Cardboard Robot Arm for Cheap Robots

This is probably the Instructable I've been looking forward to the most out of my "For Cheap Robots" series. It's the coolest I've done so far, and by the same token the most difficult.

Robotics doesn't really start to get cool until your robot can do more than roll around following a line and bumping into walls. Your robot needs to be able to effect the outside world! Servo robotics kits can easily cost several hundred dollars, so how do we do this on the cheap? Really, this Instructable relies on the existence of very cheap micro-servos, and using cardboard instead of expensive specialized mounting brackets, but this ends up being the difference between a cost of $100 (or more!) and less than $30.

Hi! I'm Jay Weeks and I've got a passion for cheap robots! I want to make robotics more accessible for everybody because when I was a kid, hobby robotics kits cost a lot of money that I didn't have! My goal is to show everybody how to apply arts and crafts skills to turn everyday household materials into functional and educational robots!

So let's get started!

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For more Instructables on building cheap robots, head to the For Cheap Robots collection, or for more things that I've done, check out my profile page!

For more info from Digilent on the Digilent Makerspace, check out the Digilent blog!

Step 1: What You'll Need

For this project you'll need:

• A roll of duct tape.
• Five cheap servos. (I'll explain how to go about getting these in the next step.)
• A pair of scissors.
• A nice large piece of cardboard. (Preferably free dents, bends, scrapes and perforations.)
• Five small paperclips. (The ones that are about an inch long.)
• Two thumb tacs.
• Some pliers and wirecutters. (I use a multitool because mine had the best pliers, but when it came time to cut wire, I wish I had a set of wire cutters.)
• A pen or pencil. (I've come to prefer pen over pencil for these projects, but you can't erase pen.)
• A ruler
• A hot glue gun. (Make sure you've started preheating it!)

Step 2: Finding Cheap Servos

This Instructable isn't as immediately accessible as I'd like because it relies on finding cheap servos, which isn't always the easiest thing to do but it's certainly possible! These cheap servos have plastic gears, so they won't be able to stand up to very much torque, and they'll wear out much sooner, but in exchange you'll have quite a lot of them so you won't ever have to worry about doing something that messes any one up!

Servos come in all kinds of sizes. You can usually find a pack of ten cheap microservos (the second to smallest size) for somewhere between $20 and $30. Doing a search for "bulk micro servos" or "ten micro servos" on Amazon, Ebay, and the Google Shopping pages, and then restricting the price range to $20~$30 gave me a couple of good results, with only a little bit of digging. As a general rule of thumb, you really shouldn't be paying more than $2~$3 for each servo, because that's what they cost to buy wholesale, so if you find servos priced individually at $2.80, go for it!

Step 3: Cleaning Your Cardboard's Edge

Corrugated cardboard has, you guessed it, corrugation inside! This corrugation gives the cardboard a sort of grain to it, so it'll be stiffer when bending it one direction than when bending it another. In this Instructable it's more important to pay attention to corrugation than any of my previous Instructables, because we're going to need to cut in between corrugation "bumps".

I started off by trimming the end of my cardboard, which was squished and dented. I wanted to make sure I was cutting exactly parallel to the corrugation so that my parts would all work nicely.

Turn your cardboard so you can see the corrugation bumps along the edge. I counted three bumps in from the edge, but you may want to count more or less depending on how rough your cardboard's edge is. Then make a mark over one of the valleys. Do the same on the other side.

(If you're having trouble seeing the corrugation bumps because the edge of your cardboard is squished like mine was, you can stick the tip of your pen into them to make them expand a little.)

Now connect your two marks with a ruler, and cut along the line. If you're successful, you should be able to look at your newly cut edge and see that you're not cutting across any corrugation.

Step 4: Cutting the Cardboard for Your Arm

Turn your cardboard so the edge with the corrugation faces you again. Make a mark two, four, and six bumps in from the edge. Do the same on the other side, and connect all three pairs of marks.

Now cut along the third line from the edge.

