Ankle Compass (North Paw): Finer resolution idea

David A. Wheeler

2013-09-03 (revised 2013-09-04)

I think the North Paw is an interesting device. Currently, however, only 1 motor (of 8) turns on to indicate north.

Once it's calibrated, I suspect that the North Paw could express finer angles by turning on & off the motors in varying percentages (presuming the motors can turn on & off quickly). Here's my idea, if you're curious.

I think two motors, by alternating how long each is activated, could simulate an "in-between" angle. Only 1 motor would still be on at any one time, but the resultant apparent angle would be the weighted average:

Resultant angle = p*M1 + (1-p)*M2

In this equation M1 and M2 are the angles of the closest motors, and p is the percentage of time M1 is active. Solving for p:

p = (M2 - Result) / (M2 - M1)

Example: to report 50 degrees, that's M1=45 degrees, M2=90 degrees, p = (90-50) / (90-45) = 40/45 = 89% for M1 (45 degrees). So you could rapidly cycle between M1 and M2, with M1 getting 89% of the power, to simulate a 50 degree angle.

A minor complication is the motor at 0 degrees. When considered M1 it is 0 degrees, and when considered M2 it is 360 degrees, so that it can handle averaging either direction correctly.

You could probably turn on this mode after 10 minutes, to give people time to calibrate 1 motor at a time.


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(C) Copyright 2011 David A. Wheeler.