I want an electric motor that works a bit like a servo motor with a steering horn on it, like so: http://www.buggy-sport.info/index.php/gallery/image?view=image&format=raw&type=img&id=7191 But it needs two specific properties: - it creates a controllable amount of force along a given axis, independent of the arm's location, up to the arm's limit of motion - it allows the arm to move freely when required This is different to a servo motor: - servo motors move the arm to a specific location, independent of how much force is applied, up to the stall force - servo motors leave a lot of resistance on the arm even when completely unpowered The design I'm thinking of involves having a magnet inside a coil, and attaching the arm to either the magnet or the coil and letting it slide freely. This would create linear motion, as opposed to the servo pictured above, which creates circular motion which must then be converted to linear motion. Firstly, when a voltage is applied to the coil it should create a force between it & the magnet that is independent of their relative positions, provided the magnet hasn't left the coil. Is this correct? Secondly, if I short the coil's circuit so that it has virtually no impedance on it, this should let the coil & magnet move with negligible electromagnetic resistance. Is this correct? Thirdly, does this design already exist? No sense in developing it if I can just buy one.