Cardboard Mechanical Toy

This instructable present a way to make a simple mechanical toy - a rainbow caterpillar! - with cardboard.

To make it, I used this supplies:

• cardboard (a rigid and thick one, the thickness of mine was around - but less than - 3mm)
• a couple of wooden skewers (with diameter around 3mm)
• painter's masking tape

• paints

And these tools:

• glue
• drill (I used one with a 2.8 mm diameter drill)
• hot glue gun
• ruler
• scissors
• cutter
• compass
• pencil
• sandpaper

If you do not have a skewer at hand, a sheet of rolled paper (very tight) can do the trick! In addition, the masking tape can be replaced with papier mâché.

First of all, we need to cut out these rectangular parts from the cardboard:

• 140mm * 40mm (x4)
• 75mm * 40mm (x4)
• 60mm * 8mm (x9)
• 10mm * 25mm (x9)
• 4mm * 20mm (x18)
• 30mm * 12mm (x1, for the crank)

Also, we need to cut some rounded parts:

• radius 16mm (x18)
• radius 12mm (x9)
• radius ~5mm (x4, just some washers, size does not matter too much)

For the 4x20mm and round parts, scissors are better suited, but for others a cutter will do a cleaner job.

The round parts with a radius of 12mm can be drawn with a coin (a quarter dollar or 0.20euros) if you don't have a compass.

For the crank (30 * 12mm part) and the washers (round parts with 5mm radius) it's better to drill holes inside before cutting. For the crank drill holes spaced by 20mm in the middle of the part.

For this step, I just take those pieces:

• 140 x 40 mm (bottom an top parts)
• 75 x 40 mm (side parts)

First, on two pieces of 140 mm, I cut nine pockets in the middle (look at the picture for measurements). The two other pieces of 140 mm are glued together to make the base of the box.

Then glue the side part in pairs, and drill a hole for the axle (look at the pictures for position). Also, draw a line from 15mm from the edge (farthest from the hole) like in the last picture. This will help to properly position the pieces later.

To prevent the pillars leaning on the side, I put some holds under the skates.

These holds have to be "not to close, but not too far". This means that when we slip a cardboard between them, there is the least friction possible and the degree of freedom of the cardboard is minimal.

Check to see if the pads slide smoothly into the holes we just made before. If not, use the sandpaper carefully to solve this problem.

To prepare the wheels of the axle, I made a hole with a drill near the edge of each 12mm radius discs.

To be sure to drill all the discs in the same place, I use the first one to make a mark with a pencil on others.

On a skewer I draw nine ticks, one every 15mm (I let few cm on each side for margins). Then, insert the nine drilled wheels on the skewer, and place them just near the ticks.

After that, I rotate every wheels to give them a wave form. This is an important part since it will determine the global movement of the mechanism.

To obtain a good wave movement, I rotate each wheels to approximatively obtain an angle of 40° with the previous one (because 40 * 9 = 360 obviously). I do not have any particular technique to do it. I turn the skewer on itself and I adjust the rotation of the wheels to obtain a uniform movement.

With hot glue gun, I stick 16mm radius cardboard rounds by pair, and with scissors I adjust them to be as round as possible.

Then, I put several cardboard discs on top of each other to place some painter tape around it. Next I cut the tape between each disc.

Finally, I make a small cut (height of 5mm) of the width of my cardboard.

Now it's time to assemble all the parts! I used the hot glue gun for that. Glue the bottom plate and the two holed plates on one side, put the axle in place, and then glue the second side.

The two holed plates should be spaced of 15mm (you should have draw line marks). Ensure that the axle could rotate before applying the glue.

Once you've glued the cardboard, you should be able to activate the mechanism, check if the movement is fluid, and everything ok. Then it's a good time to put some glue on washers of the axle and mount the crank.

If the movement is not fluid, blocked, or so, cut carefully the glue, re-adjust positions of the cardboard, and give it another try!

After that I decide to put a "cap" on the box. I cut a cardboard plate of 40 x ~150mm (it depends of the cardboard's thickness, and the amount of glue you've put, so measure it!) with a hole of 4mm wide inside (distance of 10mm from each sides). Once again, be sure there is no friction before gluing it. This "cap" makes it possible to obtain a good finish, and especially it allows to put small pieces of skewer to correct the alignment of the pillars if necessary. To do so, I cut 4mm long pieces of skewer, and after correctly place them, just put a dot of glue on it. (If you do the same, be careful to not put some glue on pillars!) Take a look at the last picture of this step to see what I'm talking about.

Finally, I cut a last cardboard plate of 75 x ~150mm (same thing here, measure it!) and glued it on the front side to hide the mechanism.

Use your artistic talents and/or let your creativity speak!

When your paint is dry, put a dot of glue on each pillar and quickly fix the part of the body of the caterpillar.

If everything correctly happens, you should be able to have a smooth movement when running the mechanism, and also a satisfying "wow!" moment :)

This simple mechanical model is relatively easy to make and adapt. I chose to give it a small size to keep my cardboard for other projects I have in mind. But it could be bigger. If the nine parts of the mechanism are a little tedious to do, why not reduce that number? or, totally crazy idea, increase it? I chose a caterpillar model because it's a classic of this kind of toy. But I'm sure there are many things that could be done with the same basis! If you make yours, please send me a photo of your creation, I will really appreciate it!

I hope you've liked this instructable! Thanks for reading!

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As I participate in the contest "cardboard challenge" with this project, if you liked it, do not hesitate to vote for me :D Thank you!