Walking Robot

This is my walking robot which was built in 2003 to 2004.  It can walk, turn, squat, and shoot foam darts by standing on one foot and rotating the other foot to trip the dart launcher.

My robot is based on a mechanical design very loosely taken from an article in Servo magazine.  Unlike the magazine article’s robot, mine has joints oriented like a human set of legs, including rotating hip joints which allow it to turn. The HS-422 servos are augmented by springs to carry some of the weight. Servos and processor run from 5 NiMH cells located on the feet.  The robot is controlled by an infrared (IR) universal remote. The IR signals are received and processed by a very cool specially programmed chip called the IR-D14 that decodes Sony IR signals (unfortunately it’s out of production). The outputs from the IR receiver chip are brought into the 16F876 main processor, decoded for the appropriate function, and then the ten PWM signals to control the ten servos are output.  Also included is an onboard NiMH battery charging system based on a MAX712 chip.  To charge, just throw a switch and plug in a 12VDC wall wart supply and the batteries charge up in about an hour.  After I built this, several “humanoid” robots became commercially available, including the one from Hitec Robotics. The Hitec robot used much more powerful (and expensive) digital servos to carry the additional weight of the torso and arms.

Processor Board Schematic

This is the processor board.  A 16F876 PIC is the master CPU.  The IR-D14 decodes the infrared signal from the remote to a 1-of-14  discrete interface to tell the master processor what button was pressed.  The buttons on the remote are mapped to functions like “walk forward”, “turn right”, “turn left”, and “stop” which when pressed cause activation one of the IR-D14 outputs.  The 16F876 generates the 10 Pulse Width Modulation (PWM) signals that tell the servos what position to move to.  The MAX5008 is a power conditioning circuit that takes the battery power and provides a stable 5V for the PIC.

Battery Charger Schematic

The battery charger actually is part of the processor board, but this captures the schematic for this piece.  It’s based around a Maxim MAX712 NiMH battery charger circuit.  The top half of the second photo shows the switching scheme for the battery, charger, and processor.  The bottom half of the second photo is a schematic for a PIC programmer.  It’s a serial-to-ICSP (in-circuit serial programmer) interface.  It worked OK but required special software to use, and was rather slow to program and also not very reliable.  I frequently had to run the program cycle several times to get the PIC to program with this interface.  I have since switched over to using a Microchip Pickit2 programmer, which really works great.

Sound Generator Module

This was something I came across and decided to add to the robot.  It is a little blister-board module that outputs several gun and bomb drop noises.  Four of the noises are triggered by spare outputs from the IR-D14 interface.  If you look close at the photos above you can see this module – it’s the little green board at the left side of the processor on top of the robot.

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