AeroElectric-List Digest Archive

Fri 02/17/12


Total Messages Posted: 5



Today's Message Index:
----------------------
 
     1. 06:36 AM - Re: Looking for a used PC680 battery for testing (hotwheels)
     2. 11:50 AM - autopilot servos (David)
     3. 01:10 PM - Re: autopilot servos (Robert L. Nuckolls, III)
     4. 01:30 PM - Re: autopilot servos (Peter Pengilly)
     5. 04:02 PM - Exciting News from Aircrafters (Timothy Farrell)
 
 
 


Message 1


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    Time: 06:36:18 AM PST US
    Subject: Re: Looking for a used PC680 battery for testing
    From: "hotwheels" <jaybrinkmeyer@yahoo.com>
    Thanks to all that replied to my query. I'm going to find something local that's close enough. Regards, Jay Read this topic online here: http://forums.matronics.com/viewtopic.php?p=366467#366467


    Message 2


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    Time: 11:50:52 AM PST US
    From: David <ainut@knology.net>
    Subject: autopilot servos
    Guys, can you help guide me towards what the specs are for autopilot motors? My idea is to use high-torque steppers so that they can be computer controlled by software that I write in a computer that I design (maybe an Arduino.) This is being done mostly for fun but also to be safe and practical in my OBAM aircraft. How much torque do I need? The Mustang II takes very, very small stick movement once airborne and the faster you go, the less torque required. Basically, once airborne, you weld your hand to your leg and just think about which direction you want to go and that is enough to turn or climb. I think it would be easiest, in programming, to have feedback from the servo on it's current position and there are other methods but the encoded type sounds easiest to implement. Thoughts? Lastly, AIUI, most steppers become free-wheeling once power is removed so that gives me control back instantly in event that is necessary simply by turning them off, leaving no drag on the stick or ruddders. I would like to control all 3 axes. So which steppers and corresponding controllers do you guys recommend? Or am I barking up the wrong tree? Once fully debugged, I may play with automated take-off and landing but that will be very, very closely watched if I ever get to that phase. Too easy to break something important (like me!) Thanks, David M. -- Tell the truth. Be honest. Be responsible to and for yourself. We want our freedoms back. Strike the illegal legislations called: 1) obamacare, 2) "Patriot (HA!) Act", and 3) 'presidential orders' that affect anyone besides gubmnt worker bees. Hate crime laws? Really? Thought police? Orwell would be proud. Every gram of cocaine you buy from elsewhere contributes to an innocent being murdered in Central and South America. Grow your own or Stop taking it.


