Ball Knocker Advice

Here’s our basic setup so far. We’ve got about a 4’2" 1.5" PVC Tube set to be mounted to the kitbot frame at about 5" above the ground. We plan to knock the ball off with a telescoping PVC pole.

We /had/ planned to run it up using the black ribbing in the KoP and the gears provided, which if we measured correctly should give us about a 3:1 gear ration and about 26"/sec.

While assembling yesterday, we came across a slight problem: our setup yesterday had used 2" pipe with 1.5" inside, with a track milled out because the ribbing wouldn’t quite fit into the 2" pipe.

After this, we’re strongly considering a winch and pulley. It’s simpler overall, I think, and we could still gear up the spool; in order to get the same 26"/sec I think we need about a 2" spindle.

I’m asking here whether any of you teams with more experience can advise us in either direction. The milled pipe wouldn’t be to hard to fix, but the winch is looking pretty good right now too.

cap the top of the pvc pipe and use a compressor to shot about 30 psi. into the pipe to launch the second pipe up to knock off the ball

With a winch, you need to be wary of tangling. If set up and operated correctly (have some sort of indicator when fully retracted and extended so the RC knows when to stop based on sensor feedback, perhaps a string pot or an optical sensor) it is normally not a problem.

Will that be enough power to get the ball up? Due to the robot’s height, we need to extend a pipe roughly 4’2" up at least 2 feet just to hit the ball, and then it’s unpredictable as to where it goes. A pro of the winch/gear thing is that you get controlled speed, so you can go with either reckless flying balls or just tip the ball off more slowly.

You might want to consider a hinged mechanism also…and if it has pneumatic actuation it will be kind of “springy” and might not need to be retracted to go under the overpass. also think about using a flexible part to knock the ball off.

We don’t have any solid part of our robot extending past about 75" height, ever. We discovered that it really is not very difficult to knock the ball off. And catching it is the fun part…

we tried it by regulating the pressure so that it went up fast but as it reached the top it started to slow down just enough to pop it off

We are working on our “ball popper” as well. We have a 24" throw piston to play with for actuation. We’ve run into two problems: 1. Where to place the device so that it won’t tip us over when it strikes the overpass and where it won’t interfere with our other device. 2. The Geometry of the ball makes punching it off the overpass a very interesting challenge. I guess this is the problem with putting something in as an after thought.

here’s an example of knocking the ball off and catching it…

and I think there is video of it somewhere also, but I can’t find that just now.

(they’ve reinforced the “twisty” parts since this picture was taken!)

Are you talking about hitting it off with some device, or actuating something and then running into the ball? Has anyone calculated approximate forces required to do either of these actions?

You could just run into the ball, I think 842 either runs into it or flips up the arm to hit it (ask them, they’ll probably tell you). Try it, see what happens.

That would constitute a Pneumatic piston and you are not allowed to build your own.


As of last night our plan was to have a 2" diameter pipe with a 1.5" pipe inside. Mount a pulley of some sort at the top to prevent cable wear and friction, and then increase the inches/sec by either attaching the winch spool to either a gear geared up to a better ratio or by using multiple pulleys.

Steve is right. Chad, what you describe is not a legal use of pneumatics, and will not pass inspection. It’s kind of unfortunate, but it’s good that you still have time to come up with a new solution.

to nock the ball off make an H out of pvc that flips up before you get to the overpass then just drive under the ball and the ball falls off

we can knock the ball down by extending the top of our elevator up to about 6’ 5" and just run under the ball and it just pops right out

we haven’t used it, it was just an idea we had, but as of right now we use our forklift to knock the ball off