the actual track from the Skymap was m
iles away from that set on the Trutrak. In that situation the servo went a b
it crazy and rotated its arm by many more degrees than it could ever do in t
he plane. Is this to be expected in this rather 'offline' mode? I can imagin
e that when the Trutrak senses that its control input is not creating the so
rt of aircraft track change that it had expected, that it just moves the ser
vo even further in order to try to get aircraft to do something?
iii) Clearly my mock-up does not provide any sort of 'force feedback' to th
e servo control arm (ie the arm is completely free to rotate as it likes). I
n an aircraft, would this be taken care of by aerodynamic feedback via the a
ileron torque tube? What happens to the servo when it reaches the full movem
ent that the aileron would allow (the point when the control column hits its
roll stops)?
iv) I can imagine that I wouldn't want the servo ever applying full aileron
to create a turn as that would make for a very violent manoeuvre! I see tha
t there are settings that can be adjusted in the Trutrak set-up menus that c
ontrol activity level and also control maximum torque. What values have peop
le set in theirs? I note that when I have set the recommended value of 12 fo
r the torque, it is almost impossible to override the servo arm when the A/P
is engaged (though I appreciate that with no control column attached the le
verage I can apply to the servo arm with my fingers is very low. I also appr
eciate that normally if one wanted to override the A/P you would disengage i
t first).
v) Lastly (for now!) has anyone fitted physical 'stops' to the servo body t
hat the servo arm would hit to ensure that the servo can never try to move t
he pushrod beyond the point where full aileron is applied?
Apologies for all the questions but I want to make sure it is really workin
g correctly before I contort myself to fit it into the aircraft itself!
Best regards
David
On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-server@matronics.co
m <mailto:owner-europa-list-server@matronics.com> on behalf of alanb@dpy01.c
o.uk <mailto:alanb@dpy01.co.uk>> wrote:
alanb@dpy01.co.uk>>
Ok I=99ve had a. Ha ce to fly mine with the GPS feed off.
As Duncan says below the display drops to show -|=94|- but maintains the tr
ack last set or you are holding when you switch it on.
The are no heading digits on the display so you will need use your compass/
DI to show that.
If you press the left or right =A4=B5=EF=B8=8F buttons then you can alter the track
the AP is following either left or right and a number appears which if you p
ress the button you can increase or decrease after the AP locks on the numbe
rs disappear and you have the -|=94|- on the display.
Useful if you have a GPS failure but wouldn=99t want that as normal mode of
operation so my suggestion is you need a GPS feed with the right NEMA messa
ge set to get the most out of the AP and the ability for it to follow a trac
k you have programmed in is a bonus.
One word of caution, I have come across some GPS that don=99t put out any m
essages, even the position message for driving a Transponder ADS-B output, u
nless there is a track in the GPS. That was how some of the older version wo
rked, GARMIN 430 and possible the early AVMAP were guilty of that.
Hope that helps.
Alan
Sent from my iPad
On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talktalk.net <mailto:a
mi-mcfadyean@talktalk.net>> wrote:
<mailto:ami-mcfadyean@talktalk.net>>
Digitrak only needs basic positional information from the GPS on a regular
basis. It will use this information to fly the track that has been set on th
e Digitrak.
If a route is programmed in to the GPS, it will fly that too (with differen
t commands being set at the Digitrak control head to enable this), so long a
s the GPS is also putting out the crosstrack error signal; not all of them d
o.
Duncan McF.
s.com/Navigator?Europa-List>
ion>
Message 3
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| Subject: | Re: Trutrak AP with Garmin GPS 18x 5Hz |
With a failed pin, there would now be no shear connection between the servo
hub and the arm other than friction. So, given enough torque it will slip,
and it must have slipped at some point otherwise the pin wouldn't be shear
ed. The earlier servos had a nylon washer under the crosshead screw to help
it slip!
I guess if you take off the arm, the remains of the shear pin may be projec
ting from the hub sufficiently to get a grip on it.
Duncan mcF.
> On 04 January 2023 at 12:21 David Cripps <dpc@knightonweb.com> wrote:
>
>
> Thanks very much for this extra info, Duncan.
>
>
>
> If you can find that spare stop that would be great. I had seen a pic
ture similar to the one you sent of the stops in another aircraft applicati
on.
>
>
>
> Following your comments about the shear pin, I think this is the smal
l brass screw located just above the main central cross-head screw that hol
ds the control arm onto the servo in the photo I=99ve attached here?
I looked at mine more closely and saw that the head of that brass screw app
eared to be slightly loose and with some tapping I could get the screw head
to drop out of the arm. If that is the shear pin you=99re referring
to then it appears mine is already sheared! However, the arm doesn=99
t show any tendency to rotate on the hub? I guess the cross-head screw is h
olding it onto the hub pretty firmly, but I can see that the arm could pote
ntially rotate against the hub without the pin being there (since there is
no positive locking mechanism against rotation), but the cross-head screw w
ould need to be looser than it currently is for rotation of the arm to be p
ossible. Should the arm be free to rotate against the hub without the pin t
here? Question also now is how to get the threaded bit out and the pin repl
aced?!
>
>
>
> Best regards
>
>
>
> David
>
>
>
> I'd not seen before the clip on the servo arm; there was an earlier F
actory 'fix' of Loctited replacement screws. Later servos have a stud and p
inned locknut instead (I guess the stud is held in only by Loctite!).
