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newguy
04-08-2004, 11:49 AM
Im new here so take it easy on me if i sound stupid. Anyway i have three slow syn unipolar stepper motors i came across that have the following specs.


2.64 volt
5.5 amps
450 hold oz ( thats a lot of torque )

Looking around i can find somewhat inexpensive drives for low amp but nothing for this high of amperage. I see there is a schematic for a higher amperage drive on this site that can be built somewhat inexpensively and ive built my own curcuit boards a time or two before but they never come out very good . ( they work , well sometimes they do ) Does anyone know of a fairly inexpensive route that i could get some drivers for these motors? Also if anyone here might have an excess of drives that will work on these i can come up with more of these motors and maybe we can work out a trade or something.

balsaman
04-08-2004, 12:16 PM
Sell the steppers on ebay. Buy some that will work with a cheaper drive. What sort of machine you building?

Eric

newguy
04-08-2004, 12:41 PM
4 foot by 6 ft router but i figure if i design it properly ill be able to use just about anything as the machine head. And as for selling them on ebay i thought about that but i would also like to take some of these motors and use them to make my lathe and possibly my mill cnc hence the need for torque.

Mariss Freimanis
04-08-2004, 12:49 PM
Sounds like you have some M093-FD11 steppers. Those are excellent motors; hang on to them.

Mariss

newguy
04-08-2004, 01:02 PM
yes those are the motors , pretty pricey to my understanding but i got them for pretty much scrap metal prices, along with some hardened rods and sleeve bearings.

Chagrin
04-08-2004, 03:16 PM
Stepperworld.com's FET-3/4 is capable of handling up to 15 amps.

balsaman
04-08-2004, 04:42 PM
I doubt it. The FETS are RATED at 15 amps, but there are no heatsinks, and no room for any. Also, the circuit board can't handle that kind of current. Also its a unipolar board, so the current limiting resistors needed to get any kind of perfomance would be HUGE. Gecko's are the only cost effective drive for those motors IMHO. You're looking at $345.00 plus powersupply. You would have a nice motor setup mind you.

I would build first, worry about the drive last.

Eric

rvan
04-08-2004, 06:29 PM
Check out http:\\www.Stepper3.com

They sell:
(S3HPPWM) 3 AXIS 8 Amp Pulse Width Modulated Stepper Motor Driver

for $369.00 for three axis. Considering that you would need to buy three separate geckos at least $114, its reasonably priced. Note Gecko only sells Bipolar and Servo drives. Although you could use Gecko Bipolar drives to power Unipolar steppers, they will only operate under a fraction of their speed and torque capabilities.

With this board, you do not need power resistors to drive unipolar steppers. Its also allows you to use separate power supplies for each motor (see the user's manual for details), output power is controlled using on-board potentialmeters.

ger21
04-08-2004, 09:45 PM
Although you could use Gecko Bipolar drives to power Unipolar steppers, they will only operate under a fraction of their speed and torque capabilities.

I believe that this statement is false. I've never seen anyone who has used both bipolar and unipolar drives recommend the unipolar drives. It seems like bipolar always gives better performance.




Its also allows you to use separate power supplies for each motor

I read the manual, and to calculate the current for the power supplies, you need to take the current rating for each phase of each motor, and add them together. So, (5.5 + 5.5) x 3 motors=33amps MINIMUM. Geckos, on the other hand, are much more efficient, only needing 2/3 of ONE phase rating for each motor. (5.5 x 2/3) x 3 = 11 amps MAXIMUM. This smaller power supply could save you quite a bit of money.

Another thing is that the Gecko 201's have 10x microstepping, versus 1/2 step for the Stepper3. With microstepping, you'll get much smoother running motors.

I'd keep the motors and buy Geckos.

