- Pancake Motor Current 1 - Initial Measurements
Note: This article was published on the interim web site on 6 May 11. Since we have so many new folks, and so many "old" folks back now, I decided to republish, and start a new dialog in this area.
Just before we went "stealth" I made some armature current measurements on an A/FX Chassis.
Here is a plot of some of the data.
The pink (magenta?) line is from the laser tachometer. For every two cycles of the tachometer, the motor makes one revolution, so what the image above represents is just a little more than one revolution.
The blue line is the current, as measured by an inductive ammeter. The actual value of the current is not important in this discussion. The interesting part is the variation in current during the different segments of the pancake motor propulsion cycle.
The second image shows a representation of 60-degrees (1/6 of a revolution) of the pancake propulsion cycle. (I think that was Big-T's annotated armature photo. Thanks!) You will notice that the resistance value (these values are calculated, not measured) changes during each segment of the cycle. This is based on my assumption that for a few degrees of armature rotation, a brush bridges the gap between two segments of the commutator, putting two windings in parallel, and changing the DC resistance of the motor circuit. It remains to match the cycle phases to the data. I expect that this will require accounting for the inductance changes, and the effects of the magnetic field generated by the permanent magnets.
More to come!