My team is doing the ball magnet idea with the rollers to posses the ball and we are having only moderate success with it. We can get a ball if we creep up y on it and give it time to “connect” then the robot can’t move fast without losing the ball. we have seen the videos of people just holding onto the balls and we want to know if there is some special material people find helpful, or is there a trick with the ball collector. Right now the ball collector can’t really change position drastically but we can change the roller all we want. Right now we have tested Rollers with Duck tape, straight up PVC, and hockey tape. Has any one done something different that works well?
Apparently 148 spent a few weeks figuring out how to make theirs work well. We spent a significant amount of time on ours too, with not quite so good, but still usable results.
One way to make the thing work is to have a really sticky material, and have it spin very fast, and have it mounted kind of low on the ball. We did not figure out how to make it work like this, though.
Another way is to have a normally grippy material (wheel tread?), have it spin kind of slow with a lot of torque, have it mounted as far up/forward as possible, and have a low friction part that meets the ball sort of low on the robot behind the ball, and prevents the ball going under the robot. This is what we did.
The 3" incursion rule makes it challenging.
We for a cheap, low weight solution, we took a bike tire (the inner tire tube, not the wheel) and slide it onto a section of PVC pipe. It was a little tricky to do - we had to close one end of the PVC, get the tire started over the other end, then inflate the tire with enough pressure that it could slide on easily, but not so much that it burst. Once the air pressure is gone, the tire fits very snugly.
We are using a piece of pool noodle over a rotating spindle, which is a 3/4" dia aluminum tube. The noodle slips on the spindle when it has a ball in possession, but that seems to be OK. The ball does not have active backspin while in possession. The front of the noodle is even with the bumper perimeter and the height is such that the ball hits the noodle about 1/2" or so before it hits the 3" backstop - that defines the “pinch”. We are currently spinning it about 500 rpm (no load). It holds the ball during turns, allows us to pick it up at nearly full speed, and we can hold during reverse at about 1/4 speed. We found that the inside of the noodle gets shredded over time, so it needs to be replaced occasionally.
If you don’t have time to do a spinning ball collector, we found that a stationary piece of foam rubber in the same location does an adequate job of keeping the ball from bouncing away when you come up on it. It doesn’t help for backing up, and provides a bit of help during turning.
You should be going for stickier material than the carpet.
Spacing the ball magnet is important.
Ball magnet rotation speed a little less so.
If I knew anything else, my team would be doing well right now.
could we see some pics? sounds awesome
We went for the high speed/somewhat slippy method that make contact with the ball at 5-6" off the floor. We simply used the sturdier non slip drawer lining found at Lowes.
The final version of the NERDS ball magnet uses wedgetop conveyor tread, as seen here:
The frame member the ball sits against is set back 3" and covered in felt, the idea being that the roller sticks to the ball and the ball slips on the carpet and frame member. Ideally the ball is touching all three surfaces at once.
Something to keep in mind is that these devices are very finicky (at least from what I’ve seen/heard). You need to play with the dimensions a lot to get optimal performance out of the mechanism, and even then it can be easy to loose the ball while turning.
There are some more pictures of 1726’s device in this gallery: http://photos.project1726.org/
For those of you who are getting backspin on the ball:
- Are you pinching the ball between the roller and floor, or just getting approximately simultaneous contact on the roller, backstop and floor without significant interference fit (pinch)?
- If you are not pinching the ball, how do your magnets work with high speed pickup? Does the ball bounce out?
- It sounds like you should be able to back up rapidly without losing the ball. How well does that work for you?
We chose a pool noodle with some simple “stuff” on it, since it wasnt as rigid as pvc with a sticky material. A hard roller was worse, IMO, because it caused the ball to bounce at times and fall out of place.
We did two major additions that now allow us to move full speed forward and back and never lose the ball.
I dont know what 148 did (doesnt appear to have spin), and its not apparent how effective they are moving backwards (not that they need to or not).
But for us, having the ball spin better was highly effective for us.
In summary, we have only one point of friction (relatively speaking) preventing the ball from spinning…i.e. the carpet.
Yep, we visited Lowes too…HURRAY FOR SHELF LINER!!
Dave Brown Lite Flite airplane wheels. Enough said.
We went with latex tubing that sticks out like a vacuum cleaner brush. It whacks the ball when you get close, putting backspin on it, letting the ball follow you backwards if you go slow enough. The roller is about 2/3 the height of the ball and spinning pretty fast. When the ball gets too close, the tubing folds against the roller and acts more like wedgetop tread on a cylinder.
For our ball manipulator its a combination of Hockey tape, rollers with a gap in the middle, and some allowable movement of the height of roller. So all in all its a little complicated and has required a lot of prototyping, testing, and tuning.