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Offline Davek0974

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Re: Only X-axis motor is working
« Reply #120 on: March 31, 2018, 04:46:52 PM »
The extra vibration at certain speeds sounds like resonance.

Mass i.e. a load should alter that but sometimes you have to work round it.

Steps per rev is usually fixed and written on the motor - generally 200 or 1.8deg per step, do you mean you set micro steps to 400??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: Only X-axis motor is working
« Reply #121 on: March 31, 2018, 05:00:34 PM »
First posting on steppers: 18/March
This posting on steppers: 31/March
The learning curve has been steep but effective?

Cheers
Roger

I'm not sure if this was sarcasm or praise.
Most of the time has been spent trying to get the stupid bad cable diagnosed. Now that that is over with I am free to tune.

The extra vibration at certain speeds sounds like resonance.

Mass i.e. a load should alter that but sometimes you have to work round it.

Steps per rev is usually fixed and written on the motor - generally 200 or 1.8deg per step, do you mean you set micro steps to 400??

I think you might be right about the resonance. I have everything mounted to 1/4" plastic sheets right now so any vibration is enhanced in sound. Watching the zip tie I have on the motor shaft helps me see if there's more vibration or less depending on the configuration.

Yes, the motors have the steps per rev on them and yes it's 1.8 deg per step. The drivers, however, have the capability to microstep (apparently) and when I set the drivers to microstep I seem to have a better result in the accuracy of maintaining step. If I set the driver to 200 steps then I seem to lose staps. If I set it to 800 steps then I seem to have a better accuracy.

If I end up using the most accurate settings then I'm going to have to have some serious gear reduction in the final build. 

Offline rcaffin

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Re: Only X-axis motor is working
« Reply #122 on: March 31, 2018, 05:15:14 PM »
I'm not sure if this was sarcasm or praise.
It most emphatically was not sarcasm or criticism.
Actually, I think once again it illustrates the differing senses of humour between Australians and Americans. I get into so much trouble over it.

If I end up using the most accurate settings then I'm going to have to have some serious gear reduction in the final build. 
Not so. Mach3 looks after the micro-stepping. Using it does not mean any changes in gearing. What micro-stepping can do is to make motion smoother. So, do all your calculations about gearing withOUT considering any micro-stepping.

Cheers
Roger

Re: Only X-axis motor is working
« Reply #123 on: March 31, 2018, 06:23:51 PM »
I shall than you, then, for what could be considered a compliment. ;)

I have a dry sense of humor, myself, so no worries.

What I had read, and gathered, is that microstepping would have less torque than full stepping, hence the thoughts on adding gear reduction.
The trade-off being that gear reduction would add in a component of inaccuracy or slop when shifting directions. This is something I do not want to introduce, especially when I migrate from the CNC build to adding CNC capabilities to my home mill and lathe. I had considered other methods to insure the accuracy of the direction change in that project, though. I imagine that, once it's calculated, I could add the necessary correction to the G-code generation and/or the Mach3 profile. But that's a way down the line so I won't focus on it yet.

My next step is to determine which setting on my drivers will yield the best results. And determine which stepper motors I want to invest in.

I wanted to go to a NEMA 34 with dual shaft (dual shaft for my X-axis only needed) but there's a decent set of NEMA 23 with a reported over 400 oz/in rating
It's a few dollars more I can get 1600 oz/in in a NEMA 34.

When I say "a few dollars more" I mean it's almost twice the price.

My CNC mill will only be a 24" X 48" (or 650cm X 1300cm for the Aussie)

Offline rcaffin

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Re: Only X-axis motor is working
« Reply #124 on: March 31, 2018, 08:07:29 PM »
Hi Inferno

Micro-stepping does not really have significantly less torque. There are many myths on the web, and this is mostly one of them. The explanation of the origin of the myth gets rather technical: lets just skip it for now and ignore it. Do all your planning on the assumption that you do not have micro-stepping, even to the point of getting Mach going without it. Then ... if you decide you want to implement 8x micro-stepping, do so, and change the calibration in Mach by the same factor. You will get slightly smoother movement.

If you wish to have some 'gearing', do NOT use metal gears, or gears of any sort. Go for modern toothed belts, such as GT2. They work extremely well, do not have backlash, and have oodles of power rating. But note: 'modern' toothed belts. The older and possibly better known 'timing belts' do have backlash and should be avoided. They will only bring grief. Fwiiw, I use a GT2 9 mm wide toothed belt to give a 3:1 reduction on each of my axes. I replaced the older timing belts the machine came with.  The spindle still has a timing belt drive ... so who cares?

The resonance problem is more technical - but it is also far more important. If your drivers do not support resonance suppression, then there are going to be some limits to what you can do. You will have to avoid a middle speed band. That too is possible at the start. You will find out about that when you get going.

Stepper motor size: my CNC machine is not large - it is a dual axis CNC 4-axis MACHINE, not a router. It has 300 W DC servo motors on the axes, 3:1 reduction, 5 mm pitch ball screws. I have current meters on each driver. I very rarely see any movement in the meters at all. I do not think they ever draw more than 10 - 20 W at full slewing speed. I rather suspect that a lot of builds have motors way bigger than they will ever need.

Of course, once you have built a CNC, you can always make new improved parts for it! Some of our readers seem to spend most of their time doing just that.  :)

Cheers
Roger


Cheers
Re: Only X-axis motor is working
« Reply #125 on: April 01, 2018, 12:32:50 AM »
Hi,
the real figure of merit when it comes to steppers is inductance. Inductance affects how quickly current can build up in a coil. Lower inductance windings mean that the current builds up faster
and therefore the stepper can rotate faster without a significant reduction in torque.

Not all manufacturers make plain what the inductance is on their motor, I would ask. If they can't tell you don't touch it. For 23 size steppers 2mH or less is good. For 34 size look for motors of 4mH or less.

Craig
My wife left with my best friend...
     and I miss him!

Offline rcaffin

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Re: Only X-axis motor is working
« Reply #126 on: April 01, 2018, 12:49:32 AM »
And putting two windings in parallel effectively halves the inductance too.

Cheers
Roger
Re: Only X-axis motor is working
« Reply #127 on: April 01, 2018, 12:59:52 AM »
Right now I have the windings in series. So should I put them in parallel for a better performance?

(still trying to figure out why they even have an 8 wire model.
Re: Only X-axis motor is working
« Reply #128 on: April 01, 2018, 01:40:00 AM »
Hi,
the parallel combination is better for performance. Provided it does not get too hot that's the way to go.

A four winding two phase stepper can be run flexilbly as unipolar or bipolar and therefore potential OEMs sales increase because of the flexibility of application.

Craig
My wife left with my best friend...
     and I miss him!
Re: Only X-axis motor is working
« Reply #129 on: April 01, 2018, 01:45:49 AM »
Hi,
the parallel combination is better for performance. Provided it does not get too hot that's the way to go.

A four winding two phase stepper can be run flexilbly as unipolar or bipolar and therefore potential OEMs sales increase because of the flexibility of application.

Craig
When I had them in parallel they did get pretty warm. Maybe 110-120 degrees F

I've read unipolar and bipolar several times but still can't fully comprehend what that means.