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Unread 03-02-2017, 18:16
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gerthworm gerthworm is offline
Making the 1's and 0's
FRC #1736 (Robot Casserole)
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Re: Path Planning and Trajectory Troubles

If you haven't done so yet, plot your commanded left/right velocities against your actual left/right velocities. Because position error will accumulate over time, the control loop needs to be quite tight in keeping the actual velocity close to the real velocity.

We did something similar last year, and definitely had lots of issues with turning at first - the wheel scrub was higher than expected, and fairly inconsistent. What allowed us to start nailing the paths was adding a gyro with a simple P feedback to help keep the robot pointed along the right heading.

Other thing to try would be to slow down the path traversal - does that make your end point any more accurate?

Also, you did mention something about total distance of each wheel being all that is necessary - this isn't 100% true - Think if you ran just the right side of the drivetrain for the desired distance, then just the left side of the drivetrain. (you basically stay in one spot). To maintain a certain heading, the relative speed of the sides of the drivetrain at all times does matter. For this reason, the path planner would need to calculate velocities at all times, and the control algorithm needs to get the sides of the drivetrain to those velocities.

Last edited by gerthworm : 03-02-2017 at 18:20. Reason: more explanation
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