Stepper motor Torque ratings

Bearings/Motors/Belts/Gears/Etc.

Stepper motor Torque ratings

Postby rkovvur » Mon Jan 18, 2010 5:30 pm

I am trying to figure out the size of the stepper motors i should be getting for my setup. My planned area for the laser engraver is 22"x22"

I already have a 5phase stepper with torque (230oz/in). I am planning on using this for y-axis to move the gantry. Will this be sufficient?

Any idea what size motor i should be using for the x-axis? This motor will mount on the gantry and move with it. Should it should be lighter than the y-axis one.

Thanks!!
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Re: Stepper motor Torque ratings

Postby bdring » Mon Jan 18, 2010 5:52 pm

I use 269oz steppers for both axes and they are more than enough.

If you plan on doing engraving, speed and acceleration will be a factor. I determined early on that I would be OK with always doing the engraving raster direction in the X-Axis. This meant that I would not need a lot of speed on the Y-Axis. My machine is not very robust with high speeds and accelerations on the Y axis because I am only driving it from one side. I was able to go as fast as I dared without stalling the motor or loosing steps. So, bottom line...if you do not need to raster in Y, the mass of the gantry due to a heavier motor will not be a factor. I would either go with two 230oz motors or use the 230 for the X and get a slightly bigger one for the Y.


If you really want to do the math you need to know...

Mass each axis must move.
Maximum speed.
Acceleration.
Gear ratios.
Speed vs. Torque curves.
etc.
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Re: Stepper motor Torque ratings

Postby rkovvur » Mon Jan 18, 2010 6:27 pm

Thanks a bunch !!

Yup, i too am designing the gantry to be driven from one side only. I am not sure how this is going to affect the motion...
Driving the gantry from the center is too much work :)

The reason i was hoping to use a smaller motor (48oz/in) for x-motion is because the x-axis stepper will also be hanging at one end of the moving gantry. I was not sure how a heavy 230oz/in motor that weighs almost 2lbs will affect the gantry.

Do you have any pictures that you can post on your XY travel system?

Thanks!
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Re: Stepper motor Torque ratings

Postby bdring » Mon Jan 18, 2010 6:36 pm

My design is pretty well documented on my buildlog. Start it here http://www.buildlog.net/cnc_laser/buildlog_2.html#LogStart

My advice advice for a gantry driven from one side 1: Keep the weight toward the driven end. 2: Make the connection to the rail as ridged as possible. My 3 point v-wheel system would be better as a four point. 3: Dont put rails on both sides. I tried this and the extra resistance made it twist.

I may upgrade my system to be driven from both ends.
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Re: Stepper motor Torque ratings

Postby rkovvur » Mon Jan 18, 2010 6:58 pm

How do you plan on driving from both ends?? The steppers need to be synchronized, right?. Or you'll have to drive it from the center.
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Re: Stepper motor Torque ratings

Postby bdring » Mon Jan 18, 2010 7:04 pm

It is called a slave axis. Most controller software can handle it like Mach3 and EMC2. You need another motor and a free motor controller axis of course. On my big router I just manually linked to two sides with an extra belt.
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Re: Stepper motor Torque ratings

Postby lasersafe1 » Tue Jan 19, 2010 2:28 am

You can also use a single motor that drives a long shaft that extends to both sides of the machine. Two drive pinions will be mounted so there is one on each side of the machine. These drive pinions will drive the belts that pull the gantry forward and back. This is how the Chinese M40 does it and it works quite well.

I would always avoid driving from one side or it will "wobble" unless it is quite stiff.
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Re: Stepper motor Torque ratings

Postby bdring » Tue Jan 19, 2010 2:36 am

Could you post a picture of that?...you knew I was going to ask ;)

Thanks
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Re: Stepper motor Torque ratings

Postby lasersafe1 » Tue Jan 19, 2010 2:38 pm

bdring wrote:Could you post a picture of that?...you knew I was going to ask ;)

Thanks


I'm not at my machine today, but this quick google sketchup drawing should give you the idea. The motor in the M40 is double ended and one pulley is mounted directly and the other end has the shaft attached. Not shown in my drawing is one simple radial bearing at the far end of the shaft to support the far pulley. This could of course be modified to use a single ended shaft motor mounted on the outside left or right.
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Re: Stepper motor Torque ratings

Postby bdring » Thu Jan 21, 2010 3:13 pm

Thanks for the info. If you get a chance could post details about the motor. If you don't know any, just the motor frame size would be OK. Thanks alot.
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