Re: Prototype Small Wheeled Shooter
 

Very nicely done.

Re: Prototype Small Wheeled Shooter
 

Think its due to our base flexing, it will not in the final model. We did shoot from around the Pyramid so it may be 30, 27 was in straight line

Got slow mo of two wheel
http://www.youtube.com/watch?v=cq3feDdl6A0

Re: Prototype Small Wheeled Shooter
 

That tells me you had a lot of slipping in the 3rd stage. Maybe you still do. Try 2:1 for that second stage.

Re: Prototype Small Wheeled Shooter
 

Just measured the latest distance in the hallway, from video last posted of three wheel shooter. 48feet! from 2 1/2 feet above floor

Re: Prototype Small Wheeled Shooter
 

isn't it illegal to trim the shaft of the motor down?
Well not illegal in Texas perhaps but illegal in FIRST?

R

Re: Prototype Small Wheeled Shooter
 

4.1.7.2 R33-A

Re: Prototype Small Wheeled Shooter
 

R33 give us permission to modify the output shaft otherwise tightening a set screw too hard would be illegal.

Re: Prototype Small Wheeled Shooter
 

Thanks to Allen & Ether for posting the relevant rule. It is allowable per FRC Ultimate Ascent rules to modify a CIM shaft in this way.

I have contacted the Texas state legislature regarding your question, but have not heard back yet. My buddy is a cop, and he says he's never had to arrest anyone for it, and thinks that if there is a law against it, it is probably one of those ones which isn't strictly enforced. I think we can assume it is okay until we hear otherwise back from the TX lawmakers.

Luckily, Gov Rick Perry is a fan of robotics and FRC -- if there is a problem in TX maybe he can help us resolve it?

-John

Re: Prototype Small Wheeled Shooter
 

No we just turn robotics into an underground sport down here. Think of the wonderful and terrifying implications.

Re: Prototype Small Wheeled Shooter
 

There is a special place in the afterlife down under (hint: not Australia) for people that crank down set screws into keyways.

Re: Prototype Small Wheeled Shooter
 

Unfortunately, 2:1 is not an easy off-the-shelf gear ratio to come by. These small wheel shooters are super easy to build with a vex planetary and just about any kit motor. Available reductions are 1:1, 3:1, 4:1, 5:1, 10:1 and any combination of those you would like. You can still adjust the tangential velocity of the wheels by changing wheel size (2", 3", 4", 6" are easy from Banebots) or input motor. Bag motor spins at 14k rpm, AM motor at 16k, and Banebots 550 at around 19k Our best setup at the moment is a 5:1 Bag, 3:1 AM, and 1:1 Bag.

Just looking at the math, it's obvious we have a lot of slipping on the last wheel. By my calculations the tangential velocity of a 3" wheel on a 1:1 Bag motor is roughly 175 ft/sec. If a frisbee had no slippage when contacting a wheel in this type of shooter, I would expect it to leave at about 85 ft/second! This is waaay higher than what we are seeing, so I have no doubt that there is a lot of slipping going on.

Something interesting to note: we put a new frisbee into our two wheeled shooter (3:1 Bag, 1:1 Bag) and analyzed the marks left by the shooter wheels afterwards. It looked to me like the 3:1 wheel had more slippage than the 1:1 wheel, since the 3:1 had a shorter 'burn' mark left on the frisbee and shorter overall contact period.

Also interesting to note: given the frisbee compression and wheel spacing involved, the frisbee contacts two adjacent shooting wheels for a substantial amount of time. I'm not sure exactly how they all interact at this point...


TL;DR: I gave up on calculating this stuff, we're just going to go with quantitative results! Also, I need a better high speed camera.

Re: Prototype Small Wheeled Shooter
 

Trying slowing both motors down, to get faster exit speed. Easy enough to do: run them with motor controllers instead of straight off a battery.

Re: Prototype Small Wheeled Shooter
 

We will try slowing down the last motor and then experiment with the others as well. Thanks!

Re: Prototype Small Wheeled Shooter
 

You can also try speeding up the second wheel by putting in a BB RS-550. Or for prototyping purposes, one of the super-powered FP 801-0673 motors from last year. We prototyped with a FP and were getting some pretty impressive velocity. Mind you, we also have a larger wheel spacing, which means less time with the 'bee contacting two wheels.

Re: Prototype Small Wheeled Shooter
 

Better yet:

a) remove wheels 2 and 3, and adjust the speed of wheel 1 until you get the fastest exit speed (call it s1), then

b) keeping wheel 1 at speed s1, add wheel 2 and adjust its speed until you get the fastest exit speed (call it s2), then

c) keeping wheels 1 and 2 at speeds s1 and s2, add wheel 3 and adjust its speed until you get the fastest exit speed.