Just how important vibration isolation is with an APM become clear to CanberraUAV this week. We were testing flying Jacks SkyRaider (a low wing sports plane with a 0.5ci engine) on Sunday, and found that we got severe gyro drift. The first minute or so of flight was OK, but the plane quickly developed severe roll and pitch drift when it stabilize mode. We were recording the flight using a mavlink log which showed that the roll went from -2.97 radians to 3.09 radians, when in fact we were flying fairly level!

We tried swapping out various APM components with known good bits from my SkyWalker, with no luck. Chris Gough then suggested that the problem may be vibration, given that the SkyRaider has a glow engine,  and the only vibration isolation was some double sided tape between the APM and the fuselage. On Wednesday we tried again with a thick layer of foam beneath the APM (see the above picture), and it worked fantastically! We would quite surprised quite how much vibration isolation mattered.

I've mounted the APM for my Senior Telemaster with an even thicker layer of foam:

 

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Developer
Comment by Jason Short on June 30, 2011 at 5:11pm

Do you have your filter pads soldered? I would recommend that now for planes too. There was some confusion before about it. The filter helped my quad tremendously.

Jason

Comment by Clark Hymas on June 30, 2011 at 5:43pm
Here is what I have done.  Its pretty simple, I am running a four stroke .70 and I'm not having any trouble with gyro drift.

Developer
Comment by Andrew Tridgell on July 1, 2011 at 4:47am

nice idea Clark!

Jason, no, we haven't soldered the filter pads. Do you know what filter function that adds? What is the time constant of the filter?

 

Comment by Gerard Toonstra on July 1, 2011 at 9:36am

I can certainly contest in this regard. I run a setup with the APM zip-tied to a piece of fiberglass, supported by some plastic standoffs. The quad has four props+motors, where the motors are mounted on fiberglass plates, which are in turn bolted onto aluminium arms. I've been taking off a couple of times getting not so good results. The quad went up quite ok, but in less than a minute starting taking off sideways or forward towards some destination that I could only compensate by the controller, all during low-wind (2/3/4 Bft.) conditions. I've taken the quad back the bench and then discovered that in all the flights, the nuts weren't exactly super-tight, but could be tightened by another 1/4 turn or so. It felt very secure though.

Miracles happened to stability after that. When the bolts felt really tight before, it didn't like being in the air for more than 2-3 minutes before it became difficult to control. After the tightening of everything, it went happily in the air until the battery was dead. Whenever I launch the copter now, I first tighten every bolt/nut on it even if it's only for a 1/8 turn, then take it for a spin. Does wonders to stability.


Developer
Comment by Michael Oborne on July 2, 2011 at 3:04am
you should start monitoring imu health, this is a clear indicator if vibration is a problem.
Comment by John Cousins on July 7, 2011 at 5:27am

I'm pretty sure i'm going to have to deal with this problem shortly. I will be running a big 111cc twin cylinder. They are supposed to be a "low vibration design" but they all say that. There is a mob out there somewhere who build a tiny ltttle mounting chassis that suspends the APM on a little platform mounted on springs in 3 different axis. It looks the goods but makes me wonder about harmonics! Could actually make thing worse at certain RPMs. Foam looks ugly and crude but seems to be the mounting of choice...

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