My place...

'Type in your company slogan here'

29-09-2009 15:49



 Two wheeler



    Base rebuild



Your Link

Your Link

Other balancers



Your Link

Your Link

Your Link

Your Link


Text Box

Use this box to type any specials, new updates or even gallery pics here.


Robots - Two wheeler - Crawl before you walk.

To be able to make the robot balance I realised I needed some sort of control algorithm and I decided that a PID regulator probably would provide the the largest chance of success.

To develop and test the code for the PID regulator I used the same approach as the nBot's creator with a pole pivoting on top of the robot. A potentiometer measures the angle of the pole and sends that value the PIC's onboard A/D converter. The A/D converter sends the value to the PID regulator whose job is to calculate how to drive the motors so that the pole remains upright.

A PID regulator is basicly three regulators running in parallel, each acting on the Error signal, in other words the difference between the desired value and the actual value. Each regulator, or term, has it's own gain, that way you can adjust how the regulator responds to various situations.
  • The P-term is the proportional term. The larger the error is the more it will contribute to final output of the regulator.
  • The I-term is basicly the sum of all errors in the past. That is, the longer there's an error present at the input the more will the I-term contribute to regulators total output.
  • The D-term is the derivative or difference between the current error and last error. This can respond quickly to sudden changes in the error signal and as well as having a damping effect on the total output when the actual value is getting closer to the desired.


Here's two photos of the testbed. The first shows the overall mechanical platform. The motor driver IC's are mounted on a solderless breadboard on the lower deck and the pivot joint for the inverted pendulum is mounted on the second deck.

There's two support 'struts' acting as casters that prevents the robot from tipping in any direction. For this test setup the signal from the potentiomter as well as power and PWM signals to the motor drivers were fed to the CPU via cable so that I didn't need to worry about battery voltage or my PIC development board suddenly taking off, heading for the wall.


Here's a shot of the PIC development board. The black cable coming in from the lower right corner is the power to and signal from the potentiometer and the grey and green ones are the PWM and direction signals to the motor drivers. This board will eventually be replaced with one dedicated to the robot.



After quite a few hours (days actually) of coding and trial and error I finally managed to get the robot to balance the pole (well almost). Here's a couple of low-res videos of the balancing act.
After I got the robot to balance the pole I was eager to make it balance itself.

Copyright 2006 Henrik Olsson. All Rights Reserved.
Template downloaded from:
FrontPage Templates