Re: Top/bottom roller shooter vs. bottom roller only
 

My team is going with a one wheel shooter because it is more compact for being on a turret

Re: Top/bottom roller shooter vs. bottom roller only
 

Ok so, I am design our shooting system and have designed a two roller shooter, however I was informed there is an optimum roller diameter based on the rpms it will spin and the ball diameter and I was told there where calculators. I found jvns design calculator but there wasnt anything about shooting. Does anyone know about any calculations and formulas I can use or of a Design calculator for this?

Re: Top/bottom roller shooter vs. bottom roller only
 

There should be an optimum diameter, but it will also depend heavily on your design, including variables like how many motors (not just RPM, torque will play a role), moment of inertia (if you have a flywheel, or just the inertia of the roller), friction in the bearings, and perhaps most importantly, how much you compress the ball. An analytic solution for the best diameter would be difficult if not impossible because some of those variables are very hard to measure and quantify. So your best choice is probably just to test a bunch of rollers until you get something that works.

Re: Top/bottom roller shooter vs. bottom roller only
 

A decent estimation is that the ball will get moving at 60-70% of the ideal free speed of your shooter roller's tangential velocity. Aim for 1-2" of pinch, with some adjustment (we're using 1.5" of pinch). Wrap your rollers in a grippy, compliant, material.

Hope this helps.

Re: Top/bottom roller shooter vs. bottom roller only
 

For a 2-wheel (top and bottom) shooter with both wheels the same diameter and powered and spinning at the same speed: If you assume that the ball exit speed is equal to the tangential velocity of the wheels then

wheel rpm = 720*V/(pi*d)

V is ball exit speed in ft/sec, and

d is wheel diameter in inches


For a one-wheel shooter, the required rpm will be approximately twice that.


As for motor selection and gear ratios, here are some thoughts:

http://www.chiefdelphi.com/forums/sh...3&postcount=15

Re: Top/bottom roller shooter vs. bottom roller only
 

Hey Ether, why is that? Are their techniques to make it less than 2X?

TIA

Re: Top/bottom roller shooter vs. bottom roller only
 

Think about the tire of a car going down the highway at 60mph.

At any instant in time, the center of the tire is translating at 60 mph. The bottom of the tire, touching the ground, has zero speed at that instant. The top of the tire, at that instant in time, is going 120mph.

Re: Top/bottom roller shooter vs. bottom roller only
 

This needs a poll

Re: Top/bottom roller shooter vs. bottom roller only
 

Excellent illustration - thanks!

Re: Top/bottom roller shooter vs. bottom roller only
 

We are talking about an observation in the road's frame of reference?

Re: Top/bottom roller shooter vs. bottom roller only
 

Well I did say:...so that would be "yes".

Re: Top/bottom roller shooter vs. bottom roller only
 

But our "car" is not moving. The speed on the edge is r * omega where omega is rps * 2 * pi. If there is a second wheel above the first why would it increase the speed on the edge of either wheel? Perhaps the real issue is that single-wheeled shooters lose velocity because of the balls interaction with the hood? And double-wheeled shooters (which generally have no hood) do not?

Jeez - I should have paid more attention in physics but I don't get it. How could you possibly accelerate the ball to an initial speed greater than the speed on the edge? Happen to know any illustrative web sites?

TIA

Re: Top/bottom roller shooter vs. bottom roller only
 

The problem is very simple.

With single wheel shooters, the ball has to roll along the hood. When you make the edge of a rolling object move at 1x ft/sec, the object as a whole moves forward at 0.5x ft/sec.

With double wheeled shooters, the ball is just pushed through the two wheels. It doesn't have any backspin and leaves at a maximum velocity of 1x.

Re: Top/bottom roller shooter vs. bottom roller only
 

OK, that makes more sense - and what I was meant by "interacting" with the hood. Ether's explanation also makes more sense now.

Thanks