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In lugnet.robotics.rcx, "Elizabeth Mabrey" <emabrey@storming-robots.com> wrote:
>
> Hi
>
> I am curious how the power levels are being implemented. I am not talking
> about the icon level navigation. How the motor actually adjusts to the
> different levels setting? Gear slipping?
>
> Thanks in advance...
> --
> Elizabeth
Others have explained Pulse Width Modulation. However, if the kids are old
enough to understand the difference between linear (straight line) and square
law (curving ever upwards) and electrical voltage, resistance and power, you
could say that the power of the motor is proportional to the square of the
proportion of time for which power is applied. For example:
Power level 3 = 4 parts up + 4 parts down = 50%. Squaring this gives 25% power.
Power level 5 = 6 parts up + 2 parts down = 75%. Squaring this gives 56.25%
power.
Power level 6 = 7 parts up + 1 part down = 87.5%. Squaring this gives 76.5625%
power.
Power level 7 = all 8 parts up = 100%. Squaring this gives 100% power.
A model with a high load on the motor might be able to demonstrate this by the
inability of the motor to move the load at low power levels.
That reminds me - has anyone managed to change how the RCX sets it motor power
levels (the proportions of time for PWM)? I guess it means rewriting the
firmware. The idea would be to make a scale of speeds with linear power
increments rather than linear proportions of time.
Mark
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