This is to report an erroneous speed - with a divided by two speed - for the Motor Control Workbench and its associated Motor Pilot version 6.4.1.
The speed information throughout the Motor Control Workbench generates twice the mechanical speed with F.O.C algorithm and STEVAL-SPIN3202 control board.
The measured tachometer shaft speed which leads to confirmed motor speed and associated computations are the following:
Motor Speed (RPM) = 2 x BEMF(Freq)(Hz) x 60 seconds / Poles pairs
Note: 2 factor meaning: Each magnet passes over the coil used to sense the Back-EMF twice during each rotation, once over each end.
BEMF(Freq) is matching HALL(Freq) in our application.
These checks were carried out with two motors:
1,400 RPM with a 10:1 gear ratio delivering 140 RPM at the shaft and 155 RPM with no gear
In both cases, we have correct mechanical speed for half the speed entered within Motor Control Workbench and Motor Pilot. Motor Pilot reports half the speed of the actual motor rotation measured with a tachometer at the shaft.
The scope capture below shows the 1,400 RPM motor HALL or BEMF (brown trace)
Motor Speed in RPM = 2 x HALL Freq (or BEMF = same Freq ) * 60 s / pole pairs = 2 x 70.17Hz * 60s / 6 = 1403 RPM - matching the shaft speed with 140 RPM with a certified and confirmed 10:1 gear
