---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 02/16/12: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 11:02 AM - Re: Looking for a used PC680 battery for testing (Richard Girard) 2. 11:05 AM - Looking for a used PC680 battery for testing (Charles Brame) 3. 05:59 PM - Servo problem (Etienne Phillips) 4. 07:27 PM - Re: Servo problem (Robert L. Nuckolls, III) 5. 07:37 PM - Speaking of EMC filters (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 11:02:03 AM PST US Subject: Re: AeroElectric-List: Looking for a used PC680 battery for testing From: Richard Girard For what it's worth, I went to the Allpak battery store in Wichita just last week for an 18 amp SLA battery. I bought a Powersonic with bolt terminals for $44 plus tax. Which only goes to underscore that the HFT package is a good deal, but if you just want a battery there are probably local sources where you can get a new one for not much more than the shipping cost or a used one. Rick Girard On Thu, Feb 16, 2012 at 7:36 AM, Bill Watson wrote: > Reeeeeeecycle! > > > Sent from my iPad > > On Feb 15, 2012, at 11:15 PM, "Mike Creek" > wrote: > > Bob,**** > > ** ** > > I have two thoroughly abused PC680=92s complete with heat deformed jacket s. > One reads 12.5 volts but the other is only at 8.25 volts. I=92m at zip 8 9801 > and can ship this Friday if you are interested in these derelicts.**** > > ** ** > > Mike **** > > ** ** > > *From:* owner-aeroelectric-list-server@matronics.com [mailto: > owner-aeroelectric-list-server@matronics.com] *On Behalf Of *Robert L. > Nuckolls, III > *Sent:* Wednesday, February 15, 2012 6:48 AM > *To:* aeroelectric-list@matronics.com > *Subject:* Re: AeroElectric-List: Looking for a used PC680 battery for > testing**** > > ** ** > > At 05:06 PM 2/14/2012, you wrote: > > **** > > jaybrinkmeyer@yahoo.com> > > I'm at the point of transitioning from a jury rigged power supply to > "real" battery in place for ground testing. Does anyone have one (or two! ) > used PC680s they'd be willing to part with?**** > > > Consider too the acquisition of an "instant > power" or "jump-start" product from Wallmart > or perhaps Harbor Freight. I see devices in > both catalogs for $50 or less. > > > > > These products come with built in charger- > maintainers, a SVLA battery capable of cranking > an engine and handy soft cables that you can > cut shorter, apply terminals and bolt right > into your ship's system. So for not much more > than the cost of UPS to ship some used batteries > around the country, you can get a new battery > that is in a handy package, self maintaining, > convenient to attach to your airplane, and > convertible back to it's original purpose when > you're through stroking your airplane with it. > > > **** > > Bob . . .**** > > * > =========== > =========== =========== =========== > > * > > -- Zulu Delta Mk IIIC Thanks, Homer GBYM It isn't necessary to have relatives in Kansas City in order to be unhappy. - Groucho Marx ________________________________ Message 2 _____________________________________ Time: 11:05:45 AM PST US From: Charles Brame Subject: AeroElectric-List: Looking for a used PC680 battery for testing I found a 17AH SVLA battery at a computer hardware store for about $30. Its been running an electric gate for over five years with a Battery Tender Junior charger. I have a friend that has been running a similar computer store battery battery in a T-18 for several years. Charlie Brame RV-6A N11CB San Antonio ________________________________ Message 3 _____________________________________ Time: 05:59:05 PM PST US Subject: AeroElectric-List: Servo problem From: Etienne Phillips Hi All I=92m hoping that an RF greybeard will be able to offer some advice=85 I=92 ve built an elevator trim system for my aeroplane, using an RC servo mounted in the control surface, which is driven by a PIC18F microcontroller. This has worked flawlessly for 2 years. On the back of this success I built another identical one for a friend, and due to the difference in installation which I=92ll explain shortly, I am being plagued by a fault that I haven=92t been able to solve. The instigato r for this problem is the RF emitted by the COM antenna, which on my aircraft is between the undercarriage (taildragger), and on the friends is inside the vertical stabiliser. The design of the friend=92s antenna is as follows : The braiding of the coax is stretched out in one direction whist the core is stretched out in the other. Since it=92s a fiberglass aeroplane, the