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Postby Harry Dalek » Sun Feb 17, 2013 10:07 pm

Hi Gary yes i am confused i think i need to see where i am getting it wrong a picture or drawing would be great .
I'd rather get it right first time so yes please.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Mon Feb 18, 2013 10:33 am

Hi Harry I hope this makes it a bit clearer:
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Postby Harry Dalek » Mon Feb 18, 2013 2:55 pm

gary wrote:Hi Harry I hope this makes it a bit clearer:



Well i have done both ends of the Thread with bearings as in your picture with the nuts same .

The long threaded nut in the middle connected to the gantry i want to cheat and use 2 or 3 normal nuts spread out and weld them to a steel plate then to the gantry .

So apart from that all thats the same .

Now the flexible coupling i have not got that far i see the best there the lovejoy coupler...
Looking on the net the rubber tubing seems to work but i always hear their not happy with it ....
Before i talked to you about it i was thinking of making the coupler out of wood or steel which now seems way wrong ...could you use a spring that would have a bit of give to it ..would be good Masters hardware sells boxes of them every size like the nuts and bolts box you see next to my build.
Its either that or i find some rubber and make a rubber version of the wood or steel one i was thinking of making./
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coupler_pic.png
something like this out of rubber but like the spring idea better
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Mon Feb 18, 2013 3:15 pm

Yes couplers can be made like a spring - in fact you can buy them. However, it is important to note the two major requirements of a coupler:

1) it must be forgiving of slight misalignments between the stepper and the drive screw, and

2) it must NOT have any (appreciable) backlash.

now any "flexible" coupling must have the ability to return to the "non-deformed" position when it gets to it's destination. In other words when the machine has stopped there must not be any tension on the spring otherwise the screw hasn't turned all the way to where it should be. In fact, even if the spring coupler returns to the exact position, during motion, whenever there is a change of direction (or acceleration) there will be a bit of displacement, so, say, a diagonal line will be generally correct but will have the "wobbles" along it's path. So the important this is to have some spring or give in the lateral direction (to account for misalignment) but little or no spring (or deformation) in the angular direction.

Don't forget a coupling need not be "springy" to be flexible - i.e. a cars universal joint is flexible but not "springy".

The Lovejoy couplers have very hard rubber or plastic between the two jaws but the flexibility is actually provided by the faces of it's jaws being able to slide across each other - therefore there is virtually no angular deformation (or offset).

In any case - give something a go - if it doesn't work try something else - there are lots of examples on the net.

A coupling is something easy to replace later.
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Postby gary » Mon Feb 18, 2013 3:20 pm

Here is an example of a commercial spring coupler - actually I think they are called "bellows" couplers.
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Postby Harry Dalek » Mon Feb 18, 2013 4:54 pm

I like the look of the spring coupler really need a motor before i can do any thing on this which is a pain ,all i can do is hook my cordless drill up the the thread and see how its moving the Axis.

Good advice Gary its made that part easier i will just have to tinker at it till the mechanical part is done and wait and wait for an ebay sale :roll:
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Postby gary » Mon Feb 18, 2013 5:53 pm

Shipping is the killer... :-(
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Postby Harry Dalek » Mon Feb 18, 2013 6:05 pm

gary wrote:Shipping is the killer... :-(


I have seen prices in the usa pretty cheap on the motors but yes mailing is the killer !

China is the place to buy i have seen free postage on cnc stepper motors communist postal system more than likely made to help their countries businesses winning out over capitalism seems to be working !

Where all i have to buy is the motor and nothing on the postage its a no brainer ...

China wins
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Mon Feb 18, 2013 6:14 pm

Most of them come from China anyway...
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Postby gary » Mon Feb 18, 2013 6:17 pm

Strangely though, I look all the time (I want to upgrade from a measly 35 oz to 200 oz) and have yet to see the killer deal that forces my hand...
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Postby Harry Dalek » Mon Feb 18, 2013 6:52 pm

gary wrote:Strangely though, I look all the time (I want to upgrade from a measly 35 oz to 200 oz) and have yet to see the killer deal that forces my hand...



Theres a big difference between the smallest nema 17 size to 23 and up i know biggers better but you are right no killer deal to make you want and buy ,i will have to be stuck with the 17 size i know i have to be careful as their torque will be all different .

I tend to look for cnc Nema 17s they are 50 to 80 oz torque i think least they tell you some times .

Wonder what the old floopy drive steppers would be i am sure.... they would be all different ...would there be a test you could do as in lifting some weights mmm the OZ as in weight it can move if thats a silly question !

These things also run at different voltages i am not sure the controller and driver would drive different types of steppers if this would be a problem or it would just drive them at different speeds due to this .

