Top/bottom roller shooter vs. bottom roller only

[gpetilli]

Originally Posted by JamesCH95

I vote for two-roller (NOT two-wheel) option as well for the reasons Don highlighted.

I think that rollers are more tolerant to ball variances than wheels are because they're wider (either in feed, density, compressibility, etc). Our two-roller shooter this year (and in 2006) was VERY consistent, to within less than a ball radius over 20-30ish shots in our short-range prototype being fed by hand (i.e. inconsistent feed) with 6 different balls.

My $0.02

What diameter roller and how much compression? We are looking at a hybrid with 1.75" roller and 1.5" compression. I am worried that we need to have more compression or risk the dreaded orange snow.

[JamesCH95]

Originally Posted by gpetilli

What diameter roller and how much compression? We are looking at a hybrid with 1.75" roller and 1.5" compression. I am worried that we need to have more compression or risk the dreaded orange snow.

Our tests were done with 1.5" rollers running about 1.5" of compression. No-slip carpet material is a good roller wrap.

[MrForbes]

I've seen how challenging it is to make one wheel spin with controlled speed....I have little desire to double our workload.

[wilsonmw04]

Greetings,

I will have to agree with Todd on this one. A one axil shooter has been much more consistant than the 2 axis shooters we prototyped. We found that two
8" AM wheels roughly 2-3 inches apart running at 3500 RPM will shoot 1/2 court with a success rate ~40% with a rough prototype and hand feeding. We think we could get that up to 60%. As Todd stated before, the variation of the balls will make consistant long shot extremely difficult.

[Aur0r4]

Interestingly enough, we prototyped both 1 and 2 wheel shooters and got exactly the same error with both (about 0.4" for every foot of distance). However, the two wheeled design shot much farther, as would be expected. The advantage of a one wheel design is that it gives wickid backspin and we found that this gave a higher shot percentage (with the same overall shot error) because balls that hit the backboard tended to shoot down into the hoop.

Our team went with the one wheel design. We agreed, though, that either could be made to work. We also agreed that a catapult would be immune to the ball error, which I discussed our attempts to quantify in another thread (squishimetrics).

The most interesting test was last night when the local police brought a radar gun over to test our shot speed. After adding aluminum foil to reflect the radar, we found that our shots were coming out at about half of the theoretical value. We, therefore, need to really investigate the energy transfer efficiency at different speeds, and its likely not a linear relationship.

[wilsonmw04]

Originally Posted by Aur0r4

We, therefore, need to really investigate the energy transfer efficiency at different speeds, and its likely not a linear relationship.

That's the disadvantage to the wicked backspin. The impulse given to the ball is split between angular and linear momentum. The more backspin, the less forward velocity we will see off our shooter.

[Aur0r4]

Exactly... That, and we can hear that there is some degree of slippage on ours. There is also energy loss in compressing the foam, deforming the device, etc...

[MrForbes]

You need to have some wicked rpm on a single wheel to get good distance with it, but imo having the ball bounce off the backboard, into the basket, is worth it

[dellagd]

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

[dragonman]

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?

[John]

Originally Posted by dragonman

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?

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.

[JamesCH95]

Originally Posted by dragonman

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?

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.

[Ether]

Originally Posted by dragonman

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?

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

[wireties]

Originally Posted by Ether

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

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

TIA

[Ether]

Originally Posted by wireties

Hey Ether, why is that?

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.