antenna is bonded to the skin of the vertical stab, without worry of electrical problems. The design of the trim system is as follows: Ship=92s power is fed through a 7805 (with required smoothing caps) to the 18F4520, which generates the 1-2ms square pulse required by the servo. The output of the PIC is protected by a polyswitch and zener diode combo, resulting in a fairly low impedance output. Meanwhile, the power is fed into an off-the-shelf RC power converter, which has a 6V, 15Amp capable output. Signal and power is fed through a shielded 4-core tefzel wire to the back of the aeroplane where it breaks out into the connections required by the servo motor. The 6V power line is fed over two cores, whilst ground is connected via one core and the shield. The problem: when transmitting on the radio at the low end of the airband spectrum 118Mhz, the servo goes bezerk. At 125MHz it twitches occasionally, but is mostly usable. I took an oscilloscope out to the aeroplane, and tested at points =93A=94, =93B=94 and =93C=94 whilst both transmitting and not. At =93A=94, the signal output by the PIC is clean, and unaffected by the no ise induced by transmission. The same signal is measured at =93B=94 whilst not transmitting: When transmitting, however, the signal at =93B=94 becomes completely degra ded: The amplitude of the noise is approximately 5Vp-p, superimposed on the desired 5Vp-p signal. No wonder the servo doesn=92t know what=92s going on! The power line is completely clean on both ends of the wire, at =93C=94 and the output to the power converter. I am aware that the suitability of using an RC servo in a real aircraft is a concern, but as has been proven in my aeroplane, mechanically and aerodynamically the system works well, providing enough authority to trim adequately without being so powerful that it cannot be over-ridden using excessive force. The microcontroller code and electrical design of the board has also proven to be reliable, and the installation in my aeroplane has been robust and able to withstand the noise generated from the com radio, although the distance to the antenna is much greater (not closer than 2 meters). We both have the same radio, an MGL VHF-10. In the knowledgeable opinions of those who have RF experience, will I be able to implement a filter at the servo end of the wire to filter out the 120MHz-odd signal whilst retaining the integrity of the pulse? I tried using a 1uF electrolytic cap as a filter (this was the only cap I had on-hand, as the aeroplane is a 90min drive out of town), which had no effect on the noise, and only degraded the underlying signal further. I know that the cap isn=92t rated at high frequencies, so I only include it a s an anecdote. I=92m concerned about putting a ceramic cap in a EM field ' will this not act as an antenna and make the problem worse? Any advice would be appreciated! Thanks, Etienne ________________________________ Message 4 _____________________________________ Time: 07:27:42 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Servo problem In the knowledgeable opinions of those who have RF experience, will I be able to implement a filter at the servo end of the wire to filter out the 120MHz-odd signal whilst retaining the integrity of the pulse? Absolutely. The variable position pulse is about a half light-year away from the antagonistic signal . . . well . . . maybe not light years but certainly separated by many decades of RF spectrum separation. We're talking sub killohertz versus 100 mHz or about 5 decades. A filter crafted to attenuate 100 mHz is totally transparent to your signal-of-interest. Based on your explorations and observations, it seems likely that the RC servo is having problems with the stronger RF field. RF, like all electro-magnetic propagation attenuates based on the "square-law". If you double the distance between emitting and detecting devices, effects on the detector are reduced to 1/4th of the original. That's a FAR FIELD condition where there are no, distortions to the field as it crosses the gap. We know that the closer proximity of antenna to servo can offer a profound increase in potential interference. You also have NEAR-FIELD effects airplane and wiring geometry. Far-field effects are only slightly affected by frequency, near-field effects include the effects of standing waves on airframe and wiring which can be VERY sensitive to changes of frequency for the antagonist signal. I can show you data gathered in the hell-hole of a Hawker 