Hardware Configuration

Power System

Trip Levels

To prevent damage to the power supply, you must configure the ODrive such that it never pulls too much power out of the power supply, or puts too much power back into the power supply.

For this, the ODrive continuously measures the supply voltage and estimates the current going in and out of the power supply (referred to as DC voltage and DC current). When DC voltage or DC current exceeds the user-configured limits, the ODrive turns off the motor to prevent damage to the power supply (and/or itself).

  • DC voltage Limits:

    In almost all cases, you should at least configure the overvoltage trip level.

    In general it is also advisable to set the undervoltage trip level, although most AC/DC supplies will simply shut down and not take permanent damage if the ODrive pulls too much power.

    Both voltage limits should be set to the rated voltage of your power supply, with a bit of a margin in both directions. This margin accounts for the voltage drop between the power supply and the ODrive. For most systems, a margin of ±2V is a good starting point, but may need to be larger if your DC cables are long or thin.

    Note

    These limits cannot be set beyond the ODrive’s own rated limits.

  • DC current limits:

    These limits are typically only needed for batteries.

    Set them according to the discharge and charge rating of your battery. The ODrive’s DC current estimate can be quite noisy, so you will need to add a bit of a margin.

Active Power Limit

⇒ New in Firmware 0.6.9

Note

This feature is experimental. It has been tested on some setups, but we’re looking for more validation on more user setups. Please let us know how it works for your setup!

In addition to Trip Levels, the ODrive also supports active DC power limiting. This means the ODrive can actively reduce the motor torque to stay within a specified DC power range.

In other words, at low speeds the motor’s torque capabilities can be optimally used whereas at high speeds the power supply’s power capabilities can be optimally used.

../_images/torque-and-power.png

Torque and Power vs Speed.

The permissible range can be expressed in terms of DC power (in Watts) and/or DC current (in Amps), using the properties below (click for details).

The lower bounds must be negative and the upper bounds must be positive. Both ranges default to -INFINITIY … INFINITY, which effectively disables them.

Regenerated Power

When operating at speeds exceeding those commanded by the controller, or during braking, the ODrive functions as an electrical generator, feeding current back to the power supply. The maximum regenerated current is set by dc_max_negative_current. If this limit is surpassed, the ODrive will trigger a DC_BUS_OVER_REGEN_CURRENT fault. It is important to set this value in accordance with the allowable negative current of your power source.

Some AC/DC supplies have sensitive overvoltage protection, and any amount of regenerated power will cause the supply to shut down. To avoid this, a high power diode can be installed between the power supply and ODrive. The diode should be rated for above the operating voltage of the ODrive, and for the maximum continuous current that will be drawn from the power supply.

A suggested diode for this application is the SMC SK2S120-100. It is a dual diode array, however only one of the internal diodes needs to be used.

Note

  • It is strongly suggested that a diode on the power supply should only be used with ODrives that have a brake resistor control feature, with a properly connected brake resistor and proper software configuration.

  • additionally, Voltage Feedback (S1 Only) should be enabled when using a power supply diode.

  • Using an external regen clamp removes the requirement for a power supply diode.

Brake Resistors (S1 Only)

Important

For ODrive Pro, an external regen clamp module can be used instead of a brake resistor

The brake resistor control feature can dissipate surplus regenerated energy through an external brake resistor. If enabled, energy dissipation begins once the regenerated current reaches max_regen_current, and continues until the regenerated power drops below this limit or until the resistor is fully saturated.

../_images/regen_current.png

To enable the brake resistor control feature:

Voltage Feedback (S1 Only)

ODrives equipped with a brake resistor control feature can guard against the DC bus voltage rising. This feature requires the brake resistor to be active, and enable_dc_bus_voltage_feedback must be True. If the detected DC bus voltage goes above the provided limit, surplus power is diverted to the brake resistor:

Suggested settings:

Note

This feature is active even when all motors are disarmed.

