Driving Straight With Encoders

[microbuns]

Originally Posted by Ether

Here's some info that may be of interest.

Drive straight with encoders:

http://www.chiefdelphi.com/forums/sh...89#post1446789

Use motion planning for best results:

http://www.chiefdelphi.com/forums/sh...ad.php?t=98358

http://www.chiefdelphi.com/forums/sh...d.php?t=134965

Do some simple system identification[1]. For example, take the wheel diameter problem Todd mentioned. Drive the vehicle in a straight line (by tweaking the left-right motor commands) and note the ratio of the left and right encoder values. Use that ratio to fudge your setpoints, or use it to fudge your encoder readings before using them as your process variable.

[1] http://en.wikipedia.org/wiki/System_identification

We may have done some of this "system identification" unintentionally. We did a test where we pushed the robot straight and looked at the encoder values after a certain distance - the two wheel systems seem to be more than within our error tolerance, as we saw a <0.1% error arise (little enough error to just be caused by how we conducted the experiment). We believe the difference is in friction on the two wheels, but we are unsure of a way to quantify that.