800 were standing waves generated by a poorly designed antenna system would offer 1000:1 variations in interfering signal while standing in one place and moving a probe around within arm's reach. Further, the effects varied profoundly from airplane to airplane. I tried using a 1uF electrolytic cap as a filter (this was the only cap I had on-hand, as the aeroplane is a 90min drive out of town), which had no effect on the noise, and only degraded the underlying signal further. I know that the cap isnt rated at high frequencies, so I only include it as an anecdote. Im concerned about putting a ceramic cap in a EM field will this not act as an antenna and make the problem worse? Ceramic capacitors are not counter-indicated for this task. The few R/C servos I've played with all had plastic cases and ZERO provisions for managing electro-magnetic compatibility. Without taking your servos to the lab and doing the full DO-160 work-up, I cannot offer anything like an elegant, optimized solution. I will suggest some sledge-and-crowbar techniques with a high probability of success. I would "wrap" the servo in copper tape to craft a metallic enclosure. I would fabricate two, pi- section filters on the outside surface right where the wires come out of the actuator. The actuator ground would tie to the outside copper shell. Two capacitors for each of the two filters would also solder directly to the shell. The schematic would look something like this. http://tinyurl.com/6vekr2o The actual parts values are exceedingly un-critical. Components spanning perhaps 1000:1 ratios of value would do the job without degrading the command signal. The elegant components are driven more by physical characteristics that lend themselves to "spider-webbing" onto the side of a thin walled, copper box. If you could send me one of the servos along with a picture of the installed servo showing where the envelope could grow some warts without hitting anything in the airplane, I can pretty quickly accomplish the proposed modification. I would take pictures of the process and provide a bill of materials. If the mod proves successful, I'll publish the solution to the AEC website. If there's a demand for these filters, we could do an etched circuit board layout and fab a Mk II filter from surface mount components. More elegant yet. If you'd like to take a whack at a DIY solution, I'd start with inductors on the order of 1 uHy and capacitors on the order of 1000 pF. And yes, they could be ceramic disks . . . just keep the leads short. By the way, ferrite beads on the wires are exceedingly unlikely to fix this. Benefits of ferrites as over-the-bundle solutions to EMC problems are exceedingly over-rated. Any device destined to fly on a TC aircraft would have run the DO-160 gauntlet and enjoys necessary filters INSIDE. Any installation instructions that call for external fixes or prophylactics to be added as part of the installation process says the designer has not done their homework. Bob . . . ________________________________ Message 5 _____________________________________ Time: 07:37:57 PM PST US From: "Robert L. Nuckolls, III" Subject: AeroElectric-List: Speaking of EMC filters I have received a couple of HID lamp kits for evaluation with respect to EMC characteristics in OBAM aircraft. The first thing I did was order some HID conversions for the high beams on my Sedona. Noises from these lights are readily detectable while tuning around on the AM radio. The kit ballasts appear to have some sort of filter in the harness between the ballast and lamp. However, there is no such filter in the power input lead. I've been side-tracked on a task for a customer but I think I can get back on the bench next week. I'll light one of these kits up on the bench and then tune around with my DC-to-Light receiver. I can get a rough idea of the fundamental excitation frequency. I'll take a whack at some filtering on the DC input leads which goes to conducted noise. However, if there is significant radiation from the output leads and/or lamp, the problem is significantly different. I just learned today that I may be joining with NIAR at WSU on some interesting endeavors. The folks I used to work with at HBC in the EMC/EMI business now work at NIAR with all new facilities and gear. If the problem proves intractable using shade-tree techniques, maybe I can get into the screen room and secure a quick look-see with spectrum analyzer and probes. Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.