Another week and a little bit of progress.

For the last few weeks I've been looking for solutions and probable causes for the EMI that influences the compass and now I have a small list which can be usefull for anyone who wants to use a compass succesfully. 9/10 times it's a combination of problems and not just one.

- Problem 1: Motor noise, brushed motors can generate noise on their powerlines because of the brushes making contact with the stator inside the motor.

Solution 1: Apply 3x 0.1 uF ceremic capacitors on the motor, two from motor terminal to the motor casing and one between both motor terminals.(there are more variations with more or less capacitors and some with inductors).

My motors had these build in. Check if your do, otherwise the motor or the capacitors might get damaged.

- Problem 2: Electromagnetism(1), long wires between your motor controller and motor can generate a magnetic field which can distort other electronics.

Solution 1: Twist the motor wires, atleast 1 full turn every 4-5 cm.

Solution 2: Apply shielding on these wires and connect these to your ground.

The wires to my motors are quite longso, so I chose to apply shielding, it's a metal sleeving, coverd by plastic sleeving.

- Problem 2: Electromagnetism(2), the motors themselves are large electromagnets with magnets inside them.

Solution 1: Shield the motor with a metal casing and ground it.

Solution 2: Create distance between your electronics and these motors.

In my situation there's very limited space around my motors, so it was not possible to build a casing around it, I opted for solution 2 and placed my compas on a pole. I measured with an other electric compass(my watch) on what distance the motors started to influence the compass where it started to point towards the motors instead of the north. It was about 15-20cm where the field ended.

- Problem 3: Conduction(1), noise traveling from the motor, through the controller into other electronics.

Solution: Separate the motor and controller from the rest of the circuit by using a BEC and a motor controller with optical insulation. Or use separate batteries.

In my case, I do not know if the Kangaroo/sabertooth are optically insulated, however I am using a BEC and have the possibility to use separate batteries.

- Problem 4: Conduction(2), this one is only useful for those with a metal framed robots. The switching magnetic field of your motors can create small currents inside your metal frame which will cause noise.

Solution: Ground your frame.

In my case, my entire robot is made out of aluminium, except for my gear boxes, wheels and battery tray. I connected a wire from my frame to the ground.

Here's a measurement without grounding:

Here's a measurement with grounding:

By applying this I removed most of the noise from my system, which is good. However this did not improve my compass readings...

By doing more tests I found out that vibrations are a major player in my problem aswell. The gears in my transmission, connecting the motors to the transmission generate a lot of vibrations. The moment I disconnected the pole with my the compass attachted to it, the readings stabilized.

Now for all those wondering if all of the above was useful and how I know it was useful. Well it didn't stabilize before. I have tried to solve the problem by disconnecting the compass from frame and it would still be unstable.

To conclude this post, I have reduced, if not mostly removed the noise from my system by applying multiple solutions to different causes of noise and EMI. In the end I could not remove all EMI from my system as the motors are just magnets where the only solution in my case was to move the compass away from it. And finally there was also a mechanical influence on the compass which effected it. I'm still working on a solution.

So it's been a while since I posted anything on this project, been very busy, it happens. But Im still working on it when I have the time

In anycase, I think I managed to solve the vibration issue in my robot with a flightcontroller vibration damper and a software based filter. Which is a major milestone if it works as planned.

The issue I've been having is that the vibrations caused by the gears in the robot were causing osscilations in the compass, which would cause the measurements to vary within 50 to 100 degrees in compairison to a measurement with the motors turned off.

So I added a vibration damper and mounted the IMU to it, which reduced the osscilations within 30-40 degrees, which is a lot better than before. To get even better data I also added an exponential filter to filter the measurements. With the filter the values vary within 10-20 degrees and that's within an acceptable range.

Now I only need to do some outdoor testing and see if it's still swerving around while heading towards the set GPS location. If it works I'll add a video.

Arduino filter Vibration damper

While working on the vibration problem I added a few more features, mainly revolving around a SD-card module for local data storage. This gives a lot of possibilities. Namely:

• Sensor data logging: The arduino logs the GPS position, together with compas heading and the ping sensor data. Collecting a large amount of this data could be used to make a low resolution map, based on its location, heading and distance measurements.
• Return to home: It stores it's starting possition when it's turned on or you can set a specified starting point and command it to go there.
• Waypoint logging/storage: Add waypoints on the fly, giving the possibility to make routes and set destinations manually.

In the future I might store all variables on the SD-card to reduce time between tests when changing certain settings and not constantly have to reflashing the arduino.