Hopefully Mariss or someone else will step in and provide a more eloquent explanation.

radio-op
04-08-2004, 11:58 PM
I'll give it a shot.
The highest torque is developed in bipolar mode due to the fact that the full length of each coil in the stepper are always energized. Whereas in the unipolar mode, the center tap on each coil is used and only 1/2 of each coil is energized.
As to the question of a bipolar drive and a unipolar motor, that is partly true. You can wire a unipolar motor(6 or 8 wire)as a bipolar, but you can not wire a bipolar motor (4 wire) as a unipolar. A bipolar drive will only drive a bipolar motor and a unipolar drive will only drive a unipolar motor. An 8 wire motor can be more useful because it will allow you to configure the most modes.
Rvan you are correct that a PWM or chopper drive is more efficient then a linear drive. In order to control current flow, a linear drive will require a bias resistor. The size will be dependent on the Voltage and the current rating of the motor. With the high current motors discribed, the resistor or network would be in the 300-400 watt range. A quick check at Digikey will show that to handle that much power will cost a arm and a leg.
By and large the most cost effective and powerful setup would be a bipolar chopper or PWM drive system.
Hope this helps,
Bill

Mariss Freimanis
04-09-2004, 02:13 AM
If it helps, you can use the following as a means of calculating how much bang you get for your buck. It applies as a rough measure to all drives you may be considering:

Value = (Max Amps times Max Supply Voltage) / Price

Example: G201 is (7A times 80VDC) / $114 = 560 / 114 = 4.91

The bigger the number, the better the value for your money. Try this on some other drives and see what number you get.

Another one might be (2Amps times 36V) / $35 = 72/35 = 2.06

You are getting about 40% for your money with that one.

This number does not take into account microstepping, midband compensation and other factors that enhance a drive's utility.

Mariss

ehiebert
04-09-2004, 05:52 AM
Value = (Max Amps times Max Supply Voltage) / Price

Hey that's a pretty reasonable value formula. It works out to power delivery per dollar. I like it!!


Eldon.

balsaman
04-09-2004, 07:31 AM
Of course, if you are running 1 amp motors, with some drives you may be paying for un-needed "value". Like using an elephant to step on a fly when you could have used a fly swatter, and the fly swatter is cheaper. A fly swatter cant kill a bear, but you only have flies to kill, no bears. OTOH, this is not the case with the motors mentioned above, they are bears.

Eric

tpworks
04-10-2004, 04:20 AM
Check this link out http://electronickits.com/kit/complete/motor/ck1406.htm

6 amp bipolar $19.95 it is in kit form and I 'm going to substitute the fets with irf540's and irf9540's the one that come with it are 60 volt 12amp on the low side and the irf9540n is 23amp at 100volt = cooler running

ESjaavik
04-10-2004, 07:13 AM
And what is restricting the current into your motors?
Too much current over time will cook the motors. If way too much it will demagnetize the motors and this will happen in microseconds, so even if the power supply is current limited, just the capacitors after this limiter may have stored enough energy to do that.

balsaman
04-10-2004, 07:32 AM
If you run the motors at rated voltage, the windings restrict the current.

If run at over the rated volatge, you need current limiting build into the drive or external resistors in series with the motor.

Tpworks,

That drive is not a chopper drive. It will need external resistors to limit the current unless you run at rated voltage. For high current motors these can really be expensive. What motors will you run? what voltage power supply?

Eric

rvan
04-10-2004, 11:52 AM
Originally posted by ger21
I believe that this statement is false. I've never seen anyone who has used both bipolar and unipolar drives recommend the unipolar drives. It seems like bipolar always gives better performance.


I think you misunderstood me. He said he purchased "Unipolar" steppers. If you use a Bipolar driver board (like Geckos) with Unipolar steppers they will have to be operated under reduced power or speed (from the Gecko User's manual). I wasn't comparing efficiencies between Bipolar and Unipolar motors.



Originally posted by ger21
I read the manual, and to calculate the current for the power supplies, you need to take the current rating for each phase of each motor, and add them together. So, (5.5 + 5.5) x 3 motors=33amps MINIMUM. Geckos, on the other hand, are much more efficient, only needing 2/3 of ONE phase rating for each motor. (5.5 x 2/3) x 3 = 11 amps MAXIMUM. This smaller power supply could save you quite a bit of money.
[/B]

All I said here was that you have the option to use multiple supplies if need to with the Stepper3 driver board. Most if not all 3 or 4 axis drivers only permit you to use one power supply. If for instance you wanted to mix different steppers (requiring different voltages), you could do it with the stepper3 board. Of course using a single power supply would be the best option, but In some cases it can be cheaper and easier to find two or three smaller Power supplies than one larger one.

ger21
04-10-2004, 01:41 PM
If you use a Bipolar driver board (like Geckos) with Unipolar steppers they will have to be operated under reduced power or speed (from the Gecko User's manual).

