Proposed Layout
I find that if I install the magnets lengthwise around the inner circumference, leaving a similar relative spacing between the magnets as when they were fitted to the original motors,
that the required quantity to span around the inner circumference of the ring is 168. This is exactly 3 times the 56 magnets on the Smartdrive motor.By also arranging the coils lengthwise, and multiplying by 3 x 42 coils, we are able to arrange
126 coil positions. As I anticipate that this motor is very low torque, I intend to set the coils out in 14 equally spaced sets of 3. That is, each 2nd and 3rd set of coils will not be fitted.
This motor will need to switch at 3 times the rate of the Smartdrive to achieve the same revs.
The individual magnets can be removed from the original plastic casing. Behind the magnets is a lamination of 6 layers of 0.6mm sheet steel, one continuously wound band.
I thought that the steel was to eliminate "eddy currents", and this may be true, but it is also apparent that the magnetic field strength of the individual magnets, when installed in contact with the steel backing, is far stronger than than when the magnets are removed. It should be simple to slice the steel backing into narrow strips, therefore keeping the materials and magnetic properties as similar as possible to the original Smartdrive motor.
While I am still using the Smartdrive coils, a change has been made to using easily obtained 40 x 25 x 10mm thick ferrite magnets laid out lengthways to form 160mm drive magnets for greater magnetic field strength and far slower switching requirements. The coil setup has also changed to work with the extended drive magnet length. Sep 2013
I thought that the steel was to eliminate "eddy currents", and this may be true, but it is also apparent that the magnetic field strength of the individual magnets, when installed in contact with the steel backing, is far stronger than than when the magnets are removed. It should be simple to slice the steel backing into narrow strips, therefore keeping the materials and magnetic properties as similar as possible to the original Smartdrive motor.
While I am still using the Smartdrive coils, a change has been made to using easily obtained 40 x 25 x 10mm thick ferrite magnets laid out lengthways to form 160mm drive magnets for greater magnetic field strength and far slower switching requirements. The coil setup has also changed to work with the extended drive magnet length. Sep 2013
