Electric motors would not work on the moon

[smartcooky]

So motors on spacecraft in zero gravity can go infinitely fast?

I seem to recall posing some variant of this very question (after picking myself up off the floor from a laughter-induced coma) and he responded that a motor in zero-g would continue to speed up until it burns out.  I tried looking up the thread, but it's apparently been deleted, as the only references I could find were dead links to it in the cosmoquest archive.

Well actually, that isn't so silly, but it doesn't take ZERO-G to achieve that. A series DC motor can run itself to destruction if it is run under "no-load" conditions.

[ka9q]

And as I recall, the drive motors on the Apollo LRV were series wound. Ah ha!

[ka9q]

The local science museum has a simple motor physics exhibit where the visitor can hold a horseshoe magnet around a stator and see the effect of moving the magnet. If another visitor happens to be there I'll reverse the magnet and demonstrate how that reverses the direction of the motor. Then I'll ask whether the motor will speed up or slow down as I slowly pull the magnet away. When I actually try it, they're invariably surprised at the result.

I worked briefly on the electric car project as a Cornell undergraduate in the 1970s. This was before power MOSFETs and IGBTs, so the only high power solid state switches available were power SCRs. The school's cars were all built as pure field control systems; full battery power was applied to the armature through a contactor, and the field current was varied with SCR choppers. Again students (at least the ones who hadn't yet taken the advisor's DC motors class) were often surprised at how the accelerator actually behaved.

The electric motor idled just like a gasoline engine so it required a clutch and transmission. Seems pretty clunky now, but it was still fun.