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  • Ritchie October 25, 2010 at 3:51am
    Jordi runs his FunJet with AP or APM and that has a little screamer motor so 70mph+ is possible but this is the man that builds the AP so knows exactly what he is doing.
  • FLick October 25, 2010 at 1:27am
    Please consider that I hve no apm, I fly with a stabilizer arduino based. apm is actually no more than 50hz as I was guessing before (I checked the code and found a "we want this to be 50hz if possible" on the main loop)
    For what I have learned a fast plane can be stabilized by a 50hz refresh with a simple pid control like the one on apm, at least it is the same refresh of our std radios so you can implement a code to make it do that in the right way. Just don't ask too much (too near waypoints, too small radius, too quick maneuvers).
    I'm not aware of a limiter for the gforce induced by the autopilot, so a fast plane with lot of throw control can go into a strong gforce when you are tuning the pid by trial and errors, unless there is a limiter and I don't know about it.
    I'm sure that lot of people use the funjet with apm, can someone post his high and avg speeds so we can have some numbers?
  • FLick October 24, 2010 at 1:56pm
    fast planes can be moved by the apm for sure, the problem is only the performance you are expecting from it. you have higher turn radius, less reaction (airframe reacts more quicker and this is a problem when you have a slow harware that wait too much time to make a decision while the airframe has moved a lot). In my opinion based only on experience with other arduino based ap I can say..it will if you know how to use it, even a 200mph jet will fly if you don't demand too much.

    I still wonder what is the refresh rate of apm (I'm planning to buy it but actually I run on my own code on arduinopro),
    if apm use a standard 25ms ppm frame it can't run (if it does is absolutely useless) over 40hz. even at 40hz in the next frame the servos are only starting to move to the previous sent position so he is calculationg based on a wrong feel by the sensor.
    To me this a good reason to think that apm is not suitable for really fast maneuvers and/or corrections (that is different than fast planes).
    One simple way to see this is to make a video of the roll resonance induced by the apm, the quicker it is the quicker is the control loop. I really wish too see this! on an easyglider or cularis the best because are my 2 platform.

    I really wish to know more about that and have real data because those are speculations that I'm making while choosing if I have to buy or not the apm. His slowness is my main concern because I fight against that a lot with mine. Actually I'm so quick that had to write some code to avoid to burn my aileron servos (It happened, servo was so quick reversing that motor burned even if on 5V only, you can't do this with ppm even if you try because 40hz reversing is accepted by servo, I was reversing it much quicker).
    I mounted the imu on the servo arm to see where I can go. in flight is different because you have airframe inertia helping to slow things, with fast reacting planes maybe it could happen with fast code like mine. don' want to terrify anyone, with my easyglider it was impossible to burn it but on a dive I melt some cables when it reached the resonance on roll. Emax 9g digital servos, I melt the long cables in the wing that are not cooled in any way, on the ground I warped the wing and they made a short.. I never read about this with apm so I think that you are not going so fast.

    Anyone want to make some try? :)
  • Logan Greenlee October 23, 2010 at 6:00am
    The speed of the model is not really the issue so much as the stability of your model. As long as your model "behaves" well the autopilot will function well. As with any model you may need to adjust the PID terms to fit your aircraft's control response rates, though the default terms seem to work pretty well.

    One thing to note, the navigation control loop in the mega beta processes at a rate that is not high enough to fly real jets with with the default waypoint radius of 30 meters. What this implies is that if your model is going fast enough, it can "miss" the waypoint and will go into an orbit around it due to a roll limit of 30 degrees.
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