Quote:
Originally Posted by apalrd
We bagged the robot with a higher-speed top roller and played like this at Kettering. We then looked at several other robot's up close, and built a pincher-roller for Troy using the practice robot as a guide. This taught us two things:
1. pincher rollers are waaay better
2. the practice bot is really far off of design specs
Ours was a floating design, so the entire assembly was a four-bar linkage. The two horizontal bars supported the bottom plate and top roller, one vertical "bar" was the chassis, and another held the two pieces a fixed distance apart. Using bungee, we sprung it down to avoid carrying penalties, and put some little wheels on it so metal never touches the ground. We had an issue with carrying penalties at Troy, so we fixed it in software and haven't had problems since.
We actually had an interesting problem with ours: It had such a good grip we could no longer kick more then about 3 feet. So we fixed it in software and can now kick the full 33 feet (+ a few more) it could with the old roller.
We carefully tuned the depth of the top roller and bottom plate, as well as the distance between the two, to get the most grip while not allowing a piece of paper to go under the ball. Software helps with this: If the roller is allowed to run continuously, it will gradually suck the ball in more, and carry it. If you just kill the roller, then it will loose the ball. We implemented a duty-cycle based roller kill to pulse the roller when holding a ball (determined by a broken-beam sensor), and to continuously run the roller when going backwards (both joysticks are positive, reverse) to prevent loosing the ball. Timing this was tuned to 5 iterations on for a 20 iteration cycle.
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That's pretty funny - we found the exact same thing. We had this design installed about a week before ship but were tuning it right up to the day we sent the robot out. It took us a while to get the hang of setting it up so it stayed on the ground, but once we had a system of setting it up it worked well.
The first iteration didn't allow us to kick very far either - we adjusted our backstop and bottom bar to get just the right amount of grab.
We also realized that on our practice bot we offset the middle wheels down. On the comp we offset the front and rear wheels up. Oops.
We used a simple vacuum cleaner belt to drive the roller - once the ball hit the backstop the belt slipped on the upper roller so the window motor didn't stall. Ours didn't float, but we did make sure it kept the ball on the floor all the time. We never changed that belt once. $2.49 from Ace Hardware.