If the old motors work it might be worth just trying for the controller driver but i still would rather a stepper made for the job when i could .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Viewmaster » Mon Feb 18, 2013 7:17 pm

Harry, other than using bellows or rubber there is another type of coupling that was used on tuning for short wave receivers etc, where zero back lash was essential.
Eddystone Radio made them many years ago and they are seen on ebay
from time to time.
Consisted of a two pieces of brass mounted either side of a circular plate. riveted each side (or use bolts). Coupling boss each side in centre.
The Eddystone one took a 1/4 inch dia shaft.

You could easily make one to suit requirements using 2 pieces of spring steel etc. or something along this principal design.
See piccy of the Eddystone one here.
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Eddystone non backlash coupling.
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Postby gary » Mon Feb 18, 2013 7:33 pm

Harry, I have addressed this before but you mustn't have got the reply, but the NEMA rating is to do with the physical size of the motor not it's holding torque. For instance a NEMA 17 has a diameter of 1.7" if round or has a side length of 1.7" if square shaped.

Now obviously the larger the casing the more copper you can get in it so the more powerful motors are the larger sizes.

But, my steppers are NEMA 23 but are only 35oz-in so you can't assume the larger the motor the more powerful.

Having said that if you want 200 oz-in (generally recommended for your size machine) you would need to go to NEMA 23.

Floppy disk drive motors are NEMA 14 I think with very very low holding torque.

Some typical NEMA sized steppers:

NEMA 8 0.8" square
NEMA 11 1.1" square
NEMA 14 1.4" square
NEMA 15 1.5" square
NEMA 17 1.7" square
NEMA 23 2.3" square
NEMA 24 2.3" square
NEMA 34 3.4" square
NEMA 43 4.2" square


Yes if you are using a recycled motor and it doesn't have the holding torque written on it the only way (if it doesn't have a model no you can look up - many do) is to measure it the way you mention - there are some tuts on how to do that on the net. Persoannly I think it would be just as easy to hook them up and see how they go - if they don't have enough grunt then you need to source other motors.

But if you buy new motors the holding torque is always specified.
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Postby Harry Dalek » Mon Feb 18, 2013 8:33 pm

Viewmaster wrote:Harry, other than using bellows or rubber there is another type of coupling that was used on tuning for short wave receivers etc, where zero back lash was essential.
Eddystone Radio made them many years ago and they are seen on ebay
from time to time.
Consisted of a two pieces of brass mounted either side of a circular plate. riveted each side (or use bolts). Coupling boss each side in centre.
The Eddystone one took a 1/4 inch dia shaft.

You could easily make one to suit requirements using 2 pieces of spring steel etc. or something along this principal design.
See piccy of the Eddystone one here.


Hi Albert
I have never seen one of those before made in the days when every thing was hand made i bet .
Is the back the same as the front visa versa ?
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Harry Dalek » Mon Feb 18, 2013 9:06 pm

gary wrote:Harry, I have addressed this before but you mustn't have got the reply, but the NEMA rating is to do with the physical size of the motor not it's holding torque. For instance a NEMA 17 has a diameter of 1.7" if round or has a side length of 1.7" if square shaped.



Gary i understand but what i am confused about is i have seen NEMA 17 saying its rated 80 oz ! and others lowwer so they are all over the place its not like your buying this size and you get this power out of them...i'd rather stuff the size and they say we are selling a 50 oz Torque stepper motor .


Now obviously the larger the casing the more copper you can get in it so the more powerful motors are the larger sizes.


Wonder why there is a jump from the 17 to 23 size .....it also sounds like if they are telling the truth about their motors power rating the wire size is varying depending on who made them ?



But, my steppers are NEMA 23 but are only 35oz-in so you can't assume the larger the motor the more powerful.


This is what i have to be careful about as i don't understand why they sell them in a size and you think they are more powerful sounds a bit of a rort !

doing a quick google on 17s and oz i get a few come up nema 17 62oz nearlly twice your 23s ?

Having said that if you want 200 oz-in (generally recommended for your size machine) you would need to go to NEMA 23.


So what ever i buy i better make sure i look into that mother OZ as it could be anything from the sounds of it .

Floppy disk drive motors are NEMA 14 I think with very very low holding torque.


That sounds pretty low then it never had to work hard in those floppy drives
Yes if you are using a recycled motor and it doesn't have the holding torque written on it the only way (if it doesn't have a model no you can look up - many do) is to measure it the way you mention - there are some tuts on how to do that on the net. Persoannly I think it would be just as easy to hook them up and see how they go - if they don't have enough grunt then you need to source other motors.



This looked like a good test
http://www3.telus.net/schmaus2/elcts/mtest.html

But your more than likely right just to hook it up to what ever and see .

But if you buy new motors the holding torque is always specified.


I wanted to talk about this as i just didn't under stand why size and torque
are different in the same sized motors i would not have known there could be such a difference i have to check it out if price and oz is a factor or its pot luck you'd think higher torque higher price i will study this !
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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