Speed Delta test

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Someone e-mailed to ask how quickly the wheels could change direction so we put together a quick and crude test using an Arduino.

We used the quadrature encoder and wrote an interrupt function that captured the time from micros() into a 100 element array of unsigned long ints - the interrupt would fire every time the QEI channel changed state.

The wheel (120:1 gear ratio) was then spun at full speed forward and reverse, changing direction every 0.1 seconds (we had already established that it went from zero to full speed in under 0.1 sec).

When the array was full the wheel was halted and the array contents printed out.

The graph below shows the elapsed time between each interrupt, shown in seconds.(click for a bigger version)

SpeedGraph1_.gif

The peaks in the graph (approximately every 0.1 seconds) are the direction changes so it looks like the wheel will go from full speed forward to full speed reverse in around 0.065 seconds (Running on 7.0V under no load).

If you are wondering why the elapsed times show as a jagged line, oscillating between higher and lower values, we would guess that this is down to some imprecision in the quadrature sensor disk and the sensor components. The Arduino interrupt fires on every rising and falling edge, so the sensor is measuring the black and white stripes on the encoder disk as being of slightly different widths.

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