Warning

Setting dc_bus_voltage_feedback_ramp_start below the nominal bus voltage will quickly saturate the brake resistor. The brake resistor will not be able to dissipated any regen current, and can produce unintentional and potentially dangerous amounts of heat.

Temperature Regulation

Thermistors

Over Temperature Current Limiting

The ODrive monitors the temperature of the inverter (the onboard power electronics) and optionally the motor and automatically reduces motor current when either of them approaches a predefined limit.

Both thermal zones are handled independently. For each enabled thermal zone, the ODrive starts limiting the motor current when the temperature exceeds temp_limit_lower. The current limit will then ramp down, ending with 0A once temp_limit_upper is reached. If the temperature continues to rise past 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 thermal zone exceeded this threshold.

../_images/current_limiting.png

Current Limit vs. Thermistor Temperature

The variables related to thermal current limiting can be found here:

The inverter’s current limit ramp is always active while the motor ramp can be enabled by setting motor_thermistor.config.enabled to True.

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.

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.

Fans (ODrive Pro Only)

The ODrive Pro has one 12V supply with a switched negative lead (Fan- (Pro, S1)) on J12. This is designed to power an offboard fan which can be controlled by either of the 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.

Note

If both modules are activated at the same time, the hysteresis control runs for each module separately and the fan is switched on when either of the two modules requests it to be on.

Encoders

Overview

All encoders supported by ODrive require that you do some sort of encoder calibration. This requires the following:

  1. Selecting an encoder and mounting it to your motor, refer to Known and Supported Encoders to make sure your hardware is compatible.

  2. Connecting the pins to the ODrive

    1. Each encoder types will require different connections, please refer to the relevant section below for instructions specific to your encoder type.

    2. Information about the ODrive’s GPIO can be found on the datasheet (Pro, S1).

  3. Configure the ODrive

    1. Set <axis>.config.load_encoder and <axis>.config.commutation_encoder to the appropriate EncoderId.

    2. Additional configuration may be necessary, please refer to the relevant section below.

  4. Encoder calibration

    1. The calibration procedure may vary depending on the type of encoder, please refer to the relevant section below.

    2. During calibration the rotor must be allowed to rotate without any biased load during startup. That means mass and weak friction loads are fine, but gravity or spring loads are not okay.

    3. The current limit during encoder calibration is set with <axis>.config.calibration_lockin.current. The default value is enough for most applications, but can be increased for larger motors or loads.

    4. Verify calibration.

  5. Save the settings in the ODrive for correct bootup behavior by running <odrv>.save_configuration().

Verify Calibration

After the calibration procedure has completed, verify that procedure_result is equal to ProcedureResult.SUCCESS. This can be done easily from odrivetool by running dump_errors(odrv), or from the GUI by inspecting the ODrive icon in the bottom left corner. If instead, you see ProcedureResult.BUSY then the calibration has not yet completed, check again after a couple more seconds.

Onboard Encoder

ODrive Pro and ODrive S1 both come with an integrated magnetic encoder. To use this encoder, a diametric neodymium magnet must be mounted to the end of the motor shaft. For general purpose use we recommend the 6x5 N45SH magnets sold in our shop If this isn’t suitable, any diametric neodymium magnet with a diameter ≥ 4 mm and thickness ≥ 2.5 mm will work.

When mounting, a 1 mm gap between the onboard encoder and the magnet is ideal.

Incremental Encoders

Note

If the index (Z) signal is not used, ENCODER_OFFSET_CALIBRATION must be run after every reboot before CLOSED_LOOP_CONTROL can be used. If you would like to automate this process at startup, set <axis>.config.startup_encoder_offset_calibration to True.

RS-485 Encoders

  • RS-485 encoder signals use a differential pair A, B and will require power and ground from the ODrive.

    Encoder

    ODrive

    Vcc

    5V

    A

    RS485_A

    B

    RS485_B

    GND

    GND

Important

At this time, only the CUI AMT21 series of encoders and the ODrive OA1 encoder are supported by the RS-485 interface

Hall Effect Encoders

Important

Due to the relatively low resolution of hall effect encoders, ODrive Robotics recommends a different encoder type for position control or applications requiring high performance at low speeds.

