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Repto The Servo Robot

This Cute Robot Was Created On A Budget And Is A Real Head-Turner

Repto the Servo Robot. In the January/February 2009 issue of Robot there was an article by a man named I-Wei Huang, who had created small organic robots he dubbed Swashbots. I read the article and then later viewed Huang’s YouTube videos, blog and website, www.crabfu.com. I found myself truly inspired. Here was someone with a similar skill set to my own and who had created simple and engaging robotic creatures. I could not wait to try and do the same. Immediately I started sketching ideas for the robot I would create. Once I had the basic concept of how I wanted my robot to look I had to figure out how I would get it to work mechanically. I wanted my bot to be small, simple, fun, and interactive. After pondering how to achieve my goals of motion and having a few drinks with some friends I scribbled some schematics on the back of a napkin and with that was ready to start building.

I had in my possession a JR Sport 4 channel radio control system from a previous RC helicopter project. I quickly pirated the RC servos, servo horns, helicopter ball links, the RC receiver, and its 4.8v NiCad power source. My plan was to use two servos for the left and right leg and one servo to move the bots hips. The bot would move by waddling its hind legs while supported in the front by casters. The hip assembly would allow one leg to be touching the ground at a time so the operator could alternate between the left and right leg while moving forward and backward or keep pressure on one leg while turning. An example video can be found at http://ad-concepts.com. The 4th servo I decided to use to add character and life to a robot whose purpose was to interact with its surroundings. Since I had designed my new bot to crawl on its belly using pirated RC servos I decided to call my new bot Repto, which in Latin means to crawl or creep over.


To create Reptos frame I hand bent pieces of 1/8x 1-inch aluminum stock. Using the stock I created a mount for the head and jaw servo to rest on, another separate mount for the casters and hip servo to rest on, and a spine to enclose the receiver and power source. The hip assembly would also carry the servos for the left and right legs. Once I had the 4 pieces of the frame made I bolted them together and used a modified door hinge to allow the hips to sway from side to side. I then screwed the servos into some homemade brackets epoxied to the frame and wired them to the power source now located on Repto’s back. I wanted the head and legs of Repto to be organic to give the robot character and life. Haung’s most aesthetic Swashbot was built from a material called Shapelock which is a material used for rapid prototyping and can be melted and formed in a home kitchen. After a short experimental phase with Shapelock I was ready to use the material to create parts. Since I needed to attach servo ball links directly to the legs I decided to form the plastic around two metal frames with all the necessary hardware already attached. The frames were made of 1/8 inch threaded bar stock with some modified bolts and washers welded in the appropriate spot. I also created some threaded rubberized feet to screw on to the bottoms of the leg frames to give Repto some friction against the ground so it could crawl with ease. The skull and jaw took a bit more effort and a few more tries to get right. Using some of the remaining Shapelock material I attached two stainless steel ball bearings to the skull as Repto’s eyes. Since Shapelock is very easy to sand and drill it was no trouble creating mounting points to attach the legs and head to Repto’s metal frame.

After my success with the head and legs I decided to create a small tail to give Repto a bit more animation. The tail is attached to the hips and wiggles as Repto walks.

To create a suitable home for all of Reptos electronics and moving parts I grabbed an old and hopefully unused piece of PVC pipe from my basement. I diced it up and then using a plumbers torch, I heated a small area towards the front of the pipe which allowed me to bend it to the desired shape. I wanted to create a heavy industrial looking shell to contrast the smooth organic limbs and head. Afterward, I painted the shell metallic gray and yellow to portray an industrial look and even added a bit of flat black and copper overspray to give it a dingy weathered appearance.

With the shell complete Repto was done and I was ready to conduct the first test run. The JR Sport 4 channel control system allows for two servos to be controlled with one joystick, so I assigned the left hand joystick to control the hips and jaw while the right hand joystick controlled the left and right leg. With a little practice I began to move Repto forward by moving the left joystick clockwise and the right joystick counterclockwise. Reversing the motion allowed Repto to back up and toggling the right joystick while leaving the left in a fixed position allowed Repto to turn.

From start to finish creating Repto took about a week of my spare time. It required no special programming and was built of scrap parts found, more or less, around the house. Repto was a fun robot to build because I was able to take basic ideas and concepts and create something simple and unique. Because of the simplicity behind Repto, I hope that other builders will get inspired to create their own servo robots. To see Repto’s build and Repto in motion check out http://adconcepts.com !

Robert Antonuccio


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Words by Robert Antonucci