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Robokids is an introduction to the fascinating world of robotics for primary students. If your little scientist likes building things, especially things that move, they will love Robokids! Test your robot boat in the water tank and watch your robot car shift into high gear! Campers will build a robot hand, a robot arm and experiment with motorized Capsela kits as they explore how electricity, gears, circuits and a little creativity can bring a robot to life.

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Friday, May 11, 2007

MiniMechadon Robots

MiniMechadon was designed/constructed from Nov '02 to Dec '03. Currently, the mechanics and electrical hardware are complete. I have written some test code to exercise the servos and demonstrate the flexibility of the robot and for basic walking.

The main goal of the project is to experiment with learning algorithms that will allow the robot to learn how to walk, rather than programming it to do so. The physical design is intended to be a simpler version of my Mechadon robot (12 DOF). While simpler than Mechadon, I feel there is still enough complexity to make the problem interesting while not being overly elaborate. My hope is that the techniques developed with MiniMechadon can be extended to more complex robots such as Mechadon.

There are 4 DOF, each powered by a high speed nano servo (Tower Hobbies TS-5). These servos are rated at 20.8 oz-in of torque at 6.0V and only weigh 0.34oz. The final weight of the robot is about 12oz. The sensor array consists of 4 touch sensors on the bottom of each foot, Left and right IR obstacle detection, and 4 CdS photo detectors located on all four sides of the robot. The heart of the control system is a Microchip PIC16F819 micro-controller and a separate 8 channel A-D converter. I originally designed the control system using a PIC16F84, but I later switched to the PIC16F819 so I could use the Microchip ICD2 in-circuit debugger/programmer. The PIC16F819 is pin compatible with the PIC16F84, but has more peripheral options like a built-in 10-bit 5-channel A-D converter. The ICD2 has worked great (unlike the original ICD) and I would definitely recommend it.

Most of the construction of the robot is brass tubing soldered together with a small pencil torch. The wiring on the legs was run through the tubing so it is not visible. The brass tubing is also used for the bearings in the leg joints. The white plastic pieces were machined from UHMW (a plastic similar to nylon). To be different, I made the circuit board for the control system into a 3-D shape out of 9 separate panels to give the robot a unique look (intended to be a streamlined version of the AT-ST walkers from the Star Wars movies). This was also my first attempt at a homemade surface mount double-sided PCB. The IC's are SOIC packages and the resistors and capacitors are 1206 size packages. It was really no harder to make than a through-hole PCB. I used a product called "Press-n-Peel Blue" to make the boards and I tin plated them with "Tinnit" so they don't corrode. It was interesting to do a PCB layout for a 3-D shape. It gives flexibility that you don't have with a typical flat PCB. I'm currently designing another robot and plan to try some smaller IC packages and to use 0805 resistors and capacitors. Stay tuned for the results. source

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