It worked!! , sort of. After several iterations of isolation designs, plus replacing just about every bearing on the heli including a set of ceramic bearings in the engine itself. My heli flew over the weekend. It was very brief and not without issues. However, at this point I'm very confidant that it will work.
So I've attached a couple of pics showing my isolation, which is pretty much a fusion of what the multi guys are doing and Manfred's earplugs.
Also I've attached my parameters, but these are not even close to the final numbers. Here's basically what happened: ArduCopter130414-0813.param
I started going straight off the wiki for tuning the PID's. I set Ch6 to adjust the Rate P for pitch and roll. It was flying quite well with very low P values (.01 or something) which I found odd because I was expecting almost unflyable which is what the wiki says. but I couldn't increase the dial more than 2 clicks before I would get wobble in the Yaw just prior to lifting. This was very confusing to me because I was expecting the wobbles to occur in pitch and roll not yaw, also the values were way lower than I was expecting to get any wobbles. Anyway I left the pitch and roll where they were at (before the wobbles) and set ch6 to adjust the rate p for yaw. this was a divergence from the wiki which says to dial in the I terms before going to yaw but I figured the wobbles were occurring in yaw before I could even get off the ground so I should turn the yaw p down a bit. on this try with very little yaw authority the heli started to get away from me and I had to bring it down quick. fortunately I only broke my training gear, but I wasn't going to risk tuning the PID's with out training gear so I was done for the day.
I know that nobody else is flying nitro's but I have no experience tuning a PID controller so I just want to make sure that i'm going about it correctly. the following are the specs:
Raptor 50v2 FBL converstion
600mm blades
TT.56 engine
JR8103 radio with FrSky module and receiver.
APM2.5 firmware 2.9.1
Also i'm sure that some of you are interested in my vibration logs, I not entirely certain that I know how to record them, I do remember reading about how to do it somewhere in the forums so I'll brush up on that and be sure to get them next time.
on a final note I'm currently in the process of moving from Hawaii to San Diego, the movers came yesterday and packed up all of my stuff. So there won't be any new progress on my part till Mid-June at the earliest.
Replies
Anthony: that makes sense but why would the yaw wobble kick in after increasing the rate p for pitch and roll? when the pitch and roll rates are very low there is no yaw wobble and the bird flies. shouldn't the yaw wabble occur indipendant of pitch and roll p?
Robert: when the engine is running up and the blades are still below flying rpm the helicpter is vibrating alot and i can see the apm bouncing around, but once the blades get to flying rpm everything smooths out i can't really see the apm vibrating at all. what is the best way to "tune" the isolation? should i pull the vib logs and just do it by trial and error? or is there a more elegant way to go about it?
Make sure that your anti-vibe system isn't *too soft* and allowing the board to move around at the airframe control frequency.
If the airframe can jerk one way, while the board goes the other, it's REALLY bad. Getting anti-vibe right on a heli is quite tricky. You have a narrow window of natural frequency for the APM. Lower than the vibration frequency, but higher than the airframe frequency. If the board can shake relative to airframe control frequency, you get control oscillation.
I suspect that you are getting the "wobbles" in the yaw axis prior to lift off is that as you increase rotor speed you get a yaw component and the controller is trying to control it, not getting any movement from the heli because it is on the ground and so it puts in more yaw and still doesn't get the expected response so puts in more....
You need to get the heli into the air so that the controller get the feedback its expecting.
To avoid yaw oscillations prior to lift off make sure you throttle up slowly so as to limit the amount of yaw imparted to the heli and therefore the controller.