Step 5: Scouring and Trimming the Cardboard for Your Arm

Use your scissors to scour along the remaining two lines. This can be a little dangerous, so kids may want to get an adult to do this for them. You shouldn't need to press very hard, because you only want to cut through the top layer of your cardboard, leaving the corrugation layer, and the bottom layer intact.

My edges were kinda squished and rough, so I chose to trim a little bit off to clean it up. I marked half an inch in from the edge, but you may want to go further depending on how rough your cardboard is.

Step 6: Measuring and Cutting Your Pieces to Length

Measure six inches from the edge you just cut. Mark it on both sides, and then cut.

Now measure three inches from either end to cut that piece in half.

The result should be two, three inch pieces that can be folded along your scour marks to make an approximately equilateral, triangular tube.

Step 7: Gluing Your Tubes

Hold one cardboard piece so it forms a triangular tube. Then use your glue gun to glue along the edge. Use plenty of glue here, and keep holding it steady so the glue can set properly.

Do this for both pieces of cardboard and you've got two tubes!

Step 8: Wrap Your Servos in Duct Tape

Normally, I don't make wrapping your motors into its own step, but motors are round and servos are square, and I like to be very neat about it.

Start by ripping a piece of duct tape, about three or four inches long. Then tear or cut that piece in half, lengthwise. (If you save the other half, you'll have a second piece for wrapping another servo.)

Place the small side of your servo (the one opposite the side with the wires) approximately halfway along your piece of duct tape. I like to make sure that the smooth, non-ripped edge of my duct tape butts up against the servos mounting brackets.

Now fold both sides of your duct tape around the servo, and trim the edges so they end just at the edge of the servo's other mounting bracket (like in picture five).

Turn your servo so that the bottom (opposite the round nubbin where you mount your arm attachments) faces you. Now fold over the edge of your duct tap so it forms two 45 degree angle folds along both sides, and press it firmly against the bottom of your servo (like in picture six). Now fold both flaps over so they cover the bottom of your servo.

Turn your servo so the side with the wires faces you. Fold over the bottom edge of your duct tape like you did before, to make two 45 degree angle folds (see picture ten). Now fold over both flaps, and you're done!

Now you should have a servo wrapped up like a present! Do this for all five servos.

Step 9: Mount Your Servo Arm Attachments

This step gets kinda complicated because there are a lot of servos and it's very important to get their arms mounted correctly now because it's very difficult to change them later.

Servos have a range of angles that they can move to, measuring a little over 180 degrees of rotation. You want to make sure you mount your servos' arms correctly so that your robot arm will have the correct range of motion to function as an arm. It helps a great deal if you start by drawing a rough sketch of your robot arm, how the servos will be mounted, and what range of motion they should have.

My drawing is a little bit hard to read if you don't already know what I'm doing, so I've included pictures of all five of my servos, and the ends of their range of motion. Each picture set shows the arm rotated fully counter-clockwise, fully clockwise, and then a picture of the side with a label for which servo it is. You don't have to get your servos to look exactly like this, but you should get them close, and don't forget to label all your servos with sharpie so you can keep track of them!

Once all your servo arms are pressed on with the right range of rotation, use your screwdriver and the small screw that came with them to screw the arm attachments on.

Step 10: Mount Servos 2 and 3 to Their Arms

Take servos 2 and 3 and rotate their arms to match the first picture above.

Now take servo 2 and press it up against one of your triangular tubes, towards one of the ends. Make sure that the longer end of the tube is on the same side as the longer arm of your servo.

Now, very carefully glue your servo's arm to the cardboard tube. You may want to glue just one or two spots very lightly, and let those set to hold your servo for you before gluing the rest on.

Do the same with servo 3, and you'll have two servos with arms attached!

Step 11: Glue Your Arms Together

Take servo 2's arm, and add some hot glue to its end.

Then press that end up against the side of servo 3. Make sure that servo 3 faces the opposite direction of servo 2 (like in the third picture).

Servo 2 is going to be the shoulder for our robot arm, and servo 3 is going to be the elbow!

Step 12: Add Servo 1

Take servo 1 and rotate it to match the first picture.

