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  #1  
Old Thu 12 March 2009, 06:06
MachineMonkey
Just call me: Kalo
 
Marysville
United States of America
Ordering parts: Marysville, CA-USA

The story so far:
Have ordered the "Sweet Home..." set through Joe. Arrival scheduled for Monday, March 16.

Planning to order:

From Keling--
4 x KL34H260-42-8B Steppers
4 x G203V drives

From Antek--
1 x 8N63R12 Power Supply

From PMDX--
1 x PMDX-122

First fabrication projects:
4 x 3.6:1 timing belt torque multiplier ala JR Hatcher
1 x Make or modify control cabinet

Found parts:
1 x 10x5 plasma table skeleton to use as machine base

Pix to follow next week.

Thoughts?
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  #2  
Old Thu 12 March 2009, 06:26
Jayson
Just call me: Jayson #18
 
Horsham
Australia
How about good luck and looking forward to seeing it come together.
Apart from that I am of no help at all since I am not familiar with the parts.

Jayson.
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  #3  
Old Thu 12 March 2009, 10:09
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The voltage on the power supply seems to be too high unless you wire the motors bipolar series. The KL34H260-42-8B motors are rated 1.65 mH inductance for bipolar parallel or unipolar (half-coil) wiring. 32 X SQRT(1.65) = 41VDC maximum. Unless you are planning to wire the motor bipolar series (which limits speed), a power supply in the range of 35VDC to 40VDC would be better.

The KL34H260-42-8B motors are rated at 400 oz*in when wired bipolar parallel and 282 oz*in when wired unipolar (half-coil). Most motors, when wired parallel, run hot.

I would pick a slightly larger motor, such as the KL34H280-45-8B motor which is rated at 637 oz*in parallel and 450 oz*in unipolar. With a 3.6:1 belt drive, the larger motor when wired unipolar (half-coil) would give you about 1,000 oz*in of torque, which is slightly higher than the popular PK296A2A-SG7.2 geared motor from Oriental Motor. The smaller motor would give you slightly less torque than the PK296A2A-SG7.2 motor. Personally, I would prefer more torque, especially when the difference in price is minimal.

The larger motor is rated at 2.2mH inductance, so a power supply from 35VDC to about 45VDC would work. The PS-6N38 from AnTek would be a good fit if you wire the motor unipolar (half-coil). Wiring the larger motor half-coil and using a 3.6:1 belt-drive would be my choice if I used a non-Oriental Motor stepper motor.

The cost to add a belt-drive to a non-geared motor will probably be higher than buying the PK296A2A-SG7.2 motors that others are using. I've built several models of belt-drive transmissions. A belt-drive works very well, but the Oriental Motor geared motors are a lot less hassle to install.
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  #4  
Old Thu 12 March 2009, 12:33
MachineMonkey
Just call me: Kalo
 
Marysville
United States of America
Richard,

Got it. My plan is to wire these bipolar series (and eat the top-speed) while leaving room for upgrading to a bigger motor in future. Assuming I stay with NEMA-34 (and I see no reason not to), the 3.6 belt drives will serve those motors in half-coil just as they will these in series. The power supply will also serve a larger motor set (within reason). Finance influenced these decisions a bit: voltage is cheaper than current.

These motors with belt reduction will give quite a bit more torque than the Orientals, even if I choke the pulley ratio down a squoshe or two.

As far as the relative difficulty in installing a belt reduction set rather than a factory-mounted gearbox, you are clearly correct. But I don't agree these hobby-built belt drives will run more that $150 each in frustration and parts.

I appreciate your input.
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  #5  
Old Thu 12 March 2009, 23:54
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
In checking some of my older notes, when I was comparing bipolar series to unipolar (half-coil), the bipolar series wired motors really bogged down at speeds as low as 200 RPM and none tested well at 500 RPM. The unipolar (half-coil) connected motors easily hit 1,000 rpm and most didn't start to complain until they were pushed past 1,500 RPM. With only a spring scale and some nylon twine available to test torque, my methods were too crude to give printable data; however, at 200 rpm (or slightly higher), the bipolar series wired motors gave up on doing any heavy work. The unipolar (half-coil) wired motors had plenty of torque at 1,000 rpm.

With a 1.25-inch pitch diameter spur gear (25-tooth with my rack), 200 rpm with a 3.6:1 belt-drive transmission is about 218 inches per minute. 1,000 rpm, with the same 3.6:1 belt-drive transmission is about 1,090 inches per minute. That's why I always recommend wiring a motor either unipolar (half-coil) or bipolar parallel.

