So my PWM field controller system isn't perfect. I ran into an unexpected problem where the motor gets into a very quick (many times per second) surge at part throttle, high motor rpm.
The reason is simple. At a given speed, increasing field current also increases back EMF in the armature which slows armature current down. Since my field controller reads armature current to determine field output, it reacts by reducing field current. Back EMF goes down, allowing more armature current. This oscillation happens 10 times per second and shakes the whole car. Not good.
A simple solution was to increase the "Throttle Up/Down Rate" in the field controller:
I initially had it set to 1, which is very quick reacting. I moved the setting up incrementally, test driving each time. I now have it set to 9, which has eliminated the oscillation. The throttle still feels a bit "surgy" at part throttle but at least it doesn't vibrate my whole car and risk breaking things.
Here is a labelled picture of my entire control system as of right now:
This weekend is "heater weekend". I plan to increase the output of my heater by removing a few rounds of heater coil to reduce resistance. I also plan to switch it with my ex-field interrupt solenoid instead of a 12V 5-pin relay that basically welds internally every time the circuit opens.