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Author Topic: Mach 3 & Lathe Spindle Encoder Recommendations  (Read 24441 times)

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Offline Hood

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #10 on: July 09, 2009, 07:28:21 AM »
A huge disadvantage of an AC servo is that my wife will kill me if I spend any more money on this CNC project . . . LOL!!


Tell her once you have it perfected you will be able to make all sorts of fancy ornaments for the house and jewellery for her, that should allow you some tinkering money ;)

Hood

Offline Dan13

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #11 on: July 09, 2009, 09:48:21 AM »
Simpson,

This is true for any DC brushed motor. You may want to review this link:

http://lancet.mit.edu/motors/motors3.html#tscurve

Actually, it is even true for AC servos, but the torque of an AC servo doesn't fall that rapidly with increasing the speed as in DC motor, and the motor can still deliver torque at its max speed. Thus, practically an AC servo may be considered as delivering a constant torque through its practical operation speed range.

Haven't heard about the superior holding power. I think the same power rated DC and AC servo would have the same holding capability.

Yes, AC servos are quite expensive. I'm looking for one as well to replace the DC motor on my mill's spindle and can't find anything reasonably priced for my pocket...


Daniel

Offline simpson36

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #12 on: July 09, 2009, 11:26:22 AM »

It is really only useful to speak in terms of power. Torque is a static measure, and has no meaning by itself. For example torque being zero at max speed is not meaningful because that is no load speed and the motor is not doing any work. As soon as you place a load on the motor, it slows but begins to produce a measurable torque. The more load is placed on it, the more static torque it produces,  hence the torque curve you referenced.

Some confusion results when torque is discussed as if it is power. Seems I have contributed to that in this instance. Power is what moves things and power is work done over time. In the case of motors, power is torque x RPM so the faster the motor rotates the more power it is generating until the point where the torque is dropping faster then the speed is increasing.

In the case of steppers, the torque falls off very quickly per speed increase and therefor they are actually making significantly less power the faster they go. Servos on the other hand, continue to make relatively contant power over their RPM range. From the actual power curves I have looked at for servo motors specifically (as opposed to a regular DC motor as for a treadmill, etc) the motors are not linear in response. That supposedly is the difference in a servo motor and hence the high cost comparatively speaking.  The skewed rotor designs have something to do with that, but that level of tech is over my head.

I don't know how or why AC motors are different performance wise, but I have read in enough places (including manuf who make both types) where the AC motor's superior holding power are cited as as justification for the higher cost, that I believe their must be some credibility to that claim.


Offline Curtis_F

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #13 on: July 09, 2009, 12:00:34 PM »
Thank you for all the replies!

Sounds like an AC Servo is the way to go.

There is some posistional data loss when using anything but a direct drive coupling system, but if Mach 3 will work with a Servo that'll be more than close enough for my work.

-----------------------------------------
Curtis,
Curious, what are you turning at 30,000 RPM??
Rich,

I, and a bunch of my friends, do model building that often requires very small pins and screws.  Here's what I posed on the CNCZone.com forums when asked this same question:
Quote
The Machinery's Handbook 26th edition says; when cutting Brass with a Carbide cutter the optimal Surface speed is in the 440 to 1170 Feet Per Minute range.

The major diameter of a #0 thread is: .060"
The major diameter of a #2 thread is: .086"
The major diameter of a 1/2" thread is: .500"

Therefore:
Optimal RPM for turning the major diameter of a #0 screw is: 28,000 to 75,000 RPM
Optimal RPM for turning the major diameter of a #2 screw is: 20,000 to 52,000 RPM
Just for comparison;
Optimal RPM for turning the major diameter of a 1/2" screw is: 3,400 to 9,000 RPM

After researching bearings a little I found that the off-the-shelf ones of the size needed to fit around a 5C collet spindle (45mm I.D.) topped out at a little over 30,000 RPM if oil lubrication is used.

Here's a link to the thread at the CNCZone if you're really bored. :-)  http://www.cnczone.com/forums/showthread.php?t=84133

---------------------------------------------------

You should check out the thread "Success, mini machining center . . . " in this forum. I just finished building what amounts to a lathe head using a 5C spindle and it is servo driven. You might get some ideas there.
I'm going to read that right now!


Thank you again,

Curtis F.

Offline simpson36

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #14 on: July 14, 2009, 09:34:50 AM »
Just an FYI . . 

I am awaiting a new servo drive from a company called American Motion Technology. That same company makes a very reasoanbly priceS ($180)  AC servo DRIVE as well as matched small AC servo motors. I have not found pricing on the motors, but they seem to be new and have not made it into the product lineup for the US.

Might be worth a look see.

http://www.americanmotiontech.com/Products/

Offline Hood

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #15 on: July 14, 2009, 09:47:34 AM »
Thats Leadshine stuff, Chinese, but the stepper drives certainly seem to work well so no reason to think the Servo ones be different :)
Hood
Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #16 on: July 14, 2009, 10:16:43 AM »
Might be worth a look see.

http://www.americanmotiontech.com/Products/

I checked the link out and it does not seem very clear as to if they are true AC servo's drives or DCBL, they do use UVW hall input commutation, which occasionally is used by AC sinusoidal at start up, rather than continuously as in DCBL.
They mention a trapezoidal test signal.
Nosmo

Offline simpson36

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #17 on: July 14, 2009, 11:41:56 AM »
Hood,

The factory is ISO 900x in contrast to some of this stuff that seems to be made with a soldering iron at the Kitchen table . . . not saying there is anything wrong with that, but ISO certs are not handed out like candy and I woud not be surprised if China now has more of them than any other country. You know where the money is coming from for the stimulus, yes?

NosmoKing,

I only wish I had a clue what you just said . .  :-[

EDIT: Seems you know your way around the AC servo areana. Any chance you might cruise ebay and pick out a couple of (hopefully sub $100) motors that would be compatable with the Leadshine AC drive?
« Last Edit: July 14, 2009, 12:05:08 PM by simpson36 »
Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #18 on: July 14, 2009, 01:26:53 PM »
I looked at the manual this time and it appears they are AC servo drives, they use the hall effect commutation pulses to start up and then use the encoder for commutation, so you need to look for a AC or DCBL motor that has encoder and the 3 Hall effect outputs which now a days has them simulated on the encoder disk, so you also need a motor with encoder with these features.
When looking for a motor, beware that many AC motors have resolver, which cannot be used with these drives.
I look for Tamagawa, or Applied Motion, which are the same motors, also good,  Aerotech, DMC, & Reliance, which are now owned by Allen-Bradley.
And it also depends on what torque range you need.
There are many Yaskawa motors, which are supposed to be excellent but I have never personally used these.
I would get the 60v versions as the drive is 80vdc max and they also state to not used any supply that is more than 5v of the rated motor voltage.
Nosmo

Offline simpson36

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Re: Mach 3 & Lathe Spindle Encoder Recommendations
« Reply #19 on: July 14, 2009, 01:53:13 PM »
I really do appreciate your effort, but you're over my head. I'm going to need to do a lot of homework on this topic obviously.

If I want to dabble in the AC servo game, I should start with a NEW drive and motor from the same company.

Check this out!  Already set up to work with MACH3!  Do you have any opinion on this?

http://www.dmm-tech.com/Pricing.html