Hello, this is my first time designing anything for a robotics team. What gear ratio would you recommend for a 2017 style ball shooter shooting tennis balls using one 775 pro? Thank you!
You have to do the math. As a general guide line
- How far do you want the ball to go
- Work out the ball velocity from ballistic equations
- Work out the surface speed of the ball perimeter that gives you that velocity which will give you the wheel speed.
- You can work out the reduction using about %50 of the motor free speed. JVN’s gearbox spread sheet is a good tool.
That will give you a starting point. Keep in mind you have friction and other losses to take into account. You might find one motor isn’t enough. (Vex has a fix for that.
Although FrankJ’s answer is correct, there are more factors that affect this.
How much compression will you be applying to the balls?
how many inches of engagement in the launcher?
how accurately will your shooter hold the ball against the wheel?
what’s the friction surface that’s engaging the ball?
How much rotating inertia?
how much power input power in watts? (multiple motors ? )
How much time between balls?
So yeah, even though Frank is correct, I’m just going give you an easier answer.
Try for 2000-2500 rpm on a six inch shooter wheel. If that doesn’t work, speed up or slow down. Bigger wheel slower. Smaller wheel faster.
And the one thing that FrankJ touched on but didn’t elaborate on: What trajectories do you want the ball(s) to fly on? Sometimes it’s better to throw the ball a little flatter; for 2017 most teams wanted a higher arc due to the “smokestack” goal. These are the “ballistic equations” you need to look at (think parabolic formula).
You’ll set up a different shooter overall if you’re trying to go horizontal or slightly rising at 10’ off the floor and 20’ downrange , vs trying to have a fairly steep downward angle at 10’ off the floor and 3’ downrange, for example.
With the 2017 game and how quickly teams were shooting, this arc was also important for making sure the balls didn’t collide at the apex of the arc. Hereis an example of a higher arc causing balls to collide, here is an example of a flatter arc allowing a faster stream. This is why many shooters decided to forego the protected key in favor of shooting from farther back. Our feeder had two speeds so we could shoot from both slowly from the key and more quickly from farther back.