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Author Topic: Stepper motor size  (Read 4608 times)

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Stepper motor size
« on: June 28, 2008, 12:23:56 PM »
Hi all,

I am just finishing the build of my second CNC router but I am having problems with drive to my X axis.

I am using my Nema 23 motor from my smaller machine to drive a 1000mm X 20mm lead screw

The lead screw turns freely by hand over the full travel so there is no bind up

I have put a 2-1 reduction via timing pulleys and I have tried several settings in motor turning but I guess it just is not man enough for the job.

I was thinking of getting a Nema 34 motor but I am not sure if this will be man enough any thoughts on this ?

I am using a routout control box with a 2.5 amp output will this be man enough to drive a larger stepper motor ?

Any ideas on this

Ray
Re: Stepper motor size
« Reply #1 on: June 28, 2008, 12:56:30 PM »
Hello Ray,
Here are a couple of clips that I saved from earlier topics.
There are more scientific approaches but they are above my head. ;D

"From what I have researched and found, the motor sizing is directly related to the mass of the object being moved, the presented inertia of such mass, and the "drag" or friction of the moving components such as linear bearings, rack and pinion, ball screws, etc, combined."

Gecko Mariss wrote once in another thread.......

"So, how do you figure the power you need?

Method 1: You have a plasma table, wood router or some other low work-load mechanism. You have a clear idea of how many IPM you want but your'e not sure of what force you want at that speed.

Pick the weight of the heaviest item you are pushing around. If it weighs 40lbs, use 40lbs. Multiply it by the IPM you want. Say that's 1,000 IPM. Divide the result by the magic number "531". The answer is 75.3 Watts so use a step motor.  Eq: Watts = IPM * Lbs / 531"
« Last Edit: June 28, 2008, 01:20:20 PM by Overloaded »

Offline RICH

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Re: Stepper motor size
« Reply #2 on: June 28, 2008, 05:55:43 PM »
Ray,
There are a few nice engineering software programs out there  ( free ) which allow you to define your system.
The software does all the calculations and then provides for motor selection. Nice thing is you can play with the program
and see the different results. They are rather easy to use ( back in the old days all this stuff was done manually).
RICH
Here's a link to the one of them :

http://www.danahermotion.com/website/usa/eng/support/design_tools/114867.php
Re: Stepper motor size
« Reply #3 on: June 28, 2008, 06:41:09 PM »
Hi Rick,

Thanks for that I will give it a go
Ray
Re: Stepper motor size
« Reply #4 on: June 28, 2008, 06:45:03 PM »
Thanks for that I will try Ricks method I like the idea of someone else / program working it out
my usual method is try it and see but I need to get this right first time

Thanks again 
Ray

Offline RICH

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Re: Stepper motor size
« Reply #5 on: June 28, 2008, 08:49:33 PM »
Ray,
Just remember that garbage in garbage out in any computer program.

If you gave some more info on your router like basic dimensions, desired travel velocity, and what your going to route thru, etc there are folks in here that could probably relate to your machine and give you good recomendations based on their experience.

When you fool around in the program, model your first router and then the second and compare results.
Try differerent accelerations and velocities and compare a few of the recomended motors. Check out the
motor curves for a few and relate the info from the program to the motors. You will quickly learn a lot.

Additionaly go in and do some things based on what Overloaded gave in method 1. Mariss (Gecko Drives)
is one the most expert persons  when it comes to drives and motors so don't discount his recomendations.
Sometimes a computer program can't replace tried and true experience.

Have Some Fun,
RICH


Offline jimpinder

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Re: Stepper motor size
« Reply #6 on: June 29, 2008, 04:32:19 AM »
I used Routout 2.5 amps drives on my machine to drive 220Ncm steppers. These were 8 wire motors rated at 2.5amps at 7.5 volts

Originally I wired them in series, and, like you, I found them lacking - only moving my lathe at 4 inches pm (reliably). (Mine is geared down at 3 to 1)
I wanted then to "rewire" the motors in parrallel. The problem was, of course, when I checked the windings and did the sums, the rating was for a single coil, and as soon as I put the coils in parrallel, I neede more omph than the Routout could provide.

To be fair, the Routouts did run the parrallel set up, better than when the motors were in series, but they were limited to 2.5amps and 24 volts.

I got a Gecko from a friend (and have since bought another) - and these are in a different league. They are adjustable, and rated up to 7 amps, and up to 80 volts. Fastening these on (using the same motors at 24 volts - same as Routout) my speeds went up to 40 ins per minute. I admit they are not reliable at that speed and I have dropped them down to 20 ins pm but a five fold increase is great. I am still using the Rotout card to run my milling head - but when I have the cash to invest in a third Gecko, I will then try a higher voltage - maybe 36 volts, and see what improvement that brings.

Before you rush to change motors, I would honestly fit yourself up with 3 good drives - the Gecko 201's are ideal. The beauty about that is you have the capacity to change current and voltage to your motors, without have to change your drives again. You can then see if you can coax any better performance from your motors.

Not me driving the engine - I'm better looking.
Re: Stepper motor size
« Reply #7 on: June 29, 2008, 12:52:44 PM »
Hi, That sounds good advice, I think I have sorted my drive I fitted a 3 to 1 reduction and this works

The speed is not as fast as I would like in line with what you found but it does work.

I will try the the Gecho as you suggest as this would seem the best option before I go to either a larger motor
or I was considering buying a more substantial control system but they are £750.00

Thanks again for all the help and advice
Ray

Offline jimpinder

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Re: Stepper motor size
« Reply #8 on: June 29, 2008, 01:24:36 PM »
Are you stepper motors 8 wire, and if so, how have you got them wired.
Not me driving the engine - I'm better looking.
Re: Stepper motor size
« Reply #9 on: June 29, 2008, 01:34:59 PM »
They are 4 wire motors
Ray