Upscaled Motor Advice

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theshrub
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Upscaled Motor Advice

Post by theshrub » Sat Feb 16, 2013 3:27 pm

Hi All,

I'm going to be building an upscaled shapeoko (1m x 1m) and need a bit of advice.

I am in the middle of trying to work out what electronics i need and have decided upon a smooth stepper into a breakout board and then will probably use drivers such as these: http://www.ebay.co.uk/itm/CNC-Kit-5-Axi ... 04f&_uhb=1.

I would like to go as large as i can get away with on the motor front but i'm not sure how far i can go. Could i use these for example: http://www.ebay.co.uk/itm/New-Nema-23-S ... vi-content, weighing in at 1.2kg and 306 oz/in.

Is this too big and if so how big can you sensibly go?

What have other builders used and has anyone "gone too far"?

I will be using dual y motors and dual x rails. I will also be looking to support the y rails as here: http://www.shapeoko.com/forum/viewtopic.php?t=645, and will be cutting pieces of hardwood as well as looking to do finer inlay work. I will also be using a kress 1050 spindle which may add to the weight issue on the gantry?

Thanks,

Shrub

jsbannis
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Re: Upscaled Motor Advice

Post by jsbannis » Wed Feb 20, 2013 9:50 pm

I'm not certain why you want to use such large motors. User ImprobableConstruct is running a scaled up 'oko similar to that size, and is still using nema 17s if I remember correctly. Adding that much weight to the gantry is just going to make it require more power and supporting electronics to maintain the same speeds. The delrin v wheels also have a weight limit, but you should be below that in any case.

I think that huge motors like these will add more problems than they'll solve. A good set of medium holding strength 23s is more sensible and should be adequate for all that the rest of the machine is capable of cutting.
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Improbable Construct
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Re: Upscaled Motor Advice

Post by Improbable Construct » Wed Feb 20, 2013 11:07 pm

I was rocking some NEMA 17 69 oz/in motors on my up scaled shapeoko, and they were just fine.
I was building another shapeoko though and thought why not try NEMA 23s.
I had to buy new pulleys anyway so I picked up some 175 oz/in motors and swapped out the NEMA 17s.
I don't really notice much of a performance difference, but it does make a lot more horrible noises if/when you crash the gantry.
At 175 oz/in the motors have way more power than the mechanical can ever handle.
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WillAdams
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Re: Upscaled Motor Advice

Post by WillAdams » Wed Feb 20, 2013 11:15 pm

Would a NEMA 23 motor be appropriate for the Y-axis on a Shapeoko w/ a drive shaft?
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cvoinescu
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Re: Upscaled Motor Advice

Post by cvoinescu » Wed Feb 20, 2013 11:30 pm

A small NEMA23 (125 oz in) is only moderate overkill. I think NEMA17s are enough, but if you really want to go with NEMA23, stick with the small ones.
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WillAdams
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Re: Upscaled Motor Advice

Post by WillAdams » Thu Feb 21, 2013 12:44 am

cvoinescu wrote:I think NEMA17s are enough
For a dual-drive machine. That's why I was specifically trying to ask about the suitability of using a _single_ NEMA 23 on a unit w/ a drive shaft upgrade.

William
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cvoinescu
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Re: Upscaled Motor Advice

Post by cvoinescu » Thu Feb 21, 2013 3:29 pm

You have a single NEMA17 on the X, and the gantry isn't all that much added mass to accelerate, so do you really need double the torque on Y? I don't actually have the answer to this question. By all means, use a small NEMA23 if you want, and let us know whether it makes any difference.

This is slightly off-topic: when using a dual-motor Y drive, each motor needs to have about three quarters of the torque of the X motor to be able to withstand the same cutting forces in the Y direction at all points of the working area. This is because when milling near max X or min X, one of the Y motors will take most of the force, and the other one only a little. With a shaft dual-drive, the one motor distributes the torque as needed to both ends, so (discounting the extra mass of the gantry) the same torque as on X is sufficient.

I say, then:
  • If you feel you need a NEMA23 on Y with a shaft upgrade, you probably need one on X too.
  • If you have a dual-motor Y and feel you need just a little more force, get a NEMA23 on X and keep the NEMA17s on Y.
    • If you need even more force, get two NEMA23s for Y too.
    • If you need even more force, think before getting heavier motors. You're already using a lot of the load capacity of the V-wheels just to move the motors around. You probably need a different kind of machine.
    • Then again, what's the worst that can happen? V-wheels are cheap.
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theshrub
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Re: Upscaled Motor Advice

Post by theshrub » Tue Feb 26, 2013 8:31 pm

Thanks all,

That's exactly the sort of info i was looking for and makes my decision that much easier. If i go for nema 23's i will keep it under 125 oz/in and let you all know how i get on.

Now i just need to get my head around CAD!! :?

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