EASY traction control?

[vamfun]

Well, we decided traction control was not necessary by default... i.e. the encoders were inop so the driver learned fast to take advantage of our maneuverability to do a kind of self induced pit maneuver to spin the trailer around and avoid a pursuer. So a short wheel base and a "squared" stick transfer function seemed to work well.

We actually had the software/encoders for a three level traction control.

The first level was a backup and just the rate limited stick which others have mentioned. It does limit accel but drivers complain of sluggishness. This is caused by the rate limit being upstream of the motor lag. The motor follows the rate limited stick but its response is delayed about .4 sec. This delayed acceleration response is noticeable by the drivers. Also even though the wheels are not slipping, the delay reduces the benefits over a slipping robot.

The second level was a motor torque limiter. This was achieved by limiting difference between motor speed and commanded speed (effectively a current limiter). Only motor encoders are necessary for this and several teams were very successful with this approach.

The third level was real time adjustment of the motor torque limit value based upon wheel slip speed. The wheel slip speed requires reference wheels with encoders. V_slip = V_wheel-V_ref. If V_slip>0 then the limit was reduced by some factor.


I wrote a small ppt paper to introduce the subject of traction control for the software group early on in the project. I offer it as an addition source of confusion for you