What kind of electrical motor can resist motion when stopped?

[PomPom]

I'm not very well versed in motors.

I'm looking for a motor (DC or AC, i really don't know the difference, probably DC, seems easier to design a control system).

It needs to be able to move in both directions, but also have an ability to "stop" and resist motion. But also, I'd like to to be able to just have no torque at all, and be allowed to rotate freely. My guess is that short circuiting a motor will make it hard to move (the emf produced by motion will cause a large I in a short circuit, thereby more torque, hard to move), while open circuiting it will allow it to move freely--but I really don't know much about motors so it's just a stab.



On that note, is there some definitive guide to motor selection, because obviously i don't know squat about motors.

DC, brushed, brushless, AC, 3 phase... what's it all mean!!!!


Thanks folks!

 

[FvM]

A shorted DC motor generates a speed proportional braking torque, but no "holding" torque at zero speed. To achieve the latter, you'll need a step motor, a motor with servo control or a mechanical brake.