COMS Commander

Receives cmd_vel and passes it on to the steering and accel, brake actuator.

Dependencies

• coms_msgs

Parameters

• steering_gear_ratio: to turn the wheel X radians, we need to turn the steering wheel steering_gear_ratio * X radians
• wheel_base: distance from the front wheel to the rear wheel
• update_rate: how often to publish the commands
• steering_vel: steering angular velocity limit. Details later.
• steering_acc: steering angular acceleration limit
• KP, KI, KD: PID control parameters

Steering Angular Velocity Limit

When turning the steering wheel, we need to limit the angular velocity at which the steering wheel turns depending on the current velocity of the vehicle. That is, when not moving, we don't want to turn the steering wheel at all, and when moving slowly turn it slowly. After the vehicle gains speed, we don't have to worry about how fast we turn the wheel.

Really, the reason why can't turn while stopping is because we use a belt (rather than a chain), which slips when the load on the belt is too high.

The three values indicate the vehicle's velocity required to turn the steering wheel, velocity required to turn the steering wheel at the angular velocity limit (third parameter). For example, [1, 3, 0.031416] means that the steering wheel won't turn until the vehicle is moving at 1.0m/s, and after that the angular velocity will increase linearly until the vehicle reaches 3.0m/s, which is the velocity at which the steering wheel will turn at 0.031416rad/s.

Subscribed topics

• cmd_vel: target linear and angular velocity

Published topics

• cmd_steer: commanded steering angle
• cmd_gab: gear, accelerator, brake percentage

License

MIT License

Author

Naoki Mizuno