Introduction: Simple Robo-Dog (made of Piano Keys, a Toy Gun and a Mouse)

About: I'm Mario Caicedo Langer (M.C. for short), a Colombian STEAM educator living in Azerbaijan, BSc in Naval Sciences and former Navy officer. I am a CAD and 3D Printing enthusiast and an artist specialized in jun…

Oh, Azerbaijan! Land of fire, great hospitality, friendly people and beautiful women (... sorry, woman! of course I only have eyes for you, my gözəl balacaana ördəkburun wife!). But honestly, this is a very hard place for a maker, especially when you only use plastic trash in your creations. The reason? environmental issues aside, consumerism is relatively new and people prefer to keep or fix their stuff before throwing it away. No flea markets, no thrift stores, scarce e-waste on the streets. Toys are made of the cheapest Chinese plastic possible. Buying on Internet? The shipping is more expensive than the components. Radioshack? In your wildest dreams. Arduino and 3D Printers? Wake up, Latino Sunshine AND GET A JOB!

Anyway, everybody in my new Azeri family started to ask to my wife "when will Mamed (everybody calls me Mamed for unknown reasons) show us his creations? You said he's smart, but looks like he doesn't even know how to change the light bulb of the restroom. And he's fat. Looks like he only thinks about food."

Considering my advanced Azeri language level only allows me to reply that judgement with the words "ice cream" (dondurma), "sandwich" (dönar) and "kebab" (kebab), and keeping in mind that I won't risk my life against the 220v electricity of the restroom, I decided to build a simple robo-dog using the toy gun of my little nephew Nuran and things I found on the street (and that includes an abandoned piano!).

Luckily, I always carry my Dremel rotary tool and some extra nuts and bolts. Because in this city, if you go to a hardware store to buy stuff and the seller finds out you are a foreigner, he will charge you the double (Rookies! In Colombia, we charge foreigners the triple). OK, no more bad jokes about countries, or Azerbaijan will deport me and Colombia won't accept me back. Let's make some cheap robots!

Step 1: Materials

I used the following materials (probably you can easily find better materials and substitutes):

  • 1 broken mouse (it doesn't matter where you are; you can always find a broken mouse. Or you can "accidentally" break one.)
  • 1 gearbox (with motor) from a toy. I used the one from a cheap toy weapon. You can use the one from a toy car with good traction.
  • 4 black keys from an ABANDONED AND BROKEN piano. Not the one from your mother in law, not the one from the museum, not the one from the restaurant (just in case, run when you get them)
  • 2 small gears or plastic discs
  • 2 small metallic angles
  • 1 small spring (for the tail)
  • 1 switch (you can find one in a broken toy)
  • 2 plastic coathangers
  • Wires
  • Nuts, screws and iron washers
  • Extra plastic and metal trash
  • Superglue
  • Soldering tin
  • 2 AA batteries
  • 1 AA batteries holder (if you are lucky enough, your can use the one from the toy)


  • Dremel rotary tool
  • Screwdrivers
  • Pliers
  • Soldering iron
  • Knife

Step 2: Extracting the Gearbox

I started opening the toy weapon. Here in Azerbaijan, battery operated toy weapons are very popular among kids. Each one has multiple features, like movements in different places, lights and sounds (mostly "RATTATTATTATA!... GO! GO! GO!... BOOOOM!" ad infinitum) .

So, I removed the screws and located the gearbox. Then, I carefully removed it. If you can't find a toy gun, try with another toy with a good gearbox, like the cheap cars that go straight forward and are more powerful than fast. The basic requirement is the main axis of the gearbox goes outside the gearbox in both ends, so you can attach the legs mechanism on each one.

Step 3: Placing the Big White Gears

I modified the red plastic pieces in each end of the main axis, in order to made them fit into two big white plastic gears (it's not mandatory the pieces to be gears. These can be discs, as long as they are made from a good hard plastic that doesn't break easily). Even I expanded the hole of the gears to get a better attachment. I pressed each red piece into the white gear, using the tip of the pliers, and fixed the parts with superglue.

Step 4: Holes in the Big White Gears

I drilled a hole in each wheel. Near the border, but not so close. Now, there is something important: the robo-dog walks alternating the legs of one side with the legs of the other. In order to achieve that, the hole of one gear must be exactly opposite to the hole of the other gear. So, if in the left gear you drill up, in the right one you have to drill down.

Step 5: The Coathangers


- Lalush, M.C. Langer's sister in law

I found some interesting plastic coathangers. Not the best plastic, but strong enough. I extracted two T shaped pieces. From each one, I cut the shortest segment (that will connect each front leg to the dog's body) and I kept the longest one for connecting each front leg to its respective back leg.

I drilled two holes in each shortest segment.

