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There will be plenty of challenges in the design of a useful and affordable mobile robot.  The number of challenges can be kept down by keeping the design as simple as possible.  The design should be kept as simple as possible to eliminate unnecessary complications and challenges.  The simplicity of the design will be governed by the requirements and features outlined in the last blog.  The principle of keeping the design simple will be applied to all aspects of the robot, including the chassis.

I'm making a mobile robot intended to move on the floor or ground.  It could do this by walking or rolling along.  One leg of a walking robot will require at least two servo motors.  A walking robot will require at least four legs.  This puts the minimum servo count at eight.  That's eight servos to mount and control.  A gait algorithm would be needed, and it won't go very fast.  If it rolls, it would need two wheels and one motor per wheel for a total of two motors.  No gait algorithm would be needed either.  Right off the bat, the rolling robot seams much easier to implement. 

DC electric motors are commonly used to drive wheels on a robot.  And of the various wheel configurations, the differential steer locomotion is the most common because of the simplicity of controlling motors for both speed and direction.  Differential steer of two wheels can require as little as only two control signals.  I want the robot to have the ability to drive up and down ramps.  This requirement rules out one differential configuration where the two drive wheels are placed in the mid-line of the robot, and the front and back of the robot each mounts a castor.  As the robot drives up the ramp the castor makes contact with the ramp first and the drive wheels loose contact with the floor 

Less is more.  If we eliminate the front castor and move the drive wheels near the front of the robot, we get a simple footprint and the ability to ascend and descend ramps.  I’ve used this wheel and castor arrangement on a couple of other robots, and it has performed very well on carpet and hard surface flooring. Robots also perform well when making the transition to and from both.  This footprint also makes it possible to drive over low profile obstacles like pencils, magazines, and electrical cords.  

- keep rockin