Team 125 Ball Shooter Prototype!

[Brandon Holley]

check out this lil site and look at the simple prototype we made using a cim motor and 6" wheels. It shot 19 feet across the room and 7 feet high at an angle of 22 degrees, so there is improvements to be made.

There is also a video of a compressed air prototype we made, it shoots a foam dart across the quad at Northeastern University.

http://h1.ripway.com/mortgeek/index.html


Let us know what you think!!!

[Rick TYler]

Thanks for posting the link! I noticed that your machine seemed to give the balls topspin. Maybe the wheels should be underneath the all to give it backspin instead?

[Greg Needel]

I am curious how far that distance is and what RPM you were spinning the motor at.

[Henry_Mareck]

looks like a great start. I too would like to know your RPM.
It seems that all the good prototypes i see are not double wheeled, and i find that suprising. None have been conveyor belts.

now, what are you doing posting prototypes at 1 am?
and, why am i answering?

[Rick TYler]

Originally Posted by Henry_Mareck

None have been conveyor belts.

* ahem *

[Brandon Holley]

We used a variable power power supply to power the motor, so the motor was running at 9Volts or 3/4 power, and there was a reduction on it to the shaft which was 2:3, so overall it was running at around 2250 rpm. The ball shot 19 ft at a 20 degree angle, so we are hoping for this weekend, to get it at 35 degrees and see how it works out for us!

Also it is a one wheeled design for simplicity, and the sheer fact that 1 is easier to prototype than 2. The wheels spinning are two of the 6" skyways side by side to give the ball 2 contact points.

[Brandon Holley]

Apparently this website is down because it has a VERY low amt of bandwidth, anyone know of a site that hosts videos for free??

[generalbrando]

If the video is small and you zip it, you can attach it to the forum here.

Brandon (the other other Brandon), please speak up if we should refrain from posting small video clips so we don't cause you more pain than we already have

[chris31]

I could host it on my server, it would be kind of slow though.

[DKolberg]

Originally Posted by MORT~11

We used a variable power power supply to power the motor, so the motor was running at 9Volts or 3/4 power, and there was a reduction on it to the shaft which was 2:3, so overall it was running at around 2250 rpm. The ball shot 19 ft at a 20 degree angle, so we are hoping for this weekend, to get it at 35 degrees and see how it works out for us!

Also it is a one wheeled design for simplicity, and the sheer fact that 1 is easier to prototype than 2. The wheels spinning are two of the 6" skyways side by side to give the ball 2 contact points.

with a 6" dia wheel and 2250 rpm you exceeded the max velocity. 2250 with a 6" wheel is 58.90 ft/sec or 17.95 m/sec and the limit is 12 m/sec.

[Biff]

Originally Posted by DKolberg

with a 6" dia wheel and 2250 rpm you exceeded the max velocity. 2250 with a 6" wheel is 58.90 ft/sec or 17.95 m/sec and the limit is 12 m/sec.

That is assuming all the rim velocity from the wheel(s) are transfered to the ball, As I understand the design the ball is only driven on one side. If you have wheels on both sides of the ball then you are more likely to have a closer match between wheel speed and ball speed, There is still going to be some slippage unless you have a very long contact surface. IE the belt idea.

[Rick TYler]

Originally Posted by Biff

That is assuming all the rim velocity from the wheel(s) are transfered to the ball, As I understand the design the ball is only driven on one side. If you have wheels on both sides of the ball then you are more likely to have a closer match between wheel speed and ball speed, There is still going to be some slippage unless you have a very long contact surface. IE the belt idea.

Just to expand on Biff's ideas, I think with a wheel you are going to have to measure velocity rather than calclulate it. Look at it this way, if you have a single long belt and the ball is pressing against something to provide traction against the belt, the ball will come out of the launcher at half the speed of the belt (but spinning rapidly). You can mock this up easily -- put a tennis ball on a table and move it along by pressing down with a book on top of it. The tennis ball will always come out because it is going slower than the book. With twin belts completely gripping the ball, it will exit at a speed that is the average of the two belts.

A wheel launcher is more problematic. In a single-wheel launcher, the maximum speed that ball can be released at is half the speed of the wheel at its rim. Because of slippage -- something that we assumed was zero with the belt launcher -- the bal won't really come out at that speed. It will be slightly (or a lot) slower. A 2-wheel launcher has a theoretical maximum speed of the speed of the wheel at its rim.

Generally speaking, if you are trying to get maximum ball velocity with a minimum of energy used, you are using either a 2-wheel (or, more properly, two or more wheels on each side of the ball) or 2-belt launcher. Unless you are using a pneumatic, trebuchet, spring, or cold fusion launcher.

[Brandon Holley]

The motor will slow down as soon as contact is made with the ball. We are all assuming that the ball contacting the wheels will have absolutely no effect on the motor, but it does.....actually it effects it ALOT

[Rick TYler]

Originally Posted by MORT~11

The motor will slow down as soon as contact is made with the ball. We are all assuming that the ball contacting the wheels will have absolutely no effect on the motor, but it does.....actually it effects it ALOT

I know we are supposed to be, like, all sekrit and stuff about what we are doing, but this is the biggest reason I like a belt-driven launching system. Combined with an encoder and a high-torque motor system (big CIM, anyone?) I believe a long belt (something like 24") will give more consistent launches -- both in terms of orientation and in velocity. We are prototyping right now, and, if it won't violate the FIRST secrecy oath, I'll share our results when we are done.

[artdutra04]

Originally Posted by MORT~11

Apparently this website is down because it has a VERY low amt of bandwidth, anyone know of a site that hosts videos for free??

Try Put File. They will host unlimited amounts of videos under 25 Mb each for free.