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  #1  
Old Mon 08 March 2010, 14:37
Supertechster
Just call me: Steve
 
Denver CO
United States of America
Inexpensive 3-axis driver boards

I want to build one of these - 2 actually... but want to cut cost to the bone to do so, so I am looking for very low prices on parts.

I found this 3-motor driver unit for a good price of $44.00 USD: http://www.chromationsystems.com/sto...roducts_id=207

Does anyone here have any knowledge of or experience with this model?
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  #2  
Old Mon 08 March 2010, 14:53
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
That link doesn't go anywhere, but poking around that site I found a 3 axis driver card that is designed for very small stepper motors and will not work for the MechMate.

At the very least, you'll want something with published specifications. Continue to search section 701 and you'll see some good and bad experiences.

I suspect you'll find after some research that it's difficult to save money building your own drivers for motors powerful enough to drive the MM well. There are several budget options however, available from both US and Chinese suppliers.
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  #3  
Old Mon 08 March 2010, 19:48
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Steve,

Because you are in the United States, your lowest cost high quality stepper driver / break-out-board is the Geckodrive G540.

You can build the MechMate for less than 1/3rd the price that I paid for a Shopbot, and the MechMate will be a better machine.

There's a certain point where cost cutting cuts into the quality of the tool. Don't cheat yourself by buying parts that are not dependable or parts that cannot drive the machine fast enough to make cutting worthwhile.

As hard as jobs are to find nowadays, it should still be possible to find a part-time job somewhere that would pay the difference between junk and quality parts.
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  #4  
Old Mon 08 March 2010, 23:12
Supertechster
Just call me: Steve
 
Denver CO
United States of America
Brad, Mike.... Thanks for the tips.
I went back and looked at that $44.00 one, and even though it is cheap, it uses IRF-xxx MOSFET on the output - basically your/my choice of driver transistor typically giving 50-100v of drive @15-40amps. I still don't know the techspec on it, but it def. caught my eye b/c of cost and it is a BOB and 3 motor driver all in one. Have asked the mfg for details ;-)

I'll look at the Gecko 540 (and other) tomorrow AM and if you want, share all the other Bi- and Uni-polar stuff I've found. Linistepper looked interesting too - Kit of 3 driver boards and 1 ParPort interface for USD$119.99. http://www.piclist.com/techref/io/st...step/index.htm

Thanks again!
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  #5  
Old Tue 09 March 2010, 08:28
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
You can't just up the MOSFET sizes and go. You need to make provision for the extra heat dissipation, and the design of that board doesn't really have room for heat sinks. Those that do generally make arrangement for the MOSFETS to bend 90 degrees so that they can all be mounted to a common backplate, often the driver case. Since that driver doesn't have very sophisticated current management, you're going to have a lot of waste heat.

You see a variant of that physical design on the Linistepper, but it tops at at 2A, and you need to be looking in the 4A range.

None of those hobbiest drives are going to allow working voltages much over 20V or so, and that's going to mean a slow top speed for your motors.

The G540 is very tough to beat in price/performance terms. I'm quite happy with mine.

But we're always open to look at new solutions!

-Brad
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  #6  
Old Tue 09 March 2010, 12:23
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Steve,
You mentioned the board you are looking at is a three motor driver, you will need 4 motor drivers for the MM.

If you want to to the DIY route see www.pminmo.com they have a lot of info on stepper drivers. Many people have build drivers from their info. Compare costs and the Gecko line starts to look more appealing. They also have the BEST customer service in the industry.
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  #7  
Old Tue 09 March 2010, 18:21
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I'm always concerned when price becomes more important than function. I've built several stepper drivers, back when commercial-off-the-shelf stepper drivers cost many times the price of the stepper motor. None of my stepper drivers offered anything other than a cheap price (even including the week that it took to design and the $250 minimum charge for a prototype circuit board back in the 1980s).

A CNC router is a big, robust machine. It takes well designed electronics to make it function properly. Geckodrive has a number of relatively low cost stepper drivers. Those who live outside the United States have found other products that are similar to the Geckodrive products. None of those stepper drivers is cheap. From what I've read, they all work well.

Some people are happy just to see an axis move. A CNC router operator expects that an axis will move, with sufficient torque to cut his material, at 180 inches per minute or faster. Doing that takes power. The 'cheap' stepper drivers that I've read about just aren't designed for that use. They're more suitable for the small mills and lathes that only need 100 oz*in motors.

I would caution anyone who hasn't used high performance stepper motors that trying to save money on the stepper electronics can be both expensive and frustrating.
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  #8  
Old Tue 09 March 2010, 21:41
Supertechster
Just call me: Steve
 
Denver CO
United States of America
Point taken. Thanks for sharing your experiences. I'll forgo the possibility of lackluster performance or crispy-critter parts and invest in something that is proven to handle the workload you describe.

Can you ID a set of good beefy motors for me, to go with the Gecko 540 I have 'nearly' decided to get?.

I understand that the MechMate requires 4 Axis controller for its CNC motion... so most of the stuff I was looking at (3-Axis) is already forgotten.