>
> The control column stops should take priority, as the servo stops are
probably too light to limit enthusiastic control movements by the pilot, b
ut should at least contain a runaway servo or some other breakage in the se
rvo. I might have some spare stops (if I can find them). The stops are half
-visible and annotated 'F' in the photo at: TruTrak-RV10-Roll-Installation-
Guide.pdf (bendixking.com) https://www.bendixking.com/content/dam/bendixkin
g/en/documents/document-lists/downloads-and-manuals/TruTrak-RV10-Roll-Insta
llation-Guide.pdf
>
> The shear pin is merely a 6-32 screw with a short part of its length
(where this crosses the interface between the mating arm and hub) necked an
d polished to the roots of the screw thread.
>
> My own servo is mounted towards the back of the Europa 'tunnel' and c
onnects to a horn bolted to the rear end of the roll torque tube. This area
used to get hot under certain situations via heat from the stainless firew
all and no tunnel ventilation. Subsequently a 'fire blanket' (two thin laye
rs of woven Kevlar with thin fibreglass loft insulation sandwiched between,
rather like Orkotek) placed on the back of the firewall enabled cooler tem
peratures. I've not heard of the standard under-seat servo location getting
too hot.
>
>
>
> Duncan McF.
>
> > >
> > On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com>
wrote:
> >
> > Thank you for the comprehensive reply, Duncan, and also for the
replies from Alan and Peter. I really appreciate the feedback.
> >
> >
> >
> > It seems that the Skymap III should work OK for us, despite its
0.5Hz data refresh rate. A bit of =98hunting=99 shouldn
=99t really be a problem. We hadn=99t planned to have it fly a full r
oute and navigate itself around turning points. I had thought we=99d
be manually changing the selected track at each turning point, and then loc
k the tracking to the new direction required. However, the Skymap III does
have a =98Turn Anticipation=99 feature if we should in the futu
re want it to follow a route, and not overshoot a waypoint. Do most people
use it to follow a full track, and make all the waypoint turns?
> >
> >
> >
> > Good to know about the shear pin in the arm as a last resort! D
o you have any drawing of the necked stainless pin that you got the LAA to
agree to?
> >
> >
> >
> > The servo that I have came out of an old Europa and didn
=99t seem to have any physical stops on the servo arm. It did, however, hav
e the extra alloy =98clip=99 to secure the screw that attaches
the arm to the servo. I=99ve seen that that clip was an LAA requireme
nt too (see photo). For the physical stops, I did see on another forum some
thing that looked like it would do the job on this servo (may even have bee
n a Trutrak part). Does the LAA specify what these stops should look like o
r be made of? Should they be set so that the servo arm touches them at the
same time as the control column reaches its full deflection (if not, then w
hich stop should =98take priority=99 and be hit first)? Does an
yone have a photo of what the stops look like in their setup? I imagine the
m being mounted on the bolts that attach the servo motor to its mounting fr
ame.
> >
> >
> >
> > My servo would be mounted under the pax seat per Mod 75, so the
re is not really any ventilation there. Is it worth adding a little cooling
fan to the seat locker to keep the air circulating around the servo?
> >
> >
> >
> > Many thanks for all the input!
> >
> > David
> >
> > i). The Trutrak will work on a Europa at 0.5Hz update frequency
(i.e. every 2 seconds). Sometimes the AP will hunt gently (yesterday was a
case in point, but there were sites yesterday that were GPS-jamming as wel
l, so that might have been a cause' or possibly I have a too low torque set
ting than optimal in order to limit servo overheating). If too many options
of output data are requested in the GPS NMEA output setup then there won't
be enough time to output all that data within a faster update period; the
GPS set will normally tell you if this is going to be the case.
> >
> > iii). The servo does not care about torque feedback. The servo
will provide a force (torque) only up to the maximum value that has been pr
eselected.
> >
> > iv). The Europa needs quite a high torque setting (10 or 12 fro
m memory, which can on hot days plus a high 'activity' setting result in se
rvo overheating and shutdown if you have a trigear with 'heated'/unventilat
ed fuselage tunnel and depending where the servo is mounted).
> >
> > The pilot stick force required to overcome maximum torque will
be applied without even thinking about it and in any case there is a necked
brass shear pin (comprising a modified 6-32 brass instrument mounting scre
w) in the servo arm that can be easily sheared (even without knowing it, an
d then you wonder why the AP is not tracking!). I agreed with LAA to replac
e this with a (necked) stainless steel pin in order to provide a little mor
e strength and haven't sheared it since.
> >
> > I also think that when the servo gets very hot (as above) it's
internal voltage regulator starts to shut down (as many are designed to do)
. Again, there is no way of knowing when this happens until realisation tha
t the AP is not tracking!
> >
> > v). The LAA will insist upon the stops on the servo, although t
hese stops are not particularly robust and the set up would be better adjus
ted so that the stops never have to resist the pilot's stick inputs.
> >
> > Otherwise, the Trutrak system and its dynamics work extremely w
ell and can do a much better job than the pilot, especially in turbulent co
nditions.
> >
> > Have you found a setting on your Skymap that allows adjustment
of the pre-emptive steering sensitivity (or "turn anticipation")?
> >
> >
> >
> > Duncan McF.
