Problem Summary: Using Trampa VESC75/300 in a heavy robot that needs to be able to operate at temperatures down to -20C. Below about +20C the VESC will not run the motor smoothly at high torque/low speeds for some period of time after the VESC is turned on. For 20C this lasts about 1 minute. For lower temperatures this can be many minutes of poor performance making the robot drive very badly. Once the system is warmed up it functions smoothly with great torque and power.
Symptoms Details: During this "cold start" period the motor's motion is jerky. The motor repeatedly loses torque for periods of 0.5 to 10 seconds and during those times makes a high-pitched whining/grinding noise. On the Realtime Data, "current motor" gets stuck at some low value (10 to 30 amps) and the motor does not move despite "duty cycle" increasing. The motor is effectively cogging like a poorly tuned sensorless motor, despite having a properly set-up encoder, and running in sensored mode.
- VESC is in Duty Cycle mode, controlled by PPM. For testing this problem it is manually controlled via a Futaba transmitter/reciever.
- VESC is in FOC mode.
- Motor is instrumented with AS5047 Encoder, VESC is set up to use AS5047 encoder. Encoder is configured to 3.3V. VESC is set to 3.3V. According to terminal, no encoder faults or spi transaction failures occur. Setup is mechanically solid and works smoothly once VESC is warm.
- The motor is a large in-runner. Kv = 69rpm/volt. Continuous output 3100watts.
- The battery is 14S7P made of LG HG2 18650 Cells. BMS is rated for 300A for at least a minute.
- Symptoms occur well below the erpm for sensored to sensorless transition.
Testing: I have isolated this problem to the VESC specifically. If the VESC is cold (10C) and all other system components are warm (30C), jerkiness, whining and torque loss will occur. If the VESC is warm (30C) and all other system components are cold (10C), jerkiness, whining and torque loss will not occur.
- Is poor performance when cold a known issue on the VESC75/300? Has anyone else had similar experiences?
- Is there any known reason that this behavior would occur? Perhaps there are specific parts whose performance is degraded at low temperature like an oscillator or a DCDC converter?
- Can anyone with some VESC experience suggest tests that would help me further isolate and eliminate this problem?