Walking Gonk Droid

Gonk Droids are the little boxy, walking droids you see in Star Wars movies if you're really looking. And I've seen plenty of people make replicas of them from a couple rubbermaid totes. But, I've never seen anyone actually make a WALKING Gonk droid. And that's kind of all they do in Star Wars, they walk. And I really wanted a walking Gonk droid.

• Aluminum Stock
• 3D Printed pieces
• 1/2" Sintra
• Automotive seat motor
• Sparkfun mp3 trigger
• Syren motor controller
• Storage totes
• Various bits and bobs.

Bipedal walking is tricky, just ask Boston Dynamics. But I was inspired one day by a simple wind-up toy. It seemed to me this walking penguin had all the engineering I needed to create a walking Gonk. I just had to scale it up!

First, a bit about HOW these toys walk: This method of locomotion stars with a single motor that transfers its power out to two legs. At the top of each leg is long vertical slot that rides on a shaft coming out of the body. At the bottom of each leg is hole that rides on the rotating shaft of the motor. There's usually some sort of cam that offsets the two legs from each other. As the motor spins, the legs move back and forth, but also up and down.

A VERY important feature of these walking toys are what I call the Foot Pegs. These two little pegs on each foot that face inward toward the other foot. Those pegs actually support the weight of the body as the other foot goes in the air. SPOILER: I would find out how critical getting those right are as I scaled up.

DISECTION:

I started by taking my penguin apart. In it, I found the structure I needed. The body was a rectangular gear box with the 4 rotational shafts that interact with the legs. What I really wanted to get right was the legs. I assumed the various proportions of leg to foot size, to rotational distance was important.

I'm a huge fan of building with foam-core to work out the engineering. I started by measuring the details of the Penguin's legs and scaling them up. I planned on building my Gonk body from some medium size totes I had purchased, so overall scale would target that. This quick foamcore mock up was really instructive. I use my power drill to provide some rotation to the shaft to see how the legs worked.

I quickly decided to shift from the offset cam design of the penguin to a smaller cam on the other side of the leg.I also saw that I needed to make the core body as narrow as possible to keep the legs close together

From here I felt I needed a step where I work out the structure more specifically. I jumped into Fusion360 to do this. I had previously found the perfect motor. A 12v power cat seat motor. It was geared slow with lots of torque. I began by building the rotational cam system around the scale of this motor. I planned on 3D Printing the gears and cams you see here. They would be custom enough that I didn't think I'd find something off the shelf. From there I could work out the dimensions of the other parts surrounding the "drivetrain"

To orient yourself, any part that is yellow in the illustrations is a 3D printed part.

Jumping back to the real world, I felt confident enough to start mocking-up the body and legs in the final material. For the majority of the build I'm using 1/2" black Sintra (an expanded polystyrene board). I wanted my droid to be light and strong. Sintra gave me both. To make the pieces a bit more rigid I attached aluminum U-channel along edges of the boards. THis will keep the legs and frame from flexing as the droid walks.

This allowed me to see how the actual motor worked as a power source for the legs. Initial tests showed the motor was still too fast for the legs. He's a walker, not a runner. So In Fusion360 I redid the gears to steps down the overall speed of the legs.

With the legs sorted out I moved onto the feet. I knew the droid would need large wide feet. But I wanted to see if I could get them as small as I could to look more like the Gonks on the Star Wars films. For initial feet I attached a piece of 1/2" Sintra and created the Foot Pegs out of more aluminum U-channel.

What I found is there is a massive relationship between the size of those foot pegs, how the droid walks. My prototype spent more time falling because weight was shifting wildly from side to side. Drunk Droid Syndrome.

I went back into Fusion360 to work out the details of the feet. Including some thin outer foot shells that will cover the foot when I'm done.

In this video you can see I tried adding some pegs out the side of the feet to keep him from tipping sideways. What I found later is extending this INNER pegs solved things. It might be obvious, but the droid needs to be able to stand on one foot without tipping. Those foot pegs in between his legs are what allow that. I kept trying to make the feet narrower. But the key was the right length of the Foot Pegs. An engineer friend gave me this bit of advice "Think about walking as 'controlled falling'" ... He's totally right.

My Gonk was walking but he was still connected by a cord. I wanted to control the motor via a wireless remote. To do this I bought a cheap 3-channel remote for a remote-control car. A Syren10 motor controller would ... control the motor. And a Sparkfun mp3 player. I planned on getting him to talk as he walked. I wired up the motor controllers to the remote. This allowed me to walk him forward and back wirelessly!

For the talking part I created a sound file of the "GONK!" sound from the movies and added it to the mp3 player – triggered by a button on the remote. I struggled to get the remote to trigger the mp3 player. I later found out I needed a "PICO switch" between the player and the remote receiver.

With the inner-working of my Gonk complete, I began working through the exterior design. His outer hull is two medium-sized storage tubs from Home Depot. To get an authentic Star Wars vibe, I used a bunch of found objects to add texture and mechanicals to the body. This part always feel more like sculpting ... trying bits and parts on to get proportions and geometry feeling good. I love scavenging from American Science and Surplus, Goodwill, flea markets. I'm trying to use things that are not easily identified so it feels "galaxy far, far, away"

His blinky lights are simply a battery powered LED Holiday light string. It's an easy way to add some lighting drama.

To get ready for his debut at Maker Fair, G-O (his new name) was weathered to look good and dirty (as anything is Star Wars should be). I have an R2-D2, and I'll tell you, little G-O draws quite a crowd around too. He's got a distinctive saunter that drips with attitude. ... GONK GONK!!!

I've uploaded a bunch of files to Thingiverse. The files there are NOT everything you will need to print one of these robots. Many of the parts I used were handmade made from extruded aluminum, sheet plastic, storage tubs, electronics, and other materials.

But, you will find all the parts I did 3D print, including his feet, the various fittings, and spacers, and the two gears used to propel the robot forward. Also the Fusion360 file I used to design the robot, from it you can take measurements.

It is intended to be a resource for anyone interested in completing a similar project.

https://www.thingiverse.com/thing:4178647