Sensors on gas powered plane (vibration with IMUs, RF interference)

We're trialling an 5DOF Sparkfun IMU on a 50cc gas plane with less than great results. 

The sensor output with our EKF implementation works fine in normal conditions. However when the motor is started and real vibration comes into play, results are all over the place. The data just isn't good enough. The gas engine is attached to the firewall with rubber vibration dampeners. 

What are your experiences/thoughts on the following:
1. How should sensors be attached to to the airframe (hard mounts, soft mounts)? 
2. What should the data acquisition rate be in high vibration scenarios (max available or happy medium)?
3. What are the "9" DOF IMUs good for? Are the magnetometer signals useful as extra input into fusion algorithms or is it on the board purely for compass purposes? 
4. Has anybody fused thermopile results with gyro/accelerometer results? 
5. How tolerant are gyros and accelerometers of RF interference? 
6. What indications should be used for measuring quality of sensor data when on level plane? 

Any extra recommendations for making a significant leap in the quality of results? 

p.s. Another issue we faced was that Arduino keeps restarting with vibration. Apparently the USB connection with an external computer is not tight enough. Based on preliminary tests, applying some tension on the connector fixed the issue. 

Views: 429

Reply to This

Replies to This Discussion

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.
Something like this could help you out.

You should have used double rubberbands then verify that single and double both provide accurate damping.
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.
Any single rubberband can break.
Jonathan, did you face any issues with RF interference on your earlier tests (without metal box)? Is that a real concern with IMUs?
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.
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.

Reply to Discussion


© 2020   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service