DBW: Tuning of DBW node PID

[Deborah-Digges]

We can also consider using MPC

[zerepolbap]

We may also tune linear PID, to reduce throttle/brake cycles.

[zerepolbap]

Note from the specs:

As in the Path Planning project, acceleration should not exceed 10 m/s^2 and jerk should not exceed 10 m/s^3

[zerepolbap]

Also from the project description:

Note that throttle values passed to publish should be in the range 0 to 1. Brake values passed to publish should be in units of torque (N*m). The correct values for brake can be computed using the desired acceleration, weight of the vehicle, and wheel radius.

[zerepolbap]

In my view, as of today, steering is quite OK. Acceleration/braking works OK too. Some suggestions for "improvement":

In twist_controller.py:

• Max acceleration is currently set to mx=0.5 * accel_limit. It could be set to mx=accel_limitand it would still be within the 10 m/s^2 allowed margin.
• Braking is set to 1000*abs(throttle). To actually have a torque value, it could be changed to wheel_radius * car_weight * acceleration provided that acceleration can be approximated by abs(throttle).

But I have tried this approach and the result was worst that what we have today, so it'll probably require some more tuning. Or just leaving as it is :-)

[Deborah-Digges]

• Removed the hard coded value and compute torque from vehicle_mass: https://github.com/tokyo-drift/capstone-project/pull/20/files