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Author Topic: Why the Windup??  (Read 853 times)

Offline Wynn Robins

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Why the Windup??
« on: November 01, 2010, 07:58:20 PM »
Pretty windy at the contest we had in the weekend  but not too bad - I had a few issues with my Legacy winding up during insides  - thought electrics were suppoed to slow this down somewhat.

I am running in Governor High  - should I perhaps be running in set RPM????

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Offline Dean Pappas

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Re: Why the Windup??
« Reply #1 on: November 01, 2010, 09:50:54 PM »
Hi Wynn,
No, the RPM range or set RPM are not interesting here.
Resistance to wind-up is dictated by three things:
1) Governor gain,
2) Governor response time,
3) prop pitch and drag.

Bigger diameter, lower pitch props with slightly thicker airfoils will reduce the windup at whatever RPM the motor turns.
Adding gain tightens the control loop so that the motor "never" winds up more than maybe 50 RPM.
Speeding up the response time may help make the backside of the consecutives feel more like the up-sides.
Yes, thicker prop airfoils will lead to a small loss of efficiency, unfortunately.Other have messed with 3-bladers too for this reason.

Hope that helps,
Dean P.
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Offline Keith Renecle

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Re: Why the Windup??
« Reply #2 on: November 02, 2010, 12:24:19 AM »
Hi Wynn,

I can only agree with what Dean says here. What sort of wind speed are we talking about here? Any idea? We must also remember that our models become something like kites in high wind, especially that downwind leg where they accelerate like crazy. I was testing some new software for my governor timer the other day, and the big windsock at our club was blowing dead level. I would estimate a wind speed of around 30 knots.....one of those days where you can do lazy eights downwind without the motor running! No governor/prop setting can eliminate windup in those conditions.

I was using all 3 of the standard PID (Proportional, Integral, Derivative for feedback systems) formula's in my software with the gain bordering on oscillation, and the windup was there, although I must admit that it handled the conditions better than my .49 diesel mods. I was using a standard APC 12 x 6 prop on a MVVS 6,5/910 motor. I could even hear the governor working hard (oscillating) under these conditions.  A few times the wind was so strong that I could not get the model high enough to get in an outside square loop. Although it was fun to see if the model (and me!) could survive these conditions......there is definitely a cut-off point to where a half decent pattern can be flown. In FAI stunt this point is 9 metres per second...........fortunately! To actually get through some of the maneuvers, you end up having to bias them to either side. The strong wind is one thing, but add a couple of buildings and trees etc., then the fun becomes a nightmare!

Keith R
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Offline Wynn Robins

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Re: Why the Windup??
« Reply #3 on: November 02, 2010, 02:35:51 PM »
thanks guys - I will change my settings and go give it a try -  to start with I set everything right in the middle -  gains, response time etc.....will up it all

Keith, I have been conversing with Loren Nell - (I am in NZ too) and he has been speaking of your timers etc - would be interesed in seeing what you have come up with.

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Offline Keith Renecle

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Re: Why the Windup??
« Reply #4 on: November 02, 2010, 10:46:46 PM »
Hi Wynn,

Yup, I know that you're in NZ. I told Loren to contact you a while back. He was here last month for a couple of weeks, and I let him fly my system in two of my models. He mostly flies tuned pipe engines, and was most impressed by my setup. He has one of my governor timers now and is busy working on an electric Trivial Pursuit. He loves this design and has built many of them through the years. Loren is also a very good stunt pilot as well, and we certainly miss him here in Darkest Africa.

I will post more details about my governor timer on this forum soon. I just need to stop modifying the software! Right now it is pretty solid, and I'm waiting for some feedback from a few people. Dennis Adamisin has some to test and a few other pilots overseas also have some. The original idea was to provide a simple, low-cost power package that works at least as well as the popular sport glow engines, like the OS FP and LA series. It should also cost around the same price. As things turned out, it works much better than any of these sport glow engines (and many of the expensive glow stunt engines), and uses basic esc's like the Hobbywing, Turnigy etc. that do not have governors in them. My timer monitors one of the motor wires to give rpm feedback to the processor, and then I use this to keep the rpm constant. Right now I would say that I'm 98% happy with this project and I will post more details shortly.

Keith R
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Offline Wynn Robins

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Re: Why the Windup??
« Reply #5 on: November 03, 2010, 01:17:55 PM »
sounds good Keith - I will look forward to seeing more information on your system...
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Offline Dean Pappas

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Re: Why the Windup??
« Reply #6 on: November 03, 2010, 06:19:15 PM »
Way to go, Keith!
The funny thing is that back when Bob and my involvement with E-Stunt began, I started designing a governor until Bob Boucher, at Astro, chided me for re-inventing the wheel. "It's already inside the ESC" he said, so I set it aside and started playing with the Castle heli software. I liked what I found, aside from the fact that the brake was sensibly disabled in heli-mode, and never picked it back up. Now, of course, we may be at the point where we want better visibility into the control loop gain, bandwidth/response time, and damping characteristics.
again ... bravo,
Dean P.
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Offline Howard Rush

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Re: Why the Windup??
« Reply #7 on: November 03, 2010, 07:13:04 PM »
I want the visibility.  Is anything published, or do we try to find out by experiment?
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Offline Tim Wescott

