Hello! I’m hoping folks can help point us in the right direction on troubleshooting a problem we’re having.
We’re building auto paths to the centerline and trying to see how fast we can get our bot to go. We’re starting with a simple straight line - going from the speaker to the centerline and back.
When we have the bot going at our “default” auton speed (3m/s for max velocity and 3m/s for max acceleration), it works perfectly fine - gets to the exact point on the centerline we’re aiming for and goes back to the starting pos. Once we change any of the numbers (ie, 7m/s for max velocity and 5m/s for max acceleration), it goes from speaker to centerline fine, but it stops about a meter short when returning to the speaker. If we have it go from speaker to centerline and stop (again using 7m/s and 5m/s), it’s fine. If we have it go from the centerline to the speaker and stop (again using 7m/s and 5m/s), it’s fine. It’s only when we combine the paths into the auton that we have an issue.
We’ve printed out the pos of the robot on our dashboard, and the robot knows it’s a meter short. For example, if it’s supposed to stop at 1m x 0.5m, it actually stops at 1m x 1.5m and it prints the pos as 1m x 1.5m.
It doesn’t matter what combination of numbers we use, we see the same behavior, and it’s pretty consistent - also stopping about 0.5 to 1 m from where it’s supposed to.
Does anyone have any tips on where we might look to see what might be happening here?
It sounds like your wheels are slipping during the change of direction. It makes sense that it happens when you increase acceleration…more torque is going into the wheels increasing the chance that they slip. When you are changing direction, the acceleration is so great that it causes the wheels to slip a bit before gaining traction. This makes your odometery think the robot has driven further than it really has, and so it appears to stop short of its target. Try leaving velocity where it is and decreasing acceleration until things look good.
@cantogr07@NewtonCrosby thanks for the pointers on the PID. We haven’t checked those, so we’ll do that next.
@MrNick we definitely noticed slipping when we were running on bare floor. Carpet was much better. We did introduce a pause at the center line in case there was some skidding - we’ll add a longer pause. We’re basically trying to figure out how to run a centerline auto fast enough that we can get at least 2 of the notes - right now we can only get 1.
We did some PID tuning today, that didn’t help (but seeing the robot do a little wheely as it started the path was fun to watch!).
We even tried a slightly different path - instead of going back and forth between point a and point b, we did a teardrop-shaped path. Even with that, it didn’t start and end on the same spot.
We’ve set it up so we’re outputting the x and y positions to our dashboard as it drives. When it starts, the X pos is 15.15 and the Y pos is 5.53. When it finishes, the X pos is 14.4 and the Y pos is 4.17 - however, in path planner, the ending X pos for the return path is set to 15.15 and the Y pos is 5.53. So clearly is stopping early for some reason and drifting slightly off target.
Is there anything else folks can recommend we look at?