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### Author Topic: Motor counts per in  (Read 1266 times)

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#### barnettch3

• 3
##### Motor counts per in
« on: December 17, 2015, 07:56:46 PM »
I was wondering if there is anyone out there who would be able to shed some light on the formula for calculating the "count per in" when calibrating the motors.
I running a NEMA 34 but I'm at a little loss on the process. I'm using a chain drive with 14 tooth drive sprocket and a 20 tooth idle sprocket each with .25 pitch.

Really at a loss for whats next.

Thank you.

#### ger21

• 6,293
##### Re: Motor counts per in
« Reply #1 on: December 17, 2015, 08:21:26 PM »
If it's a fixed chain, the machine will travel 3.529548 inches per motor revolution, if the sprocket is mounted to the motor.

I used an online calculator to find the diameter of your sprocket, and multiplied by pi.
Gerry

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#### garyhlucas

• 660
##### Re: Motor counts per in
« Reply #2 on: December 17, 2015, 08:35:03 PM »
I don't think this is going to work out with the pitch diameter because a chain sprocket is chordal, not round. So for one revolution the distance will be number of teeth times the pitch or 14 x 0.25 = 3.5" However chain does not run smoothly like a belt. It oscillates forward and backward. You can see this clearly on sprockets with a very small number of teeth and it can produce violent vibration.  You also can't tighten a chain up taught without causing tight and loose as the sprockets turn.

So chain is kind of a bad idea for linear motion, but if that is what you have my explanation of the math above will work.