# pic: TechTigers shooting prototype

Today we put together a simple prototype that shoots balls. We used our kit transmission from 2005.

The rpm at the wheels is about 500 after a sprocket adjustment.

Video can be found here:

the link appears to be broken…but i really want to see it

I’m also very interested in seeing the video and it appears broken to me, too.

By my estimates, at 500 rpm, you should be shooting at around 1/2 (17fps or so) of the max velocity allowed. Is that what you are seeing?

Yes, the link broke for some reason, but we will be uploading something tomorrow because some one else has the video file and I haven’t been able to get a hold of him.

We calculated that the ball was coming out at a little less than half of the allowed speed. Did not go too far.

The wheels are at a 45 degree angle and by the time it had traveled about 6 or 7 feet it was already back to the height of the wheels. I’m not sure how to explain this better.

Dave

by shooting the ball at 500 rpm, you will never achive the length you need. unless you are shooting while parked on an angle on the ramp. if you were to be scoring from a distance of 20+ feet, it would have to at least spin around 6000-9000 rpm depending on the size of your wheel and the motors you use. try a direct drive from the chips and c what you get from them. id step up to a higher rpm motor. by using chain and sprocket you lower the rpms dramatically.

We knew that it was not going to go far enough, we were simply making something quick with the kit transmissions.

Also you do not want to spin those wheels at those RPM you are talking about because the ball will exceed the speed limit.

Edit: The link should be working now. The website that was hosting it was temporally down.

3000 rpm and a 12.5" wheel does the trick, but of course this needs to be refined a lot. We probably don’t need it to be 12.5" for starters.

is that tank tread i see

just for general knowledge assuming close to complete transfer of speed to the ball you threw that ball about 50 meter/second well over the maximum.

If you you kept the same RPM and used a 3 inch wheel you would be right on the speed limit of 12 meters/second

Yes, this was our 2005 practice robot that we took apart but we left the belts on. This years drive system is surprise

We’re not sure about that. The ball doesn’t go that fast based on timing and measurements from the video - it goes about 2X the max speed. The motor doesn’t provide much torque at that gear ratio (1:1), so all the energy comes from the rotational momentum of the wheel.

We’ll continue to experiment and figure out how large of a wheel we really need both in diameter and weight. I just want to make sure for the benefit of those designing prototypes without the ability to do testing that everyone understands that in this case it’s not a matter of motor torque.