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Old 03-18-2013, 04:10 PM   #251
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Huaco and JeepinJeepin,

I design stepper motor drive systems among other things. You do NOT want to try to use a stepper for milling grain. They can't just be driven by a DC or AC voltage applied to the terminals, they need to be manually phase-controlled (using a microcontroller or PLC) and they are FAR more expensive in terms of dollars per torque than AC and DC motors.
So, a 12vdc stepper motor cannot be driven at a steady 12 volts? What if it doesn't have an encoder? Just the motor? I'm just beginning to read up on servos and steppers and such(starting to play with Arduino).
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Old 03-18-2013, 04:28 PM   #252
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Huaco and JeepinJeepin,

I design stepper motor drive systems among other things. You do NOT want to try to use a stepper for milling grain. They can't just be driven by a DC or AC voltage applied to the terminals, they need to be manually phase-controlled (using a microcontroller or PLC) and they are FAR more expensive in terms of dollars per torque than AC and DC motors.
Great... thanks man.
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Old 03-19-2013, 12:27 PM   #253
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So, a 12vdc stepper motor cannot be driven at a steady 12 volts? What if it doesn't have an encoder? Just the motor? I'm just beginning to read up on servos and steppers and such(starting to play with Arduino).
That's correct. A stepper is a very different type of motor. I think they are really awesome for what they do because other motors can't do what they do. Their strong points are absolute fine control and "holding torque". Generally they have 180 "steps" per rotation but with some advanced techniques you can "microstep" (more on that later).
A stepper motor has 4 leads coming out of it (sometimes they have more, but then you'll tie pairs of them together to reconfigure and you always end up with 4 leads to drive). The leads are in two pairs, A and B which corrospond to a pair of coils. If you drive both A and B with forward voltage the motor will snap to nearest forward-forward position. Then you can reverse polarity on A and it will snap to the nearest reverse-forward position. Then reverse B and it snaps to the nearest R-R position, then forward A again and you get to the nearest F-R position. You've just moved 4 steps of 180 and the motor has turned 8 degrees.
If I haven't lost you yet, that's the 4 possible combinations of forward/reverse polarity on A and B coils. To move in one direction you do this: FF, FR, RR, RF, FF, FR, RR, RF. To move in the other direction you do this: FF, RF, RR, FR, FF, RF, RR, FR.
At any time you can leave the coils charged as they are and the motor will hold still with a lot of torque. You can transition those "states" as quickly or slowly as you like and move forward and backward at your whim. These are why they are great for low-cost CNC machines.
To drive one with an Arduino you have two choices. First, you can learn how to use an "H-Bridge", which is a way of forward/reverse/off/short polarizing a coil using two arduino outputs (10 is forward, 01 is reverse, 00 is off, 11 is short). An H-Bridge is just 4 mosfets and you can google the configuration and usage. You'll need one for each coil.
The other way to drive them is with a specialized motor driver chip. We like to use A3977 by Allegro. These let you just use a Direction, Step, Enable and Sleep input and it does all the sequencing for you. This is where "microstepping" comes in. You can actually get a little finer than FF, FR, RR, etc... you can do FF, 80%F20%R, 20%F80%R, RR... this "steps" the motor between the regular locations and the Allegro chip takes care of all of that. This nets you up to 16 times the steps (depending on the chip, usually 8, SOME do 32) so you're now in the thousands of microsteps per rotation range. And THAT is why you'd want an stepper, so you can make good use of all that accuracy to do things like CNC or tracking camera or robotics. The encoder is used for feedback to make sure you aren't "cogging", or skipping from one FF position to the next because of external force, or not moving forward because of a blockage. If you try to go really fast against a torque load it will skip back to the previous cog and you don't know that unless you're reading an encoder.
The wikipedia page on steppers is actually a pretty precice read for you to get started.


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Great... thanks man.
No problem - we finally hit a topic that I have some solid input on
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Old 03-19-2013, 04:44 PM   #254
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Awesome! Thanks MazdaMatt. The one experience I had with a "stepper motor" some time ago wasn't actually a stepper motor. The things you learn on a beer forum...

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Old 03-20-2013, 01:08 AM   #255
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Here is my MM2. Currently drill powered. I will motorize it in the near future.

