Let's Make Robots!

Motor control

hi all,

does anyone know if its possiable to control the speed of a stepper motor/ Dc motor with a pot?

also if you have any schemtics on how to do this it would be helpful

 thanks to anyone who replied :) 

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Is it a DC motor or a stepper motor?

They're quite different.

 my goal is to make a record player...sort of and  my goal is to make it without a uController and only a few componets. so i probably dont need a big stepper motor to turn a record around so im going to say a dc motor. and thanks for the fast reply

There are several options depending on how complex you want to go. If you just connect a pot in series or parallel with a DC motor for example you can use it to control the speed, but this is a terrible idea =D (high value pot needed, no direction control, very inefficient).

If you're planning on using a microcontroller somewhere in this project then you can use the micro to read the pot, and then have the micro control the motor speed via a normal motor driver. There are plenty of examples for reading pots and controlling both DC and stepper motors already floating around, so I won't elaborate on that here. This approach is nice and flexible, but if you weren't planning on using a micro already it's a bit overkill for this task.

The simplest way to control a DC motor that I can think of that doesn't completely suck uses an NPN transistor and a few resistors:
This circuit only runs the motor in one direction (it can be upgraded though), but with a bit of tuning on R1 and R2 you can use the pot to control the motor from a stop all the way up to full speed. It won't be flawless, as the controller is non-linear, but it does a great job for so few parts.

Stepper motors require somewhat more specialised controllers, but you could make one with a 555 timer or two that would 'translate' the pot value into stepper motor speed. As the stepper motor controller requires more parts, the cost of using a micro starts to get more justifiable, so I'll let you ponder your options on this one =)

thanks i will use the uController option because im using one in a different part of the project.