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  #61  
Old Fri 16 May 2008, 05:49
Robert M
Just call me: Robert
 
Lac-Brome, Qc
Canada
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Marc, thank you for sharing this valuable link.
Robert
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  #62  
Old Fri 22 August 2008, 13:08
PEU
Just call me: Pablo
 
Buenos Aires
Argentina
I have a question regarding the Vexta PK292A2A-SG7.2 motor, as suggested in the 1st post Im thinking about purchasing them with a rear shaft for an encoder.
Reading the vexta catalog for series PK2 page C231 I read that the doubleshaft model is the PK296B2A but next to the part number it says its unipolar, am I reading it correctly? or what should be the doubleshaft equivalent of the PK296A2A-SG7.2?

Or it refers on how one wires them? in this case the PK296B2A-SG7.2 should be the motor I need.

Im confused

Thanks!
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  #63  
Old Sat 23 August 2008, 05:18
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The PK296B2A-SGxx is the motor that has the shaft extended out the back. I have four PK296B2A-SG3.6 motors on my test bench. The PK296A2A-SGxx motor is the standard motor without the shaft extension.

Both the A2A and the B2A have the same electrical specifications and the same six wires per motor. Either can be wired full-coil or half-coil, depending on your needs.
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  #64  
Old Sat 23 August 2008, 16:54
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Mike,
I have looked on the oriental motor site for an equivalent pk296a2a with 8 wires but dont see any. I was wondering if they had one so you could run a paralell combination. Or do you think parallel is not needed?
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  #65  
Old Sun 24 August 2008, 08:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
My guess is that since that family of geared motors is limited for torque by their gearboxes, it doesn't make sense for them to give you 8 wires so that you can increase the torque with parallel coils.
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  #66  
Old Sun 24 August 2008, 09:33
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald is right.

A six wire motor can be wired series or half-coil when connected to a Gecko stepper driver. You need an eight wire motor if you need parallel coils.
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  #67  
Old Tue 26 August 2008, 23:11
sprayhead
Just call me: Francis
 
sydney
Australia
Someone able to tell me how much force/Weight a 5N.m motor can hold (holding torque) @ 25mm from the center of it's shaft?

The PK296A2A-SG7.2 gives out 5N.m from 0rpm to ~100rpm.

I am wondering what kind of push (in kilograms) this thing is able to put on the racks, so I can have a better idea of what's really going on.

thanks
Francis
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  #68  
Old Tue 26 August 2008, 23:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
5 N.m = 5 Newton.meter = 0.5 kilogram.meter = 500 kilogram.millimeter

which is 20 kilogram at 25mm
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  #69  
Old Wed 27 August 2008, 00:17
sprayhead
Just call me: Francis
 
sydney
Australia
20.41Kg

Recalculated using G accel.

They are quite good these little motors huh!!! makes me feel good.

Thanks
Francis
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  #70  
Old Wed 27 August 2008, 00:31
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Sounds like you are starting to believe us
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  #71  
Old Fri 10 October 2008, 06:58
sprayhead
Just call me: Francis
 
sydney
Australia
For a heavier Z unit... say it is an extended version, or it is carrying a heavier spindle of a different kind or just some gadget of a different nature...

What are the thoughts of the people on using the PK296A2A-SG18 ?? It has a lot more holding torque then the PK296A2A-SG7.2.... It might even be interesting to use this motor and not use a gas shock on the original project? Proceed?

Francis
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  #72  
Old Fri 10 October 2008, 07:39
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Francis,
Dont forget the reason most people dont go to the higher gear ratios are the fact that to get any decent speed, the computer and paralell port cannot keep up. Mach3 is also limited to the pulse stream it can handle. I would look carefully at the calculations and limitations of the hardware and software first. See Mike Richards post in this thread for more info.

http://www.mechmate.com/forums/showt...8&postcount=64
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  #73  
Old Fri 10 October 2008, 08:30
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Heavier Z

As it so happens, I am not in the process of working on my Z axis. My machine is not the conventional Mechmate design, however, I may have some insight. My Z axis is about 24" long, and weighs about 80#. I originally tried the PK296A2A-SG72, and it would not lift it. I also tried the PK296A2A-SG36 - again, without success. In both cases, either the spur gear slipped on the gear rack, or (when locked into place), the motor bogged down - lifting it a fraction of an inch - then dropping it. I am therefore working with a combination of gas springs to counterbalance the weight. When I installed a single spring (and limited the travel to 13") the SG72 model worked great.

