Many matches will be lost this year because of upside-down discs getting stuck under robots.
After kickoff our members powered up some of our old bots and tried driving them over the discs. We did tests with Ball-Shark ('10) which has 6" wheels and lots of ground clearance and with G-Wrath ('11) which has 4" wheels and only about a 1/2 inch of ground clearance.
In normal driving, G-Wrath pushed the upside-down discs out of the way. When the robot was pushed on-top of the discs (lets say by a defender, or by its own power against a wall) a serious problem occurred. The discs became caught on the wheels and the robot lost traction. The wheels touching the ground continued to propel the robot but the wheels trapped inside the discs spun freely.
Driving over right-side-up discs caused G-Wrath to pitch violently.
Similar problems occurred with Ball-Shark, only that robot was able to drive out of the discs more easily due to its larger wheels.
Anyone else concerned by this? Strategies to overcome it?
I’d hate to see a field of robots spinning in circles helplessly on piles of discs.
It is difficult to speculate without ever seeing a match played, but it seems likely that this will only become a real problem in the last 30 seconds when the supply of discs on the field really starts to grow. However in some matches it could happen much earlier if there are a lot of quick but inaccurate shooters (that said, the concentration of discs should remain around the goals).
Thanks for testing this out - perhaps drivers will need to learn to maneuver around frisbees (blind spot cameras?) rather than assume they can power over them.
I was thinking frisbees flipping wasn’t going to be a huge problem per say, because frisbees are giant gyroscopes I think if they hit a wall, they will keep spinning into a wall, then fall. This leads to my second point that of they are upside down, I’m assuming it will be near the scoring walls, because they were attempted to be scored. In this case,… stay away from the wall. Also. I should include, only high upside down frisbee field time would be humans throwing them in, in my opinion, maybe a frisbee hits the 68 degree bar, and it flips over by hitting the Pyramid. So what I’m saying is maybe the frisbee thing isn’t a threat at all. I would be prepared for both situations I guess we will only know at scrimmage.
Despite all that, you always design to make sure that it won’t happen. If it can, it will, and teams that say “it’s pretty unlikely” are doomed to have it happen. Many times at the worst possible time, like in the semis or finals of a competition. Top bots take everything into account - especially stuff like this that can wipe out your mobility for a match.
Perhaps this is a call for a drivetrain with an unbelievably low ground clearance? The only problem I see with that would be the little hump with the pyramid.
Well, the great majority of frisbees that are going to be “in the way” are missed shots, which will all be in the front of the goals. And by the time 30 seconds hits, most all teams will be at their pyramids and climbing.
So unless you run though where your missed shots end up I don’t really see much of a problem here.
Food for thought…there will be “minefields” on both sides of the field, so 2/3rds of field may present a challenge for some teams as they traverse from load in to the other side to score.
This was a problem for my team last year. Our robot had six inch wheels and about five inches of ground clearance. Sometimes when we would drive over a ball on accident it would get lodged in between two wheels, which kept us from moving at all. I could see the same happening with a Frisbee that is upside down to a robot with wheels that are close together.
ground clearance > 1" combined with “skirts” of thin polycarb or zipties should mitigate the problem. (especially angled ones that allow the Frisbee to come out easy but not get in easy)
Or a set of tilting wheelies, like this, to keep the CG low.
The spacing of the wheels is also important. We found that robots with 6" wheels spaced closely together also have trouble getting out of the discs because the inner disc edge will want to ride tangent to the inner side of the wheel, presenting a poor angle of attack with which to climb out.
Sorry if that didn’t make any sense. You need to do some testing yourself. But my point is, the problem is more complex than just bigger wheels.
I don’t think it will be much of an issue. The majority of teams are going to most likely hit their shots, unless there is a team sitting by their feeder station and rocketing them all over.
I’m not saying it’s a non-issue, but I think that most all teams will end up immune to it if they have a solid drive train to handle the discs.
I think we are planning on putting covers down over the wheels with about 1/2 of ground clearance, and still letting our bumpers be high enough so we can drive over and collect frisbees. Seems simple enough, I dont see why it poses a huge problem- the frisbees glide around a good deal on the carpet.