Best wheels for football field?

We finished our first show bot (a T-Shirt cannon) and proudly showed it off at founders day today. After the parade, we were asked if we could shoot T-shirts during football games next year, and agreed to give us at least $500 for everything we needed to make sure it would work in the grass. $300 is going to T-shirts, while the rest is going to getting wheels and anything else we need to keep the bot going while on the field.

This brings up my question. We are using the 6" KOP wheels, but we rather not use those as we are afraid that they will wear too fast. One wheel we have looked at is the 8" pneumatic wheels from andymark, along with the plaction and the rubber treaded wheels. From looking in past threads many have said to go with the pneumatic wheels, but most threads were a couple years old and i wanted a more recent opinion.

Which wheels should we go for, and why?

While I’ve never actually driven a T-Shirt Cannon robot on a Football field, my past experience with pneumatic wheels vs. other common FRC wheels tells me that pneumatic wheels are probably the way to go for driving on turf/grass. The one thing you will want to watch out for though is that if your center drop (I’m assuming you’re running at least 6 wheels, in the standard tank configuration) is too small then the deformation of the pneumatic wheels under the weight of the robot will cause all the wheels to touch the ground and cause increased turning scrub. Therefore you may have to play around with finding the right pressure to inflate the wheels to and the right amount of center drop.

It is possible to vary the pressure by individual wheel to exaggerate the drop, too.

Incidentally, some 6" McMaster pneumatic casters with custom hubs could be used–I haven’t seen them much lately on FRC fields, but there are some that were routinely modified to be run in an FRC drivetrain. If you have some machining options available, you might find that to be a good way to go, as you can swap in your current wheels if you aren’t running on the football field.

We’re working on a t-shirt cannon as well! In the past, we’ve run robots with 6" traction wheels on football fields with no problem.

We are actually running a 4 wheel standard tank, i am guessing that might make a difference.

What’s the wheelbase and track width? That’s what would really make the difference, in terms of turning a 4WD tank.

Wheelbase: front axle to back axle (actually wheel point of contact with ground, but axle is usually close enough)

Track width: distance from left wheel to right wheel

If the wheelbase/trackwidth number is near 1, you’re probably OK. If the wheelbase/trackwidth is significantly <1, no trouble at all (though I would consider adding a wheelie bar). If it’s significantly >1, you will not want high-traction pneumatics on all 4 wheels, and may want to put some Colsons or slick-ish wheels on one end or on diagonal corners. Speaking of Colsons… that’s another option to think about; I happen to know that they’ll work in some fairly non-typical-FRC applications and keep coming back for more.

i will not have this for a few days, until then what else can you recommend?

Not much–I haven’t done much robot driving on anything but carpet. That being said, I’ve been on a team that built one to handle a very dusty surface.

Though… I would suggest checking ground clearance. You won’t need much, but you’ll need more than in FRC

We use pneumatic wheels for our t-shirt cannon. Our chassis is AM 31" nanotube (27.5" wheelbase, 6 wheel, with 1/8" drop) using Harbor Freight pneumatic wheels with the bearings removed and replaced with bushings for keyed shafts. Don’t do this! The scrub is pretty bad, as we can’t get the bushings in tight enough to get rid of the wobble. We’re upgrading to AM pneumatic wheels and hubs this summer. Between the more solid hubs and slightly underpressuring the corner wheels, we figure we can make a much more nimble robot. Time will tell; if this doesn’t do it, we may have to modify the center axle to lower it a bit more or replace the nanotube frame.

As far as pneumatic wheels, I definitely recommend them over solids; much less likely to tear up grass and race track surfaces due to the larger area of coverage.

Our t-shirt shooter, seen here, http://www.chiefdelphi.com/media/photos/31867, is several years old but we are still running all the original wheels but one. They are solid, but wide and have a lot of rubber on them. After a recent upgrade to a four cim drive it runs with almost no problems on grass, pavement, and all floors.
Edit: I think they are old from am, but I’m not sure.

832 uses 2 powered pneumatic wheels and 2 casters on their t-shirt cannon. No scrub, but going straight can be iffy at times. It’s been working well for years.

One thing you can do is try these 6in wheels from AndyMark

They should bolt right onto your existing setup and if I recall correctly from when I was playing around with one of these, they are cast with a relatively hard urethane rubber and should wear very slowly. Also I believe they are fairly slippery so if you don’t have any problems with your current drive setup in terms of turning scrub, these should sub in really nicely for driving on pretty much any surface. The only place that pneumatic wheels would give you a significant advantage is on uneven surfaces where the wheels will absorb some of the shock load. If possible you may want to test both wheels or some combination of them on a variety of potential surfaces to find the best combination.

This year, our t-shirt cannon runs on tank tracks from BrecoFlex. We got the idea from team 1619’s design

We use pneumatic scooter wheels in the front, casters in the back, 4 CIM tank drive geared for a fast walk, around 10 ft/s. The casters give you zero scrub. Makes turning in grass easier. It is also non marking on the basketball court. Our previous chassis was our 4 wheel narrow from breakaway.