    Message 3


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    Time: 01:10:33 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    Subject: Re: autopilot servos
    At 01:21 PM 2/17/2012, you wrote: > >Guys, can you help guide me towards what the specs are for autopilot >motors? My idea is to use high-torque steppers so that they can be >computer controlled by software that I write in a computer that I >design (maybe an Arduino.) This is being done mostly for fun but >also to be safe and practical in my OBAM aircraft. How much torque >do I need? The Mustang II takes very, very small stick movement >once airborne and the faster you go, the less torque >required. Basically, once airborne, you weld your hand to your leg >and just think about which direction you want to go and that is >enough to turn or climb. That's been the fondest wish of probably every a/p designer since WWII. Guys like Ed King, Honeywell, Bill Lear, Jim Younkin, et. als. can point to many decades of development spanning dozens of recipes for success. >I think it would be easiest, in programming, to have feedback from >the servo on it's current position and there are other methods but >the encoded type sounds easiest to implement. Thoughts? What have you read about autopilot history? Have you studied any of the legacy design goals for failure mode effects? >Lastly, AIUI, most steppers become free-wheeling once power is >removed so that gives me control back instantly in event that is >necessary simply by turning them off, leaving no drag on the stick or ruddders. Sort of. Steppers have a small but noticeable "cogging" in back drive torque. Jim Younkin went to stepper motors with a step down gearing on the order of 10:1. Typical torque needed at the aileron bell crank on an RV is 30 oz inches. So the stepper would need to supply about 3 oz inches of torque. At the same time, gearing magnifies the backdriving forces for the de-energized motor. 10:1 is probably a golden goal for trading off physical size of motor and tolerable back-drive forces. Gene Brown and I discussed a stepper motor driven a/p design probably 25 years ago at Electro-Mech. It's the easiest to implement both mechanically and electrically. No disconnect clutch needed. Have you considered an RC servo driving a tab on the surface to be controlled? RC servos are cheap and easy to integrate. They need some 'help' in the EMC department but that's doable. Driving a tab keeps you totally disconnected from primary flight surfaces and in absolute control for over-ride forces needed to deal with a tab that's jammed to the stop. Most AUTOPILOTS are designed to do pretty much everything a MANPILOT would do. But my idea of an small-letters autopilot is to keep the airplane pointed in the right direction with a minimum of maneuvering . . . very light fingered touch from the electronics. This suggests that you don't need fat servos capable of 2G loops and 360 degree per second aileron roles. >So which steppers and corresponding controllers do you guys recommend? >Or am I barking up the wrong tree? There's LOTS of trees to contemplate before you start barking. Exactly what do you want this product to do for you? >Once fully debugged, I may play with automated take-off and landing >but that will be very, very closely watched if I ever get to that phase. >Too easy to break something important (like me!) I can tell you that we had some VERY talented folks working that problem on the AGATE program. There is a Bonanza fitted with standard controls and 14v hardware for the right seat and fly-by-wire, glass- cockpit, highway-in-the-sky hardware in the left seat that ran from a totally independent 28v system. We installed our own SAAS (small aera augmentation system) right on Beech Field to give us real-time, centimeter correction for GPS signals. I wont suggest that you can't do it . . . but I've seen it done and the task is . . . shall we say . . . monumental? Your probability of success for any phase of your endeavors begins with small goals with stopping places for evaluation of results. Suggest you start with a simple mod to one aileron to add a tab, drive it with a servo that you can fit into your aileron, then go fly it with manual control knob on the servo. Can you achieve a servo/ tab combination that gives you the control authority you need to be a precision wing-leveler/heading-hold system in moderate turbulence? If the servo drives to either stop, is the airplane manageable without breaking a sweat? Tame that dragon to the extent he's not trying to eat you, then let's talk about ways to make him heel on a leash . . . and ultimately tap-dance. Bob . . .


