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  #1  
Old Thu 18 October 2007, 16:23
cbboatworks
Just call me: Gene
 
Wilmington NC
United States of America
Should I buy these "surplus" motors?

Another Motor question

I have a chance to buy a few stepper motors for next to nothing. Can someone take a look below at the spec. and tell me if I can use them? I am building my control box now and I have every thing but the motors to start. these motors are close by an may get me through until I get my motors I will be using on the MM. Thanks

Frame Size: 34
Shaft Diameter (inches): 0.5
Shaft Style: w/flat
Second Shaft Diameter: 0.5
Second Shaft Style: Round
Torque Rating (oz inch): 595
Current Rating (amps): 3.0
Resistance (ohms): 0.8
Voltage: 2.5
Inductance (mH): 8.5
Winding: bipolar - 4 wire
Steps per revolution: 200
Degrees per step: 1.8
Length (inches): 3.15
--------------------------------------------------------------------------
Frame Size: 34
Shaft Diameter (inches): 0.5
Shaft Style: w/flat
Second Shaft Diameter: 1.5
Second Shaft Style: Round
Torque Rating (oz inch): 920
Current Rating (amps): 7.0
Resistance (ohms): 0.3
Voltage: 1.8
Inductance (mH): 2.4
Winding: bipolar - 4 wire
Steps per revolution: 200
Degrees per step: 1.8
Length (inches): 3.83
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  #2  
Old Thu 18 October 2007, 17:37
driller
Just call me:
 
nope, they are no good.
can you send me the name and phone number of the seller so I can jump on them really quick ?


Just kidding.

they sound pretty good. get them. they will be useful.

Dave
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  #3  
Old Thu 18 October 2007, 18:06
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The problem, as I see it, is that because the motors are so different, you might have to use two different power supplies. The first motor could use a power supply up to 80VDC since 1000 * SQRT(0.0085) = 92.2. Using Gecko's formula to determine the size of the current limiting resistor, 47 * 3) / (7 - 3) = 35.2K, so a standard 33K resistor would work. The second motor could use a power supply up to about 50V since 1000 * SQRT(0.0024) = 48.9; however, I would run that motor with a power supply of 35V to 40V to keep the heat down. Also, even though the motor is rated at 7 amps, I would limit the current to 6 amps because of heat. You would loose a little torque, but that motor has torque to spare. A 270K or 300K current limiting resistor would give you about 6A.

If I had to use those two dissimilar motors, I would run both motors from a 35VDC power supply before installing two different power supplies.
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  #4  
Old Thu 18 October 2007, 18:32
cbboatworks
Just call me: Gene
 
Wilmington NC
United States of America
I can buy all 12 motors at a real good price. there is 6 of each one. if you were going to buy only 4 or 5 of the motors which ones would you recommend? Thanks for the replies.





Quote:
Originally Posted by Richards View Post
The problem, as I see it, is that because the motors are so different, you might have to use two different power supplies. The first motor could use a power supply up to 80VDC since 1000 * SQRT(0.0085) = 92.2. Using Gecko's formula to determine the size of the current limiting resistor, 47 * 3) / (7 - 3) = 35.2K, so a standard 33K resistor would work. The second motor could use a power supply up to about 50V since 1000 * SQRT(0.0024) = 48.9; however, I would run that motor with a power supply of 35V to 40V to keep the heat down. Also, even though the motor is rated at 7 amps, I would limit the current to 6 amps because of heat. You would loose a little torque, but that motor has torque to spare. A 270K or 300K current limiting resistor would give you about 6A.

If I had to use those two dissimilar motors, I would run both motors from a 35VDC power supply before installing two different power supplies.

Last edited by cbboatworks; Thu 18 October 2007 at 18:41..
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  #5  
Old Thu 18 October 2007, 19:15
driller
Just call me:
 
I would highly recomend you buy all 6 of one type.

I would buy the larger motor and use 24 volt transformers. that gets you a decent 35 volts. very easy to find 24 volt transformers.

I would get all 6 motors just in case you ever needed a spare or two. remember, you can always add a rotary unit to make spindles. needs a stepper.

And since you have one extra, just send it along to dave at......

Dave
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  #6  
Old Thu 18 October 2007, 21:18
GregW
Just call me:
 
Quote:
Originally Posted by cbboatworks View Post
I can buy all 12 motors at a real good price. there is 6 of each one. if you were going to buy only 4 or 5 of the motors which ones would you recommend? Thanks for the replies.
Hey Gene, Buy them all and then build some smaller machines for lighter work. Keep spares on the shelf! Just my 2 cents if the prices are right.

Greg
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  #7  
Old Fri 19 October 2007, 03:00
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The Shopbot machines that I'm familiar with use geared motors that would be in the 300 oz*in range (without gears) and non-geared motors that are about 600 oz*in, so I would favor the first motor in your list. Also, after looking at the specs again, I noticed that the first motor has a voltage rating of 2.5V and an inductance rating of 8.5mH. Using the inductance rating to compute the power supply's voltage gives a much higher number than just multiplying the voltage rating by 20X to 25X. None of the motors that I use have that characteristic. What I'm trying to say is that, based on my own experience, I would try a power supply of about 35V to 40V for the first motor on your list.

Before Mariss posted his formula that uses inductance to compute the maximum power supply voltage for a motor, I used the ball-park figure of 15X the motor's rated voltage to compute the power supply's voltage. For me, that gave a voltage that kept the motor at a reasonable temperature and still gave excellent speed. In your case 15 X 2.5V = 37.5V.

As to the second motor on your list, to me it is too big. Although the Gecko stepper drivers are rated for motors drawing up to 7A, I've found that motors with a current rating of 3 to 4.5 amps run the smoothest and still have adequate torque. My favorite motor, the PK299-F4.5 is an exception to that rule. That PK299-F4.5 motor is an eight wire motor that I wire in bipolar parallel mode with the current limiting resistor set for 6A. However, it's bipolar series rating is 3.18A, so perhaps that motor even falls within the 3 to 4.5A catagory if it were wired as if it were a four-wire motor.

The sad fact is that by buying untested motors, you might find yourself spending a lot of time and a lot of money experimenting with electrical components before you find the 'perfect' combination of parts that work reliably for you.
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