Navigating the Minefield

[=Martin=Taylor=]

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.

[Undertones]

This was a concern of mine. Thank you for testing.

[dcarr]

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.

[GaryVoshol]

And remember, if you're dragging a couple discs along with you as you move, they count as part of your allowed 4.

[AndyBare]

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.

[Tom Line]

Originally Posted by AndyBare

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.

[AndyBare]

Yeah, definately agree.

[Finkmeister]

This was one of my biggest concerns this year, glad someone went out and tested it.

The obvious option is giving the robot plenty of clearance. Maybe a "snow plow" type thing in the front?

[Anupam Goli]

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.

[Mongai]

This is precisely the reason why we are using custom tank treads again this year.

[Tetraman]

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.

[JB987]

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.

[pfreivald]

Originally Posted by Tetraman

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.

What about frisbees accidentally/intentionally plowed around the field?

[DonRotolo]

Originally Posted by =Martin=Taylor=

4" wheels and only about a 1/2 inch of ground clearance.

Strategies to overcome it?

more ground clearance?

[camalex3999]

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.