You'll build the slider crank assembly from three craft sticks. The mechanism consists of these key parts:

  • Crank shaft
  • Connecting rod
  • Slider (also known as a piston in some mechanisms)

We'll drive the crank shaft with the servo motor, and the slider will translate back and forth along a guide block made of cardboard.

Build the Linkage

Start by getting the three craft sticks.

Prep the Linkages

Here, they've been marked 'CS' for crank shaft, 'CR' for connecting rod, and 'P' for piston (this is the same piece as the slider).

  • Mark a point 'A' near one end of the crank shaft
  • Measure and mark a line 2-1/4" from the A pivot end of the crank shaft
  • Cut the crank shaft to length
  • Punch a hole at each end of the crank shaft
  • Punch a hole at each end of the connecting rod
  • Punch a hole at one end of the pivot or slider

Next, we'll join the linkages using the brass paper fasteners.

Fasten the Pivots

  • Overlap the connecting rod on top of the B pivot end of the crank shaft, then join them with a paper fastener
  • Spread the fastener tabs wide on the other side, then fold them in
  • Repeat this process, overlapping the connecting rod D pivot with the E pivot of the piston/slider and then fastening it as shown

Servo Horn Connection

Use hot melt glue to adhere the A pivot end of the crank shaft to the large, round servo horn. Once it cools, press it onto the servo's splined shaft.

Use the horn to rotate the servo shaft to the far left and then remove, rotate, and reattach the horn to the shaft so the linkages are in a straight line to the left as shown.

You can secure the servo horn to the servo shaft with the small screw and a screwdriver.

Wire the Servo

You'll power and control the servo with the Circuit Playground Express. Plug the three alligator clip jumper wires into the servo cable housing:

  • Black to Brown
  • Red to Orange
  • Yellow to Yellow

Connect the alligator clips to the Circuit Playground Express pads:

  • Red to 3.3V (or, you can connect to VOUT for more power!)
  • Black to GND
  • Yellow to A1
3.3V power configuration
Alternate VOUT power connection

Next, we'll program the Circuit Playground Express using MakeCode.

This guide was first published on May 05, 2018. It was last updated on Mar 08, 2024.

This page (Build the Slider Crank) was last updated on Mar 08, 2024.

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