Designing a 3D Printed Beaded Ball Chain Drive Pulley for Stepper Motor NEMA 17 on TinkerCAD

In this instructable, I will explain how to design a 3D printed beaded ball chain drive pulley that works with the Stepper Motor NEMA 17.

In one of my projects in the CMSC838F class at the University of Maryland (taught by Prof. Jon Froehlich), we put a stuffed bunny on the lab's window, and using Microsoft Kinect, we track people passing by the window and move the bunny such that it's located in front of them. This project was inspired by http://www.niklasroy.com/project/88/my-little-piec....

Since we needed the bunny's movement to be accurate, we decided to use a Stepper Motor NEMA 17, which can be controlled accurately. In order to move the bunny when the motor rotates, we decided to attach the bunny to a beaded ball chain, and wrap the beaded chain around a pulley that is attached to the motor (see the pictures). To make sure the movement is accurate, we designed a pulley that has holes for the beaded chain balls so that the beaded chain would grip perfectly on the pulley, and move accurately when the motor rotates.

In this instructable, I will go over the 3D design process on TinkerCAD step-by-step.

The design was inspired by http://www.thingiverse.com/thing:70179 but this pulley is too small for our case, making it too slow. Since we didn't find a way to modify the STL file that is available for download on thingiverse, we decided to implement our own. As this was my first 3D design, I used TinkerCAD due to its simplicity over most/all of the other alternative software tools.

You can see the final result at: https://tinkercad.com/things/gTCbJVjU1tu.

And designs for the steps at: https://tinkercad.com/things/j0seCAPRueN.

In the images, you can see that we added two additional layers to the pulley, to make sure that the balls do not slip. That is because the beaded chain is defective in some areas, and the balls are not spaced as they are supposed to be, causing them to slip out of the pulley when rotating. This part is simple, and we will not go over its design. You can see it at https://tinkercad.com/things/b8ilZ38X6eR.

You can also find this on thingiverse: http://www.thingiverse.com/thing:445171.

On the other side, we used a regular pulley.

Watch the project video to learn more how we used the 3D printed pulley:

For more details on the project itself, please see: http://cmsc838f-s14.wikispaces.com/Bunny

For more details on the class and to browse other projects, please see: http://cmsc838f-s14.wikispaces.com/

Step 1: Creating the Balls Shape Generator

Go to tinkercad.com, and follow the steps above to create a shape generator.

We start from the sphere template, and modify it to make it create 72 spheres along a circle.

We use these later as holes, which the beaded chain balls get inside and grip on.

Step 2: Creating the Pulley Structure

Follow the steps above to create the main pulley structure, including a dent in the center to make it grip perfectly on the stepper motor (NEMA 17).

Step 3: Adding Holes for the Beaded Chain Balls

Using the shape generator we created earlier, we now create holes in the pulley, for the beaded chain balls.

Step 4: Adding a Hole for the Beaded Chain String

Finally, we make some space for the beaded chain string to go in.