In my case, to offset the 80# weight, I am installing 100# springs.
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  #74  
Old Fri 10 October 2008, 08:41
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Hi Francis,

Take a look at Mike's response to my post in this thread. Valuable information on holding torque.

http://mechmate.com/forums/showthread.php?t=56
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  #75  
Old Fri 10 October 2008, 08:50
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
When your motor is de-energised, the holding torque disappears and the router falls . . . . .

A typical solution for loooong z-slides is a pneumatic cylinder, adjustable pressure regulator and a compressor.
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  #76  
Old Fri 10 October 2008, 21:52
sprayhead
Just call me: Francis
 
sydney
Australia
Jeopardy,

Do you use any parts of the MechMate on your Z axis? Same spider plate and Z slide perhaps? or it all had to be modified to fit both the gas springs? I am scratching my head thinking how to use 2 springs and get them to work together to be effective for the whole length.


Boys,

As far as speed and lack of pulse frequency that should be fine because I intend to use the smoothstepper anyways. My application won't require much in terms of speed from the Z axis, so no visible problems there yet.

Gerald,

I obviously didn't realize that when you turn the motors off the Z slide slides and goes baang, if there is nothing extra to hold it.
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  #77  
Old Fri 10 October 2008, 22:00
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
There apparently are big systems with electric/spring brakes. . . when the system is de-energised, the springs apply brakes to fight the gravity that never de-energises.
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  #78  
Old Fri 10 October 2008, 23:12
sprayhead
Just call me: Francis
 
sydney
Australia
like a Stepper Motor with electromagnetic break? I think I have seen that on Servos.

Another thought I had why the PK296A2A-SG18 would be good is when the Gecko drops to 70% the torque... recirculating.

If one could attach an electromagnetic break to the PK296A2A-SG18 that would be a good solution, I guess.

This thread then drifted to other counterbalance methods:
http://www.mechmate.com/forums/showthread.php?t=1026
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  #79  
Old Fri 14 November 2008, 02:48
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Selecting motors for the MechMate - Revised Nov. 08

A newbie opening this current thread for the first time was confronted with a confusing first post. Two years have taught us a lot about motors and we have settled onto some comfortable choices. I have rewritten that first post and edited/pruned some of the subsequent posts. However, the earlier version of this thread is here in the Archive.
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  #80  
Old Fri 14 November 2008, 07:15
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gerald,
That is a great summary. I especially like the links to other threads on motors, belt reduction and the like. Excellent.
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  #81  
Old Mon 24 November 2008, 02:40
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
My apologies. I had a couple of posts here about confusion of motor specs. I do believe now that the links in the first post go to valid spec pages. There is a grey area with specs from other Oriental Motor sites showing something different, but let me check around a bit before making a storm in a teacup.
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  #82  
Old Mon 24 November 2008, 09:54
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Here is Oriental Motor's numbering system for motors in some countries.

Clipboard01.gif
-----Direct motors --------------------------- Geared Motors-----

The "Rated Voltage" numeral (where the 1 is used in the above examples) is what causes the confusion . . .

If a PK296-03AA motor is coupled to a 7.2:1 gearbox then it becomes a PK296A2A-SG7.2 motor. The 3 becomes a 2 and the voltage rating drops from 2.8 to 2. Since the resistance and inductance values stay the same, the reason for de-rating the voltage is not known. (Some have observed that the geared motors run hotter than ungeared motors - might be because they aren't de-rating the voltage?)

