Materials:

Two rubber wheels with 1/4" inner diameter (something like roller blade or skateboard wheels: https://www.sciplus.com/wheel-212-dia-x-78-viper-...
2" long wooden tube beads 1/4" inner diameter : https://smileyboybeads.com/products/2-inch-long-l...
Four 1/4" diameter dowel rods cut to desired length
1/2" thick material for base approximately 5"x8"
2 small cotter pins
Hot glue
Wood glue
Drill or drill press, 1/8" and 1/4" bits
Hand saw

Step 1: Drill Holes in the Base

Measure to find the center of the base and draw a line down the middle on the long side. Drill a 1/4" hole in the center, then drill 2 more holes equidistant from the center hole.

Step 2: Cut Dowels to Length

You will need two 1/4" diameter dowel rods the same length (I cut mine to 6" long) and two 1/4" diameter 12" long.

Step 3: Drill Holes for Cotter Pins

You only have to do this on one of the longer dowels. Where you drill the holes will vary depending on the thickness of your base material. The pins will hold the dowel in place but allow it to rotate. To find out where to drill, insert the dowel through the base to mark in pencil. With a small bit, drill the holes perpendicular to each other to avoid weakening or splitting the dowel.

Step 4: Add the Center Dowel

Using hot glue, secure one of the wheels to the end of the longer dowel. Insert the dowel into the hole in the center of the base. Add a washer on the top side only and use cotter pins to secure.

Step 5: Bend and Clip the Cotter Pins

Step 6: Prep the Wooden Beads

Using a vise, clamp a bead securely in place. Use a small bit to drill a pilot hole only through one side of the bead. Then use a 1/4" bit to widen the hole.

Step 7: Make Two Supports

While the bead is still in the vise, insert the dowel into the hole but not all the way through. Use wood glue to secure in place. Make a second one identical to the first.

Step 8: Cut a Bead to Make Flanges for the Supports

Clamp the last bead in the vise and use a hand saw to carefully cut it in half. Sand the cut side smooth. Insert the cut bead ends onto the two dowels you just prepped so that the wider end is facing outward.

Step 9: Assemble Everything

Slide the second wheel onto the center of another dowel (do not glue in place yet!). Slide the two prepped bead supports on either end of the dowel. Insert the 6" dowels into the two outer holes in the base and use wood glue around the base of the cut beads to secure them in place.

Step 10: Make Some Washers

Drill 1/4" holes in some wood and add to the ends to keep the dowel from sliding around. Line up the primary wheel so that it is off-set from the center of the secondary wheel and making contact with the surface. When the primary (black) wheel turns, it should cause the the secondary (blue) wheel to turn. Test multiple times to find the right spot before using hot glue to secure the primary wheel to the dowel.

Step 11: Yay! or :(

That's it! Once the glue is dry, hold the mechanism by the base and push forward and back. This is just a demo with happy and sad face drawn on two sticky notes to show the rotation direction.

Step 12: (Optional) Make a Crank

You can also flip this design upside down and add a hand crank rather than pushing it across a surface. The mechanism would need to be clamped in place or held steady by some other means (in this case I weighed it down with a mallet) while being cranked. I found the push method more successful because there was more friction between the wheels.

Introduction: Happy/Sad Rotation Toy