Spiral Ball Track

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This week in Inventors’ Lab, we’re doing our final Simple Machines unit, and studying the Screw. Yesterday, on Facebook, someone shared this fabulous project from Frugal Fun. I had to have one!

So, this is what I built last night after my son went to bed. I think it took a little less than 2 hours start to finish.

This post is a narrative of my building process, and my observations. You may want to start with Frugal Fun’s original, which describes the how-to of  this better in a tutorial at https://frugalfun4boys.com/2017/10/04/how-to-build-a-paper-plate-spiral-marble-track/.

You take a poster tube. Trace the perimeter in the middle of a paper plate. Cut that circle out with an X-acto knife. Then cut a slit from there out to the rim. Then wrap the plate around the tube, and use a glue gun to mount it so it spirals up a little bit… each level goes up about 1.25 inches, so the second edge you glue down is about 1.25 inches higher than the first edge you glued, and you’ve got a nice even ramp between them. A couple things I learned while doing it –

  • it’s easiest if you start at the bottom.
  • You need to actually cut that circle just a little bigger than the tube’s perimeter.
  • They recommend starting by marking your 1.25 inch markings all the way up the tube. I found as I went along that it was just as easy to just use my hand to gauge how deep each layer of the ramp needed to be.)
  • It’s a fairly challenging thing to get the ramp to curve just the right way in a nice smooth ramp. Do-able, but that’s why it took a couple hours – it’s got to be just right so that balls don’t get stuck where it’s too tight, or don’t launch off when it’s too loose.
  • Hmm… now I wonder – would it work better to first mark those points 1.25 inches apart all the way up, then trace a perfect spiral ramp connecting all those dots, then just glue the plates along that spiral line? (Someone try it and let me know!)

Each time I put on a layer of the ramp, I would test it to make sure the ball ran well down it then tweak it as needed before adding the next layer, since once the next layer is on, it’s hard to get your hands in there to make adjustments. But despite the thorough testing, I ran into some challenges later. When I had three layers on, the marble was running perfectly, but once I had 6 layers, the shooter marble was gaining so much momentum that it found a low spot on ramp 3 where it launches off of the ramp. I could still run a small marble successfully to the bottom. But then when I got up to 8 layers, the small marble ran too fast and found a different place to launch. I tried running a bouncy ball, and it ran slower and got stuck at one point.

So, what’s the answer to get balls successfully to the bottom? Run three together – a bouncy ball to slow things down, followed by a shooter marble and a regular marble to nudge that bouncy ball along!

This was a very fun project. My son had fun playing with it today. We’ll see how it survives a group of 20 students….

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