Biped walker with 3 servos - Arduino version

By edllew
@ December 5, 2011

• Actuators / output devices: 3x DFRobot DF15MG servos
• CPU: Arduino ATMEGA328
• Power source: 4 AA batteries
• Programming language: Arduino

This is based on fritsl's "Biped walker with 3 servos (Dead Duck Walking)", http://letsmakerobots.com/node/29379.

I am familiar with Arduino/AVR rather than PICAxe, so I adapted the code to that. I set out to use an AtTiny 8 pin DIP, but it was easier to use the Servo library as-is with an AtMega328p. I may go back to the AtTiny when/if I move the circuit off the breadboard.  Note that I didn't actually use a full Arduino board, but I did use their IDE and Servo library, and sent the resulting code to a stand-alone microprocessor.

I followed fritsl's build video (a no-talker which I really enjoyed) very closely. I cut my own wood pieces rather than starting with paint sticks, but that makes no real difference. I took my time and tried to be careful with cutting and glueing the parts, but I positioned the foot servos too low on the vertical balance pieces (not sure what to call them) and as a result I had to insert a shim between the foot servo arms and the wood feet to avoid binding.

Since it is built of wood and not metal/plastic or some other "hard" material it can feel a bit loose and clunky, but that is part of the charm I think. Working with the wood is pretty forgiving.

I had never used a hot-melt glue gun before. I used my wife's cheap crafty low temp glue gun, and it worked fine. I liked it and expect I will be using it more.  None of the glue joints have come apart yet.

A critical part of the build and code is servo alignment.  I note in the code the proper rotation of the servo arms at center setting (1500 usecs).  That should be set properly at glue-up time.  It can be tweaked a bit in the code after the gluing but it is best to get it right at first.