    Message 4


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    Time: 01:30:56 PM PST US
    From: Peter Pengilly <peter@sportingaero.com>
    Subject: Re: autopilot servos
    David, I admire your courage in taking on one of the more difficult challenges in light aircraft avionics. An autopilot is primarily a flight control/flight dynamics problem - if you know little of this subject (for example if you are unfamiliar with stability derivatives) I would urge you to read up on the subject or get help from someone who does. There are also several non-intuitive gotchas that can sneak up on you. Could I suggest you read the relevant chapter of FAR23 - I think it is para 1329. I would suggest you ignore yaw until you have the other two axes sorted (or perhaps for ever). Servo torque must the the minimum that will do the job - as the pilot must be able to over ride the servos and the autopilot must not be able to break the aeroplane if it decides to inject full deflection elevator (especially at max level speed). If possible I would measure the stick force that is required to pull 2 g throughout the flight envelope, and also the stick displacement. Then measure how much force and stick displacement to roll at 30* per second. Now calculate the mechanical advantage of the stick, and so the force the servo will have to exert at the place you decide to connect it to the control system (make sure the servo cannot under any circumstance go 'over centre'). I suspect you will have to use some rate feedback, as well as position feedback, to accurately apply the desired control surface angle. If you do not include autotrim in pitch how will you tell the pilot that the servo is about to become saturated so he can trim manually? How will you ensure there are no large out of trim transients when the autopilot is disengaged? You will find quite a change of displacement required from circuit speed to fast cruise. CG position will also affect the stick force required. The logic is also non-trivial, at what bank angles will you transition from heading hold to bank angle hold? 5* is usual. You will also have to decide which parameter to close on for altitude control. You only have control over aircraft pitch attitude, so how do you use that to control altitude? What will you control in the pitch axis if you aren't holding altitude? Speed (IAS, TAS or ground speed) or rate of climb/descent? Will you have a minimum speed that would won't let the airplane decelerate below? For example, you are holding 5000ft and the engine power slowly decreases (for whatever reason), at what point do you give up trying to hold altitude and let the airplane descend at a minimum airspeed - or will you hold altitude come what may and allow the airplane to stall? If you are trying to follow a route, and for some reason your are off the track line how will the autopilot regain track and what information do you require from the nav system (GPS?) - draw some pictures it will take me too long to type! For that matter, where will get heading information for for heading hold, if from GPS what do you do if the GPS quits? How will you tell the pilot that the autopilot is no longer in control and he should start flying the airplane again? Over powerful autopilots have the ability to break airplanes and kill the crew, under powered servos will be no use at all. Best of luck with your project, please keep us informed of how you progress. Regards, Peter As an example a military autopilot I worked on only controlled one aileron through 2* (two degrees) and the elevator through about 15% of max travel - you will need more but will not need to operate over the full control surface travel. On 17/02/2012 19:21, David wrote: > > Guys, can you help guide me towards what the specs are for autopilot > motors? My idea is to use high-torque steppers so that they can be > computer controlled by software that I write in a computer that I > design (maybe an Arduino.) This is being done mostly for fun but also > to be safe and practical in my OBAM aircraft. How much torque do I > need? The Mustang II takes very, very small stick movement once > airborne and the faster you go, the less torque required. Basically, > once airborne, you weld your hand to your leg and just think about > which direction you want to go and that is enough to turn or climb. > > I think it would be easiest, in programming, to have feedback from the > servo on it's current position and there are other methods but the > encoded type sounds easiest to implement. Thoughts? > > Lastly, AIUI, most steppers become free-wheeling once power is removed > so that gives me control back instantly in event that is necessary > simply by turning them off, leaving no drag on the stick or ruddders. > > I would like to control all 3 axes. > > So which steppers and corresponding controllers do you guys > recommend? Or am I barking up the wrong tree? > > Once fully debugged, I may play with automated take-off and landing > but that will be very, very closely watched if I ever get to that > phase. Too easy to break something important (like me!) > > Thanks, > David M. >


    Message 5


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    Time: 04:02:33 PM PST US
    Subject: Exciting News from Aircrafters
    From: Timothy Farrell <motoracer@gmail.com>
    To all our dedicated customers and collegues, Aircrafters has some significant and exciting news to announce. We have a new partial owner! Tim Farrell has become a part of Aircrafters and will b e assuming all of the administrative, sales, and marketing responsibilities =2E Dave Saylor will be focusing his time and energy on the shop floor and w orking on your airplanes. I am originally from Oregon and have recently settled in the Monterrey Bay area. I 'm an instrument rated private pilot with years of experience buil ding Lancairs. I love experimental aviation and aviation in general. I h ave experience teaching and I look forward to helping Aircrafters spread it 's knowledge about building and buying all kinds of experimental aircraft. We look forward to having you back in our hanger. This year we will celebr ate our 15 year anniversary, that makes us one of the oldest and most exper ienced builder's assistance and experimental aircraft maintenance shops in the world. Today we are still staffed 100% by A&P mechanics and Dave Saylo r is our in house IA. We have a great relationship with the Sacramento FSD O and always assure compliance with the FAA's 50% rule. We make sure that every aspect of your build is quality, detailed and lasting. As a new service, we are offering maintenance on Light Sport Aircraft, both experimental and certified, along with Rotax service. Today's Light Sport Aircraft utilize technology that is new to many shops, but old hand for us =2E We have been working with composites, advanced avionics and glass panels for over a decade, one reason that makes us the best shop around for LSAs. Considering an RV-12? Give us a call. Feel free to drop by or drop a line anytime, I can't wait to meet you in pe rson, Tim Farrell Manager/Owner Aircrafters (831) 722-9141 motoracer@gmail.com




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