Testing APM - Loiter and RTL Drift South Continuously - Discussions

Hi, I am testing my APM and for some reason when I switch it into Loiter or RTL it will continuously drift south until it is on the edge of my comfort zone and I take control again (300ft maybe).

The first circle of Loiter and RTL look good but the second is a little south and after 4 or 5 circles it way off and doesn't seem to be heading back. It does seem to be able to "fly" the plane well (PID settings seem right) Stabilize and FBW-A work great. It just seems to have a problem with navigation like the GPS points are moving south or something.

The wind was blowing south about 8 MPH but the plane didn't have any trouble flying up wind when told to manually and was making nice circles when in Loiter or RTL they just didn't keep centered on the right location or even return to the correct center once the got a long way south.

I am flying a basic Bixler with the APM mounted in a Bixler Chassis. I did have a camera on there too for some added weight but Stabilize and FBW-A didn't seem to mind the weight.

I have noticed that when on the ground and hooked up to an XBee (my xbee has very very limited range) that the compass seems to be off. It has the plane pointing in the almost opposite direction. I have checked many times to make sure the APM (new purple v2 board) is pointing in the correct orientation in the plane. Could the Magnets from the chassis be affecting the compass? could an incorrect compass cause loiter to continuously drift south?

THANKS A LOT if you help!

Ok, so while on the ground for all of this testing...I tried the calibration procedure many times while APM was in the plane and got wildly different settings and no completely funtional compass results.

I took the APM out of the chassis containing the magnets and away from the plane with the magnets, ran the calibration procedure and got excellent results and responsiveness from the compass. I brought the chassis close again and the reading skewed without moving the chip and then was no longer accurate or very responsive.

So... I guess my first step is to remove the magenets from the chassis and hold it in another way as to not interfere with the electronics. My second step is to fly again and determine if my gains need to be increased in order to give more navigational authority.

The only question I still have is if the winds are to strong for my "gain settings" and I don't have enough navigational authority will the plane still circle and start drifting down wind while circling or will it turn up wind (towards the waypoint) but just not reach it?

Replies

Chad P April 29, 2012 at 1:18pm

Ok, so while on the ground for all of this testing...I tried the calibration procedure many times while APM was in the plane and got wildly different settings and no completely funtional compass results.

I took the APM out of the chassis containing the magnets and away from the plane with the magnets, ran the calibration procedure and got excellent results and responsiveness from the compass. I brought the chassis close again and the reading skewed without moving the chip and then was no longer accurate or very responsive.

So... I guess my first step is to remove the magenets from the chassis and hold it in another way as to not interfere with the electronics. My second step is to fly again and determine if my gains need to be increased in order to give more navigational authority.

The only question I still have is if the winds are to strong for my "gain settings" and I don't have enough navigational authority will the plane still circle and start drifting down wind while circling or will it turn up wind (towards the waypoint) but just not reach it?
Chad P April 28, 2012 at 4:22pm

Yea, the wind was blowing to the south and a bit stronger than other days I have tested (maybe 10 mph). I did load the bixler config file and read through the manual files but when the stock bixler configuration worked so well for FBW-A and Stabalize I didn't go any further with tuning and maybe I should. I did have a camera on there which would add a little weight but other than that it should be the same as every other Bixler with chassis and AMPv2.

What you suggest sounds very likely and I will look into "turning up my gains". I guess I got confused when the airplane kept circling. I guess I thought it would not circle but head straight towards a loiter point or RTL point if it got to far off due to wind or whatever.
3D Robotics

Chris Anderson April 27, 2012 at 7:40am

Did you calibrate your compass in the Mission Planner?

This reply was deleted.