DC motor design project

[Ian Mackenzie]

One of my courses this term at university is a design project course, where we are asked to design something patentable. My group is planning to make a prototype of a new (?) kind of DC motor, and I wanted to get some feedback from the Chief Delphi community.

The basic idea of the motor is to have a DC motor with mechanical commutation (i.e. with carbon brushes and copper rings like in FIRST motors, as opposed to sensor-driven electronic commutation in brushless motors), but with the armature coils on the motor frame (the stator) instead of the motor shaft (the rotor).

For the sake of comparison, the attached image "DC motor - rotor armature" shows a cutaway view of a standard DC motor (like those used in FIRST), where the brushes and commutator ring result in alternating polarity of the spinning armature coils.

The other picture, "DC motor - stator armature", shows a diagram of our proposed design. Instead of a commutator, the battery leads are connected to two slip rings mounted on the rotor. Instead of using this to power an armature coil on the rotor, however, the two rings are connected to two halves of a commutator ring. Current then passes out through the commutator ring, through another set of brushes, and powers armature coils mounted on the motor housing (stator). As the motor shaft (rotor) turns, therefore, the polarity of the stator armature alternates. It's exactly the same principle as a normal DC motor, just inside out.

This has the advantage of better heat dissipation; it is much easier to dissipate heat away from coils mounted directly on the motor housing than coils mounted on the motor shaft. So, a few questions for the resident motor experts:

1) Does this already exist? We've done several patent and Google searches and haven't found anything, but that doesn't mean it isn't out there.
2) Will this work? Is there something we've missed?
3) What sort of applications would this be particularly well suited for? For instance, are there some DC motor applications where overheating is a big issue, so that better heat dissipation would be a big advantage?
4) Is there a good, reasonably cheap way of testing our prototype? I looked at a few small dynamometers, but they were quite expensive ($1000+).

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