> >
> > > > >
> > > On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb
.com mailto:dpc@knightonweb.com > wrote:
> > >
> > >
> > > So, I've slowly been making some progress on this, having
mocked up the whole system out of the aircraft. I have now been able to te
st it in the workshop and yesterday in a car (it needed to be moving to get
a track signal). See attached photo. However, I now have a couple more que
stions/observations!
> > >
> > > i) It seems that the Skymap III that I used in these test
s works in terms of making the servo move and display a track on the Trutra
k, so that's progress! However, I note from the Skymap manual that it only
gives its GPS info every 2 seconds, rather than the once every second that
the Trutrak recommends to avoid 'wandering'. Peter, in your post you mentio
ned that you were using a Skymap III - have you ever had a problem with thi
s (assuming your A/P is the Trutrak Digitrak too)? Alan, is the Garmin 196
that you've mentioned as suitable, able to be set to give data at the 'once
per second' rates, as from the manual it seems it may too default to once
every 2 seconds?
> > >
> > > ii) I noticed when testing in the car, that when the trac
k that was displayed in the Trutrak was close to what we were actually trac
king (as read from the Skymap), that the servo was more or less static, and
moved in the correct direction when there was a small deviation between wh
at was set on the Trutrak and what we were tracking. However, because our r
oads are not straight, there were frequently occasions when the actual trac
k from the Skymap was miles away from that set on the Trutrak. In that situ
ation the servo went a bit crazy and rotated its arm by many more degrees t
han it could ever do in the plane. Is this to be expected in this rather 'o
ffline' mode? I can imagine that when the Trutrak senses that its control i
nput is not creating the sort of aircraft track change that it had expected
, that it just moves the servo even further in order to try to get aircraft
to do something?
> > >
> > > iii) Clearly my mock-up does not provide any sort of 'for
ce feedback' to the servo control arm (ie the arm is completely free to rot
ate as it likes). In an aircraft, would this be taken care of by aerodynami
c feedback via the aileron torque tube? What happens to the servo when it r
eaches the full movement that the aileron would allow (the point when the c
ontrol column hits its roll stops)?
> > >
> > > iv) I can imagine that I wouldn't want the servo ever app
lying full aileron to create a turn as that would make for a very violent m
anoeuvre! I see that there are settings that can be adjusted in the Trutrak
set-up menus that control activity level and also control maximum torque.
What values have people set in theirs? I note that when I have set the reco
mmended value of 12 for the torque, it is almost impossible to override the
servo arm when the A/P is engaged (though I appreciate that with no contro
l column attached the leverage I can apply to the servo arm with my fingers
is very low. I also appreciate that normally if one wanted to override the
A/P you would disengage it first).
> > >
> > > v) Lastly (for now!) has anyone fitted physical 'stops' t
o the servo body that the servo arm would hit to ensure that the servo can
never try to move the pushrod beyond the point where full aileron is applie
d?
> > >
> > > Apologies for all the questions but I want to make sure i
t is really working correctly before I contort myself to fit it into the ai
rcraft itself!
> > >
> > > Best regards
> > >
> > > David
> > >
> > > On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-s
erver@matronics.com mailto:owner-europa-list-server@matronics.com <mailto:o
wner-europa-list-server@matronics.com mailto:owner-europa-list-server@matro
nics.com > on behalf of alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk <mailto:
alanb@dpy01.co.uk mailto:alanb@dpy01.co.uk >> wrote:
> > >
> > >
y01.co.uk mailto:alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk mailto:alanb@d
py01.co.uk >>
> > >
> > >
> > > Ok I=99ve had a. Ha ce to fly mine with the GPS fee
d off.
> > >
> > >
> > > As Duncan says below the display drops to show -|
=94|- but maintains the track last set or you are holding when you switch i
t on.
> > >
> > >
> > > The are no heading digits on the display so you will need
use your compass/DI to show that.
> > >
> > >
> > > If you press the left or right =A4=B5=EF=B8=8F buttons
then you can alter the track the AP is following either left or right and
a number appears which if you press the button you can increase or decrease
after the AP locks on the numbers disappear and you have the -|=94|-
on the display.
> > >
> > >
> > > Useful if you have a GPS failure but wouldn=99t wan
t that as normal mode of operation so my suggestion is you need a GPS feed
with the right NEMA message set to get the most out of the AP and the abili
ty for it to follow a track you have programmed in is a bonus.
> > >
> > >
> > > One word of caution, I have come across some GPS that don
=99t put out any messages, even the position message for driving a Tr
ansponder ADS-B output, unless there is a track in the GPS. That was how so
me of the older version worked, GARMIN 430 and possible the early AVMAP wer
e guilty of that.
> > >
> > >
> > > Hope that helps.
> > >
> > >
> > > Alan
> > >
> > >
> > > Sent from my iPad
> > >
> > > > > > >
> > > > On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyea
n@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talk
talk.net mailto:ami-mcfadyean@talktalk.net >> wrote:
> > > >
-mcfadyean@talktalk.net mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfad
yean@talktalk.net mailto:ami-mcfadyean@talktalk.net >>
> > > >
> > > > Digitrak only needs basic positional information fr
om the GPS on a regular basis. It will use this information to fly the trac
k that has been set on the Digitrak.
> > > > If a route is programmed in to the GPS, it will fly
that too (with different commands being set at the Digitrak control head t
o enable this), so long as the GPS is also putting out the crosstrack error
signal; not all of them do.
> > > >
> > > > Duncan McF.
