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Permalink Reply by Jonathan Brandmeyer on April 21, 2010 at 5:37am

1. As soft as you can get without sacrificing basic structural soundness.
2. For these sensors, it almost doesn't matter with respect to vibration. You don't want to propagate any engine vibration into the sensor chassis at all if you can avoid it. With a plane that big, you should have no trouble.

6. See Tuning ArudIMU and the Allan Variance threads under ArduIMU.

It is possible. This plane got a working MEMS IMU with a similar engine. We also had issues early on with engine vibration buggering up the IMU. Rigidly mounting the IMU in a heavy metal case that was itself mounted to the vehicle frame with soft rubber mounts solved the problem for us.

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Permalink Reply by Krzysztof Bosak on April 21, 2010 at 6:00am

You should have used double rubberbands then verify that single and double both provide accurate damping.

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Permalink Reply by Jonathan Brandmeyer on April 21, 2010 at 6:27am

You mean like this? That's a hard drive.

Don't mess with what works once you've gotten it to work. Soft rubber grommets was used on the autopilot. Later on, we used rubber bands on the hard drive.

From our perspective at the time, the autopilot was prohibitively expensive relative to the club's budget. We got it as a donation, so the heavy case was also intended as a means to protect that asset. I probably wouldn't worry so much about an ArduPilot.

In the end, the autopilot did die in a crash. But it survived a few others beforehand and lasted several years overall.

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Permalink Reply by Krzysztof Bosak on April 21, 2010 at 7:12am

Any single rubberband can break.

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Permalink Reply by Jonathan Brandmeyer on April 22, 2010 at 5:45am

If even one rubber band breaks, you will induce a large attitude error between the INS reference frame and the body frame. Yes, the other bands will keep the board from being damaged, but there will be some large angular error between the INS and the vehicle body.

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ModeratorPermalink Reply by Hooks on April 21, 2010 at 5:59am

Something like this could help you out.

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Permalink Reply by Lauri on April 21, 2010 at 10:06am

Jonathan, did you face any issues with RF interference on your earlier tests (without metal box)? Is that a real concern with IMUs?

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Permalink Reply by Jonathan Brandmeyer on April 22, 2010 at 5:46am

Not that I recall. We had grand dreams of building our own autopilot, but back then I was managing the imagery system.

We had some major issues getting the set of radios to work initially. GPS + WiFi + RC + RF modem was a challenge, but it was much better than GPS + video radio (2.4G) + 2xRC + RF modem (900M). But I don't recall them interfering with the autopilot, only with each other.

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