This video shows off version 3, including various features of the Inverse Kinematics engine:
This project is my first experience with walking robots. The concept is loosely based off of the SG-1 universe's replicators, although there are definitely differences. Stubby version 3 has six legs with three DOF per leg, whereas the replicators have four legs with four DOF per leg. Then there is the whole thing of Stubby not being able to consume raw resources to construct copies of itself... I figure I will add that feature in the next version.
My kids (especially my 6 year old daughter) have been bugging me for a while to make a robot with them, and I figured that this would be a good introduction to it, plus would make for some interesting programming challenges for myself. (In actual practice, the hardest part has been the frame design; building the frame with a limitation of servo strength requires knowledge of levers and mechanical advantage that I have not had to use since grade school!)
We got the first version working without much problem. It was a very simple design, with the servos directly connected to the legs. This made for an easy frame design, but even at 400g total robot weight, the servos were only barely able to support the weight of the robot. It worked but it didn't work well, and you could hear 'buzzing' frequently when the center of gravity put too much strain on a single servo.
The second version was much more complex mechanically. It was designed from the ground up with the objective of fully mechanical joints, with the servos only being used to drive the joints, using mechanical advantage to decrease the torque on the servos. Version 2 can move forward and backwards, and can rotate in place.
Version 3 (the one featured in the above video) is a complete re-design, with 3-DOF per leg (18 servos total) and a full inverse kinematics engine. It can move in any direction, rotate in place (and turn while moving), can perform body translation along XYZ axis, and can perform body rotation along XYZ axis (pitch / roll / yaw). It includes built in calibration for each leg, a battery monitor, etc. It weighs 594g, including 4x AA batteries.
On my website there are lots of diagrams and documents, but really only two are essential to understand. First is the frame plans. Stubby is designed to be cut from 1/4" MDF using a scroll saw. The frame is quite easy to make; simply print the plans, tape it to an 8.5x11" sheet of MDF, and cut along the lines.
The second important diagram is the circuit board schematic. This shows how to wire the control board so that the microcontroller can perform the needed calculations and tell the servos how to move.
All the hardware would be useless without software to control it. You can download or browse my git repository, which includes all software and libraries (written by myself and Warren), the QCad files for frame design and the KiCad files for schematic / board design. Everything, both hardware and software, is licensed under a Creative Commons Attribution-Noncommercial-Share Alike License).
Future plans for The Hackaday Prize are to implement a computer controlled API to allow for teaching programming and robotics concepts to children. See my entry video for more details: