This happens looking with a meter and DC shunt inline to measure the input current.
t would show this minus 20ma when both coil banks were hooked in seres.
The coils were 49ohms apiece, made from surplus solenoid coils.
Three coils at 120 degrees apart are on each side of rotor, for 6 coils total.
The coils are aircored, and the rotor was three 1 1/4" X 1/2 thick grade 45 neodimium magnets also postioned at 120 degrees.
Commutator was simplr roller comutator through electric bearings instead of slip ring with very light pressure to the brush. Motor ran around 200rpms when it had the negative current happen: