Robot Claw for Workshops!

This is a novel design for a simple robot claw that can be used for electronics workshops! The claw can grasp light objects like pom poms and styrofoam cups, and is a great introduction to a very forgiving linear actuator mechanism. This requires an audience that has basic scissor and tape skills, and may be too much for those under 8. It's still got some kinks, so feel free to make improvements and leave a comment!

Strip about an inch off the wires of the battery holders. Cut lengths of twine about a hand's width long. Cut the rubber band. Put materials in baggies. Cut out boards of cardboard, two for each person, one larger and one smaller. The cardboard should be at least as stiff as cereal box cardboard, otherwise the claw may not operate.

This is the start of the workshop! Ask everyone to cut out a rectangle of cardboard that's about as long as their forearm and at least twice as wide as their arm. This is a great time to observe the skill level of the room, as this first step is pretty simple. Plan ahead with how direct the following steps will have to be, and which students you can designate as helpers to students with less papercraft experience in the workshop.

Cut out a square-ish shape that's a little bigger than your palm (especially if your group as tiny hands).

Cut two strips of cardboard about as long as your entire hand and about as thick as a thumb (again, two thumbs if they have tiny thumbs). Tape the "fingers" to the edges of the "palm". Make sure they are edge to edge, with not overlap.

We'll need a rectangle that's as wide as the "palm" but only half as tall. This step can be very confusing, if you couldn't tell by that first sentence. Fold the rectangle in half, then cut a half circle shape into one of the folds. It should look like a tunnel in a hill. Point the piece out on the example that you hopefully brought to the workshop to try to illustrate.

The "tunnel" piece holds the "fingers" upright. This step can also be confusing, it's almost better to just show the step multiple times rather than use words. Tape the side edges of the tunnel to the edges of the fingers. The tunnel should be facing away from the fingers. Cover all the seams with tape.

We're going to fold the edges on the rectangle from our first step to give it some structure. Mark how wide the palm is so you can fold up both side edges of the rectangle to line up with the fingers. Again, a lot easier to just show what's going on. Tape all the edges of the "arm" and the "hand" together so they become one arm unit.

Tie paperclips to the ends of the string so that the paperclips are palm-width apart. Your group may not be able to control where their knots end up, which is why you pre-cut their string during prep into reasonable lengths so there isn't way too much slack. Test out the claw by tugging down on the string; the claws should close and open.

Tape (or try tying) one end of the rubber band to the middle of the string. Feed the rubber band through the tunnel. Place the motor so the shaft is lined up with the end of the rubber band, then tape the motor down to the arm. Use 3 pieces of tape; 1 long one across the motor, and 2 pieces on either side of the motor to keep the first tape secure. Use duct tape or other equivalently tacky, strong tape to tape the shaft of the motor to the rubber band. Definitely looking for better ways of connecting the rubber band to the shaft if you've got any suggestions.

Give everyone a AA battery and have them test their motors! When you touch the wires from the battery to the wires from the motor, the rubber band should scrunch up and pull down on the strong, closing the claws. When you've confirmed that works twist paperclips to the ends of the wires from the battery holder.

Clip one of the wires from the battery to one of the wires from the motor. Once they are securely clipped together tape the wires to the side.

Cut out a thumb size rectangle and fold it not-quite-in-half so that it looks like a "7". This is your claw's pushbutton. Tape the shorter fold to the arm. Clip your last paperclip to the fold sticking up. Make sure it can be pressed and lifts back up. Find the free wire from the battery holder and tape the wire to the arm so the paperclip from the button and the paperclip from the wire touch when you push the button down. Don't cover either paperclip with tape, otherwise your circuit will not work. Take the last wire from the motor and clip it to the paperclip on the button, you can put tape over this to secure it.

Press the button! Does your claw close? Good! Let go of the button. Does your claw open up again! Alright! If it doesn't open back up, your cardboard may be too flimsy, your rubber band or string may be getting caught on something, or there may be too much slack in the rubber band or string. Remember to bring some light stuff to pick up with your sweet RoboClaws!