Ping Pong Ball Shooter

The basis for this is the old matchbox accelerators (ask your older mentors) that used two wheels spinning rapidly to shoot a matchbox car out of a box into (usually) oblivion.

The basic concept is two motors driving 60:12 gears driving a second set of 60:12 tooth gears ending up in two 4" wheels rotating at what’s to be hoped is 2500 rpm.

Video: http://www.youtube.com/watch?v=b83M-tLR6lw
You can hear the whine as those wheels start hitting max velocity.

Images:

https://vexforum.com/gallery/files/1/1/9/8/1/048.jpg
https://vexforum.com/gallery/files/1/1/9/8/1/061.jpg
https://vexforum.com/gallery/files/1/1/9/8/1/069.jpg
https://vexforum.com/gallery/files/1/1/9/8/1/070.jpg

The base is a simple arcade drive with direct drive to the small wheels. Speed wasn’t a primary goal here. Elevation is controlled by the right stick driving a motor with a 12 tooth gear against an 84 tooth gear attached to the side of the launching mechanism. The wheels are spun from the button channel on the back of the transmitter.

I’d like a little more velocity before I build a feeding mechanism. I’m not sure if swapping to a 9.6 V battery will make a significant difference or if I need more grip on the wheels or if a little graphite on the axles will help.

cool that is pretty good distance. are you running just one motor on each wheel? it shouldn’t matter because in theory the wheels are perfectly balanced and all you meed the motor to do is accelerate them but adding a second motor on each could help you get over the friction in the gears which are only 85% effective according to the inventors guide.

are you the kid in the video?

I’m just running one motor on each wheel although the way the gears are synced, I can run the whole mechanism off of a single motor.

In theory , I could run a second set of motors off the top without regearing (just making two long axels). I don’t think it will make much of a difference but I honestly don’t know. It may be worth trying… hmmm.

Thanks for the idea!

The children in the video are my son and daughter. I’m old…

Hey,

I am a student at CU and we’re making a ping ball launcher for our system dynamics project. It’s due in a few weeks, so we want to do something cool, but we don’t have that much time to experiment and get stuff wrong.

We are hoping to have two spinning wheels that will launch the ball, and have the whole mechanism be able to rotate up and down about 45 degrees as a closed system loop. This is going to be controlled using labview.

We have all the programming done, but don’t know where to start for the actual building of the canon. We were hoping to have the spinning wheels be on the top and the bottom, so that our trajectory is guaranteed to be 2-d just in case one of the motors is spinning faster than the other one. Would you mind helping me out with the gears connecting to the wheels connecting to the motors deal?? I would greatly appreciate it, and it looks like you have it pretty well figured out.

Thanks. I’ll try to explain what I’ve done.

Looking at the second photo down, the motors are attached to the lowest pair of 60 tooth gears. Since those are already engaged with each other, if you don’t reverse the direction of one motor nothing goes anywhere and the two motors strain against each other instead of working together. The 60 tooth gears force both wheels to spin together, even if you remove a motor.

Each of those 60 tooth gears drives a 12 tooth gear attached to and underneath the top pair of 60 tooth gears. This 5:1 ratio means the top pair of gears are turning together at (hopefully) 500 rpm.

The wheels are mounted on the outside set of 12 tooth gears and so they’re (hopefully) spinning at 2500 rpm.

Now I can’t remember the term used to measure a gear from the middle of the tooth to the middle of the tooth* but for simplicity sake, we’ll call it the diameter. The 60 tooth gears are 2.5" in diameter. The 12 tooth gears are .5" in diameter.

Therefore the distance between the centers of the two outside axles is 2* 2.5" + 2* .25" (half the 12 tooth gear) or 5.5".

With two 4" wheels (radius 2" each) that means we have 1.5" between them for a ping pong ball, which happens to be the outside diameter of a ping pong ball.

It’s like the gears and the wheels really really wanted to be assembled this way…

I haven’t thought of a way to get much more speed without adding another set of gears or building a pair of 6" vex wheels.

Hopefully that makes sense and helps. If not, let me know what I can do.


*does anyone recall what the name of that measurement is? I used to know those terms but it’s been too many years since I last used them.

“Pitch Diameter” check out this link at McMaster Carr.

Woot! Thanks!

If you widened the gap of the shooter for it to hold green balls, then used a conveyer system like the ones that were used in elevation to feed in balls you could send quite a few balls over the wall. What do you think? You could also try widening even more for orange but because how they are shaped it would be to hard to do. And after watching the video the ping pong balls travel quite fast, if you were to use it in clean sweep you’d have to power it down! Or risk overshooting. Then if you could get it to move left and right to help aim and make it just so much cooler. But congrats on making that shooter even if you don’t use it in a game, those balls= soft bullets :stuck_out_tongue: