- If we are X% below the average, we are in a LOW
I attached a piece of red electrical tape to the wheel,
and counted the number of revolutions made during the
X% is currently set at 20% of the full range (max-min)
and needs to be tuned for different wheels. This leaves a
Good news: It matched the calibrated RPM value that
40% dead band around the average, allowing us to ignore
minor fluctuations in light level.
Bad news: There was a ~25% difference in RPMs
between the front right and left motors.
• We know how long the test ran.
I will be upgrading Berry’s motors in one of the
• Now we have the number of high (spoke) and low
• Matched motors (within 5% or less of each other)
• Four independent motor drivers so I can “tune” the
• We know there are five spokes on these wheels.
PWM speed per motor
• That means there are also five spaces.
I will let you know how it turns out! SV
So, we know there are 10 pulses (five low, five high)
per revolution of the wheel. Hmmm ...
If we ran the test for 60 seconds, counted the number
of (high+low) pulses, and divided by 10, we have the
average RPM for the length of the test!
Actually, as long as we run for more than two
revolutions and know how long it took to compute the
scan, we can calculate the RPM:
Computing Motor A RPM:
238 pulses, so 23.8 revolutions in 11.1943240166
seconds means Motor A ran at 127.564647752 RPM
Computing Motor B RPM:
190 pulses, so 19.0 revolutions in 11.1943240166
Motor to Motor Variations in
I knew that the rock-bottom cheap motors I was using
were not very accurate. After all, I could see Hobbit, Elf,
and Berry would not go straight when driving the motors at
the same voltage. However, I was still surprised at the
~25% variation in unloaded maximum RPM — so much so
that I had to verify my findings.
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