Prototype Small Wheeled Shooter

[Ether]

Originally Posted by falconmaster

Ratios of gear boxes go 5 to 1, 4 to 1, 1 to 1 order of motors is Bag, am, bag

The farthest we can shoot is 27 feet

Sure would be interesting to see a bird's eye view high-speed video in slo mo of the frisbee passing thru that third stage.

[falconmaster]

Originally Posted by Ether

Sure would be interesting to see a bird's eye view high-speed video in slo mo of the frisbee passing thru that third stage.

will get that on Sunday

[falconmaster]

Ok now we did 5, 3, 1 ratio

Shooting farther! Still have flex in base, will get more when we stop this
http://www.youtube.com/watch?v=wGp3M...ature=youtu.be

[Akash Rastogi]

Originally Posted by falconmaster

Ok now we did 5, 3, 1 ratio

Shooting farther! Still have flex in base, will get more when we stop this
http://www.youtube.com/watch?v=wGp3M...ature=youtu.be

Very nicely done.

[Ether]

Originally Posted by falconmaster

Ok now we did 5, 3, 1 ratio

Shooting farther!

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

[s_forbes]

Originally Posted by Ether

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

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.

[Ether]

Originally Posted by s_forbes

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.

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.

[falconmaster]

Originally Posted by Ether

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.

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

[Kevin Sevcik]

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.

[Ether]

Originally Posted by Kevin Sevcik

You can also try speeding up the second wheel...

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.

[sdcantrell56]

Originally Posted by Ether

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.

Most logical process for dialing in the shooter that I have seen yet.

[billbo911]

Originally Posted by Ether

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.

This is where a Chronograph will come in really handy!
Whether you use of a single sensor or dual sensor doesn't matter, either will take out the subjectivity of the measurement and just give you solid measurements.