VESC Interface

[HaoruXue]

Description

In Triton AI Racer, we use tai_interface/msg/VehicleControl to control the vehilce actuators (steering, throttle, braking). To control a VESC, however, to be compatable with vesc_driver_node, we need to convert and publish std_msgs/msg/Float64 for individual actuators. A package called vesc_tai_interface is needed which contains a vesc_tai_interface_node that does the conversion.

Desired Behavior

Subscribers

• The node shall subscribe to a tai_interface/msg/VehicleControl topic called vehicle_cmd.

Publishers

• The node shall publish the following std_msgs/msg/Float64 topics:
  • commands/motor/current
  • commands/motor/brake
  • commands/motor/speed
  • commands/servo/position

Parameters

The node shall share most parameters with vesc_driver_node for the actuator mappings, namely,

• brake_max
• brake_min
• current_max
• current_min
• position_max
• position_min
• servo_max
• servo_min
• speed_max
• speed_min

Read the source code to figure out their ranges and meanings.

In addition, the following three parameters are needed:

• 'servo_neutral: the neutral steerign value might not be as simple as the average of servo_minandservo_max`. Some steering mechanism would have a slight different neutral value.
• wheel_radius: useful for converting the speed in vehicle_cmd (m/s) to RPM
• rpw_to_electrical_rpm_factor: Here is why this parameter exists.

The node should also support dynamic parameter configuration with parameter-change callback.

Logics

On receiving a vehicle_cmd,

1. If longitudinal_control_type is LON_CTL_THROTTLE_BRAKE, map and publish the throttle (current) and brake values
2. If longitudinal_control_type is LON_CTL_SPEED, map and publish the speed value (remember to convert from m/s to electrical RPM)
3. If lateral_control_type is LAT_CTL_OPENLOOP, use steering_openloop to map and publish steering
   1. The mapping has two segments: servo_min to servo_neutral; servo_neutral to servo_max, each corresponding to (-1, 0) and (0, 1) in vehicle_cmd.steering_openloop.
4. If lateral_control_type is LAT_CTL_CLOSELOOP, throw an error. The VESC does not support closeloop steering at the moment.

Definition of Done

• Implement the node with basic message conversions
• Implement all parameters and parameter callback
• Test on a vehicle with joy_node and joy_tai_interface to teleop.
• Convert this issue into a design document and put in the package (vesc_tai_interface/design/README.md)

[GSam789]

VESC conventions:
brake_max, brake_min: reverse currents in mA needed to stop the motor (start at 5000mA throttle)
current_max, current_min: movement
no position_min/max (needs to be removed)
servo_max, servo_min: default (0, 1)

-1 0 1
servo_min neutral servo_max