An earlier post in another thread adds to the confusion.
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  #83  
Old Sat 10 January 2009, 08:24
gt68
Just call me: George
 
Korinthos
Greece
Calculations for selecting Stepper motors

What are the calculations needed to end up choosing a Stepper Motor?
If possible, can someone give me a real example so that I can understand the
procedure?
I'm new in this field so I would prefer a simple procedure wthout alot of c
complicated mathematics.
Thanks in advance.
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  #84  
Old Sat 10 January 2009, 17:33
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Sometimes it's easier to just use what others are using. The Oriental Motor PK296A2A-SG7.2 motors are popular. The Gecko G203v stepper driver works well with that motor. A 35VDC power supply is almost ideal when you wire the motor half-coil.

With that motor, you'll get adequate torque, adequate speed and adequate resolution for your cuts. The motors, drivers and power supply will cost about $1,800.

Testing and evaluating stepper motors takes time and some expertise. I can guarantee the it will cost much more than just buying those parts that I've listed.

One of the problems with building a one-of-a-kind machine is that you need to be the chief engineer - the chief electrical engineer, the chief mechanical engineer. Gerald has done all of the mechanical engineering for you and all of the essential electrical. All that is left to do is to scour the forum for the threads that explain why you should do something in some particular way.

If, after reading, you still have some why questions, post your question and those of us who have already traveled that road with help you find your way.
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  #85  
Old Sat 10 January 2009, 21:00
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
George, it is a waste of time doing the calcs unless you know:

1. The speed range through which you want to work the machine.

2. The cutting loads, plus cable and hose drag loads you are going to impose at all points in the speed range.

3. The friction forces versus speed imposed by your lnear bearing arrangement.

* * * * all the above needed for "static" calcs.....then the dynamic calcs:

4. The masses of the moving parts

5. The rate at which you want to change speeds (desired accel / decel.)

* * * * * and then to pick a motor:

6. The full torque vs speed curves of the range of stepper motors that you might be interested in buying.

Have too often seen that guys do "calculations" based only mass, max speed and motor's torque at zero speed.
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  #86  
Old Thu 15 January 2009, 06:01
skippy
Just call me: Paul #72
 
Queensland
Australia
What is the difference between "USA Option" and non USA Option IE PK296A2A-SG7.2 and the PK296A2-SG7.2?

As Australia is in the Asia selling region for Oriental Motor and the web site is in Singapore and only lists the PK296A2-SG7.2 see below. I don't think there is any difference but I what to be 100% sure before ordering.
Attached Images
File Type: jpg OM motor specs.jpg (41.6 KB, 1768 views)
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  #87  
Old Thu 15 January 2009, 06:07
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Paul, can you give a link to the catalogue where you got that info from?
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  #88  
Old Thu 15 January 2009, 06:17
skippy
Just call me: Paul #72
 
Queensland
Australia
Gerald, Here is the link

http://www.orientalmotor.com.sg/imag...PhaseMotor.pdf

The chart is on page 3 and the specs are on page 18 of the pdf
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  #89  
Old Thu 15 January 2009, 07:21
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The electrical specifications on page C-179 for the PK296A2-SG7.2 motor match the specifications on page C-231 for the PK296A2A-SG7.2 motor. The inductance is the same. The resistance per phase is the same. The current per phase is the same. The voltage is the same. Both motors have 6-leads. (Page C-231 has a column listing the leads. Page C-180 shows the number of leads in the dimension drawing.)

Note that the gearbox shaft is different on the two motors. The A2A has a 0.500-inch shaft (12.7mm) with one flat ground into the shaft. The A2 motor has a 12mm shaft with a single key-way ground into the shaft. Also, the rear shaft extension on the B2A motor is 0.500-inch with two flats ground into the shaft. The rear shaft on the B2 motor has a 14mm shaft with two flats ground into the shaft.
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  #90  
Old Thu 15 January 2009, 09:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The motors do look similar electrically (I can't see an inductance value?). Mechanically it will fit.
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