To make your Inchworm go, you need to attach the Circuit Playground Express board, the battery pack, and the servo to the cardboard body. And everything has to be connected with wires, without letting them get in the way of the moving parts.

Where you place them is up to you. Depending on the weight of the cardboard you use for the body and what kind of feet you give it, you may get better results by putting more weight in the front, or lower down, or other variations on the arrangement shown in this example. Play around and see what works best for you!

Velcro on the CPX

Peel-and-stick Velcro dots let you reposition or remove the CPX as needed. They also give you some clearance between the CPX board and the cardboard. That makes it easier to attach alligator clips to the board.


Just press one side of the Velcro onto the back of the board  and the matching side on the front of the Inchworm.


In the example here, the hook (scratchy) side is attached to the CPX and the loop (soft) side is attached to the cardboard.

Prep the Servo

Unlike a regular motor, a servo can only swing back and forth in a semi-circle, 180 degrees. But a servo is also self-aware -- it knows which direction it's facing. That means with a little coding, you can tell it where to turn!

To make the Inchworm crawl, you will program the servo to turn all the way towards the front, and then swing all the way towards the back, over and over. This motion pulls the front and back of the Inchworm together and then releases them, so the Inchworm moves slowly forward.

But before you attach the servo, you have to set it up so that the arm is facing in the right direction.

Hold the servo so the end with the wires is facing up when you are looking straight down at it. Press the one-armed horn (also called a half horn) onto the shaft of the motor so it is pointing to the right (three o'clock position).

Then use the arm like a handle to turn the shaft of the motor as far to the right as it will go.

Next, lift the arm off the servo, and replace it so it is back in the three o'clock position.

You should now be able to turn the arm 180 degrees from right to left.

The last step in preparing your servo is to wrap a piece of masking tape around the body from one side, across the bottom, and up the other side.


This way the adhesive dot you use to attach the servo to the cardboard robot body will stick to the tape instead of the servo. It makes the servo easier to remove -- and also helps keep the servo firmly attached to the cardboard.

Attach the Servo

Now that it's prepped and ready to go, you can attach the servo to the cardboard. Extra-strength adhesive dots are a simple way to glue the servo in place.  

With the wire end of the servo facing up, stick an adhesive dot onto the right side of the servo.


Press the glued side of the servo onto the cardboard with the wire end facing the front of the Inchworm.


When the Inchworm is standing up, the wires face up towards the top fold in the cardboard.

Battery Holder Options

The battery holder contains your robot's On/Off switch. Make sure to attach the holder with the switch  facing out! And position it so the wires face the CPX, since you have to plug them into the JST connector.

Tip: Keep in mind that the battery holder is the heaviest part on the Inchworm. You may want to try sticking it on with tape in different places and giving it a test run with all the electronics working before attaching it permanently.

If you have the battery holder with the belt clip, you can cut a slot in the cardboard and clip it right on. Be careful not to bend the cardboard as you insert it.


If there's no belt clip, use two or more adhesive dots to attach the battery holder to the cardboard.

This guide was first published on Oct 25, 2018. It was last updated on Mar 08, 2024.

This page (Add the Electronics) was last updated on Mar 08, 2024.

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