Evening all. My first post here, but hopefully a productive one
(I have also tried a search, but can't find anything similar to my problem)
I am trying to drive a large (24V, 30-40A) DC brushed motor, on a small electric car.
We are using a proprietory motor driver (a 4QD, if you are interested) which contains far more functionality than we require. This drives our motor at about 20KHz, and in itself works quite effectively.
We have a variety of sensors attached to the arduino, sensing motor speed, wheel speed, motor current, throttle position (in fact a button pressed or not) temperature, etc. We are also logging our data on an SD card logger.
Now, for the problem. No matter what we do, we are getting horrendous noise on the sensors. For example, the motor speed (sensed using an optical sensor and a slotted wheel) will suddenly jump from around 2,000 to 2,750,000 and then back again.
At the same time, the wheel speed (sensed using a magnet and a hall effect sensor) will also jump the same amount.
Bizzarely, the throttle button (push to break button) is now also seeing noise on its line. (jumping from logic 0 to 1 unexpectedly, etc)
Noise wise, we have tried adding a capacitor across the motor to little benefit. Removing the heatsink from the motor has made the noise much worse (the motor is only rated to about 240W, but we are running it much harder.)
The motor also contains 2x 1uF caps, one across the supply and one from +ve to the case.
The 4QD driver contains about 3,700uF of capacitance across its supply.
The noise appears to be airborne RF, rather than ground lift etc, as we have run the logging arduino on a fully isolated system to the motor, with similar results.
Any thoughts? We are getting a bit stumped now... Is the RF likely to be causing the internals of the micro on the arduino to get upset?
Brownouts on the supply are unlikely, as we are powering the arduino from a 11.2V LiPo, through an external and very efficient voltage regulator, capable of a sustained 3amps.
The vehicle isn't chassis grounded, everything is earth returned. Traction batteries are a pair of 12V AGM batteries, similar to large motorcycle batteries.