Running an electric motor backwards is less efficient?

Maybe. Maybe not. There, isn't that nice?

I'm assuming that you mean permanent-magnet commutated DC motors (the kind that just have two wires coming out).

The armature current in a DC motor lags the voltage on the armature coil a bit, because of coil inductance. You can tune a commutated DC motor to run more efficiently by advancing the brushes a bit on the commutator -- this is rarely done, but there is a large body of lore associated with it among slot car racers.

However, most run of the mill small DC motors are designed to run the same in either direction. You may get motors that run a bit differently in one direction than the other due to manufacturing variations, but that would be a consequence of chance, not design.

So, probably not.

That depends hugely on how the motor is driven. The same effect with lagging armature current exists, and you can make things a bit better by advancing the commutation, but first the brushless driver designer would have to care, and then he'd have to dare.

If you had a brushless drive sophisticated enough to give a bit of lead to the voltage then it would probably be easy-peasy to extend this to do so in both directions. But I very much doubt that a cordless drill, if it's brushless at all, would have such a feature.

brush-less should be easy, just swap two phases. Either physically or in how the drivers are sequenced. Any lead should be speed dependent so I'd assume the controller adds it and thus it should work the same in both directions

-Lasse

I suspect that the gears are cut to optimise running in the forwards direction

Its common to angle the brushes to reduce bounce. How much effect that has during reverse running I've no idea.

NT

I removed the controller from an impact wrench and stuck it into a same brand hammerdrill. Now apparently it runs just as fast backwards as forwards. The motor metal gets hot within ten seconds on high-speed, but I guess that's normal.

I wrote:

The DIY electric car builders are into adjusting brush position in their motors also.

Mikek