Now press it up against the underside of servo 2 (like in the second picture), and glue it on. Make sure to use a lot of hot glue for this connection, because it'll be under a lot of stress when your arm moves.

This will form a sort of swivel mount for our robot arm.

Step 13: Add Servo 4

Take servo 4 and rotate it's arm to match the first picture.

Now add hot glue to the end of servo 3's cardboard arm. Press it up against servo 4 and hold it until the glue sets. Servo 4 will create a wrist for our robot arm!

Now you should have a mostly completed robot arm like in picture 4! We're leaving servo 5 out for now, because it will be used for our robot's claw.

Step 14: Cutting Out the Cardboard for Your Claw's "Palm"

We need to cut out some more cardboard for our claw, so get your piece of cardboard out again.

Measure out and cut a two-inch wide strip, making sure the "grain" of the cardboard runs lengthwise along it (you can see the grain in the first picture because I rubbed my cardboard with chalk).

Now, make lines along your cardboard piece at the 1, 3 1/2, 6, and 7 inch points, and cut those pieces out. The end pieces are scrap, but you'll want to keep them for later.

These pieces of cardboard will make a sort of "palm" or main body for your robot's claw. The third, thinner piece will end up being a spacer piece.

(NOTE: I made the mistake of throwing away the 1 inch piece of cardboard because I thought it was too thin, and I cut another thicker piece. That was a mistake, as you'll see later.)

Step 15: Shape Your Cardboard "Palm"

I based this claw off my previous prototype, which I considered to be about as small as I wanted to make it, so the measurements for this part are a little specific.

Make a line lengthwise along your piece of cardboard, 1 3/8 inch from one side. Make another, perpendicular line 1 inch from the bottom. (I made mine 1 1/2 inch from the bottom, but this turned out to be a mistake, as you'll see later.) Cut out the small rectangular piece formed by the two lines.

Now take that piece of cardboard and place it over the second piece that you cut out in the previous step. Make sure they're lined up properly, and mark the rectangle with your pen. Now cut out the corner rectangle. You should end up with two pieces that are approximately the same shape.

Step 16: Cutting Out the Cardboard for Your Claws

Cut out another strip of cardboard, this time 1 1/8 inch wide. Make sure that the grain of the cardboard runs lengthwise along it.

Now make lines at the 1, 2 5/8, 4 1/4, 5 7/8, and 7 1/2 inch lengths. Cut all these out, and discard the ends.

Step 17: Shape Your Cardboard Claws

Take one of the pieces you just cut out, and make a mark 1 1/8 inch from one end (like in the first picture). Use your ruler to draw a line from that end to the nearby corner (like in the second picture).

Cut along this line, and also cut a small bit off the far corner.

Now use this piece as a template to draw lines on the other three pieces. Cut those pieces and you should have four identical cardboard pieces.

Step 18: Punch Holes in Your Claws

Place two of your claw pieces over one of your palm pieces (put them on a piece of scrap cardboard so you don't mess up your table). Make sure their tips line up, and that they're centered nicely (like in the first picture). Now push your two thumb tacks into their corners. Punch all the way through both the claw pieces and the palm piece. The two claw pieces should be able to rotate outward without hitting each other.

Now you have the holes that will act as hinges for your claw. Remove the tacks and look to see where your holes landed on your palm piece. If you think that they're too low, try again, but lower your claw pieces a little. (Make sure to mark out which holes you don't want to use.)

Step 19: Transfer Your Holes to the Other Pieces

Place your two claw pieces over the other two claws, make sure to line them up properly (NOT like the first picture. Make sure your claw pieces line up perfectly). Then take a thumb tack and press it through the first hole and into the second piece to transfer the hole.

Take a moment to label your claws for "right" and "left" so you don't lose track.

Do the same thing for your palm pieces. (Make sure not to transfer any holes you don't want to use).

Now that you've got your holes transferred onto your palm pieces, take your scissors and cut their corners off (like in picture five). Make sure to leave a little bit of material so that your claws won't rip out later.