monster-mill-build.jpg

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Old 03-20-2013, 03:07 AM   #256
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Here is my MM2. Currently drill powered. I will motorize it in the near future.
That looks awesome. What plate did you use to mount the bottle to the mill?
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Old 03-20-2013, 05:29 PM   #257
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That's correct. A stepper is a very different type of motor. I think they are really awesome for what they do because other motors can't do what they do. Their strong points are absolute fine control and "holding torque". Generally they have 180 "steps" per rotation but with some advanced techniques you can "microstep" (more on that later).
A stepper motor has 4 leads coming out of it (sometimes they have more, but then you'll tie pairs of them together to reconfigure and you always end up with 4 leads to drive). The leads are in two pairs, A and B which corrospond to a pair of coils. If you drive both A and B with forward voltage the motor will snap to nearest forward-forward position. Then you can reverse polarity on A and it will snap to the nearest reverse-forward position. Then reverse B and it snaps to the nearest R-R position, then forward A again and you get to the nearest F-R position. You've just moved 4 steps of 180 and the motor has turned 8 degrees.
If I haven't lost you yet, that's the 4 possible combinations of forward/reverse polarity on A and B coils. To move in one direction you do this: FF, FR, RR, RF, FF, FR, RR, RF. To move in the other direction you do this: FF, RF, RR, FR, FF, RF, RR, FR.
At any time you can leave the coils charged as they are and the motor will hold still with a lot of torque. You can transition those "states" as quickly or slowly as you like and move forward and backward at your whim. These are why they are great for low-cost CNC machines.
To drive one with an Arduino you have two choices. First, you can learn how to use an "H-Bridge", which is a way of forward/reverse/off/short polarizing a coil using two arduino outputs (10 is forward, 01 is reverse, 00 is off, 11 is short). An H-Bridge is just 4 mosfets and you can google the configuration and usage. You'll need one for each coil.
The other way to drive them is with a specialized motor driver chip. We like to use A3977 by Allegro. These let you just use a Direction, Step, Enable and Sleep input and it does all the sequencing for you. This is where "microstepping" comes in. You can actually get a little finer than FF, FR, RR, etc... you can do FF, 80%F20%R, 20%F80%R, RR... this "steps" the motor between the regular locations and the Allegro chip takes care of all of that. This nets you up to 16 times the steps (depending on the chip, usually 8, SOME do 32) so you're now in the thousands of microsteps per rotation range. And THAT is why you'd want an stepper, so you can make good use of all that accuracy to do things like CNC or tracking camera or robotics. The encoder is used for feedback to make sure you aren't "cogging", or skipping from one FF position to the next because of external force, or not moving forward because of a blockage. If you try to go really fast against a torque load it will skip back to the previous cog and you don't know that unless you're reading an encoder.
The wikipedia page on steppers is actually a pretty precice read for you to get started.



No problem - we finally hit a topic that I have some solid input on
I was scrapping out an old large format copier in our shop (Well, I scrapped part of it. The base is becoming my brew stand!) and I found a decent sized motor inside. It's a "synchronous" motor. The description I read online didn't give me any idea if it could be used for milling. It's a 115V motor. There are 2 leads for power, and then there are 2 wires coming out which run into what might be a capacitor.

I can't tell if it's 115VAC, or 115 VDC. I'm guessing AC, because I've only ever seen 115 VAC equipment, but I have seen 90VDC stuff, and it looks like it might be DC, but heck if I know.

The description I read indicated that a synchronous motor is used for high precision, which makes sense when feeding copies and accurately duplicating.

I'm tempted to plug it in and see what it does, but I have to know how to tell if it's AC.
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Old 03-20-2013, 08:03 PM   #258
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DC motors don't use caps

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Old 03-21-2013, 01:30 AM   #259
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That looks awesome. What plate did you use to mount the bottle to the mill?
I used a couple 1x6's and mounted an ABS female clean out adapter to them. On the bottle I used an ABS male adapter. I had to do a little sanding to make it fit though. I think it turned out pretty good. You can take to bottle off the mill for storage.
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Old 03-21-2013, 03:56 PM   #260
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I was scrapping out an old large format copier in our shop (Well, I scrapped part of it. The base is becoming my brew stand!) and I found a decent sized motor inside. It's a "synchronous" motor. The description I read online didn't give me any idea if it could be used for milling. It's a 115V motor. There are 2 leads for power, and then there are 2 wires coming out which run into what might be a capacitor.

I can't tell if it's 115VAC, or 115 VDC. I'm guessing AC, because I've only ever seen 115 VAC equipment, but I have seen 90VDC stuff, and it looks like it might be DC, but heck if I know.

The description I read indicated that a synchronous motor is used for high precision, which makes sense when feeding copies and accurately duplicating.

I'm tempted to plug it in and see what it does, but I have to know how to tell if it's AC.
Not to turn this into a science of motors thread, but we're not TOO far off topic because people need to know their motors to build motorized mills. Anyway, I'm willing the bet that the two small wires coming off are actually for a hall effect sensor so the printer knows the speed/position of the roller. A Synchronous motor is one that turns in time with the AC signal being fed to it. A 60Hz ac signal will make it turn at (correct me if i'm crazy) 3600rpm, though it may be some divisor based on internal windings (1800, 1200, 900, 600, 400, 300... depending on the windings). If you plug it into the wall I foresee two things happening. It either slips because it can't keep up with the sudden 60Hz (because the printer would ramp up the freqecy in conjunction with the motor speed read by the hall sensor) and burns out, or it suddenly pounds into action at whatever RPM it will run at 60Hz. I fully expect that it will have a hard time starting under load.

If it were me and I had no other use for an AC sync motor, i'd attach it to a switch, run a wire out to the middle of my driveway, hide behind a wall and turn it on If that works, find a way to load it and repeat the test.
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