From what I've gathered, NEMA 24 size 6 or 8 wire motors is what I am after?
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  #9  
Old Tue 09 March 2010, 21:57
KenC
Just call me: Ken
 
Klang
Malaysia
Steve,
Like most things in the market you can only choose 2 of the followings, Price, Quality, Customer service.

To be very specific. MM plans is a 3 axis machine and you can add the A-axis of your own design, the 3 axis consist of 4 motors (2 for X-axis, 1 for Y-axis & 1 for Z-axis), each motor requires a driver. When you add A-axis, you need to add a motor & a driver.

Read here for more stepper motor info.

Hope this helps.
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  #10  
Old Tue 09 March 2010, 22:17
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
I know folks are running the 540 with no issue really, but doesn't the Gecko site stear you away from the 540 for Nema 34 motors above 3.5 Amps?


The below comes from here

http://www.geckodrive.com/upload/G54...4%20MANUAL.pdf

1) MOTORS: One to four step motors are required. All NEMA-17, most NEMA-23 and a few NEMA-34 motors are acceptable. The
motors preferably should be square in cross-section, not round. The motors can be 4, 6 or 8-wire motors. 5-wire motors cannot be
used with the G540. Choose a motor that has a rated current of 3.5A or less. Choose a motor that has a rated winding inductance of
2.5mH to 3mH if maximum power output (>100W mechanical) is a requirement. Never use a power supply voltage greater than 32
times the square-root of the motor inductance expressed in milli-Henries (mH). Using a higher inductance motor will result in a loss of
speed as a higher voltage will be required.
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  #11  
Old Wed 10 March 2010, 06:06
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Mike
True. The choices in the Nema 34 frame size that meet the frugal spec's of the 540 drive are very few. It's just great coincidence that the Oriental Motors packaged with a gear box are a very good match for the MM basic needs.

...just another choice I guess
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  #12  
Old Wed 10 March 2010, 06:14
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Yeah - The 7.2 OM are a good match, but still seem to me to be on the outside edge of the specs.

What non OM geared motor would be a good fit for the 540? For folks building belt drives.


Mike
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  #13  
Old Wed 10 March 2010, 08:18
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I've extensively tested the G540 with my PK296B2A-SG3.6 motors. (My motors have the unneeded rear shaft and they are also 3.6:1 instead of the more popular 7.2:1.) I use a 35VDC power supply and use a 3K current limiting resistor to limit the Amps to 3A.

I've tested the PK296-F4.5A motor at 35VDC and 3A with good results. The larger PK299-02AA motor and the PK299-F4.5 motors were tested at 3A and 48VDC.

My testing shows that even motors that are 'too big' for the G540 can be used with excellent results IF your keep the voltage at 50VDC or lower and IF you limit the current to 3.5A or less.

Using Mariss' formula, the best matches would be motors with an inductance rating below 2.5mH because of the 50VDC limit and Amp ratings of 3.5A or less.

The PK296-02AA motor is rated at 620 oz*in, 3A, and 6mH. I thought that it would run too slowly because the maximum voltage rating for that motor would be 78VDC; however, it easily runs at 1,000 RPM which is faster than you would ever run a CNC router, even if you geared the motor 4:1 with a belt drive.

I haven't tested brands except for Oriental Motor and some older Superior motors that I had, so I can't tell you how other motors would work; but, if the motor's data sheets is accurate, motors that draw 3.5A or less will give you full torque. Motors with a unipolar inductance rating of 6mH or less will still give you excellent speed, even if you limit the voltage to 50V (for motors with more than 2.5mH inductance).

Right now I'm building a 6:1 belt drive for a PK268-02AA motor to test with the G540. That little motor has 190 oz*in of torque, so 6X that would be 1140 oz*in. I've kept away from the size 23 motors because they have a 1/4" shaft and they also tend to hold on to heat more than the larger 34 size motors. The PK296-02AA motor doesn't get hot when I run it from a 50VDC power supply and preliminary tests show that it can easily drive a 3/8" XL size belt (10-tooth pulley on the motor, 60-tooth pulley on the shaft). The torque is almost exactly what the 7.2:1 Oriental Motor Alpha motors provide, so in theory everything should work properly. Running that motor as slow as 750 RPM would still give 10" per second jog speeds.
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  #14  
Old Wed 10 March 2010, 09:22
rayditutto
Just call me: Robin
 
Victoria
Canada
Send a message via MSN to rayditutto
there's a rather short but rich thread . . . Why a stepper motor should not be too big that i keep coming back to (it may be short but the content is rich and i've had to re read it several times)
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  #15  
Old Wed 10 March 2010, 09:28
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
For a non-OM motor for a belt-drive and G540, I would be tempted to consider MotionKing 34HS8801 rated 4 Amp and with 3 mH inductance. data . . . . from the perspective of a kit assmbler, looking for a reliable bulk partner in China.
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  #16  
Old Wed 10 March 2010, 10:04
rayditutto
Just call me: Robin
 
Victoria
Canada
Send a message via MSN to rayditutto
Just last evening i was comparing (but no conclusions yet) the 34HS8801 (425 oz-in) and the 34HS6801 (at approx 300 oz-in) in the context of a 4:1 belt reduction using a G540

cheers,
robin
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