Team 4388 has an invite to drive our t-shirt shooting robot at a professional hockey game. We will have an audition in a week. Right now our robot has 6” mecanum drive wheels that we use for exhibition at basketball games. We’re thinking that mecanum is probably not a good choice for ice!
We’re considering adding tie-wraps to act as studs to treaded wheels (e.g. am-0940). We found that the head of a tie-wrap will fit into the wheel tread space and still stick out.
There must be some ice driving experts in our FRC community. What’s your advice?
Those videos make me wonder if we’re making too big a deal about driving on ice. Yes we’re in Colorado but it’s been warm here lately. Apologies to those in the north eastern part of the USA that could probably drive test on ice easily.
I would agree that mecanum wheels are not the best choice for ice. I would stay away from studs, as they maybe chew up the ice a little bit, which is not the most desirable outcome.
I would recommend using a solid rubber wheel, either the kop wheels or Colson wheels or something similar. As I recall, kop wheels on ice have a similar coefficient of friction as lunacy wheels on regolith, so watching videos from 2009 will give you an idea of what you’re in for. As long as you accelerate slowly you should be able to maneuver your robot relatively easily.
I would absolutely ditch the mecanum.
Few questions before I go on
Do you guys have access to a 3D printer?
Did the venue give you any information on rules you would need to follow?
Do you have a gyro?
Im sure there are more questions but lets start here
I don’t know if they would work with you robot, but something like these Andymark pneumatic wheels would probably be my first choice for driving on ice. A soft roughtop/wedgetop tread might also work reasonable well.
I’d try putting a zip tie around the central bulge of each mecanum roller. If they are small and sharp enough, they’ll act like mecanum ice skates.
With enough time to prepare, I would suggest fabricating hard plastic “screw wheels” with a coarse, sharp, 45-degree helical tread pattern. You’d want to mount the wheels so that the ridges form an “X” against the ice.
If you are out on the ice BEFORE the Zamboni resurfaces, roughtop tread would probably be your best bet. The ice would be covered with snow from the hockey action in the previous period. And dial back the power to the wheels. Once you start slipping, its all over, you’re out of control.
(Or like we say here in New England while driving in wintery conditions, “Here, hold my coffee and watch this!”)
FRC190 has dropped the puck at a couple Worcester Sharks games with different robots but all have been 6-wheel, rubber-wheeled robots. I can’t imagine mecanum being a huge issue as the advice Dana gave applies to all robots (and cars).
Go slow and be careful of oversteering. Once you close control, don’t keep spinning the wheels more!
And when our robot did the groundbreaking ceremony and ribbon-cutting ceremony for the new WVU basketball facility and new Physics building, all in the snow and ice. We had mecanum drive, and it slid all over the place. If you can, don’t use Mecanum.
Roughtop tread worked decently for us shooting off shirts at the local ECHL affiliate games. The rivets acted like spikes and it seemed we had some semblance of control. The tread does get loaded up with snow.
Thanks so much for all the experienced and expert advice. It seems like the key points are:
mecanum = No!
Normal wheels will probably work OK. Roughtop tread seems like it’s worth a try and we do have those wheels on hand.
It’s ice! Controlled acceleration and turning will be vital. Skip trying to show any elaborate driving.
We will be on the ice during intermission so the ice will be resurfaced afterward. Regardless, it would be better manners to not be creating a mess. I do have some worry about leaving tie-wraps as trash. Again, resurfacing would likely pick them up but we need to be careful.
We have access to a 3D printer but its sloooow.
The audition focus is to see how we drive on ice. We have not received any rules / expectations yet. They pack a lot of activity during these game intermissions so I suspect the concern is having the robot get stuck and taking time to get off the ice. Typically their dance team does some routine and the dancers and mascot toss / shoot t-shirts after. I’m guessing we’ll join that and get a PA mention. I’m sure we’ll be told clearly where and when the robot needs to run. They assign a handler to anyone performing to help ensure things go as they like.
We have a gyro and an accelerometer. I’m expecting we’ll be doing some special acceleration control programming next week. We switched from tank drive to mecanum on this robot to increase the show factor on gymnasium floors. The driving certainly has become part of the show.
We can agree with this vital advice for anyone driving in these big public venues. At first we just naively ran with our standard ssid broadcast configuration. Duh! No surprise that there are a lot of smartphones willing to attempt to chit chat with any wifi device nearby. We’ve beefed up the wifi link and I expect to further improve it in the future. Practice can be misleading since the audience is not present. We got the OK to go to a big event and practice on the sidelines to learn more about dealing with all that rf noise.
For the curious, this is an early video of the robot:
It has 8 t-shirt barrels with separate air tanks for each. We preset different pressures for hitting different levels in the stands.
Firstly I agree with everyone in this thread, mecanum definitely won’t suit the surface. We used traction wheels and retained most of our speed and turning ability, both on used surface and new.
Secondly, you might want to tether the robot (if you have a long enough cord). We tested the robot an hour before and everything was fine, but five minutes before we went on suddenly our testing showed that some drive signals weren’t transferring properly. We still could drive, but it was a bit hit or miss due to a few motors constantly driving. If you can bring it to test off ice during another hockey game, you can determine if that will be an issue.
And be careful about what you put on the ice. We were warned that we had to keep moving the robot every 30~ seconds while on ice to avoid melting small spots, plus any studs that are put in the tires will leave divots. Honestly as long as you have grip on your wheels, you’ll retain most of your driving ability.
If you can, try to see if a local team will let you share their ice to test the robot before the match, just to give your drivers some practice. You can do some really fun spins and maneuvers on ice. Good luck!