Step 20: Add Your Spacer Piece

(NOTE: I'm going to point out again, that my pictures will look a little different from your pictures because I made my spacer piece too thick.)

Take one of your palm pieces and add a thin layer of hot glue to the lower half. You can also use a glue stick or regular glue for this part, but I don't feel that glue sticks adhere well enough and I had a hot glue gun on hand.

Press your spacer piece so it covers your lower half.

Now you should have two palm pieces, one with a spacer and one without.

Step 21: Add Spacers to Your Claws

Pin one of your claws to your palm piece with a thumb tack again. Place the claw piece over a scrap piece of cardboard. Leave a small amount of space between the edge of the palm and the edge of your scrap piece.

Now trace the outline of your claw on the scrap piece of cardboard and cut it out. This will be your spacer.

Glue your spacer onto your claw. Do this for two of your claw pieces, one right and one left piece.

Step 22: Unbend Your Paperclips and Thread Your Claw Together

This is another complicated step to explain, but it amounts to threading your claw pieces onto two unbent paperclips.

Start by unbending your paperclips. You don't have to make them perfectly straight wires, but get them as close as possible.

Now take all your claw pieces and two unbent paperclips and make sure you know which one is which, right vs. left, spacer vs. no.

Start by threading the first claw piece onto one of your wires. I started with one of the claws without spacers. Do this for the opposing claw piece as well, so you have both right and left claws with one wire each.

Now thread those into a palm piece. Make sure the ledge that you cut out points to the left of the palm piece (like it is in pictures three through five) because that will be important later on.

Once you have those wires through, thread on your second layer of claws (making sure that the spacers for the claws rests between them) and then the second layer of your palm (once again, making sure that the spacer lays between the palm pieces).

Make sure a little bit of your wire sticks out the other side as well, to keep the pieces from falling off during the next step.

Step 23: Glue Your Pieces Together

Now we're going to glue our palm and claw pieces together! We have to do this with the wires in because it makes the holes line up properly.

Start by gluing your palm pieces together. Use plenty of hot glue, and make sure that they line up perfectly.

Then glue your claw pieces together. Make sure they line up as well.

Step 24: Fixing the Mistake That I Made

So all throughout this Instructable, I've been telling you about the mistake I made when sizing my spacer for my claw. After gluing all my pieces together, I finally realized that my claw could not open fully due to interference. Fixing this required that I cut a corner off my palm piece, and trim the corners off my claws.

If all goes well, you will not have to do any of this, but even if you do, it is good to know that your project is still workable.

Step 25: Gluing and Cutting Your Wire

Start by retracting your wire until just a little bit pokes out the other side of your claw pieces. Add a small dab of glue to this, which will secure it in place. Do this for both wires.

Trim the wires on the other side so that just a little bit of wire pokes out (like in picture five). Keep the trimmed pieces of wire.

Make sure that you keep your claws closed while you add another dollop of glue to this side, and you're done!

Your claws should open and close with some small resistance, as they will prefer to stay in whatever position they were in when you added the second set of glue spots.

Step 26: Add Servo 5

Rotate servo 5's arm so it matches the first picture.

Test out positions for your servo by pressing it against the palm. Try to find one that has its arm lined up right between your two claws. Add a bit of glue and glue it in place.

After last step, you should have four pieces of wire, two shorter and two longer. Take one of the shorter pieces and thread it through the topmost hole of your servo. Get it as close to halfway through as you can, and glue the wire in place.

Step 27: Adding Actuator Wires to Your Claw

Take one of your thumb tacks and push it through your claw, a little under the outside corner. Press hard to make sure it goes most of the way through (you should see a small divot on the opposite side like in picture 3).

Pull the thumb take out, and push your wire through. It will be a little difficult because you're also pushing through two layers of glue. Keep pushing until you get a little bit of wire sticking out the opposite side. Glue this in place.

Do this for both claws, and try to keep them symmetrical.

Step 28: Bend and Trim the Acutator Wires

Start by rotating servo 5's arm so it matches the first picture above. Now bend the wire at about the same height to a 90 degree angle. Once you do this for both wires, your claw should look like the third picture above. Try to get the wires to cross at approximately equal distance from the servo arms so they're symmetrical.

