9g Tai Chi Stepper


This project was defined as the construction of a self powered bipedal walker using cheap 9g servos and applying the principles of Tai Chi. A Picaxe ‘training program’ was written to use a universal IR remote controller to directly address each of twelve servos. A number between 75 and 255 can be entered then a ‘nudge up’ or nudge down’ key allows precise adjustment of rotation - useful when first assembling the unit and setting the servo arms and linkages. It also allows any ‘posture’ to be achieved. The 20X2 has sufficient pins to accommodate the 12 servos, the IR input and program I/O. It also has enough scratch pad memory to store ten ‘postures’. These stored positions can be retrieved immediately or an interpolation routine can be used to move slowly from one position to the next. Dividing the difference in servo values into sixteen intermediate positions, the servos will move at different speeds to reach the new position at the same time. Once a usable routine is tested, it can be transferred to a Look Up Table in the main program then called up via the controller as one of 10 sequences. Additional tools and translation symbols were developed to help my understanding and therefore the progress towards walking. The model was designed in 3D using Sketchup and is constructed mainly from 2mm plywood and white glue. After some major reconstruction it became clear that the 9g servos could not be bullied into working. Balanced on one leg, the lower servos simply collapsed. Just as Tai Chi uses technique to defeat superior force so various techniques were employed to overcome these problems In summary, working sequences allow turning, stepping forwards and backwards and are fascinating to watch. The program code should allow any robot project using multiple servos to be developed quickly.
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