SPI Encoders

SPI encoders usually measure an absolute angle, which means you don’t need to repeat the encoder calibration after every ODrive reboot.

Some of these chips come with evaluation boards that can simplify mounting the chips to your motor. For our purposes if you are using an evaluation board you should select the settings for 3.3v.

Note

The AMT23x family has a hardware bug that causes them to not properly tristate the MISO line. To use them with ODrive, there are two workarounds. One is to sequence power to the encoder a second or two after the ODrive receives power. This allows 1 encoder to be used without issue. Another solution is to add a tristate buffer, such as the 74AHC1G125SE, on the MISO line between the ODrive and each AMT23x encoder. Tie the enable pin on the buffer to the CS line for the respective encoder. This allows for more than one AMT23x encoder, or one AMT23x and another SPI encoder, to be used at the same time.

  • The SPI interface has three required and one optional signal connections: clock (SCK), data (MISO), chip select (nCS), and optionally data out (MOSI). Additionally, the encoder will require power and ground from the ODrive.

    Encoder

    ODrive

    Vcc

    3.3V

    SCK

    SPI_SCK

    MISO/DATA

    SPI_MISO

    MOSI (optional)

    SPI_MOSI

    nCS

    SPI_nCS

    GND

    GND

Note

If you want to save a wire with AMS encoders, you can also connect the encoder’s MOSI to the encoder’s Vcc instead.

Important

Only the following modes are supported at this time:

  • CUI protocol: Compatible with the AMT23xx family (AMT232A, AMT232B, AMT233A, AMT233B).

  • AMS protocol: Compatible with AS5047P and AS5048A.

Note

If you are having calibration problems, make sure that your magnet is centered on the axis of rotation on the motor. Also make sure that your magnet height is within range of the spec sheet.

Sensorless

Warning

Sensorless mode is considered experimental in this firmware version.

The ODrive can run without encoder/hall feedback, but there is a minimum speed, usually around a few hundred RPM. In other words, sensorless mode does not support stopping or changing direction!

Sensorless mode starts by ramping up the motor speed in open loop control and then switches to closed loop control automatically. The sensorless speed ramping parameters are in <axis>.config.sensorless_ramp. The sensorless_ramp.vel and sensorless_ramp.accel (in [radians/s] and [radians/s^2]) parameters control the speed that the ramp tries to reach and how quickly it gets there. When the ramp reaches sensorless_ramp.vel, <axis>.controller.input_vel is automatically set to the same velocity, in [turns/s], and the state switches to closed loop control.

If your motor comes to a stop after the ramp, try incrementally raising the sensorless_ramp.vel parameter. The goal is to be above the minimum speed necessary for sensorless position and speed feedback to converge - this is not well-parameterized per motor. The parameters suggested below work for the D5065 motor, with 270KV and 7 pole pairs. If your motor grinds and skips during the ramp, lower the sensorless_ramp.accel parameter until it is tolerable.

Below are some suggested starting parameters that you can use for the ODrive D5065 motor. Motor calibration and setup must also be completed before sensorless mode will work.

<axis>.controller.config.vel_gain = 0.01
<axis>.controller.config.vel_integrator_gain = 0.05
<axis>.controller.config.control_mode = ControlMode.VELOCITY_CONTROL
<axis>.controller.config.vel_limit = <a value greater than <axis>.config.sensorless_ramp.vel / (2pi * <pole_pairs>)>
<axis>.config.motor.current_soft_max = 2 * <axis>.config.sensorless_ramp.current
<axis>.config.load_encoder = EncoderId.SENSORLESS_ESTIMATOR
<axis>.config.commutation_encoder = EncoderId.SENSORLESS_ESTIMATOR

To start the motor, set <axis>.requested_state to AxisState.CLOSED_LOOP_CONTROL