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I've come across several discussions {on other R/C forums} where folks vaguely talked about their model plane Altitude Hold projects. I've even seen some nice looking photos of their beta PC boards too. But I don't think I have come across any forum discussion that describes a successfully completed DiY project. Does anyone have any links to a success story?

Is there any serious interest in this sort of DiY project? It seems to me that a altitude hold controller would be a good accessory for the RCAP system. Or for convenient model aircraft loitering during a photo shoot.

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Its on my ever increasing to do list. I had a stab at the basics a while back but it never came together. I to would be interested in the details of such a unit, also air speed hold is on my list.

Terry

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I too would be interested in the details of such a unit ...

I'm beginning to believe that no one has published a working model airplane altitude-hold project. Either it is a challenge to design something that works well or the demand for such a gadget is essentially non-existent. I suspect it is a bit of both. Regardless, it sounds interesting, so I'll take a stab at it.

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Hi.

I hope this does'nt sound like another "allmost there project" BUT I think with all my other projects aside. I'm a few weeks away from a full baro. altitude logging/hold system. As I'm a hardware guy at heart,it's the software for the AVR thats been ,and still is, a steep learning curve! Well O.K. that and trying to stay away from Jack Bauer and the 4th series of 24.

Lyn.

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The last do it yourself altitude hold project that I seen was the one from Mike P. He had the proto just about finished before he dropped off the face of the earth. I still have the circuit and source code somewhere.

I would be interested in a altitude hold.

Crash Pilot1

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The last do it yourself altitude hold project that I seen was the one from Mike P. He had the proto just about finished before he dropped off the face of the earth. I still have the circuit and source code somewhere.

Did Mike ever release it to the public? Maybe it would be best for one of us to just complete what he started?

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I did try to find out how far Mike had got ,all I found was the schematics!

So If Crash Pilot has source code he's one up on me. Anyhow as I'v based mine around a AVR mega8 micro I don't know how much benefit the code would be to me now.

This project streches back a while as it's pressure sensor is a Freescale

4115,seemed good enough at the tlme,I'm also using an op-amp to get better resolution.

Lyn.

Edited by Johnstorm
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I'm still perplexed why so many Alt Hold projects have been started, but not finished. Has anyone come across a published design that works well? I'd hate to re-invent the wheel.

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Its also worth remembering that there are two way to do this, elevator or throttle control. If you go the throttle route then a speed hold control will be needed too but should give a better system in the end.

Terry

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I don't think it's absolutely necessary to use speed hold with altitude hold,it depends upon your intended use! If you put your platform at the disired altitude,pilot in control,it should only be necessary for the altitude hold to make small adjustments. If the throttle is given limits within software I think that's going to be enough.Feel free to let me know if you think otherwise.

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Yes I do agree to a point but it requires everything to be set up just right. Some planes will just stall if you increase the throttle too much and that would defeat the object as it is part of the gps return home safety device. It would be much easier to add altitude hold to a co-pilot leveled plane but I use a gyro instead so I need a more complicated system.

Terry

Edited by Terry
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A full scale pilot also has and uses trim tabs to help in flight to balance keeping altitude, speed and pitch setting where they want.

I find in my UAV style plane, with a fair amount of adjustment and tweaking the setup, that full throttle causes my plane to climb. I don't have to touch the elevator once I have rotated. It will continue to climb but no tendency to stall until it were to run out of fuel or lift. Then watching the video Link and GPS overlay altitude information I know that by adjusting my throttle I can get the altitude to stay reasonable steady where I want. At this setting, I can employ my UNAV Pico Alt E and it will keep it in place right there by adjusting elevator. The gain is set pretty low though. If I advance the throttle at this point, it will porpoise slightly if there is enough gain to keep it at altitude. If I let off a little gain in the Pico Alt, it won't hold it in place while powered on. Thrust at just a few degrees positive will overcome the light setting in the altitude hold.

I can smooth out the porpoising by reducing the engine thrust. But then I'm back to using elevator to get altitude. That’s OK at low altitudes but when you get high enough that you can't tell how much pitch you're using to keep your climb rate, it's pretty easy to over do it and stall. Low altitudes give the pilot the ability to manage it all. But it's very nice to have the plane set up so that it takes care of itself with just throttle once the pilot is more distant.

I also have the balance set up so that from a spec in the sky, I can simply reduce throttle to an idle and the plane will loiter its way down. No elevator needed. Again, it simplifies the pilot’s job. Sorry if this seems a little off track. I have gradually turned from using a well set up RC plane to finding it's better for me to have a hint of full scale operation. Leaving the elevator alone is a big help. (I do use it of course for take off and landing)

I would also state that this is going to vary in ability to dial in when you consider Power to weight/ lift etc ratios as well as how much wind there is. I feel the smaller and lighter the plane is, the smaller of an operational envelope you can safely operate in when flying autonomously. My plane is a big gas powered plane at 22 pounds and 50 mph flight speeds.

The Pico Alt comes in a T and E version. The T stands for throttle and the code is optimized for using a throttle for altitude hold. The E version is for elevator and the same applies.

In the end, I think they are both workable solutions. If you set your plane up so the power changes do not cause pitch changes, you can easily use elevator to do the job if you have enough motor/engine power, and minimize the elevator deflection. Don't let the altitude hold give your specific plane full elevator deflection.

If however you set the plane up to climb with full power, the throttle would be a better control to keep altitude IMO.

I would also like to state that even though I have experience with these systems over the past few years, I'm not an expert.

Dan

Edited by kd7ost
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