With Oriental Motor Alpha series 7.2:1 motors, I jog my machine at 15-ips (900-inches per minute). The Alpha AS98 series motors are rated at 80 lb*in torque when coupled with a 7.2:1 gearbox. The motor that you specified, when wired unipolar (half-coil) and driven through a 3.6:1 belt-drive will give about 63 lb*in of torque. The slightly larger motors that I suggested will give you 100 lb*in of torque, which means that a $90 motor, a $150 Gecko, 1/4-of a $150 power supply and a belt-drive transmission will outperform a $1,700 Oriental Motor Alpha geared motor. By the way, the Alpha motor runs at 1,000 steps per revolution and the Gecko driven motors run at 2,000 steps per revolution, so the resulting resolution per step is exactly the same.

A machine that jogs at 5-ips is good, but a machine that jogs at twice that speed for less than $12 difference per motor, is much better, after all if high torque at low speed was the goal, we would all be driving cars with large diesel engines. Somewhere along the way, engineers realized that small engines running at moderate to high RPM outperformed the big engines that some of us fondly remember from the 1960's. Stepper motors are similar. A moderately sized motor running fast (and hot) performs very well.

Last edited by Richards; Thu 12 March 2009 at 23:56..
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  #6  
Old Fri 13 March 2009, 06:21
MachineMonkey
Just call me: Kalo
 
Marysville
United States of America
I had no idea the wiring differences were that stark.

I'll crunch out those numbers this weekend.

Thanks.
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  #7  
Old Fri 13 March 2009, 14:42
MachineMonkey
Just call me: Kalo
 
Marysville
United States of America
Richard,

When I read your posts about determining working voltage, I characterize your use of Mariss' formula for RPM{max} to be

(k * root(H))/(H*A{phase})

When I read your real world results, you seem to be living closer to k=1000 than 750. I was under the impression you greatly preferred using a k-factor of 750 to maximize motor life. Have your thoughts on this changed?

-K
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  #8  
Old Fri 13 March 2009, 18:45
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I use the formula 32 X SQRT(Inductance) to figure the maximum voltage, then I multiply that by 75% to 85% to get a voltage that is a good compromise between heat and power. Speed is checked on the test bench. With the Oriental Motor stepper motors that I have, that reduced voltage still lets those motors spin faster than I would ever have use for on a CNC router. (No matter how fast I can make a motor go, I still have to live with the quality of the cut.) Usually 5-ips is about as fast as I cut MDF and melamine coated particle board. Lumber cuts much slower. Plywood depends on the mind-set of the wood sprites.

Even jogging doesn't always have to be at top speed. My machine will jog at 30-ips, but I jog it at half that speed. Fifteen-ips gets the cutter from point-A to point-B without destroying the equipment.

I look at low-cost stepper motors like others look at light bulbs. They are meant to be used up. Although I've never burned up a stepper motor, it's not because I haven't tried. They are robust. If the case temperature is 65C or lower, I'm happy. If the temperature climbs above that, I start to worry.

All of the motors that I've wired half-coil at 75% to 85% of maximum voltage, run at 60C or lower. They also run at speeds faster than I will ever use on a CNC machine. 500 RPM, with a 3.6:1 gear ratio and a spur gear with a 1.25-inch pitch diameter will produce 9-ips. 500 RPM is just loafing along. Just because the motor will go 2X, and even 3X faster, doesn't mean that it has to be run at those higher speeds. However, if I had to settle for 200 RPM or even 250 RPM when I knew that 2X that speed was a reasonable expectation, I would be disappointed.

Before Gerald got me interested in Gecko stepper drivers a few years ago, I didn't expect much performance out of a stepper motor. But, after reading his posts and then playing with more than twenty-five motors, I've gained a lot of respect for what a stepper motor can do when driven with the proper power supply and the proper stepper driver.

Because Oriental Motor stepper motors have always been reliable for me and because I've personally toured the plant in Los Angeles where some of the motors are assembled, I stick with that brand. When a motor has a life expectancy of at least three-years (and very probably 2-3X that long), saving one or two pennies a day isn't worth the trouble. The last thing I ever want to have happen is to lose a customer because my machine went down because I was trying to save $0.03 a day per motor. It's not unusual to wear out a $40 cutter every day and to cut twenty or even thirty sheets of material a day. At an average price of $25 per sheet for MDF, that comes to between $600 and $700 a day for materials, or about the same as four non-geared Oriental Motor stepper motors.

Please note that I'm not trying to discourage anyone from using other brands of motors. Some brands may be better and some may be worse. I just don't have the time or resources to test all of the available motors.
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