[Curtisbeef]

Hi guys I have just recently bought some motors and im a little confused about what kind of power requirements im going to need im really electronics savvy but im just used to working with low voltage and amperage.

Here are the motors I have http://www.allelectronics.com/cgi-bi...DEG_STEP_.html

the specs that i have found:
1.8 Degree step
1.8 Volt
4.2 Amp
0.42 Ohm
127 Oz/in holding tourqe

So now im looking for a DIY/Opensource Controller that will fit my needs... or something i can modify. Im New at stepper motors and dont quite understand them fully yet. So please be gentile

[Curtisbeef]

I used the a power supply calculator here http://www.cnczone.com/forums/showthread.php?t=57118
is that only for Gecko Drivers?

It says that i should use 39.6V (22 times the voltage) at 2.8 amps does this sound correct?
with that setup i could use any bipolar stepper controller that can do ~40V at ~3A right?

[ger21]

You'll need a drive that can supply 4.2amps. Torque is proportional to current. If using the Gecko drives, the drive will only draw 2.8amps from the power supply. Some drives will need the full current from the power supply.

[Curtisbeef]

hmm k im still confused about what i need to make these motors work...

[ger21]

Sorry, didn't have much time earlier. To get the full rated torque from a stepper, you'll need a drive that can supply the rated current. Supply half the current, you'll get half the torque. Unfortunately, I'm not sure you'll find an open source design that can deliver that. Most are lower current drives. If you haven't already, check out www.pminmo.com

Before choosing a power supply, you need to decide on a drive to use and get a power supply to match the system.

[Curtisbeef]

would just a 400W computer power supply work?

edit:
what voltage and amperage rating would you run these motors at?

[ger21]

what voltage and amperage rating would you run these motors at?

Depends on ones budget. If you're only spending $7 per motor, it doesn't make much sense to spend a lot of money on a drive that would maximize their performance. You're best bet would probably be the soon to be released Gecko G250, running at 3.5amps and around 30-36V. You'll only get about 100oz of torque, but you won't find a better drive at a better price.

[harryn]

Hi, just adding to the questions about specifying a power supply.

I am looking at some motors from Danaher which are approx. 2 amps, 2 phase, unipolar, nominal 3 ohms, 6 wire. Reading the specs more carefully, it says - "current is per phase". (I did not see this detail on the Keling motor specs, but I am guessing it is similar )

The plan is to use linistepper drivers to drive them in 16x micro step mode using a nominal 12 VDC supply.

So, the questions:

a) Does this mean that I need to be able to supply 4 amps to each motor (2 x 2 phases) or is each phase only on one at a time. (I am just guessing it is something in between based on how the EE guys work )

b) I have a friend who often uses deep discharge car batteries instead of large inductors / capacitors to even out electrical power supply spikes. Is there any reason that I should not just hook up a 100 amp car battery to a healthy deep discharge car battery to power all of the 12VDC functions + stepper motor drives ?

Thanks

[jeffs555]

I am looking at some motors from Danaher which are approx. 2 amps, 2 phase, unipolar, nominal 3 ohms, 6 wire. Reading the specs more carefully, it says - "current is per phase". (I did not see this detail on the Keling motor specs, but I am guessing it is similar )

The plan is to use linistepper drivers to drive them in 16x micro step mode using a nominal 12 VDC supply.

That is a rather low supply voltage for those motors. Two amps at 3 ohms means the motor is rated for 6volts. Generally for good speed you want the supply voltage to be 10 to 20 times the motor voltage rating.

a)depends on the driver, but 2amps per motor would be probably be enough.
b)you could, but again, 12v is rather low for 6v motors and caps are cheaper than deep discharge batteries.

[harryn]

That is a rather low supply voltage for those motors. Two amps at 3 ohms means the motor is rated for 6volts. Generally for good speed you want the supply voltage to be 10 to 20 times the motor voltage rating.

a)depends on the driver, but 2amps per motor would be probably be enough.
b)you could, but again, 12v is rather low for 6v motors and caps are cheaper than deep discharge batteries.

Hi jeffs555 - thanks for the comment.

If I am properly understanding the drivers (which is of course questionable), bipolar drivers that using switching based control like geckos are designed to use the kind of supply voltages you are talking about.

Linisteppers are not switching, so they are designed to limit power by linearly burning off the excess voltage in a resistor network - so IIRC, the recommended voltage would be around 12 volts for this kind of setup.

There are definite trade offs using them (often lower torque for similar motors compared to bipolar driven setups, etc), but frankly, cost makes it worthwhile for me to see if this will work well enough.

[jeffs555]

If you are doing 3-axis, then this would be cheaper than linistepper. It is a unipolar chopper type drive and would let you run much higher voltages. http://www.hobbycnc.com/products/hob...er-board-kits/

Be aware when looking at motor torque curves, that they are usually taken at higher voltages. Running at only 2X the rated voltage, the torque at speed will be drastically less than that shown in the torque curves.

[harryn]

Thanks Jeff - I already have the linistepper kits from James Newton (under construction). Using solder paste, assembly is actually pretty easy - even for me. My soldering with wire solder was a complete failure, but with paste - easy.

I looked at the chopper vs linear discussions for quite a while, and while nothing is perfect, I came to the conclusion that for a high inductance (10 - 15 mH) unipolar motor, a linear driver would be better than a chopper for 1/16th or similar micro step mode.

My knowledge of stepper motors is just from reading various forum posts / opinions, but that is the current path. This was not an easy decision, as the motors I am looking at buying are specifically high inductance / unipolar only, which means if I am wrong, then it will cost me even more to switch over to a bipolar / chopper solution. (new motors and drivers)

The motor decision is partially driven by the desire for high axial and radial load tolerant bearings.