T-Shirt Cannon Wheels

Does anyone have any experience regarding drivetrain wheels for a T-shirt cannons? My team is looking into designing a T-shirt cannon over the offseason for use at school football/basketball games, and so it will have to be able to run over a running track without damaging the wheels too much and then a basketball court without ruining the floor. Any help/advice is appreciated. Thanks!

Suggestion: Make the wheels easily swappable, and have 2 sets. If you pick stuff up from the track/field you’re going to need to get it off before you go onto the court, might be easier to just swap wheels.


8 inch pneumatic tyres would be a good option. Won’t damage the ground and should last quite a while as well as going over most obstacles. Also works with KOP drivetrain.


What about omnis? They seem really good since they would make it nearly impossible to leave a mark on the gym floor and a drifting t-shirt bot would look pretty slick…

Thanks I’ll keep that in mind.

We made what you describe, a drift-bot powered by 6 CIMS on a custom 9:1 gearbox and 6" wheels, and it did work on concrete. The wheels do wear quickly and pick up alot of gunk and aren’t too cheap to replace, but it does make for spectacle at a loss of control. If you happen to have 8" Omni wheels a omni-tyre-omni 6 wheel setup would be quite effective, durable and controllable.

Have you had any experience with colsons in this application?

My initial gut read was Colsons for the basketball court. Not sure how they’d do against the track and turf of the outdoor venues but there’s a pretty decent chance they’ll work there too.

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While I haven’t used them in FRC applications for traction yet, from my understanding they are very durable and quite grippy but are in the end a solid wheel.

A pneumatic tyre will ride bumps all day while grabbing at ledges to pull the machine up and over. With 6 colsons (I assume you are looking at 6wd) the machine won’t ride bumps or obsticals quite as well and will leave marks where the outer wheels slid during turns and will wear faster. The advantage is simplicity, cost and if all wheels are the same they are easy to have spares.

For omni-colson-omni drive it would be optimal for basketball courts or flat non-bumpy surfaces best (on 6" or even 4" wheels) over a pneutatic drive. Could do outdoor use but would wear faster and a pneumatic drive is better there.

I would strong suggest omnis on the corners to remove skid and protect the floor, and whether colson or pneumatic tyres is up to the most common use, id pitch pneumatic as it wouldn’t care in any use case. WCP sells 6" tyres I think so one can save money over getting 8" omnis for the standard 8" tyres.

How difficult would it be to give the Omnis a wash after each football game? Basketball season is a few months after Football season ends so we don’t really have to worry about quickly swapping/cleaning wheels.

It’s not loose dirt, it’s worn in grime that makes itself one with the rubber rollers. You’d have to power wash it off, probably wrecking the wheels. It dosent end up being much of a disadvantage to performance and should be worn in too much to skid into the floor if the wheels turn with the robot so no power stops.

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Definitely pneumatics for football and other outdoor uses. 3946 was never allowed to bring a robot on the gym floor no matter what it had, so I don’t have any experience there. Remember that this is not a competition application, so don’t be afraid to only power half of your wheels. Powering two wheels in front and having a couple of casters in back will greatly reduce the skidding and how much rubber you leave behind. Also note that the lower you gear a motor, the less current you’ll draw when moving at any given speed, and the longer batteries will last. Does your T-shirt cannon really need 12-16 fps?

(And OBTW, don’t try to generate compressed air on the robot for this; use an A/C or shop compressor and have a tank on the robot (or a small scuba tank and regulator). Even on our gasoline powered golf cart cannon in 2018, the on board compressor rarely made sense.)

Maybe try some sort of treads or pneumatic tired to go on the drivetrain to be easily swapped with HiGrip wheels so you can go from “smooth terrain to rough terrain” (figured on road/off road didn’t make sense)
Either you could swap them or have just pneumatic wheels on the entire time (also offers a little bit of shock absorption depending on how much psi you have)


Another vote for gray 8" pneumatic tires/hubs. These were quite popular for the Stronghold game. Your team might have some or you might be able to find a nearby team that would be happy to do a little clean-up and get rid of some. These work great for about any surface. They are nice to have for driving across parking lots or concrete surfaces. The gray ones are non-marking, so they work equally good on the basketball floor as they do on the football field.

We used wheels, motors, gearboxes from an old electric wheelchair that was donated to the team by someone who had bought a new one. We had to get a 24V speed controller and we’re using an old cRIO we had lying around.

+1 on the scuba tank for supply. And have a second tank for working pressure.

Why do we need the two tanks? What’s the purpose of having the working pressure tank?

Are the black WCP pneumatics non-marking? Or just the gray ones.

We found that it stabilized the overall pressure of the shots at the PSI we wanted. We used a 1” NPT solenoid valve for firing, and had 3/4” NPT hoses running from the shot tank through to the cannon. This allowed for a large flow rate from the shot tank out. Then the shot tank could refill from a much smaller 1/4” line from the scuba regulator.

We have found that the black ones can leave marks. As happens with something every FRC season, robotic teams bought the world out of gray 8" pneumatic tires from Jan-Mar 2016. It was a bad time for electric wheelchair users, as that seems to be the primary normal application for those. We had to get some black ones for our practice bot and we had to be careful where and how we ran it. We did not see marks left by the gray ones.

On the other topic that has evolved on this thread, you definitely want a working pressure tank. I’m not sure about scuba tanks, but the small commercial compressed air tanks we use start out at 2000 psi. You’re going to get more consistent performance (and probably regulator life) dropping that pressure to 100 psi or so into a tank rather than just the volume inside the tubing between your regulator and solenoid valve. We use a tank/manifold less than 0.5 gallons and it works fine for us, but a 1-2 gallon tank seems to be more common and some even have larger working tanks than that.