Mexican jumping bean Hexa...

Hi all, the Mexican jumping bean reference is what my Hexa acts like when I activate RTL & Alt Hold. Please read on:Started with drifting Simple mode, heading goes off by up to 90 deg. Then a lethal problem where in Stab mode,it gradually stopped responding to the Rx, and leaned over until it crashed. Dany at Canadadrones has gone beyond the call to help, replaced the APM & helped me go over everything. I replaced the PDB & not so long ago,the GPS. Everything else checks out on the bench. The non responding to th Tx seems to have been solved with the new APM and 2.9.1, but the drifting Simple mode remains, then.....I took it out in a field to test everything else, and that's when the Mexican Jumping bean came in : perfectly stable in Stab mode. Switch to simple, it gradually drifts. In Alt Hold, it starts to jump up down - up down in a jerking motion, a few feet each time, and not stopping. I can steer it, but it still jumps. When I hit RTL, it jerks up and down as before, but gains altitude... then it spins about 130 degrees, and heads off in some random direction, lurching up and down like a lunatic!! I aborted each time, and got it back safe. To make things more confusing, Pos Hold works fairly well.Any thoughts?Mick

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Andrew Sommer May 6, 2013 at 11:34am

I agree usually too high PIDs for a high power of copter will give a up and down movement when attempting to hover.It seems you can never find the right throttle to hold a given altitude. Same thing with other control boards such as KK2.

As far as the RTL, If you've been hovering, loitering or generally staying in one spot and switch to RTL the aircraft will almost always turn 90 degrees or more head off in the new direction until it can get a compass heading cross referenced with the GPS. THEN it will actually return to launch more directly. I've done the RTL test about half dozen times from a loiter and it has done this each time.

http://hover.It/
Mick May 5, 2013 at 5:48am

More info: Hexa; motors 880 KV; APM 2.5; v2.9.1

Logs attached (sorry, no Wireless Telem).
The Sun May 4, 2013 at 6:12pm

In Alt Hold and RTL your throttle proportional (P) gains or perhaps though less likely your derivative (D) gains are drastically off (way too high)

In your simple mode your correctional proportional gains are too low (once again could be derivative, but this is rarely the case)

ALSO!

Your Integral (I) gains may be wayyyyyyyyy to high in the simple mode, which can cause long and under-responsive correctional tendencies.

I highly doubt it is a hardware issue.
Tom May 4, 2013 at 4:05am

I would lean more to the PID's for you Alt Hold/ Loiter. I had the same issue until i adjusted the PID's and the jumping bean is no more. How big (KV rating) are your motors? If they are like mine (1000Kv) then you will need to really reduce your PID's from the stock setting. I would start by reducing the P term by 1.0 (ex. stock: 2.5 new: 1.5) and see if that helps your jumping.

At the very least DO NOT try any other settings/ flt modes until you get Alt Hold or Loiter set! This WILL end in a crash/ fly away almost every time!
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Dany Thivierge May 3, 2013 at 4:32pm

Mick pleas add your logs so the "experts" can have a look.
T3

Richard Boyhan May 3, 2013 at 12:57pm

Did you check your zAccel graph? Sounds like you have a vibration problem.

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Mexican jumping bean Hexa...

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