Does the wheel have encoders?

Amlan_Balabantaray · July 27, 2023, 9:03pm

Does the wheel have Encoders? I can see the RPM data on the dashboard. But I am not able to access the data in ROS. Please help

kylecoble · July 28, 2023, 11:01pm

Hello @Amlan_Balabantaray ,

The wheels have a hall effect sensors to measure rpm. This value is available in the canbus grpc API, but is not already piped through the ROS bridge.

You could create your own ROS node that has a grpc client to the canbus service and use the streamMotorStates rpc call:

github.com

farm-ng/farm-ng-amiga/blob/v0.0.9/protos/farm_ng/canbus/canbus.proto#L27-L30


      
          // Streams the states of all detected motors.
          // Motors not actively streaming their state will not appear in the StreamMotorStatesReply
          rpc streamMotorStates(StreamMotorStatesRequest)
              returns (stream StreamMotorStatesReply) {}

If you’re doing this in python, it is wrapped for you as stream_motors in the CanbusClient class:

github.com

farm-ng/farm-ng-amiga/blob/v0.0.9/py/farm_ng/canbus/canbus_client.py#L44-L46


      
          def stream_motors(self):
              """Return the async streaming object of motor states."""
              return self.stub.streamMotorStates(canbus_pb2.StreamMotorStatesRequest())

Either will create a single stream of MotorState proto messages for each motor.

github.com

farm-ng/farm-ng-amiga/blob/v0.0.9/protos/farm_ng/canbus/canbus.proto#L114-L122


      
          message MotorState {
              double stamp = 1; // stamp of the RawCanbusMessage containing the motor state values
              uint32 id = 2; // CAN node ID of the motor
              uint32 status = 3; // Corresponds to MotorControllerStatus enum
              int32 rpm = 4; // Non-geared motor rpm. Values are inverted (negative) for flipped motors.
              double voltage = 5; // Battery voltage, as measured at motor controller
              double current = 6; // Motor current draw, as measured at motor controller
              int32 temperature = 7; // Motor temperature
          }

You could then convert that to your ROS message of choice and publish them from your node.

If you’d like to try this in Rust and contribute to the farm-ng open source ecosystem, you can open a pull request in the Amiga ROS bridge repository.

Good luck with your project!
Kyle

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Does the wheel have encoders?

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