> > > >
> > > > > > >
> > >
> > >
> > >
> > >
> > > s.com/Navigator?Europa-List>
> > > ion>
> > >
> > >
> > >
> > >
> > >
> > >
> > > > >
> > >
>
>
>
Message 4
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| Subject: | Re: Trutrak AP with Garmin GPS 18x 5Hz |
Thanks, Duncan.
I have removed the arm now (and the crosshead screw does indeed have a nylo
n washer under it). I note the LAA requirement that this screw needs Loctiti
ng when it is put back in, as well as the screw retaining clip refitting ove
r it.
I can see that the shaft of the brass pin has broken below the surface of t
he hub so unfortunately there is nothing to grab onto. However, I also notic
e that there are two other similar screw holes in the hub which could be use
d instead, by rotating the hub through 120deg. Perhaps this is a deliberate
design to give a chance of doing an in-field replacement of a sheared pin in
order to get it working again, enabling the removal of the old pin stub to
be done at a later time.
Any ideas how to remove that stub? I have some screw extractors but they=99
re much too big.
Also, do you know where I can obtain replacement pins? You probably made yo
ur own when you switched to the stainless screws? If I do the same with a br
ass or stainless 6-32 screw is there a defined amount of =98necking=99 requi
red so that it shears at an appropriate shear force?
David
With a failed pin, there would now be no shear connection between the servo
hub and the arm other than friction. So, given enough torque it will slip,
and it must have slipped at some point otherwise the pin wouldn't be sheared
. The earlier servos had a nylon washer under the crosshead screw to help it
slip!
I guess if you take off the arm, the remains of the shear pin may be projec
ting from the hub sufficiently to get a grip on it.
Duncan mcF.
On 04 January 2023 at 12:21 David Cripps <dpc@knightonweb.com> wrote:
Thanks very much for this extra info, Duncan.
If you can find that spare stop that would be great. I had seen a picture s
imilar to the one you sent of the stops in another aircraft application.
Following your comments about the shear pin, I think this is the small bras
s screw located just above the main central cross-head screw that holds the
control arm onto the servo in the photo I=99ve attached here? I looked at mi
ne more closely and saw that the head of that brass screw appeared to be sli
ghtly loose and with some tapping I could get the screw head to drop out of
the arm. If that is the shear pin you=99re referring to then it appears mine
is already sheared! However, the arm doesn=99t show any tendency to rotate
on the hub? I guess the cross-head screw is holding it onto the hub pretty f
irmly, but I can see that the arm could potentially rotate against the hub w
ithout the pin being there (since there is no positive locking mechanism aga
inst rotation), but the cross-head screw would need to be looser than it cur
rently is for rotation of the arm to be possible. Should the arm be free to
rotate against the hub without the pin there? Question also now is how to ge
t the threaded bit out and the pin replaced?!
Best regards
David
I'd not seen before the clip on the servo arm; there was an earlier Factory
'fix' of Loctited replacement screws. Later servos have a stud and pinned l
ocknut instead (I guess the stud is held in only by Loctite!).
The control column stops should take priority, as the servo stops are proba
bly too light to limit enthusiastic control movements by the pilot, but shou
ld at least contain a runaway servo or some other breakage in the servo. I m
ight have some spare stops (if I can find them). The stops are half-visible
and annotated 'F' in the photo at: TruTrak-RV10-Roll-Installation-Guide.pdf
(bendixking.com)
The shear pin is merely a 6-32 screw with a short part of its length (where
this crosses the interface between the mating arm and hub) necked and polis
hed to the roots of the screw thread.
My own servo is mounted towards the back of the Europa 'tunnel' and connect
s to a horn bolted to the rear end of the roll torque tube. This area used t
o get hot under certain situations via heat from the stainless firewall and
no tunnel ventilation. Subsequently a 'fire blanket' (two thin layers of wov
en Kevlar with thin fibreglass loft insulation sandwiched between, rather li
ke Orkotek) placed on the back of the firewall enabled cooler temperatures.
I've not heard of the standard under-seat servo location getting too hot.
Duncan McF.
On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com> wrote:
Thank you for the comprehensive reply, Duncan, and also for the replies fro
m Alan and Peter. I really appreciate the feedback.
It seems that the Skymap III should work OK for us, despite its 0.5Hz data
refresh rate. A bit of =98hunting=99 shouldn=99t really be a problem. We had
n=99t planned to have it fly a full route and navigate itself around turning
points. I had thought we=99d be manually changing the selected track at eac
h turning point, and then lock the tracking to the new direction required. H
owever, the Skymap III does have a =98Turn Anticipation=99 feature if we sho
uld in the future want it to follow a route, and not overshoot a waypoint. D
o most people use it to follow a full track, and make all the waypoint turns
?
Good to know about the shear pin in the arm as a last resort! Do you have a
ny drawing of the necked stainless pin that you got the LAA to agree to?
The servo that I have came out of an old Europa and didn=99t seem to have a
ny physical stops on the servo arm. It did, however, have the extra alloy
=98clip=99 to secure the screw that attaches the arm to the servo. I=99ve seen
that that clip was an LAA requirement too (see photo). For the physical sto
ps, I did see on another forum something that looked like it would do the jo
b on this servo (may even have been a Trutrak part). Does the LAA specify wh
at these stops should look like or be made of? Should they be set so that th
e servo arm touches them at the same time as the control column reaches its
full deflection (if not, then which stop should =98take priority=99 and be h
it first)? Does anyone have a photo of what the stops look like in their set
up? I imagine them being mounted on the bolts that attach the servo motor to
its mounting frame.
