pic: 955 T-Shirt Bot @ Halftime
 

Re: pic: 955 T-Shirt Bot @ Halftime
 

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

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

Re: pic: 955 T-Shirt Bot @ Halftime
 

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

Re: pic: 955 T-Shirt Bot @ Halftime
 

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.

Re: pic: 955 T-Shirt Bot @ Halftime
 

What was drawing so much energy?

Re: pic: 955 T-Shirt Bot @ Halftime
 

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

Re: pic: 955 T-Shirt Bot @ Halftime
 

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?

Re: pic: 955 T-Shirt Bot @ Halftime
 

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:

Re: pic: 955 T-Shirt Bot @ Halftime
 

Well, then I am out of bright ideas :)

Re: pic: 955 T-Shirt Bot @ Halftime
 

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.

Re: pic: 955 T-Shirt Bot @ Halftime
 

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.

Re: pic: 955 T-Shirt Bot @ Halftime
 

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

Re: pic: 955 T-Shirt Bot @ Halftime
 

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. :)

thanks for the pic

hans

Re: pic: 955 T-Shirt Bot @ Halftime
 

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?

Re: pic: 955 T-Shirt Bot @ Halftime
 

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?

Ha!