Help Design A CNC Unit

[Joe Wood]

I've never seen either, just trying to educate myself.

[Jim Becker]

[Alex Zeller]

I've never seen either, just trying to educate myself.

The main difference between a stepper and a servo is feed back. With a stepper motor the controller tells it how much to move and the motor moves that amount if everything it working the way it's suppose to. But there's no feedback so the controller just goes on to the next line of code.

With a servo the motor gets a signal from the controller to move. While the servo is moving it's also measuring how much it moved and it feeds that information back to the controller. The controller keeps sending a signal to the servo to move until the servo reports that it's moved the correct number of steps.

For example, if the code asks for a 10 step move the controller commands the servo to move in the correct direction. When the servo moves 1 step it tells the controller. Now the controller knows that it still needs 9 more steps. When the servo has moved 10 steps the controller then stops telling the servo to move and then goes on to the next line of code. More advanced controllers can keep track of how many steps are being lost by a servo and let the user know. With a stepper set up the controller doesn't know or care how much the stepper moved. It just moves on to the next line of code. So if the stepper doesn't move all 10 steps you've just lost 2 steps of accuracy. Obviously having feedback makes the machine more accurate.

Servos are more expensive because they have to have an accurate way of counting how many steps they move. Normally they will have an encoder to count how much it's moved. Not only does the encoder need to be able to count the number of steps but also which direction the servo is turning. Since they are more costly they often used in higher end applications. They also use things like rare earth magnets over regular magnets which also drives up the cost but does make them stronger.

[Joe Wood]

OK looks like I'll need some expert advice with this, can anyone do some paid consulting with me?

[Bill George]

OK looks like I'll need some expert advice with this, can anyone do some paid consulting with me?

Gary who replied here is in the business.