My servo would be mounted under the pax seat per Mod 75, so there is not re
ally any ventilation there. Is it worth adding a little cooling fan to the s
eat locker to keep the air circulating around the servo?
Many thanks for all the input!
David
i). The Trutrak will work on a Europa at 0.5Hz update frequency (i.e. every
2 seconds). Sometimes the AP will hunt gently (yesterday was a case in poin
t, but there were sites yesterday that were GPS-jamming as well, so that mig
ht have been a cause' or possibly I have a too low torque setting than optim
al in order to limit servo overheating). If too many options of output data
are requested in the GPS NMEA output setup then there won't be enough time t
o output all that data within a faster update period; the GPS set will norma
lly tell you if this is going to be the case.
iii). The servo does not care about torque feedback. The servo will provide
a force (torque) only up to the maximum value that has been preselected.
iv). The Europa needs quite a high torque setting (10 or 12 from memory, wh
ich can on hot days plus a high 'activity' setting result in servo overheati
ng and shutdown if you have a trigear with 'heated'/unventilated fuselage tu
nnel and depending where the servo is mounted).
The pilot stick force required to overcome maximum torque will be applied w
ithout even thinking about it and in any case there is a necked brass shear
pin (comprising a modified 6-32 brass instrument mounting screw) in the serv
o arm that can be easily sheared (even without knowing it, and then you wond
er why the AP is not tracking!). I agreed with LAA to replace this with a (n
ecked) stainless steel pin in order to provide a little more strength and ha
ven't sheared it since.
I also think that when the servo gets very hot (as above) it's internal vol
tage regulator starts to shut down (as many are designed to do). Again, ther
e is no way of knowing when this happens until realisation that the AP is no
t tracking!
v). The LAA will insist upon the stops on the servo, although these stops a
re not particularly robust and the set up would be better adjusted so that t
he stops never have to resist the pilot's stick inputs.
Otherwise, the Trutrak system and its dynamics work extremely well and can
do a much better job than the pilot, especially in turbulent conditions.
Have you found a setting on your Skymap that allows adjustment of the pre-e
mptive steering sensitivity (or "turn anticipation")?
Duncan McF.
On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com> wrote:
So, I've slowly been making some progress on this, having mocked up the who
le system out of the aircraft. I have now been able to test it in the worksh
op and yesterday in a car (it needed to be moving to get a track signal). Se
e attached photo. However, I now have a couple more questions/observations!
i) It seems that the Skymap III that I used in these tests works in terms o
f making the servo move and display a track on the Trutrak, so that's progre
ss! However, I note from the Skymap manual that it only gives its GPS info e
very 2 seconds, rather than the once every second that the Trutrak recommend
s to avoid 'wandering'. Peter, in your post you mentioned that you were usin
g a Skymap III - have you ever had a problem with this (assuming your A/P is
the Trutrak Digitrak too)? Alan, is the Garmin 196 that you've mentioned as
suitable, able to be set to give data at the 'once per second' rates, as fr
om the manual it seems it may too default to once every 2 seconds?
ii) I noticed when testing in the car, that when the track that was display
ed in the Trutrak was close to what we were actually tracking (as read from
the Skymap), that the servo was more or less static, and moved in the correc
t direction when there was a small deviation between what was set on the Tru
trak and what we were tracking. However, because our roads are not straight,
there were frequently occasions when the actual track from the Skymap was m
iles away from that set on the Trutrak. In that situation the servo went a b
it crazy and rotated its arm by many more degrees than it could ever do in t
he plane. Is this to be expected in this rather 'offline' mode? I can imagin
e that when the Trutrak senses that its control input is not creating the so
rt of aircraft track change that it had expected, that it just moves the ser
vo even further in order to try to get aircraft to do something?
iii) Clearly my mock-up does not provide any sort of 'force feedback' to th
e servo control arm (ie the arm is completely free to rotate as it likes). I
n an aircraft, would this be taken care of by aerodynamic feedback via the a
ileron torque tube? What happens to the servo when it reaches the full movem
ent that the aileron would allow (the point when the control column hits its
roll stops)?
iv) I can imagine that I wouldn't want the servo ever applying full aileron
to create a turn as that would make for a very violent manoeuvre! I see tha
t there are settings that can be adjusted in the Trutrak set-up menus that c
ontrol activity level and also control maximum torque. What values have peop
le set in theirs? I note that when I have set the recommended value of 12 fo
r the torque, it is almost impossible to override the servo arm when the A/P
is engaged (though I appreciate that with no control column attached the le
verage I can apply to the servo arm with my fingers is very low. I also appr
eciate that normally if one wanted to override the A/P you would disengage i
t first).
v) Lastly (for now!) has anyone fitted physical 'stops' to the servo body t
hat the servo arm would hit to ensure that the servo can never try to move t
he pushrod beyond the point where full aileron is applied?
Apologies for all the questions but I want to make sure it is really workin
g correctly before I contort myself to fit it into the aircraft itself!
