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  #31  
Old Tue 23 February 2010, 06:19
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by KenC View Post
BTW, regarding you transformer rating, 300VA is "enuf", more is better, & 999kVA is even better, tranny are never too small as long as you have the cash to splurge & the space to house it. Its your choice.
Big transformers trip the mains supply when you switch them on . . . . .
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  #32  
Old Tue 23 February 2010, 06:24
KenC
Just call me: Ken
 
Klang
Malaysia
That is where the extra cash & space comes in handy for additional control equipments for the obscenely huge tranny
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  #33  
Old Tue 23 February 2010, 06:27
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Stepping motors pull the most current when they're running fast and pulling a full load. If you have six motors that are each rated at 6A, you wold assume that you need a 24A power supply, but you would be safe with a 24 X 66% = 16A power supply.

As Ken pointed out, the numbers are not exact. Gerald had written many posts about sizing power supplies. He recommends using 66% of the rated current when sizing a transformer.

Your 25V + 25V, 300 VA transformer can provide 12A. (12A X 25V = 300VA) If you already have that transformer, use it. If the transformer gets too hot, then try a 500VA model. Be sure that you have a large enough filter capacitor(s). You'll need about 25,000uF. Also, be sure that they're rated at least 125% of the working voltage (62V). The irregular load placed on the power supply components is hard on capacitors. It's better to over specify the capacitors rather than have an equipment failure because of a $30 part.
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  #34  
Old Tue 10 July 2012, 17:36
litemover
Just call me: Chris
 
Auckland
New Zealand
I have a question, if I were to use the PK296F4.5a with 4:1 belt reduction, would I get cleaner cuts on plastic than the PK2997.2 with belt reduction - and which belt reduction would I go with the PK2997.2? I've really wanted to use Oriental Motors on this machine, but if they aren't that great in comparison to the keeling, I'd consider using the kelling. Just trying to decide.

This is for accurate, clean cuts in Wood, MDF, and Acrylic.
Thanks,
Chris
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  #35  
Old Wed 11 July 2012, 07:20
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Chris,

I have never heard of the PK2997.2 motor. Do you mean the PK296A2A-SG7.2, or is there another motor that you're thinking of?

All gearboxes have backlash. The SG series may have more backlash than some of the other (more expensive) gearboxes offered by Oriental Motor. Belt-drives essentially have no backlash, but the maximum single-stage reduction is about 4:1, so you would need to build a two-stage belt-drive if you need more reduction than 4:1.

Cutting plastics cleanly, without chatter, is the ultimate test of a CNC router. I've seen cuts made on "big iron" machines that had as much chatter as the cuts that I made on my Shopbot PRT-Alpha.

My advice would be to select motors that will handle the majority of your work and then experiment with cutters, feeds and speeds until you get the best possible cut in plastic.
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  #36  
Old Wed 11 July 2012, 13:08
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Chris,
You can reference my machine which for a period of about 3 months only cut plastic, acrylic, PVC sheet with great success.

OM 7.2 gearbox, 20T pinions, 5HP router, onsrud bits from Hartlauer Bits.

I have pictures up in my build thread of a pocketed 1/2" clear acrylic part I made dozens of without issues.

http://www.mechmate.com/forums/showt...&postcount=301

Last edited by smreish; Wed 11 July 2012 at 13:12.. Reason: added link
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  #37  
Old Fri 13 July 2012, 16:53
litemover
Just call me: Chris
 
Auckland
New Zealand
Quote:
Originally Posted by Richards View Post
Chris,

I have never heard of the PK2997.2 motor. Do you mean the PK296A2A-SG7.2, or is there another motor that you're thinking of?
Hi Mike,

Thanks for the info on this. Yes, I meant the first choice motor that Gerald had specified in the pinned post about motors, the PK296A2A-SG7.2 Sorry. Yes, I will be doing a considerable amount of Plexi/acrylic cutting so am looking for the cleanest motor solution for it.

I also read a post you wrote about the PK296-F4.5a using 4:1 belt drive which looked interesting. Looking at these, they are low torque (360oz/in) /high speed? Does the higher speed make them more practical in a belt drive scenario?

Have also been considering the 640oz motor by Kelling, the $89 one with belt drive. Which of all the solutions would you think would best suit cleanly cutting acrylics and plexi? 4:1 reduction should be fine.
Chris
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  #38  
Old Fri 13 July 2012, 16:56
litemover
Just call me: Chris
 
Auckland
New Zealand
SMreish

Wow, I'm totally amazed at the quality of cut with this plastic. Are those using the PK296A2A-SG7.2 ? Or a different motor with a particular OM gearbox? That is exactly the sort of stuff that I'd be cutting so will check out your build.
Thanks for the info.
Chris

Last edited by litemover; Fri 13 July 2012 at 16:59..
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  #39  
Old Fri 13 July 2012, 18:33
KenC
Just call me: Ken
 
Klang
Malaysia
Or you can build with direct drive & add-on the belt reduction later if you still want to.
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  #40  
Old Sat 14 July 2012, 06:46
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Chris,

The PK296-F4.5A, when used with a 4:1 belt-drive, has about 2X more torque and about 1.8X more speed than the PK296A2A-SG7.2. The belt-drive multiplies the torque by 4X, so you'll have about 1,440 oz*in of holding torque compared with about 700 oz*in for the SG7.2 (limited because of the gearbox).