Now use your glue gun to glue the joints, and trim the excess wire. This step was where I really wish I'd had a real pair of wire cutters, because I couldn't get my wires as short as I would have liked with my multitool's wire cutters. To fix the sharp ends so I wouldn't worry about them poking me, I added a little bit of glue to them.

Now your claw should look something like the last picture above.

Step 29: Adjusting Your Claw

If you look at the first picture above, you can see that my claw doesn't close so its tips line up. This can be easily fixed by making SMALL adjustments to the wires. Be very careful when doing this, because it's difficult to undo adjustments. Make small, incremental adjustments, and then check to see if it worked.

Step 30: Adding Grips to Your Claw

Open your claw all the way, by rotating the servo arm backwards. DO NOT try to open the claw by prying it open, as this can bend your wires, and they are difficult to bend back.

Add a thick line of hot glue along the inside tip of one of your claws (like in the second picture). Move done a ways (a little over half an inch) and add another thick line. Finally, add a third line to your other claw so it will fall between the first to when your claw closes.

Give your glue plenty of time to set.

Once my glue set, I rubbed each of the grip pads I had just made with my fingers. This coated them in some of the natural grease from my hands, which helps to keep them from sticking to each other.

When you close your claw, your pads should fall between each other like in the last picture above.

Step 31: Putting Your Claw and Arm Together

Now you should have a complete claw, and it's time to add it to your arm!

This step is very simple. Simply glue servo 4 to your claw along the side facing opposite servo 5. Make sure to use plenty of glue, because this is another point that will be under a lot of stress.

Step 32: Mounting Your Arm on a Robot

Now that we've got our arm made, we'll need to mount it to our robot. Depending on how you built your robot, you could mount your arm in lots of different ways. I will show you one simple way to mount it to a horizontal surface.

Start by cutting one last piece of cardboard out of the scrap from way back in step 6. It should be one inch wide.

Fold it so that two sides make approximately a right angle, and glue it. Then add glue to one face, and press that against the side of servo 1, with the right-angle side facing downward and flush with the bottom of servo 1. This will form a nice large surface for you to glue your arm to your robot.

Add a lot of glue to this bottom surface (both servo 1 and the cardboard piece) and press it on your robot where you want to mount it.

Now your robot arm is ready to go!

Step 33: Terrorize All the Little Robots!

This servo arm is a quick, but remarkably effective way of giving your robot some way to effect the world around it. Moreover, it can easily be drastically simplified if you simply want to add less joints. The elbow and wrist servos could easily be removed if you wanted a simpler robot arm to start.

I apologize that this Instructable was a little rougher than my previous fare, but I'm not used to doing anything this complex. I'm still very proud of how it turned out, and if you liked it, or have suggestions that you think will make it better, please let me know! (I will be posting a video for this as well, but that will have to wait for a while.)

I would be especially happy to hear from anybody who used this Instructable to make their own robot arm. I'd love to see pictures of how yours turned out!

Step 34: Inspiration Links

When I was researching this Instructable, I found a number of other projects that were somewhat similar to mine, and I used them for inspiration. You should check them out too!

Mike Estee's Cardboard Hexipod: This is a clever design for a hexipod made using cardboard and micro servos. He used a lazer cutter to cut out his legs and body, but I hope to someday make my own cardboard hexapod using more mundane scissors and glue.

Ken Ihara's Giant Cardboard Robot Arm: Ken built this giant cardboard robot arm for his year-old son, Alex. This is a really cool design because not only is it extremely large, it also uses spools of string and pullies instead of gears! Very clever. You can check out his Instructable for this arm here!

Paper Motorized Walking Machine "Sculpture" by CreativLiMade: Personally, I wouldn't have put quotations around the world "sculpture". I think his paper rendition of Theo Jansen's Strandbeest is beautiful! You should definitely check out his Instructable. I will point out that his end product seemed to have too much speed and not enough torque. Maybe he should have used a gearbox motor instead!