Best regards
David
On 19/11/2022, 16:26, "Alan Burrill" <owner-europa-list-server@matronics.co
m <mailto:owner-europa-list-server@matronics.com> on behalf of alanb@dpy01.c
o.uk <mailto:alanb@dpy01.co.uk>> wrote:
alanb@dpy01.co.uk>>
Ok I=99ve had a. Ha ce to fly mine with the GPS feed off.
As Duncan says below the display drops to show -|=94|- but maintains the tr
ack last set or you are holding when you switch it on.
The are no heading digits on the display so you will need use your compass/
DI to show that.
If you press the left or right =A4=B5=EF=B8=8F buttons then you can alter the track
the AP is following either left or right and a number appears which if you p
ress the button you can increase or decrease after the AP locks on the numbe
rs disappear and you have the -|=94|- on the display.
Useful if you have a GPS failure but wouldn=99t want that as normal mode of
operation so my suggestion is you need a GPS feed with the right NEMA messa
ge set to get the most out of the AP and the ability for it to follow a trac
k you have programmed in is a bonus.
One word of caution, I have come across some GPS that don=99t put out any m
essages, even the position message for driving a Transponder ADS-B output, u
nless there is a track in the GPS. That was how some of the older version wo
rked, GARMIN 430 and possible the early AVMAP were guilty of that.
Hope that helps.
Alan
Sent from my iPad
On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talktalk.net <mailto:a
mi-mcfadyean@talktalk.net>> wrote:
<mailto:ami-mcfadyean@talktalk.net>>
Digitrak only needs basic positional information from the GPS on a regular
basis. It will use this information to fly the track that has been set on th
e Digitrak.
If a route is programmed in to the GPS, it will fly that too (with differen
t commands being set at the Digitrak control head to enable this), so long a
s the GPS is also putting out the crosstrack error signal; not all of them d
o.
Duncan McF.
s.com/Navigator?Europa-List>
ion>
Message 5
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| Subject: | Re: Trutrak AP with Garmin GPS 18x 5Hz |
David - I found out the hard way about that shear screw - see my build
journal at
<http://www.rowlandcarson.org.uk/aviation/europa_435/200904.php> on 21st
& 30th of the month.
As you will see, I got my replacement shear screws direct from TruTrak.
I don=99t seem to have a picture of it, but I seem to recall that
there are several tapped holes that can be used for the screw so it=99
s not essential to remove the broken end.
in friendship
Rowland
> On 2023-01-04, at 16:47, David Cripps <dpc@knightonweb.com> wrote:
>
> Thanks, Duncan.
>
> I have removed the arm now (and the crosshead screw does indeed have a
nylon washer under it). I note the LAA requirement that this screw needs
Loctiting when it is put back in, as well as the screw retaining clip
refitting over it.
>
> I can see that the shaft of the brass pin has broken below the surface
of the hub so unfortunately there is nothing to grab onto. However, I
also notice that there are two other similar screw holes in the hub
which could be used instead, by rotating the hub through 120deg. Perhaps
this is a deliberate design to give a chance of doing an in-field
replacement of a sheared pin in order to get it working again, enabling
the removal of the old pin stub to be done at a later time.
>
> Any ideas how to remove that stub? I have some screw extractors but
they=99re much too big.
>
> Also, do you know where I can obtain replacement pins? You probably
made your own when you switched to the stainless screws? If I do the
same with a brass or stainless 6-32 screw is there a defined amount of
=98necking=99 required so that it shears at an appropriate
shear force?
>
> David
>
>
>
> With a failed pin, there would now be no shear connection between the
servo hub and the arm other than friction. So, given enough torque it
will slip, and it must have slipped at some point otherwise the pin
wouldn't be sheared. The earlier servos had a nylon washer under the
crosshead screw to help it slip!
>
> I guess if you take off the arm, the remains of the shear pin may be
projecting from the hub sufficiently to get a grip on it.
>
>
>
> Duncan mcF.
>
> On 04 January 2023 at 12:21 David Cripps <dpc@knightonweb.com
<mailto:dpc@knightonweb.com>> wrote:
>
> Thanks very much for this extra info, Duncan.
>
>
>
> If you can find that spare stop that would be great. I had seen a
picture similar to the one you sent of the stops in another aircraft
application.
>
>
>
> Following your comments about the shear pin, I think this is the small
brass screw located just above the main central cross-head screw that
holds the control arm onto the servo in the photo I=99ve attached
here? I looked at mine more closely and saw that the head of that brass
screw appeared to be slightly loose and with some tapping I could get
the screw head to drop out of the arm. If that is the shear pin you=99
re referring to then it appears mine is already sheared! However, the
arm doesn=99t show any tendency to rotate on the hub? I guess the
cross-head screw is holding it onto the hub pretty firmly, but I can see
that the arm could potentially rotate against the hub without the pin
being there (since there is no positive locking mechanism against
rotation), but the cross-head screw would need to be looser than it
currently is for rotation of the arm to be possible. Should the arm be
free to rotate against the hub without the pin there? Question also now
is how to get the threaded bit out and the pin replaced?!
>
>
>
> Best regards
>
>
>
> David
>
>
>
> I'd not seen before the clip on the servo arm; there was an earlier
Factory 'fix' of Loctited replacement screws. Later servos have a stud
and pinned locknut instead (I guess the stud is held in only by
Loctite!).
