[Andy A.]

You've got it mostly right.

The bot was designed with an opening move of grabbing all 20 balls in a line. Still, the rollers were the full width of the front, and could easily pick up balls randomly strewn across the field by simply driving into them. Regardless of where on the rollers a ball touched, it was sucked in. As the season went on, teams wised up to our strategy, and there were some good games of chicken as we ran down a line, and another bot tried to mess up the line to keep us from getting a clean 20. Being able to pick up the balls when they were not organized wasn't as fast, but we still managed to get at least 20 balls every match, usually more like 30-40. The great width of the rollers was a driver aid, since aiming the full width onto a moving target is easier then a much smaller width.

As to gravity, this was a minor force in jamming as compared to the balls simply getting wedged in the hopper or the force to pass through the check valve. Even the slick soccer balls could bunch up and do odd things in the hopper. I expect the nerf balls to be worse. To counter act those forces, gravity, the check valve and misbehaving balls, the roller speed was adjustable by the operators with a pot but required a very deft touch to keep up with the influx of balls. As long as the rollers where up to speed, balls would enter with enough force to easily kick balls out of a full hopper. It wasn't that the hopper filled up before gravity and jams overcame the motor power available. What happened to jam the rollers was that their speed was not increased quickly enough, and slowed down below a threshold. The gearing on the motors was such that they did not have enough torque to force the ball into a full hopper if the ball was already halfway in the rollers.

So the rollers relied on shear speed to overcome jams. This allowed us to gobble a line much faster then if the rollers had been running slower. A slower speed would have allowed more torque to clear jams, but might have caused more jams in the first place and would have required a lower bot speed. The speed down a line was important to this design, as we thought that we would be racing other teams for a line of balls. Turned out that few other teams did, and we kept going full speed to show off. Later on, opponents caught on and would try to mess up the line, so it did turn into a drag race.

Most of the time it worked out. As the season progressed the operator got better at it, which helped. What worked against us was the FP motors getting toasted, which lead to a constant drop off in available power. By the end of the season, they were pretty much shot. Replacements would have probably helped a lot in UTC.

-Andy A.