pic: 955 T-Shirt Bot @ Halftime


FRC 955’s t-shirt cannon robot at CV v CHS (rivalry) game.

That thing looks sick! The middle tube is the firing one, yes?

I’ll bet it scared the @#$% out of the other football team!

I heard that the robot didn’t turn that well. I still wish I had gone to the game.

Correct, the outer tubes are tanks and the center tube is the barrel. We can fire one tank or the other, or both at the same time. The biggest issue was the amount of energy required to operate the robot. We simply didn’t have enough batteries.

What was drawing so much energy?

Inside there are five kit compressors and four CIMs driving AM 6" mecanums through Banebots 12:1 planetary transmitions. All of the compressors are powered by one battery and the drive, elevation, and controller are powered by the other.

The issue is trying to run the compressors over an extended amount of time. We can fire about three shots at max pressure before the battery is drained. The other issue we didn’t plan for was firing when our team scored, it is unpredictable at best and holding pressure for long periods of time means the compressors tend to be “topping off” constantly. Either getting a battery better suited to the job or having a setup where we can keep it plugged in most of the time are the options we are considering.

The other slight issue is that fact that the robot weighs about 275 lbs. It is taxing our drive as is and we are considering changing our gear ratio to 16:1. Adding excessive weight at this point wouldn’t help us be mobile

Hmm, 5 compressors, I suppose that would do it. Are you cooling your compressors at all? From my experience in 2008 (my only experience with any sort of pneumatic system) we found that the compressor works much better when kept cool.

Also, and this is something that the electronic people will have to help you with, (by which I mean NOT me, I’m software) what about having 2 or 3 batteries on there? Yes it would increase weight but it would mean you have more energy stored.

And yes, at that weight I would think that the 16:1 would be a great idea, I’d be interested in knowing how hot your CIMs are getting moving that much weight.

One more question, how do the mecanums handle the track? What type of track is it?

We have 6 fans (3 pulling in air in the front and 3 pushing air out the rear) cooling the inside. There is a good flow going through the unit. We already have 2 batteries in the robot. I would rather find some other type of battery (non-kit) to run the entire system then keep adding more batteries.

The CIM motors do a great job in forward and reverse. Its the power loss when driving sideways that is gimping our movement, we believe. The only issue with the track is the red color so far. Our track is relatively new (about 5 years) and when it is damp the red gets on everything. :yikes:

Well, then I am out of bright ideas :slight_smile:

No fair, our coaches are too paranoid to allow a robot on the track because of the wheels. Nice design! Our T-Shirt launcher was just made and isn’t tested; it is backpack mounted.

The trick is to get your administration excited about it. You could only imagine the look on our athletic director’s face when the principal told him at the last minute that he was providing the shirts at the football team’s expense.

what are you using as your valve? I would be very curious to see a closeup of it and/or parts numbers.

What is your team using for a valve?
My team (2002) is also trying to create a robot mounted t-shirt cannon but we can’t find a way to fire it without a hand turned valve due to voltage and power supplies.
By the way, why are you using two tanks?
Also that is a freakishly cool design. :slight_smile:

thanks for the pic


Another way to look at the battery life problem: you’re driving more than double the weight of a typical FRC robot with only 70% of the torque you think you have. At least theoretically, mecanums give the same torque sideways as they do forward/reverse. The primary torque issue comes on the diagonals. On the strict diagonals you’re only running 2 motors, and even then you’re only getting 70% of those outputs since the rollers are still 45 degrees offset from the rotation of the wheel. Hence you’re moving 275lbs with only 35% of the available torque in the entire drivetrain.

Just to move forward, I estimate your bot draws a constant 45A through 4 motors. On the diagonals, that gets up to 56A through 2 motors – no biggie since there’s minimal impact. Yet the massive current draws come when you are moving laterally, say, 60-80 degrees off of forward where the 2 motors that strictly help move sideways pull ~30A and the diagonal motors pull ~45A – that’s a total of 75A to be able to move in a 360 degree lateral plane.

The quick solution: in programming, disable diagonal movements, even minor/gradient ones. The robot can move strictly forward, strictly sideways, or turn. It’s not as impressive, but should keep you from having to purchase additional transmissions for the moment.

As a curiosity, how much distance does your bot need to get up to maximum speed from a dead stop?

Even more important, how far does it shoot a shirt? :yikes:

Regarding holding pressure over time, could you use the five compressors to get up to pressure, and only one compressor to hold the pressure? Are all five needed for speed re-filling, or for getting a higher pressure?

Our HS has a new track and fake-grass field – no wheels allowed anytime. Last spring our team joined an overnight cancer walk with 100s of people walking the track and running all over the field. I’m sure the athletics people were shuddering in pain. I was almost sure someone would run out and tackle the Moms with strollers {nothing happened, but the thought was amusing}. I was willing to chance the robots on the track but the team’s powers-that-be didn’t – there was also some rain, which didn’t help. Would wide inflated tires help?


Sounds like you might have a pneumatic leak somewhere. We have been able to hold at max pressure without running the compressors for… 3 months (at least). Looking for that tiny elusive leak might solve the problem of constant compressor running. Either way, I wish we had the commitment to make something that awesome…

your robot = win

Thanks for the comments and I’ll try to respond to all of them.

First of all, I should give credit to team 1716 and this for inspiration.

We are using 2 tanks for two reasons:

  1. Alternating between tanks allows us a faster firing rate.
  2. Firing both tanks at the same time allows us to fire long shots.

The system is all 2" schedule 40 galvanized steel pipe except for the brass ball valves and the ABS barrel. The 2" ball valves are opened by 1.5" diameter 8" stroke pistons. We could not locate 3" galvanized for the barrel locally and buying it on line was too expensive.

Yes we have a leak somewhere in the system. Also, four of the five compressors filling a tank took 15 seconds to reach 120 psi. We had some serious run time regardless of the leak during the game.

We are scheduled to be at this Friday’s game as well and we are taking measures to improve our performance. We haven’t done much driving on the track except straight forward and reverse, it accelerates pretty well (~20ft.).

Our best shot was firing both tanks at the same time, one was at 120 psi the other was at 135 psi. I’d say it was about 90 yards with the barrel at a max elevation of 40 degrees. (For those of you wondering, the galvanized is rated for 180 psi and we have pop-safety valves on each tank that vent at 150 psi.)::safety::