Linear Puncher Help

Hi all,

So I was building a rough prototype of a linear puncher and having a lot of trouble, The launcher has the draw distance of about 2.5 inches, and makes contact with the ball with a vertical C-channel, similar to 2Z. The pullback is manual right now since we want to test the shooting ability of the launcher before motorizing it. The launcher is unable to make full-court shots, only launching the ball a few feet, and I am stumped as to why it is doing so. I have a few ideas as to how it could be improved, which I will list below, but none of them seem like they would suddenly make the launcher be able to shoot full court, so I thought I would go to the forum for advice. Anyway, here are the ideas:

  • make the kicker lighter (use aluminum instead of steel)
  • lubricate the slider
  • get rubber bands that are all quality guaranteed for equal tension
  • longer draw distance of 3-4" (which would, of course, slow down fire rate)
  • stretch rubber bands more

Below is an image of the prototype, which I plan on completely rebuilding based off of the above ideas and any advice I might receive. Thanks!


This is the right start, what type of mechanism are you using? Slip Gear?
How does the motor on the left connect to the Rack in the Center?

Remove the bracket from the front, a greater surface area would increase the distance

Increase the amount of rubber bands for more resistance

Increase the amount of pull back, you may need to add a longer C- Channel and add one or two of the rack gears

Add one or two motors to increase the amount of force in the pull back without sacrificing the fire rate.

Finally if you are still having problems after all these changes add more mass to the part of the shooter coming forward.

on our linear puncher we are using 3 racks i would also recommend using a 36 tooth slip gear. we have been using a design similar to yours and we have been over shooting the net using the things i just said.

although we do stall which we need to fix. but i am sure it is just friction.

How do you guys keep the linear punched from going haywire? When I prototyped last month, all the screws keep loosening in a very annoying rate.

use nylocks or two keps nuts one on top of the other.

Our launcher is a similar design. We have a 36 tooth slip gear that moves the length of two full rack gears. This slip gear is powered by 2 motors with a 1:1 gear ratio. We have 3 rubber bands on each side of the launcher. This gives us a fire rate of just under 2 balls per second.

And to answer Dons question, we tightened very often, and also had to add a lot more supports. When the launcher fired, the force of the piston would bend the metal the standoffs were attached to. This was a big problem at are last competition.

re enforce it with a piece of steel plate cut to size.

@cameronb996 do you use lube on the slide?

No we did not, but it is a good idea.

would you mind posting a photo of your launcher? to take tips from. cause our launcher stalls at the moment i would like to see what you have done that is different than our design.

Ok i will. Our team does not meet till monday, so I will post a video of it then.

alright Thank you

Can it launch the driver loads from the starting tiles to the nets?


Yes, I am using a 36 tooth slip gear launcher, and the slip gear is on the axle driven by the motor. My slip gear is 18 teeth and 18 teeth shaved off, resulting in a 2.5" draw distance. So, as I said, since we were just testing, we weren’t actually pulling the launcher back with a motor but rather just doing it with our hands, to make it easier to make changes.

What do you mean by greater surface area? Also, if I increase the distance that the kicker moves more than 2.5" (the length of the rack gear) won’t the slip gear have trouble catching back onto the rack again?

I currently have about five rubber bands on each side, and it is already extremely difficult to pull the kicker back. I think that if I add even more rubber bands, the 2 motors that will drive the slip gear (which I believe will be at a 1:1 ratio to preserve fire rate) will not be able to pull the kicker back.

How long did you make the unshaved section of your slip gear? I am unsure how much longer i should make the pullback.

I plan on having two motors powering the slip gear.

Towards the bottom of this thread ( @MartinMaVEXForever explains that having a lighter kicker is actually better, which is why I wanted to actually make the kicker as light as possible.

Two full rack gears is a bit more than 36 teeth (I believe its 38), so obviously you mean the slip gear moves almost two full rack gears, so maybe about 30 teeth? How many teeth did you shave off, because frankly, I have no idea how much would be the right amount. Also, how much did you stretch the rubber bands, because that problably is just as important as how many rubber bands you had. Also, I was wondering exactly how you drove the slip gear. Did you have motors on either side of the axle that the slip gear was on? Thanks!

I personally found that the most major distance increase in firing distance happened when I moved the ball holder farther forward. Now it only hits the ball for 0.5" to 1" in stead of 2".

If you don’t mind me asking, what is your draw distance? Also, when you say it only hits the ball for .5" to 1", do you mean that the launcher only moves 1/2-1" further after hitting the ball? Thanks!

I don’t actually know how long it contacts the ball for, so I just said 0.5" - 1".
I wouldn’t recommend copying what I’ve done, since it stalls, it shoots fewer than 1 ball per second, it has terrible accuracy, and it has so much recoil that a robot with no wheels got push back a bit.
I have 2 high strength elastic bands on each side stretched 6". The slip gear then pulls it back 3".

I only have about 5 teeth shaved off my slip gear. I’ll find out for sure and share it on the video Monday. When shaving off the gears on the slip gear, I marked the gear, then i rotated the gear by hand to see how much it would rotate until it reaches the end and marked that. I shaved that area and that gave me the maximum pullback distance. My 2 motors are on each side of the launcher and share an axle. Ill take some measurement of the drawback distance to. I also noticed that depending on how far forward the ball is on the launcher can vary the launching distance a surprising amount.