>
> The control column stops should take priority, as the servo stops are
probably too light to limit enthusiastic control movements by the pilot,
but should at least contain a runaway servo or some other breakage in
the servo. I might have some spare stops (if I can find them). The stops
are half-visible and annotated 'F' in the photo at:
TruTrak-RV10-Roll-Installation-Guide.pdf (bendixking.com)
<https://www.bendixking.com/content/dam/bendixking/en/documents/document-l
ists/downloads-and-manuals/TruTrak-RV10-Roll-Installation-Guide.pdf>
> The shear pin is merely a 6-32 screw with a short part of its length
(where this crosses the interface between the mating arm and hub) necked
and polished to the roots of the screw thread.
>
> My own servo is mounted towards the back of the Europa 'tunnel' and
connects to a horn bolted to the rear end of the roll torque tube. This
area used to get hot under certain situations via heat from the
stainless firewall and no tunnel ventilation. Subsequently a 'fire
blanket' (two thin layers of woven Kevlar with thin fibreglass loft
insulation sandwiched between, rather like Orkotek) placed on the back
of the firewall enabled cooler temperatures. I've not heard of the
standard under-seat servo location getting too hot.
>
>
>
> Duncan McF.
>
> On 03 January 2023 at 22:30 David Cripps <dpc@knightonweb.com
<mailto:dpc@knightonweb.com>> wrote:
>
> Thank you for the comprehensive reply, Duncan, and also for the
replies from Alan and Peter. I really appreciate the feedback.
>
>
>
> It seems that the Skymap III should work OK for us, despite its 0.5Hz
data refresh rate. A bit of =98hunting=99 shouldn=99t
really be a problem. We hadn=99t planned to have it fly a full
route and navigate itself around turning points. I had thought we=99
d be manually changing the selected track at each turning point, and
then lock the tracking to the new direction required. However, the
Skymap III does have a =98Turn Anticipation=99 feature if we
should in the future want it to follow a route, and not overshoot a
waypoint. Do most people use it to follow a full track, and make all the
waypoint turns?
>
>
>
> Good to know about the shear pin in the arm as a last resort! Do you
have any drawing of the necked stainless pin that you got the LAA to
agree to?
>
>
>
> The servo that I have came out of an old Europa and didn=99t
seem to have any physical stops on the servo arm. It did, however, have
the extra alloy =98clip=99 to secure the screw that attaches
the arm to the servo. I=99ve seen that that clip was an LAA
requirement too (see photo). For the physical stops, I did see on
another forum something that looked like it would do the job on this
servo (may even have been a Trutrak part). Does the LAA specify what
these stops should look like or be made of? Should they be set so that
the servo arm touches them at the same time as the control column
reaches its full deflection (if not, then which stop should =98take
priority=99 and be hit first)? Does anyone have a photo of what
the stops look like in their setup? I imagine them being mounted on the
bolts that attach the servo motor to its mounting frame.
>
>
>
> My servo would be mounted under the pax seat per Mod 75, so there is
not really any ventilation there. Is it worth adding a little cooling
fan to the seat locker to keep the air circulating around the servo?
>
>
>
> Many thanks for all the input!
>
> David
>
> i). The Trutrak will work on a Europa at 0.5Hz update frequency (i.e.
every 2 seconds). Sometimes the AP will hunt gently (yesterday was a
case in point, but there were sites yesterday that were GPS-jamming as
well, so that might have been a cause' or possibly I have a too low
torque setting than optimal in order to limit servo overheating). If too
many options of output data are requested in the GPS NMEA output setup
then there won't be enough time to output all that data within a faster
update period; the GPS set will normally tell you if this is going to be
the case.
>
> iii). The servo does not care about torque feedback. The servo will
provide a force (torque) only up to the maximum value that has been
preselected.
>
> iv). The Europa needs quite a high torque setting (10 or 12 from
memory, which can on hot days plus a high 'activity' setting result in
servo overheating and shutdown if you have a trigear with
'heated'/unventilated fuselage tunnel and depending where the servo is
mounted).
>
> The pilot stick force required to overcome maximum torque will be
applied without even thinking about it and in any case there is a necked
brass shear pin (comprising a modified 6-32 brass instrument mounting
screw) in the servo arm that can be easily sheared (even without knowing
it, and then you wonder why the AP is not tracking!). I agreed with LAA
to replace this with a (necked) stainless steel pin in order to provide
a little more strength and haven't sheared it since.
>
> I also think that when the servo gets very hot (as above) it's
internal voltage regulator starts to shut down (as many are designed to
do). Again, there is no way of knowing when this happens until
realisation that the AP is not tracking!
>
> v). The LAA will insist upon the stops on the servo, although these
stops are not particularly robust and the set up would be better
adjusted so that the stops never have to resist the pilot's stick
inputs.
>
> Otherwise, the Trutrak system and its dynamics work extremely well and
can do a much better job than the pilot, especially in turbulent
conditions.
>
> Have you found a setting on your Skymap that allows adjustment of the
pre-emptive steering sensitivity (or "turn anticipation")?
>
>
>
> Duncan McF.
>
> On 03 January 2023 at 13:10 David Cripps <dpc@knightonweb.com
<mailto:dpc@knightonweb.com>> wrote:
>
>
> So, I've slowly been making some progress on this, having mocked up
the whole system out of the aircraft. I have now been able to test it in
the workshop and yesterday in a car (it needed to be moving to get a
track signal). See attached photo. However, I now have a couple more
questions/observations!
