Rocking ERIC

Whereas our early robots had two wheels for driving it along and a caster wheel at the front for balance, ERIC just has two wheels, which means its circuit board, motors and batteries pivot around the axis between the two wheels.

Whenever ERIC changes velocity (speed or direction changes), the boards and batteries rotate, and if the change is too big, ERIC can go upside down when it turns itself off.

Another problem is that if the board is pointing upwards too much, the sensors may miss an object in front of the robot.

Stopping (or at least minimising) ERIC’s rock is a control problem – and as ever this requires a measurement. The fact that the board is at an angle can be detected using its accelerometer.

But how should ERIC react to this measurement?

When ERIC accelerates (its velocity changes), then immediately the board starts to rotate – so the angle can be used to adjust the velocity in the opposite direction. This affects ERIC’s speed, but only for a short time.

We can see this in the video which includes a simulation of ERIC on a web page and some film of ERIC with and without control of its rock.

If you would like to investigate further, you can try out the Control Reduces Rocking and/or Velocity Feedback Reducing Oscillation web pages mentioned in this video.