I have a project where I need to provide a variable speed, reversible dirve to a shaft.

I would like an analogue knob where neutral would stop the shaft and turning to the left or right would increase the speed in either direction.

How difficult is this to achieve with a stepper motor and controller? I not an electronics numpty but I'm a noob to this.

Does it have to be a stepper motor? If so, it could be achieved quite easily with a PIC or ATMEL type microcontroller. If it can be a DC motor with a gearbox, then the type of controller used for simple model train layouts may be an option. I'm sure there'll be plenty on eBay.

Ed.

I'd say arduino would be the easiest way, they have examples of reading potentiometers and controlling stepper motors ready written, you'd have to stitch em together though

Just search for "stepper motor driver kit". Maplin used to do one, but no longer seem to, Amazon has Amazon Stepper Motor Driver Kit and there are loads of others.

Oops, sorry, forgot the reversible by the speed knob bit, but there'll be some out there with a quick search.

[Edited on 29/9/12 by SteveWalker]

This also depends heavily on the requirements for the system. Do you expect it to maintain a fixed specific speed or just go at whatever speed you set it to and maybe change when you load it?
What torques are found on the shaft?
If you outlined the purpose it would make suggesting a product/solution a bit easier.

I would say that yes I would need it to maintain a fairly constant speed when loaded. Unfortunately I'm not in a position to know the torque loading on the shaft yet, I do know that similar applications use fairly modest stepper motors to provide CNC like control.

Then you'll either need a somewhat over-sized motor or a control system of sorts which does closed loop control on motor speed, which ups the price a bit (quite a bit).

If it's CNC-like requirements and low torque just go with a stepper and a stepper controller, because a normal DC motor will vary too much unless it's a monster.