>
> i) It seems that the Skymap III that I used in these tests works in
terms of making the servo move and display a track on the Trutrak, so
that's progress! However, I note from the Skymap manual that it only
gives its GPS info every 2 seconds, rather than the once every second
that the Trutrak recommends to avoid 'wandering'. Peter, in your post
you mentioned that you were using a Skymap III - have you ever had a
problem with this (assuming your A/P is the Trutrak Digitrak too)? Alan,
is the Garmin 196 that you've mentioned as suitable, able to be set to
give data at the 'once per second' rates, as from the manual it seems it
may too default to once every 2 seconds?
>
> ii) I noticed when testing in the car, that when the track that was
displayed in the Trutrak was close to what we were actually tracking (as
read from the Skymap), that the servo was more or less static, and moved
in the correct direction when there was a small deviation between what
was set on the Trutrak and what we were tracking. However, because our
roads are not straight, there were frequently occasions when the actual
track from the Skymap was miles away from that set on the Trutrak. In
that situation the servo went a bit crazy and rotated its arm by many
more degrees than it could ever do in the plane. Is this to be expected
in this rather 'offline' mode? I can imagine that when the Trutrak
senses that its control input is not creating the sort of aircraft track
change that it had expected, that it just moves the servo even further
in order to try to get aircraft to do something?
>
> iii) Clearly my mock-up does not provide any sort of 'force feedback'
to the servo control arm (ie the arm is completely free to rotate as it
likes). In an aircraft, would this be taken care of by aerodynamic
feedback via the aileron torque tube? What happens to the servo when it
reaches the full movement that the aileron would allow (the point when
the control column hits its roll stops)?
>
> iv) I can imagine that I wouldn't want the servo ever applying full
aileron to create a turn as that would make for a very violent
manoeuvre! I see that there are settings that can be adjusted in the
Trutrak set-up menus that control activity level and also control
maximum torque. What values have people set in theirs? I note that when
I have set the recommended value of 12 for the torque, it is almost
impossible to override the servo arm when the A/P is engaged (though I
appreciate that with no control column attached the leverage I can apply
to the servo arm with my fingers is very low. I also appreciate that
normally if one wanted to override the A/P you would disengage it
first).
>
> v) Lastly (for now!) has anyone fitted physical 'stops' to the servo
body that the servo arm would hit to ensure that the servo can never try
to move the pushrod beyond the point where full aileron is applied?
>
> Apologies for all the questions but I want to make sure it is really
working correctly before I contort myself to fit it into the aircraft
itself!
>
> Best regards
>
> David
>
> On 19/11/2022, 16:26, "Alan Burrill"
<owner-europa-list-server@matronics.com
<mailto:owner-europa-list-server@matronics.com>
<mailto:owner-europa-list-server@matronics.com
<mailto:owner-europa-list-server@matronics.com>> on behalf of
alanb@dpy01.co.uk <mailto:alanb@dpy01.co.uk> <mailto:alanb@dpy01.co.uk
<mailto:alanb@dpy01.co.uk>>> wrote:
>
>
<mailto:alanb@dpy01.co.uk> <mailto:alanb@dpy01.co.uk
<mailto:alanb@dpy01.co.uk>>>
>
>
> Ok I=99ve had a. Ha ce to fly mine with the GPS feed off.
>
>
> As Duncan says below the display drops to show -|=94|- but
maintains the track last set or you are holding when you switch it on.
>
>
> The are no heading digits on the display so you will need use your
compass/DI to show that.
>
>
> If you press the left or right =A4=B5=EF=B8=8F buttons then you can
alter the track the AP is following either left or right and a number
appears which if you press the button you can increase or decrease after
the AP locks on the numbers disappear and you have the -|=94|- on
the display.
>
>
> Useful if you have a GPS failure but wouldn=99t want that as
normal mode of operation so my suggestion is you need a GPS feed with
the right NEMA message set to get the most out of the AP and the ability
for it to follow a track you have programmed in is a bonus.
>
>
> One word of caution, I have come across some GPS that don=99t
put out any messages, even the position message for driving a
Transponder ADS-B output, unless there is a track in the GPS. That was
how some of the older version worked, GARMIN 430 and possible the early
AVMAP were guilty of that.
>
>
> Hope that helps.
>
>
> Alan
>
>
> Sent from my iPad
>
> On 10 Nov 2022, at 10:52, D McFadyean <ami-mcfadyean@talktalk.net
<mailto:ami-mcfadyean@talktalk.net> <mailto:ami-mcfadyean@talktalk.net
<mailto:ami-mcfadyean@talktalk.net>>> wrote:
>
<ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktalk.net>
<mailto:ami-mcfadyean@talktalk.net <mailto:ami-mcfadyean@talktalk.net>>>
>
> Digitrak only needs basic positional information from the GPS on a
regular basis. It will use this information to fly the track that has
been set on the Digitrak.
> If a route is programmed in to the GPS, it will fly that too (with
different commands being set at the Digitrak control head to enable
this), so long as the GPS is also putting out the crosstrack error
signal; not all of them do.
>
> Duncan McF.
>
>
>
>
>
> s.com/Navigator?Europa-List <http://s.com/Navigator?Europa-List>>
> ion>
>
| Rowland Carson ... that's Rowland with a 'w' ...
| <rowlandcarson@gmail.com> http://www.rowlandcarson.org.uk
| Skype, Twitter: rowland_carson Facebook: Rowland Carson
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