If you don't mind buying or building a belt-drive, I think you will get better overall performance from a belt-drive.

The Keiling motor that Mike (Metalhead) offers is also an excellent choice.
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  #41  
Old Sat 14 July 2012, 07:30
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
PK296A2A-SG7.2 is 850.00 in Mike's store, the 4.5 series is 138.00 (ish) online. So, for almost a similar cost you can do either within a few hundred dollars of each other.
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  #42  
Old Sat 14 July 2012, 07:47
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Wow -- That is not a current price - Motors are now 260 each plus shipping
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  #43  
Old Sat 14 July 2012, 07:59
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
OK now fixed in the store - Those were a set of NOS motors I had. The motors in the store now are $260 each plus $15.00 shipping.
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  #44  
Old Wed 21 November 2012, 12:04
hevertg
Just call me: Hevert
 
maracaibo
Venezuela
Hello good friends, someone has reference of this engine and the driver? is to assemble my mechmate.

http://www.circuitspecialists.com/ne...gh450A-08.html
http://www.circuitspecialists.com/st...ler-cw250.html
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  #45  
Old Thu 22 November 2012, 10:03
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Hevert,

There's not enough information on those two sites to offer recommendations. The stepper-driver, in particular, is lacking in information. Most common stepper motors move 1.8 degrees per full step (200 steps per revolution). With no gearing and a 1.25-inch spur gear, the resolution would be 0.0196 inches per step. That would never work. Half-step would improve that to 0.0098 inches per step. That is not good enough. Gecko stepper drivers have 2,000 steps per revolution, which would give 0.00196 inches per step (without gearing).

There are so many possibilities and so few resources that, when I get private email asking for my advice on a particular stepper motor or a particular stepper driver, I almost always respond by saying that there are several proven motor/drivers that have been used by many builders. If you pick one of those proven motor/driver sets, you can expect the same results that others have had. If you decide to buy something else, then you'll have to do all of the testing to see if that motor and that driver meets your needs. If you're comfortable experimenting with stepper motors, why not just buy one motor and one driver? Thoroughly test it and if it meets your needs, buy the other motors and drivers.
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  #46  
Old Thu 22 November 2012, 10:25
hevertg
Just call me: Hevert
 
maracaibo
Venezuela
hi richards, thanks for your reply, you're right, the trouble is that I have little experience with stepper motors, better find something that is already used in this MM, thanks friend
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  #47  
Old Thu 22 November 2012, 10:59
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Hevert,

Contact Metalhead (Mike). He sells everything that you'll need to build your MechMate.

Read carefully the "build threads" that describe how others have built the electronics for their machines.

Because I like Oriental Motor stepper motors and Geckodrive stepper drivers, if I were building a minimal machine that did not need a lot of extra inputs and outputs, I would use the Oriental Motor PK296A2A-SG7.2 motors with a G540 stepper controller as the basis for the electronics. I would use a 35VDC to 45VDC power supply. If I needed more inputs and outputs, I would use either the PK296-F4.5A or PK299-F4.5A stepper motors with belt-drives or the PK296A2A-SG7.2 geared motor driven by the G203v stepper driver and a PMDX breakout board. The power supply would be 35VDC to 50VDC depending on the motor.

The most important thing that you should do is to read the posts until you are familiar with how others have built their machines.
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  #48  
Old Sat 01 December 2012, 09:22
hevertg
Just call me: Hevert
 
maracaibo
Venezuela
Hi Richards, reading some post, I saw that you were talking of Oriental Motor PK296A2A-SG7.2 and transmicion box of 7.2:1. you were saying that it is better to use email gearbox with 4:1 would 1400oz in, but the PK296A2A-SG7.2 is limited by its gearbox and less serious in oz? that's true?

mike, you shop online? link?

Last edited by hevertg; Sat 01 December 2012 at 09:29.. Reason: mike, you shop online? link?
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  #49  
Old Sun 02 December 2012, 13:46
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Helvert,

The PK296A2A-SG7.2 motor has a 7.2:1 gearbox attached to it. The motors that I've tested had minimal backlash. Some users have reported that the backlash increased with usage and that the increased backlash is too much for accurate results. The gearbox is rated at 40 in*lbs (640 oz*in).

A belt-drive transmission has no backlash if the belt is properly tensioned; it also allows all of the motor's torque to be multiplied by the transmission's ratio. A 4:1 transmission would increase the torque by 4X. A 3:1 transmission would increase the torque by 3X.

