pic: 1726 Promobot

This is the mecanum t-shirt cannon we built to promote robotics in the school and the community, and to try mecanum drive. The frame is made from pultruded fiberglass, using c-channel for the main frame and i-beam for the suspension arms. The cannon has a 2-1/2" bore pvc barrel, and a reservoir made from 3" abs. The cannon is powered by a 200z paintball CO2 tank, regulated to 60psi. We can shoot a rubber-banded shirt about 100 feet.

It looks pretty sweet so far, and definitely looks like a great PR tool for your team. Although I have only one question on the design: is there any sort of suspension for the mecanum wheels?

The reason I ask this is because if one drives a holonomic/mecanum drive robot on anything that isn’t perfectly flat, one wheel may lift up just enough to really screw up the geometry of the vector forces from the wheels, causing the robot to spin around in some weird (and unexpected) direction.

If you search through CD Media, you can find pictures (link this one from XBOT 488) where teams used racquetballs or pieces of rubber tubing to act as a suspension for the mecanum drive bogie.

good point, and they’ve taken it into consideration.

But the bolts could be bigger…and it’s definitely not designed to withstand competition!

Nice paint. :cool:

Does it look like something you’d want to do for your competition robots? (the paint, I mean ;))

Is that tank PVC? Hasn’t there been a history of PVC tanks exploding in a million little shards? Or has the properties of PVC pipe changed?

I hope it’s safe now… it would really cut down the cost of my up-comming T-Shirt cannon project!


No. GUI’s caption says that it’s “a reservoir made from 3” abs." I assume that refers to the type of plastic, not the size of someone’s tummy muscles.

If you are really worried about PVC shrapnel, you could always wrap the tank with several layers of duct tape which should keep pieces from flying away at high velocities.

The robot is beautiful, by the way, and really makes for a professionally made product.

Hmmm… Looks like a pretty fun toy!

Take it from someone who has personal experiance with PVC chambers blowing up. Duct tape, most likely, won’t contain the shrapnel.

put a denim pant leg over the PVC tank
that’s what I heard you’re supose to do

but duct tape fixes everything from bleeding wounds to nuclear war…

There is no pvc chamber on this robot!

The barrel is pvc, though.

awesome, i want one!!!

I just love that word.

That is one sweet shirt shooter, I gotta make me one to shoot at the deer that eat my shrubbery in the winter. (The idea is to make them wear the shirts - the other deer will laugh at them and maybe they’ll stop dining here)


[Note: No, I’m not really going to do that! [i]It’s a joke.]

They did some work on it last night, after an experiment with the compressor from the 2006 FRC robot showed that it would shoot fine on about 10 seconds of compressor run time after opening the reservoir “fill” valve. We stuck a pressure gage on it, and that is only about 30 psi in the reservoir! One thing that helps, is that there is a Clippard tank that fills (quickly) to about 70 psi, then this air goes into the reservoir (evens out at 20 psi) and the compressor adds about one psi per second of run time. The Clippard tank is on there mainly to provide pressure for the “fire” pneumatic cylinder.

So, no need for the CO2 system, which makes me happy from a safety perspective.

For those who are interested, today we were at the school filming for a show for the local cable company, and we found the new system actually works better than the co2 did. We shot quite a few shots (more than a 20oz co2 tank would have allowed, I think) and the cannon shows a range between 40 and 60 yards, while the best we got with the co2 system was around 30 yards.

Where did you get the release valve for the launcher? Is that a pneumatically actuated gate valve?

Great looking launcher!

duct tape is like the force
it has a light side and a dark side
and it holds the universe together

BTW this is from a t-shirt but i couldnt resist:ahh:

Yes it is a homebrew pneumatic gate valve, see this thread

for more info.