Basic CNC

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Bill Gruby

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I have gone over this board a several times now looking for basic info. Most times I have found that it is assumed that you already know what happens up to a certain point or you would not be asking. This is not true in a lot of cases. Also there are some who will not ask for various reasons.

So here is my plan -- Ask a basic question and get the answer in this thread. Simple --- not really. I would bet there are dome here that do not know how a stepped motor works. I didn't till this morning? I didn't even know that there is more than one type.

This is stickied to the top so it does not get lost. You neophytes just post whenever you feel the need to ask about something.

One thing I woud ask of those answering, please do not assume anything. And remember you startes an sero knowledge too.

"Billy G" :thinking:
 
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Bill Gruby

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What is a Stepper Motor and why is it needed instead of a normal DC Motor?

"Billy G" :))
 

Mid Day Machining

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Great topic Bill. I'm sure there will be lots of questions. I'll chime in where ever I can help.
 

joe_m

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I'm still trying to figure out what I need to do for CNC, but I think I can answer the stepper motor question.
A regular motor just goes round and round (or back and forth if it's a windshield wiper motor.) A stepper motor shaft goes round in steps or increments. It takes a pulse of power and the shaft rotates a set amount. That amount doesn't vary - one pulse of power and it moves one step. The step might be 1/10 of a full rotation, 1/4, 1/3, whatever - but it will be the exact same each time. And since CNC relies on the computer moving the x/y/z axis of your mil or lathe in very precise measurements you need a stepper motor.
For example: Your computer program says "move the X axis .01 to the left before making this cut" and if your stepper motor is geared up to the x axis in such a way that each pulse of power makes it rotate just enough to move .005 then the computer will tell the motor to take two steps.
With a normal motor you get on and off and you just can't control the on/off precisely enough to get the controlled movement you need.

That's my understanding of stepper motors.
Joe
 

xalky

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That's a very good explanation. A servo motor does basically the same way except that it has feedback that tells the controller that it did indeed move 2 steps, at least that's how i understand the difference between a stepper and a servo.
 
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Bill Gruby

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Let's try not to add to any confusion. The original post was Stepper versus Normal DC. Once this is answered we can move to Servo Motors. We need to go sloooow here. No harm done yet folks, just staying on top of things.

DC motor move in a continuous rotation. Stepper moves in steps caused by electric impulses. Simple as that???

"Billy G" :thumbsup:
 

jumps4

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I have nothing to add here joe is right about how it moves
the size of the motor has to be large enough to make sure the step is made or everything goes out of position. the computer tells the motor to move the required amount of steps. but in most hobby machines has no way of knowing if it did move that exact amount.
the dc motor you set a speed and direction and "you" have to stop it when it reaches the point you wanted
are we going the direction you wanted bill?
steve
 
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Bill Gruby

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In less that three hours this thread is off the original question. Yes Servo motors are used -- Reason, greater accuracy. If this thread is going to work we have to stay on track. DC Motors (as in tread mill) vs Stepper Motors. That is the original deal. One step (pun intended) at a time please.

"Billy G"
 

jumps4

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if you just want to turn a motor at a set speed: dc motor
if you want to turn at a exact speed and number of turns: stepper motor
steve
 

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So to sum up so far in regard to 'regular' DC motors vs stepper motors, a regular motor will spin continuously when current is applied, while a stepper motor requires a more specialized input, usually from a computer, to tell it to move a step at a time like a ratchet.
The computer tells it how many steps and how quickly to go from step to step. If it moves from step to step really quickly it can appear to be moving like a regular motor, but that's just an illusion.

So far so good?


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