I prefer the belt-drive transmission; however, it is more expensive to build and it is bulkier than the PK296A2A-SG7.2 motor/gearbox.

Send metalhead (Mike) a private email to get information about the products that he sells. I think that you have him confused with me. I highly recommend that you buy whatever you need from him. He has had me test some components for him, so I know that he has done his best to find high quality parts for your MechMate, and then had those parts tested to verify that they worked as advertised.
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  #50  
Old Mon 03 December 2012, 06:16
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Here is my link

http://www.cvsupply.com/servlet/the-MechMate/Categories
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  #51  
Old Sat 29 December 2012, 04:54
Bob Cole
Just call me: Bob
 
Berlin Center, Ohio
United States of America
Are these any good?

I am about ready to start assembling my electronic components for my build. I no very little about the overall dynamics of this part of the build.

I have the mechanical aptitude do do any of the construction and fitment to complete this project, my hold up is the electrical side.

I have been reading and watching so much stuff about the electrical that I am COMPLETELY lost. I want as much as is possible to just buy the components, run the wiring per instructions, and get this going.

As I have been languishing on the side lines for several years now, it looks like this winter I will have time to get my build in gear.
So, I was looking on line for DEALS? [are there any really}, and I located a number of companys that are offering complete component set ups on eBay for what seem like very reasonable prices.

Here is one I would appreciate an evaluation on from the great electronic minds we have on this board.

http://www.ebay.com/itm/free-shippin...item4166c5f264

I am planning right now to go direct drive [NO GEAR BOX, no belt drives].

Is this a proper approach?
And would this set up or a similar one work? I am planning a 4'x8' work area on the MM, with about a 8" Z- travel.
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  #52  
Old Sat 29 December 2012, 05:55
ger21
Just call me: Ger
 
Detroit, MI
United States of America
Those kits deliver extremely poor performance. I've seen someone using a similar kit to that on a non mechmate homebuilt machine. He ended up switching to Gecko drives and 400oz motors (4x smaller) and got about 5x better performance.
Whenever I see someone trying to save money on motors and drives, they almost always end up replacing them, which costs nearly twice as much in the long run. I'd stick to what's been proven to work well over the years. The slightly higher initial costs are well worth it.
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  #53  
Old Sat 29 December 2012, 07:10
Bob Cole
Just call me: Bob
 
Berlin Center, Ohio
United States of America
What would you attribute the poor preformance too?

Are the motors [according to their quoted specs] not up to the job? Or is it something else in the equation that wold be an issue?

Is my idea of going direct drive a possible problem as regards finish milling quality?

PS Thank you for your reply
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  #54  
Old Sat 29 December 2012, 07:34
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Bob,
The answer to your question is very involved.
The VERY quick response based on the cost/value of that package - around 630.00 is that it might not be that good of a deal.
The very large Nema 34 like you have found, have challenges with performance.

Direct drive is not an issue - the original MM and many others are using Direct drive. The issue with any direct drive system is resolution. With the addition of a belt drive transmission 3:1, 4:1 or a 3.6 or 7.2 gearbox, you gain resolution and still maintain usable speeds. The belt drives or direct drive have limited back lash which is a plus for some CNC applications.

IF I was to go direct drive, I would use the G540 gecko all-in-one controller and either a Gecko stepper or one from http://www.kelinginc.net/NEMA34Motor.html

With any of those choices, you must pay keen attention to the inductance (mH) matching of the drive to the motor. Refer to the Mariss formula at the Gecko website or the sticky thread on the forum *how to choose your motors* for detailed math explanations.
The G540 includes the Computer breakout board in the cost of the G540. You could use that savings to buy the transmission plates or more expensive, correctly matched motors and have the best of both worlds.

Good luck with your choices.

Sean

Last edited by smreish; Sat 29 December 2012 at 07:39..
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  #55  
Old Sat 29 December 2012, 08:51
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
This is not a place to cut corners really. You read over and over folks having to re-buy drive systems. Look at proven systems. The 640oz direct drive motors, PMDX-126 and Geckodrive systems will give you a platform that will perform direct drive as well as position you to go to belt drive when/if you ever want to. It will also give you a system that many (not just here) can support. Oh - don't cut corners on wire quality either.
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  #56  
Old Sat 29 December 2012, 12:30
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
I second Sean's advice, with the caveat that at the moment, Gecko doesn't have any NEMA34 motors that match well with the G540, and Keling has a perfect match (look for the one that says it) at $70. 4 x $70 + $300 = $580, which is pretty tough to beat. I'd add the transmissions.
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  #57  
Old Sat 29 December 2012, 13:54
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Brad,
Thanks for the followup. I actually have ordered those Keling's for my next machine. I have the g540 and will use the 3:1 belt drive. Mixing it up this time around!
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