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Re: Why the Windup??
« Reply #8 on: November 03, 2010, 07:17:08 PM »
Quote from: Dean Pappas on November 03, 2010, 06:19:15 PM
Way to go, Keith!
The funny thing is that back when Bob and my involvement with E-Stunt began, I started designing a governor until Bob Boucher, at Astro, chided me for re-inventing the wheel. "It's already inside the ESC" he said, so I set it aside and started playing with the Castle heli software. I liked what I found, aside from the fact that the brake was sensibly disabled in heli-mode, and never picked it back up. Now, of course, we may be at the point where we want better visibility into the control loop gain, bandwidth/response time, and damping characteristics.
again ... bravo,
Speaking from my professional side as a guy who controls motors, working from outside the ESC will almost certainly not get you to the theoretically optimal solution.  There's information available inside the ESC that you just can't get from outside, and the path from the outside to the ESC's driving circuit is also bottle-necked.

So from a strictly theoretical point of view the best thing to drive on of our brushless motors would be an ESC that's specifically programmed for the task of running a control line stunter.  A nice bonus that would drop out of this would be a free timing function (sorry Will).  Even better -- again from a theoretical standpoint -- would be a sensored brushless motor and matching ESC.  Practically, however, this would mean that you'd have to become an ESC manufacturer and learn everything that the guys at Castle Creations know about the specifics of model aviation brushless motors.  It's humanly possible (or the folks at Castle wouldn't know it), but it'd take a lot of effort and smarts.

Practically you may do better with an external governor and a 'regular old' ESC, but only if the ESC maker doesn't address their shortcomings for this application.

Certainly if you can make an external governor and timer that brings the system cost down for low-budget operators who can't afford really fancy ESCs then that's an attractive approach.  Attractive enough that I'll be watching what Kieth's doing when my I finally stop using old used slime engines and spend the $$ for electric.
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Offline Keith Renecle

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Re: Why the Windup??
« Reply #9 on: November 03, 2010, 10:59:29 PM »
Thanks Dean, This has been a real interesting project, and I can totally agree with Tim on the external governor issue of not being the ideal method of doing this. It started out trying to make a better system than the "power-up" idea in the JMP timer, and the first few versions were useless. I was never able to use these PIC chips, as I come from a purely hardware background in electronics. I therefore had to learn to program, and it was a challenge. The last time that I did this was on the old "steam-driven" Apple 2, and mostly I used BASIC and a little assembler. Anyway, I did manage with lots of help from friends like Igor, and eventually I have a very useable timer with a pretty good governor. Sure it may be not be as good as the Jeti, CC, or Schultze systems, but then I can provide a total package here locally for a .40 glow equivalent, for the price of an OS LA 46. This consists of the E-Max/Arrowind 2820 motor, 40 amp Hobbywing esc, plus my governor timer. Making a dedicated C/L esc is the real answer, but that's way above my head, and would be pricey, so for now my system works well enough for the sport flier that wants to fly electric without breaking the bank.

I'm just waiting for some feeedback now from Dennis and a few others, and then I'll try to finalize the software, and post the details of how to get one one this forum. I am selling them now locally, but then it's easy for me to update the software when I get feedback. I would say at this point that I'm around 98% happy with the software. I have found a few real cheap esc's that don't like my system. One of the Scorpion Heli esc's also does not work too well, but then it does have a 6 volt BEC and I did not add an extra regulator on my pc board to protect the PIC chip. Anyway, as I said, I will post something shortly.

Keith R
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Offline Tim Wescott

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Re: Why the Windup??
« Reply #10 on: November 04, 2010, 11:10:46 AM »
Actually, making a big ESC that works well with any one motor isn't that hard if you've got a few brushless motor driver projects under your belt.  Making an ESC that'll work well with any motor, and is teeny, and works with poor cooling, etc., etc., is what is hard.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dean Pappas

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Re: Why the Windup??
« Reply #11 on: November 04, 2010, 11:26:52 AM »
Hi All,
Howard, so do I ... after all, I'm a controls guy too.

You're right, Tim. Different motors pose different problems: from what I gather, the problems we were running into at very high currents in Pattern forced changes in the commutation detection filtering that don't work the same in all cases, and have dramatically increased processor activity and temps as compared to older software loads in the same ESC.

So why don't "Y" wound motors come with a 4th wire that could be used as a reference for commutation detection? Never mind ...
Dean P.
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Offline Tim Wescott

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Re: Why the Windup??
« Reply #12 on: November 04, 2010, 12:28:52 PM »
Quote from: Dean Pappas on November 04, 2010, 11:26:52 AM
So why don't "Y" wound motors come with a 4th wire that could be used as a reference for commutation detection? Never mind ...
You could wind the motor that way -- but you'd still need an ESC that knew what to do with it.

You may as well ask why not an ESC/motor combo that puts an encoder on the motor?  Industrial brushless drives use an encoder with hundreds or even thousands of counts to extract the motor position with great detail, an use this for motor commutation.  A thousand count encoder is out of the question for a model, but there are some hundred-count encoders out there that are small enough they'd be practical, assuming you could ever find an ESC that would know what to do with the signal.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

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