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Author Topic: Confused about Stepper Motors  (Read 5209 times)

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Confused about Stepper Motors
« on: November 29, 2011, 12:26:22 AM »
I'm a long time lurker. I've not had much reason to ask questions about CNC stuff 'cause it's already here if I use search, but now I need to get help. I have built my third iteration CNC machine. It's all metal and solid as a rock. As I built it I tested everything slowly. When I was done I could rapid the three axises quite quickly with my battery hand drill. When I hooked up the steppers the rapid speeds were very slow. The best I can get is 65 ipm about a third of the speed of the cordless drill.  I've configured the steppers with Mach 3 and got them right on. When I go to tune the motors they lock up at realtively low speed. I was hoping with this setup to get over 100 ipm. Here are the specs:

Steppers - keling 425 oz wired in parallel/bipolar (x and Y axis) 1 pacific scientific 265 oz parallel/bipolar (Z axixs)
Power supply - 24 V at 10.5 Amps
Driver - Toshiba 5650 - 4 axis (I have 2 steppers as direct drives on my X axis) 
ballscrews - 25mm at 5 tpi
The table is 4 ft by 3 ft.

Anyone have any ideas? I'll get the xml file tomorrow and post it.

Thanks for the help,

Richard B.

Offline stirling

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Re: Confused about Stepper Motors
« Reply #1 on: November 29, 2011, 06:18:30 AM »
Posting the data sheets for your motors and drivers would have been useful but I'm thinking your present 24 Volts is waaaaaaaaaaay to low. If I've looked up the correct motor specs then to get *max* speed/torque combination you should be using around 80V. I can't find a data sheet for your drivers but having looked at other Toshiba drivers I'd hazard a guess that they can't handle this voltage.

Ian
Re: Confused about Stepper Motors
« Reply #2 on: November 29, 2011, 11:17:11 AM »
Richard,
Could be you're experiencing mid-band resonance problems.  Do your steppers react the same when disconnected from the machine?  Do the steppers sound rough?  What micro-step setting are you using?
Regards,
John Champlain
www.picengrave.com

Offline ger21

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Re: Confused about Stepper Motors
« Reply #3 on: November 29, 2011, 11:53:06 AM »
As Stirling said, you're using motors that aren't a good match for that board and power supply. The 425oz motors are probably the slowest nema 23 motors in terms of rpm, due to their high inductance.

Also, a cordless drill has 5-10 times more torque than your steppers.
Gerry

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Re: Confused about Stepper Motors
« Reply #4 on: November 29, 2011, 03:28:14 PM »
Hi Guys,

Thanks for all the good information. I kinda expected the answer about the steppers being slow by nature. I'll have to wait until after Christmas to upgrade the power supply and drivers. I was looking at a full Geco or a setup from Keling, just to get good quality. Unless you have other suggestions. 

In answer to the question about testing the motors off machine, yes I did and I wasn't very happy with those results either. I was hoping that under load they would perform better. I'm used to automotive engines where non loaded they over rev easily.  I am surprised that a cordless has more torque than these steppers. Makes me rethink the entire stepper concept (has anyone dsimantled their cordless and wired it in? LOL). I'm posting the motor specs. for recommendations on the power supply, drivers and/or new steppers. I've tried compensating for resonance and got minor change. I'm using 1/8 micro-steps and the motors sound good until they lock up. Unless whislting and other weird noises while idle is unusual. Running they are smooth. They get warm, not hot, and are great for warming your hands while working in the cold garage!

I went with the Toshiba 5650 mainly for ease of installation.  One board does all, but the board is limited to 36 volts. How do Geco or other quality systems get wired in? The multiple box setup has me confused.

Once again thank you for all the help,
Richard B.
Re: Confused about Stepper Motors
« Reply #5 on: November 29, 2011, 03:32:46 PM »
OOPs, the board is a Toshiba 6560
Re: Confused about Stepper Motors
« Reply #6 on: November 29, 2011, 03:43:33 PM »
I am having a similar problem (see subject ref TB6560) AND AM JUST AS CONFUSED!!!
Graham
Re: Confused about Stepper Motors
« Reply #7 on: November 29, 2011, 03:49:34 PM »
You should visit geckodrive.com and get all the answers about stepper motors and how to spec for your needs.  great site and, best of all their products are "made in Amaerica"

Dave
Re: Confused about Stepper Motors
« Reply #8 on: November 29, 2011, 03:51:39 PM »
I just need to learn to spell now "America"