Compassmot and compass offsets troubles


Currently trying to set up a locuste quad, and going through all compass calibrations.

In order to avoid interference, I have positioned my UBLOX GPS+compass at the very back of the quad, and up by let’s say 10cm. It seems to me like this position should be fine in terms of interference.

However, I’m getting 48% compassmot in this configuration. Also, when calibrating the compass (method described by Chris A. in one of the videos), I still get some huge values for the compass offsets - some values are within -400 +400 boundaries, but one of them, sometimes 2, are huge numbers…

When setting this huge offset to 0 (to be able to arm) and loitering, then of course I get the “toilet bowl”, which I guess is logical with such problems…

I’m out of idea, I have tried to move the compass/GPS to the front, still up by 10cm, and it’s giving me the same results after calibration. I could raise it more, but I suspect the problem is elsewhere. Even the compass sitting on the APM will give me the same results

Can anyone think about any reason why I’m getting so much interference, and why I can’t properly calibrate the compass (offsets) ? would my big motors be responsible for this big magnetic interference (when running compassmot at 50% throttle) ?

Equipment: APM2.5 (modified by 3DR in 2.6), UBLOX/Compass, Locuste frame, motors D3536 Turnigy 910kv (yes way too big and too heavy!), ESC Turnigy Plush 30A, Arducopter v3.1. Location: New Caledonia


The first thing I see is the rat’s nest of cables. You run a FrSky receiver - can’t you use CPPM? Then, twist all cables! I had the same frame and had the APM basically at the same position, using the integrated compass. My battery was in the back, though. But most important, I had all cables twisted. That makes a huge difference!

Thanks. Yes I should go CPPM, although not sure how to that at this stage. However, I guess that will be one single cable out of the FrSky, but then I don’t understand what you then have to twist if there is only one cable ? do you mean some other cables ?
I also thought about having the battery at the back, but it looks too far away from the CG that’s why I’ve placed it in the middle and perpendicular to the frame… maybe I’ll try at the back though.

Can I ask you waht kind of motor/ESC/prop your had on your frame ? planning to replace my big motors by some 880kv from 3DR…

I had a Q-Brain 20A quad ESC and NTM 2830-800kV motors.

When you go CPPM, you have one cable, but that cable will still have 3 wires. You should generally twist all cables to reduce the EMI from those.

Instructions of how to connect the PPM cable are here: … _RC_inputs

Hi, there’s lot of trick to reduce mag-EMI, first twist all the power cable (ESC, battery), then all the cable connected to the device such GPS, telemetry, etc., if the cables are not too long is not important (i mean a few cm).
Then connect only the PWM signal to the motor output, remove the ground and the BEC positive wire, of course if you use a BEC to power the board let alone only this one.
Try to keep as far away as possible the flight control board from the distribuition board.
On my Facebook public profile you can found a lot of useful (i hope) images about this, for example: … 304&type=3 … 304&type=3

More able to keep “clean” wiring and less noise you’ll have, in the picture you posted imho was not done a good wiring, keep order on your quad, he will know how to repay you… :sunglasses:
However with the “compassmot” 30% even though it is a little high you should have a good Loiter if tuned well.

Bests, Marco

ok thanks. I think I will start by twisting everything I can, then I’ll redo the calibration and let you know how it goes.
One question though… is it important to have the APM far away from the distribution board (distribution harness in my case), or is it just the Ublox/compass that needs to be away ? In my case the APM, while sitting on a rangevideo anti vibration red thing, is just kind of over the power distrib harness…

Absolutely yes, even if you use an external compass.
Please post here your result after re-wiring all, i’m curious.

Ok I went through all my wiring again
So I twisted

  • the distribution harness cables together
  • the 4 signal wires from the ESCs together
  • the wires from the FrSky RX. Unfortunately I haven’t figured out how to have CPPM working with my FrSky module. I have correctly placed the jumper on pin 2 and 3 on APM, but then it doesn’t do anything when using the remote (9X with original firmware and FrSky module) - Not sure whether I have to do something specific at the FrSky Tx level…? if anyone has a good link on that I take :slight_smile:
  • the UBLOX and Compass wires together

After all that, I did another compassmot and compass calibration

  • compassmote went from 48% to 42%…
  • compass offsets are still completely out of bounds

So what ? how far/high will I need to place APM and UBLOX/compass ? wondering how you did StephanG using an APM with integrated compass, on the same frame? would it be the sign of defective equipment (my APM had an RMA with 3DR, where it was supposedly converted from 2.5 to 2.6, same original board)

Once again out of solution here - I might try to fly with this amount of interference, although will have to set the compass offsets back to 0 I guess, but I know I won’t be able to loiter or use any of the auto mode :frowning:

Try unplugging the power leads to the motor and run the test. Those are big motors they could be the cause of the emi or try taking the props off and run the test. I ran my hex without props and my test came back at 1 percent. You could try a new gps from ebay. I got a ublox gps with compass on it for 30 dollars and a case with a stand for 10. I get 12 satellites on it outside.

With no props on the motors you won’t get any load and therefore no amperage draw so you may skew your results. Right?

Sent from my SM-N900T using Tapatalk

Yeah it’s pointless testing without props or with Un wired motors! That’s like testing how loud your car engine is with it switched off :slight_smile:

sent from my phone so apologies for any typos

My point is to narrow down where the interference is coming from. I am in the industry of electroinics and mechanical devices. I am a specialist for our company and i am sent in to diagnose and repair problem equipment that no one else can fix. You have to have a open mind and not rule out anything until testing is done. You would be supprised when i am working on the phone with another tech and they have not tried what i have asked and when I go in and and do the tests and solve the problem. You should never be closed to an idea. That is why I said to test without blades and no load. The esc can generate noise, or the motors, or esc wires, connecters arcing. I have a open mind and will try anything to narrow down a problem. It comes with my 35 years in the industry.

[quote=“RabbitStu”]Yeah it’s pointless testing without props or with Un wired motors! That’s like testing how loud your car engine is with it switched off :slight_smile:

sent from my phone so apologies for any typos[/quote]

Ok i ran motormot with my props on and i get 3percent and with the props off i get one percent. So the ball is in your park. No load on motors was only a 2 percent difference. Now i am running a power module that gives me a clean 5 volts. Mybe that is why i get low noise.