The coil setup as shown here appears to work very well off rotor. It is 4 individual sections of 3 coils cut from a Fisher & Paykel Smartdrive washing machine motor. The copper wire is removed from the outer 2 legs, and one of these wires is wound around the center coil in the same direction and connected in series. I have tried with the outer legs removed, but the coils will not work. The legs are the path for the magnetic flux.
Fitted to the front of the coils are 4 ferrite bars 40 x 12 x 5mm. These seem to smooth out the electromagnetic field and may even increase the airgap distance. All 4 coils are then connected in series. It becomes one large electromagnet with all polarities the same.
The four coils connected in this way are the best and strongest arrangement I have been able to make. However the motor requires that two of these "quad coils" are connected in series, and the coils are then not as effective. What I have done is to connect two coils of each quad coil through two parallel 3 phase bridges.
Fitted to the front of the coils are 4 ferrite bars 40 x 12 x 5mm. These seem to smooth out the electromagnetic field and may even increase the airgap distance. All 4 coils are then connected in series. It becomes one large electromagnet with all polarities the same.
The four coils connected in this way are the best and strongest arrangement I have been able to make. However the motor requires that two of these "quad coils" are connected in series, and the coils are then not as effective. What I have done is to connect two coils of each quad coil through two parallel 3 phase bridges.
There are 3mm holes at the base of most, but not all of the 42 coils of the F&P stator. With careful cutting, and using only two holes for mounting, there is no waste. The existing holes can be drilled out easily and I have connected the coils together with 3/16 brass or steel thread and nuts. This can be bent slightly to give the coil unit its required curve. The initial test running of the motor used just 1 of these coil units per coil. It was running with 6 coils, or 2 sets of three. The start of each winding is Brown, and the finish is Green.
The main reason for the change to longer magnets and coils was to get stronger magnetic fields. This has been quite successful, as the air gap between coils and magnets has been increased from 3mm to about 15mm. This may be due to to a law of magnetics which says that if you combine 2 magnets end to end, north pole to south pole, the lifting power is doubled. If you put 2 magnets side by side same pole facing out the power is squared. It may be possible to make longer coils to allow for variations in magnet / coil arrangements.
