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by superyummywonton

Published on January 14, 2016

Build and race crawling inchworm robots with some cardboard and one servo bit. Add a pulse bit to control how fast your inchworm moves. This is a simple, fun project to introduce concepts of mechanical linkages, surface friction, and basic kinematic systems. More important, robotic inchworms are inherently silly and amusing to play with.


This project is now a featured invention in the new Gizmos & Gadgets Kit, 2nd Edition.

Duration: 30 Minutes

How To Make It


Construct the body. Cut a rectangular strip of cardboard to about 3 x 11 inches. Fold the strip in half "hamburger" style. Then, fold both ends to create the inchworm's feet. They should be about 2 inches long.
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The inchworm blank should stand upright on its own when folded.


Attach the skeleton. Cut widthwise slits on the inchworm's body. Insert bamboo skewers "under-over-under" through those slits. Trim the skewers with a wire cutter, then tape them down for extra security.
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Taping bamboo skewers to the cardboard will make it more rigid.


Mount the servo bit. Cut a lengthwise rectangular slot on the inchworm's body with enough clearance for a rotating servo arm – about 0.5 x 2 inches should work. Then, mount the servo with double sided tape. If the servo arm hits the body when rotating, enlarge the slot or reposition the servo.
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The servo arm should be centered on the inchworm's body.


Reinforce the servo area. Because the servo bits are powerful enough to bend cardboard, we'll need to reinforce the servo area with extra bamboo skewers and tape. Cut two skewers and tape them widthwise at the top and bottom of the slot. Cut one more piece and tape it lengthwise, right next to the slot and under where the servo is mounted.
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Cutting a slot in the cardboard weakens the material, but it can be reinforced with extra bamboo skewers.


Link the servo to the inchworm's body. Straighten out a paperclip with pliers and insert one end through a hole in the servo arm. Bend that end to into a fish hook shape to prevent it from slipping off when pushed or pulled. Next, poke a hole (just big enough to fit a paperclip) on the opposite side of the inchworm. Insert the other end of the paperclip through that hole. Bend that end to secure it to the cardboard, and reinforce the connection with tape.
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The paperclip acts as a mechanical linkage between the servo and the cardboard body.

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Bend the paperclip to stop it from slipping through the cardboard. Tape it down for extra security.

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Bend the paperclip so it has enough clearance between it and the servo arm when the servo rotates.


Cut out traction spikes on the inchworm's feet. Cut a series of "V" shapes both both feet, all pointing lengthwise in the same direction. Then, push the tip of each shape so that it pokes down underneath the cardboard. Because the spikes are all angled in one direction, they'll slide smoothly in one direction, but catch and stick in other. The alternating "stick and slip" action is what creates forward movement.
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When the servo expands the inchworm, the spikes on the rear feet dig into the ground, whereas the front feet slips – i.e., the inchworm pushes its front foot forward. The opposite happens when the inchworm contracts.


Mount the battery pack and other bits on the inchworm. Your inchworm is strong enough to can carry its own power source everything else needed for it to move. Connect your bits together and secure them to the worm with tape or paperclips poked through the inchworm's body. You can control the speed of the worm with a pulse bit, but remember to set the servo to "turn" mode. If your feet are sticking to the ground, try adding some weight on them. Try taping on some coins.
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Congratulations! Your inchworm is ready to race!


Race your inchworms! Line up your inchworms and race them! Because of their high-traction feet, they can climb up small ramps and over small obstacles. If you have any suggestions or feedback, be sure to leave a comment!
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What would you do to improve the inchworm?

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