Rotational Motion Apparatus

by falconphysics, published

Rotational Motion Apparatus by falconphysics May 14, 2017

Design Tools


Liked By

View All

Give a Shout Out

If you print this Thing and display it in public proudly give attribution by printing and displaying this tag.

Print Thing Tag

Thing Statistics

337Views 63Downloads Found in Physics & Astronomy


This is my take on a device designed by Steve Rea. This device ended up being produced and sold by Arbor Scientific. Arbor's Rotational Inertia Demonstrator works amazingly well and is very repeatable. I highly recommend it. The cost really is quite reasonable for such a well built device. However, I decided to design a 3d printable one because our current physics teacher doesn't have the funds to buy a class set.

String is wrapped around one of the pulleys with a weight hanging from the string. There are three different pulleys to provide different amounts of torque. With an extra set of hex nuts the washers can be positioned different distances from the center of rotation changing the moment of inertia. There are a lot of experiments that students can do to investigate rotational motion.

Diameters of the three pulleys:

  • 24.5 mm
  • 49 mm
  • 73.5 mm

Update: I uploaded a new version with stops to keep the bearings from being pushed in too deep.

This was designed in TinkerCad.

Print Settings

Printer Brand:












Printed with 3 perimeters.


Parts List: (about $10 in parts/device)

  • 2 each Skateboard Bearings, 608ZZ 8x22x7
  • 4 each 6" long 1/4" hex bolts (or 1/4" threaded rods if you want longer arms)
  • 12 each 1/4" hex nuts
  • 40 each Fender washers, 1/4" hole 1.25" diameter

The bearings need to be de-greased first. The grease protects the bearings from water and road grit, but it will keep the bearings from spinning freely. I used acetone since we had it in the chemistry supplies. I just dropped them in a small beaker for 20-30 minutes. I found I also had to take them out of the acetone and spin them a couple of times then drop them back in. You need two bearings. One in each end for full support.

If you want to avoid using acetone do a little googeling for other ways to de-grease bearings. There's lots of stuff related to fidget spinners kicking around right now.

Demo Video

More from Physics & Astronomy

view more

All Apps

Auto-magically prepare your 3D models for 3D printing. A cloud based 3D models Preparing and Healing solution for 3D Printing, MakePrintable provides features for model repairing, wall thickness...

App Info Launch App

Kiri:Moto is an integrated cloud-based slicer and tool-path generator for 3D Printing, CAM / CNC and Laser cutting. *** 3D printing mode provides model slicing and GCode output using built-in...

App Info Launch App
KiriMoto Thing App

With 3D Slash, you can edit 3d models like a stonecutter. A unique interface: as fun as a building game! The perfect tool for non-designers and children to create in 3D.

App Info Launch App