Balancing Robot
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                               Parts in the kit. Not all parts were used because some parts were incorrect.                           
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                                This is the Balance Robot, motors attached to wheels, motor driver on platform above with the 9 volt battery. On top platform is the electronics, two boards stacked on top of each other an Arduino Uno MCU with Sensor Shield. The original kit had 3 levels which I reduced to two for stability.                           
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                                This is the remote control. Pretty chinzy and ugly. The black knobs left and right are joysticks, the green thing is the LCD display and the MCU board beside the battery is an Arduino Uno as well.                           
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                                Instructions showed the 3 PID pots (blue things with gold screws) plugged into sockets. Not a good idea: too loose. I removed the sockets and soldered the pots into place. These are very important pots to tweek the PID parameters for best operation, and can't be flopping around.                          
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                               Wiring for the Balancing Robot, motor driver on right, left is Arduino Uno.The Uno is underneath the shield which plugs directly into it via pins on both sides.This drawing and one following were provided by vendor.                                                           
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                              Sensor "shield" in the middle, joysticks on sides. Board at top is back of the LCD.The Uno is underneath the shield which plugs directly into the Uno via pins on both sides.                           
 
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Future Development:  Build another, scratch built, bigger, using similar components. Maybe a Segway someday...I want to use the balancing hardware and properties in a full-size humanoid robot.
Update 2Feb16: I tried to scale this up using the same small stepper motors but there is not enough torque to do the job. I think my next version will be a stepper with gearbox if I want to maintain the same control strategy, OR a standard DC motor with gearbox with slightly different control system.
Here's a video (click for YouTube link) of the robot in action. It was just "free-wheeling" and wasn't being controlled by the remote control for direction and speed.
I built this little robot so I could study and learn from it. It is a 2-wheel robot that balances much like humans do. When the robot tends to fall forward, detection circuits spin the wheels in the opposite direction. Have you seen the Segway personal transporter? Same idea.