Challenge #3: Ball sorting/reset system?


Hello everyone,

Thank you all for your ideas! They’re fantastic. We thought about making something motorized, but decided against it because we want to keep it all mechanical. We also considered modifying the board itself to make it easier to get the balls off the board, but I think what we ended up making is better. I made something like the drinking straw idea several of you suggested. It looks like this:

You push it down over a ball and the ball pushes by the rubber band, but doesn’t come back out. You can keep pushing it over balls to pick up more. You can also see how many balls you have in the loader by looking through the holes in the side. Here it is in action:

We’re going to make injection molds for this and have it available on our website, but it will take at least a few months before it’s ready. In the meantime, you can 3D print your own. Here’s everything you need:

Rubber band:

The rubber band is a #31 size (2.5" long, 1/8" width, 1/32" thick). You can find it (or something very similar) in pretty much any pack of assorted rubber bands.

STL files:

I have two options for you. If you have a 3D printer with a dual extruder, you can print the whole thing in one shot, using PVA for supports, and then you can wash the supports away afterward. Here is the STL file for that:

20181012 Ball Reloader.stl

If you have a single extruder (most 3D printers are like this), then you’ll probably need to print it in two sections. Otherwise it would be very difficult to clear out the supports inside the tube once it’s finished printing.

Here’s the ball reloader split in half:

20181012 Ball Reloader Half 1.stl
20181012 Ball Reloader Half 2.stl

What do you think? We haven’t started making injection molds for it, yet, so if you have any ideas to improve it, we can still make changes.

Thanks again for all the great ideas!



That’s an impressively elegant solution!


Thanks! I’m glad you like it!


By the way, I just ordered one to be 3D printed from for $14.80. I thought that was a shockingly good price. We’ll see how well it works when it arrives.


I’m working on printing this to try it out, but am having some trouble.

The split version has very little contact with the print bed because it comes to a sharp point.

Would you be willing to share the 3d models? I was thinking I could try reversing the pieces and printing with the flat sides down, and increasing the width of a few places to make it a bit easier to print.

Happy to share the results.


Hi chuckhays,

Here are the files in two formats: the original Inventor format (.ipt) and STP format.

Inventor format:
20181128 Ball Reloader Half 1.ipt
20181128 Ball Reloader Half 2.ipt

STP format:
20181128 Ball Reloader Half 1.stp
20181128 Ball Reloader Half 2.stp

If you print them in the orientation shown in the picture, I was able to add supports to create more surface area in contact with the build platform. Good luck!



Thanks so much for sharing Paul!

All of the links currently lead to 404 errors however.


Oops! Sorry about that. I fixed the links.


I use a magnet to pick up the balls. Advantage is that you pick up all balls with just one move. Putting the balls back into the board remains difficult.


Hi! I’m just joining in. I love the game, and I share the frustration about moving the balls from the bottom to the top. I was just about to design something very similar, and I’m glad you thought of that already!

Question: what’s the benefit of a curved design, as opposed to a straight cylinder? I’m not a 3D printing expert (just starting my 3D printing journey) but it seems to me like a straight cylinder, perhaps with a slight widening toward the back, could be printed in one piece with no support - would it not?

I’d also suggest adding an ability to stick a pin in the last hole (to prevent marbles from running away by accident) and to count balls from the other end. I’d like to control how many balls I release, rather than how many balls I have inside this device. So, if I only want 8 balls, I’d stick another pin after the mark “8” and only allow 8 balls to go out.