Step 6: Front Legs

I took two piano keys and opened two holes in each one: one in top to attach the small segments from the coathanger pieces, and two more between the top and the middle of the key, where I will attach them to the big white gears of the gearbox (not yet).

NOTE: The four piano keys, one for each leg, will have the same two holes in the same position. So I drilled the holes in the four. Then I chose two to be the front legs and keep the other two for later.

Don't tighten the nut too much. This joint has to be loose enough for a good articulation.

Step 7: Coathanger's Longest Pieces

I drilled a hole in one of the ends of each coathanger's longest pieces, and using a screw and washers, I attached each one to the front leg. Remember: This joint has to be loose enough for a good articulation. The screw needs to have a remaining part for the next step.

Step 8: Attaching the Front Legs

I attached the screw located between the top and the middle of each piano key I'm using as front legs. This joint has to be loose, too; butthe end of the screw has to be firmly attached to the hole in the big white gear.

Step 9: The Mouse

I dismantled the mouse, because I needed the plastic case. The upper case will be the head. The lower case will be the body where the gearbox and the legs will be attached.

Step 10: Starting With the Lower Case of the Mouse

I took the lower case and I drilled two holes in both sides of the back part. The shortest pieces from the coat hangers (the ones attached to the front legs) will be attached there.

Step 11: Finishing With the Front Legs

Do you remember the extra articulation I made in top of each piano key? The one made with the shortest piece of the coathanger? I attached these to the holes drilled in the mouse. Again, it's necessary to leave the joint loose, but with the end of the screw fixed to the mouse.

Then I fixed the gearbox to the bottom of the mouse, using screws and superglue.

Step 12: Metallic Angles

I drilled two holes in the back part of the mouse (using these conveniently placed circles as reference), and then I firmly attached two metallic angles, that will be for the back legs. I used screws and bolts.

Step 13: Back Legs

Do you remember the other two piano keys? the ones with the holes drilled in the same position of the ones used in the front legs? It's already time to attach them!

Now, using a screw, a nut and three washers, I attached each key to the metallic angles. It's very important to remember that the keys have to be attached through the hole between the top and the center. The joint has to be loose.

Step 14: Finishing the Legs

I attached each long piece from the coathanger (the one that comes from the joint in the front leg and the big white gear) to the top of its respective back leg, using a screw and nut loose joint. Then I cut the remaining part.

The mechanism is ready. Front legs transmit the movement to the back legs using the longest piece from the coathanger. Legs from one side are alternated to the other side, so the robo-dog can walk.

Step 15: Improving the Movement

I checked any possible failure in the mechanism, and I corrected them.

First, I found some joints were too tight, so I loosened the nuts just a little bit.

Second, I noted the nuts could fall because vibration, so I fixed them to the screw, using only a drop of superglue. Be careful: the superglue has to fix the nut only to the screw. If you add too much, the nut and the screw will be fixed to the legs and the joint will avoid the movement.

Third: remaining part of the screws could get stuck in other pieces of robo-dog, so I cut them using a metal cutting disc. Be careful (always be careful, because Physics hates you and loves to ruin your projects): constantly check if the screw is not getting to hot, or it will melt the plastic pieces where it is attached.

Fourth: because all the cutting/removing/drilling thing, gears inside the gearbox got stuck. So I had to clean inside the gearbox and add some lubricant.

Now we already finished with the mechanics part. Time for electrics and aesthetics.

Step 16: The Head

I used the upper case from the mouse as a head. I attached it to the body using two iron pieces and a remaining part from the toy gun.

It's up to you how do you want you robo-dog. Mine's looks like some strange dog/horse Alien hybrid.

Step 17: Electrics

If you are worried about the electric part of this robo-dog, relax! It's a simple circuit. Batteries wires connect to the pins of the motor, and there is a switch in the middle of one of the wires to turn it on/off.

I solder two wires to the motor pins. Then I drilled a hole to pass the wires through the body. I placed the AA batteries box over the body. Then I connected one wire to the batteries case and the other will go to the head for the switch.

Step 18: The Switch

I placed the switch in the remaining hole of mouses upper case (head). In the middle pin, I soldered the wire that comes from the batteries box. In other pin, I soldered the other wire that comes from the motor.

Step 19: Batteries Cover

Using a cap from an empty AXE body spray (not mine), I made a cover for the batteries. I cut it in half, checked if it fits into the case, then I gave shape to the cover and placed the spring as a tail. For an easy attach and removal, I placed two screws in the body that fit inside two holes I drilled in the cover.

Step 20: Final Details

I made two ears from the remaining parts of the coathanger, then I attached them to the head (it's the best place for having ears). And... It's done! Now I have a robo-dog to annoy my cat!

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