Thermistors

Over Temperature Current Limiting

There are two temperature sensitive currrent limiting modules on the ODrive Pro, <axis>.motor.fet_thermistor and <axis>.motor.motor_thermistor. The temperature reading (in Celcius) from each thermistor can be monitored from <thermistor>.temperature. Both modules can be enabled by setting <thermistor>.config.enabled to True.

When enabled, either module will start limiting the motor current when the <thermistor>.config.temp_limit_lower threshold is exceeded. The current limit will then ramp down, ending with 0A once <thermistor>.config.temp_limit_upper is reached. If the temperature continues to rise past <thermistor>.config.temp_limit_upper + 5°C, the ODrive will exit CLOSED_LOOP_CONTROL with an error of either INVERTER_OVER_TEMP or MOTOR_OVER_TEMP, depending on which thermistor exceeded this threshold.

Current Limit vs. Thermistor Temperature

Warning

The lower and upper thresholds for <axis>.motor.fet_thermistor can be changed, but this is not recommended.

Motor Thermistor Configuration

All motors with an integrated thermistor offered by odriverobotics are compatible, otherwise make sure you have an NTC type thermistor before use.

• Connect the thermistor wires to THERMISTOR+ and THERMISTOR- (polarity does not matter)

  Single Wire Thermistor

  Make sure that the thermistor shares a common ground with the ODrive, we suggest connecting to J8 pin 4 or 11.

• Configure the Thermistor + pin to GpioMode.ANALOG_IN.

• Set the thermistor parameters:

  • motor_thermistor.config.r_ref: Resistance of the thermistor at the reference temperature (usually at 25°C). This can be found in the datasheet of your thermistor and is usually denoted as R_25.

  • motor_thermistor.config.beta: Beta value of the thermistor. Can be found in the datasheet of your thermistor. Sometimes denoted as B (25/85) or similar.

  • motor_thermistor.config.t_ref: Reference temperature (in °C) for which r_ref is given. Defaults to 25.

• Set both motor_thermistor.config.temp_limit_lower and motor_thermistor.config.temp_limit_upper according to your motors datasheet.

• Set motor_thermistor.config.enabled to True.

Note

For users migrating from ODrive v3.*, no external circuitry is required to use a motor thermistor. The ODrive Pro has a built in 1k ohm voltage divider.

Fan Control (Pro only)

The ODrive Pro has one 12V supply with a switched negative lead (Fan-) on J12. This is designed to power an offboard fan which can be controlled by one of two modules:

• <odrv>.config.odrv_fan

  Used for cooling the ODrive FETs. Feedback is received from the integrated fet_thermistor

• <odrv>.config.motor_fan

  Used for cooling the motor. Feedback is received from an offboard motor_thermistor

Both <fan> modules use hysteresis control, where the fan is engaged once the temperature reading reaches <fan>.upper and remains on until the temperature drops below <fan>.lower, either module can be enabled by setting <fan>.enabled to True.