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  #1  
Old Tue 18 November 2008, 18:09
chrisd7306
Just call me: Chris
 
Melbourne
Australia
Same torque, different sized frame

Hello All,
I have the choice of some stepper motors that have approx. the same
torque but have different sized frames ( 60mm Vs 85mm).

The 60mm frame spec. is:-
1) new high torque hybrid motor
2) holding torque 31 kg/cm (430 oz.ins)
3) 60 x 60 face , 88mm long, shaft dia. 6.35mm (1/4 in)
4) 8 wire
5) 4.2V, 2.8A/phase, 6.8 mH inductance, 840 gm.cm2 rotor inertia
6) 1 kg.cm detent torque
7) 1.4 kg weight
8) 1.8 degree step angle

The 85mm frame spec. is:-
1) new hybrid motor
2) holding torque 31 kg/cm (450 oz.ins)
3) 85 x 85 face , 98mm long, shaft dia. 12.7mm (1/2 in)
4) 8 wire
5) 2.0A/phase, 18 mH inductance, 1400 gm.cm2 rotor inertia
6) 1.2 kg.cm detent torque
7) 2.3 kg weight
8) 1.8 degree step angle

Question 1: What are the advantages/disadvantages of having a small
frame over the large frame?

Question 2: Which would last the longer in service?

Question 3: Is larger better?

Question 4: Will the smaller motor be "much more stressed" due to the
loss of bulk in the motor

Some of the advantages that I see is that:-
1) the small motor will be able to accelerate/de-accelerate quicker
due to the lower internal inertia.
2) heat will disipate much quicker in a small motor
3) less mass on y and z axis

I have noticed that the new generation of stepper motor is much
smaller that those of 10 years ago and the performance has greatly
increased.

I have looked at the Vexta stepper motor catalog and a similiar
comparision is between the PV series, 2 phase motor and the standard
PK series motor but there are no details given on the advantages of
using the PV series over any of the other series of motor.

I would like to hear what other people who have possibly experienced
the differences or could enlighten me on issues that I have not
considered.
[Each motor will use a 3.6:1 belt drive reduction unit to drive each axis]

In Australia there are no agents for the Vexta stepper motor. Most of the stepper motors I have seen are from China and seem to be reasonable in quailty and price

Thanks for any help

Cheers
Chris
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  #2  
Old Tue 18 November 2008, 20:04
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The small shaft will not like to have side loads from belts or gears - good for mounting direct to ballscrews. For questions 2,3,4 I don't see any obvious difference.

However, I have a hard time believing the published spec of the small motor . . . . .
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  #3  
Old Tue 18 November 2008, 20:50
chrisd7306
Just call me: Chris
 
Melbourne
Australia
Gerald,
Please refer to Vexta catalog - page C224
The specs for the PV269-02AA and the PV269-D2.8BA are very similar to the quoted above values. According to the documentation, these motor on the average produce 1.5 times the torque of the standard stepper motor.
This looks like the next generation of motor, smaller but with much larger torque!!!
This is why I have posted this question, is a larger frame better?
Cheers
Chris
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  #4  
Old Tue 18 November 2008, 21:40
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Chris, you would have to give me a link to the catalog, they have different versions all over the world.

It is easy to get more torque from a small motor - push up the current & voltage. Which will of course make a motor much hotter.
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  #5  
Old Wed 19 November 2008, 02:00
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Have dug up some specs:
Attached Images
File Type: gif Clipboard03.gif (33.6 KB, 273 views)
File Type: gif Clipboard04.gif (34.0 KB, 273 views)
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  #6  
Old Wed 19 November 2008, 02:25
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
When you started this thread, you mentioned 2 different frame sizes giving similar torques. . . . .

What you might be missing is that for a particular frame size, the rotors can be single, double, triple or quadruple stacked. This more or less means the number of magnet sections on the rotor and it directly affects the rotor inertia and motor length. Notice how the inertia goes up in distinct steps, and check the length (and mass) dimensions of those motors. (The photos in the Vexta catalog do not show the differences in length)

From the specs above, you can see a quadruple stacked Nema 23 is in the same torque class as a single stack Nema 34
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