# Tennis ball launcher RPMs

My team and I are working on a few designs for Nothing but net what RPMs do you think will be needed in a tennis ball launcher style shooter to shoot the balls from the starting tile to the high goal (16.9 feet).

Figure out the initial velocity of the ball (projectile motion) and then work back from there.

I am sorry but I have no clue how to do that math could you tell me a website that can explain it or could you explain how to get wolfram alpha to do it for me.

This is a website that explains how to perform the calculations for projectile motion: http://www.physicsclassroom.com/class/vectors/Lesson-2/Non-Horizontally-Launched-Projectiles-Problem-Solv

Once you find the initial velocity needed for the ball, you would need to convert your linear velocity into a circular velocity, which would probably be easiest using torque.

I tried to do these calculations the other day, and I ended up getting about 1550 rpm on a 4’’ wheel. I did it by solving for the initial speed of the ball and then assuming that the velocity of the ball coming off the flywheel will be half of the tangential velocity of the flywheel. Has anybody else tried to do the math on this and gotten a similar value?

Shouldn’t be difficult. The tangential speed of the launching wheels can be assumed to be the speed of the ball. Figure out angle, projectile and find the speed. Then figure out what gearing can get you that speed with motor velocity around 60 rpm. Then use PID velocity to hit speed target. That’s what I am doing.

Edit: just thought that because you have high velocity at the output launching wheels, we can finally get some decent resolution of velocity from the big red encoders and actually do high update frequency PID velocity! Yay!!

Why half tangential speed?

Yep, that sounds about right for a two wheel shooter. It does depend upon the mass and radius of the wheels and the effectiveness of the energy transfer.

We will see in a few weeks once kits can be ordered. Darn Long Beach shut down. :mad:

That’s very close to what I got. I got that the ball needed to reach about 7. to 7.7 meters a second, 25 feet per second assuming the shooter was about 45 degrees, the ball left around 18 inches high. I used this formula derived from my textbook and got about 7.469 meters a second

After plugging it into a physics generator my friend used, he got about 7.5 meters, then he used the generator to consider air resistance and got about 7.7-7.8 meters per second