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Group4DriveCommand

4. How accurate is the Drive Direct command? Can you verify the accuracy of the velocity and radius that you use as an input? Find a way to accurately measure both. What does RADIUS and VELOCITY mean to the Create in this context? I can think of at least three interpretations from the Create's point of view--you should experimentally determine what it means. Don't presume that your logical idea of radius and velocity are the radius and velocity used by the Create, PROVE IT! USE SOME NICE DIAGRAMS!!

Hypothesis: The create considers both the velocity and the radius to be calculated from the center of the robot.

Velocity:

I used the Drive command to create a script that, when the bumper was hit, would start the robot at a constant speed. When the bumper was pressed again, the robot would stop. Along with a stopwatch, this was used to record the time it took for the robot to go a known distance, 658.8125 mm (29.9375 in). Dividing this distance by the observed time would result in the actual velocity. The percent error was calculated at numerous different speeds, and for the forward direction this error was at around 8% consistently. For the reverse direction, the error was around 2.5% for most of the trials.

Results of the trials can be found here: Lab Data

Radius:

Placing markers on both sides of the robot, I gave it a drive command traveling at 100 mm/s in circles of varying radii. Observation showed that the center of the robot would follow a circular path around a pivot point, which would normally be outside the robot at the center of the circle. If the radius was less than 7 in, though, the pivot point would be inside the robot's body (closest to the "inside" wheel) and an interesting behavior is observed - the markers on the robot's body were found to be drawing opposite sides of the circle at any given time.

The accuracy of the radius seems to be high - for most of the trials, the difference was less than 1%.