enhancement using python-control

It should be nice to use python-control to pass from continuos-time to discrete form
v_new = v + T * 1 / MASS * (u - C_DRAG * v)

https://github.com/python-control
https://python-control.readthedocs.io/en/0.9.4/generated/control.sample_system.html#control.sample_system

Thanks