Maybe I did misunderstand what you said, but I still disagree with what you are saying now. Here is what the Gecko manual says:


4-wire, 6-wire and 8-wire motor may be used. When 6-wire motors are used, they may be connected in half winding or full
winding. This is equivalent to an 8-wire motor connected in parallel or series. If a motor is connected in series or full winding, the
motor’s phase current rating is half of its parallel or unipolar rating. The choice depends on the high-speed performance required;
a parallel-connected motor will provide twice the power of a series-connected motor at the same power supply voltage.

A 6 wire motor will still be able to develop it's full rated torque using a Gecko. The manual doesn't say anything about reduced power, except when wired full winding at high speeds. An 8 wire motor wired series is no different.

On the power supply thing, I think you misunderstood me. What I was saying, is that the Stepper3 board would need a power supply that delivered 3x the current of a power supply for the Geckos.

I'm only posting the info that I've read. If I'm wrong, someone please correct me.

radio-op
04-10-2004, 03:55 PM
If I may, Gerry you are absoultly correct. The greatest torque is developed in bipolar mode. As quoted above, the best preformance is parallel bipolar, with also the highest current demand. The holding torque is the same for parallel or series bipolar, but the torque of a series bipolar drops at a greater rate as the RPMs increase. Both the parallel and series bipolar modes have a higher holding torque then unipolar due to the use of the full length of the coil, with the exception of half-winding bipolar which has the same holding torque of unipolar. As an example, below is from the http://www.pacsci.com/support/documents/stepper/stepsel.pdf, Pacific Scientific showing the relationalship of the winding modes (half-winding bipolar is not noted here).
Mode Model holding torque Current/Phase Phase resistence
Oz/In (Nm) Amps DC Ohms
Par bipolar P2HNXXH-LXX-XX-00 • 59 (0.42) 5.2 0.22
Ser bipolar P2HNXXH-LXX-XX-00 • 59 (0.42) 2.6 0.90
Unipolar P2HNXXH-LXX-XX-00 • 42 (0.29) 3.68 0.44

I had posted before that an 8 wire motor allows the greatest flexability, this is because there is no internal connection at the center tap of the phase coils. The user can choose to make the connections as parallel bipolar, series bipolar or unipolar. The user has the option to match the motor to the drive.
Bill

radio-op
04-10-2004, 04:04 PM
Well, I see that the formating for the info I posted was lost, sorry. The quoted numbers for each mode are: Oz/in (Nm) AmpsDC Ohms.
Bill

tpworks
04-10-2004, 11:47 PM
Power resisters should do the trick, I have that formula here somewhere, anybody have it readily available.for 24v 40a power supply with
option 1) 1.8v @ 4.5a Vexta ? oz/in
option 2) 4.25v @ 8a Slo/Syn hold 2400 oz/in

Ferenczyg
04-11-2004, 12:23 AM
Download StepCalc, will do the math for you, both for TRN and FET and for one or two limiting resistors.

tpworks
04-11-2004, 10:53 PM
Ferenczyg,

Where do I find this StepCalc.

Ferenczyg
04-12-2004, 04:15 AM
Send a PM to Balsaman, is the developer. I downloaded from his web page or a link to the proggie at some thread, I do not remember now. As the web is closed now, maybe balsaman could provide the link. Sorry but is too heavy for me to send you by email.

newguy
04-12-2004, 08:56 AM
Couldnt i use http://209.41.165.153/stepper/fet3.htm looks like it will run the specs i mentioned unless ive overlooked something and the board itself runs 135.00. Then get the optional 18 upgrade on the mosfets to prevent it from running hot.

newguy
04-12-2004, 09:15 AM
Addtioanally i plan on encasing this board with a rather large fan from a pc , i could also machine a block of alluminium that might fit between the mosfets and act as a heat sink but with the upgraded mosefets i wouldnt think it would run to hot.

tpworks
04-12-2004, 02:46 PM
I found the link I saved for the resistor formula


http://209.41.165.153/stepper/Tutorials/BiTutor.html


Selecting a current limiting resistor

It is important that neither the motor nor controller exceed their rated currents. The value of a current-limiting resistor in series with the motor can be determined from the following equation...


Vsupply = Vdrop + (i * Rmotor) + (i * Rlimit)

Vdrop = voltage drop of Transistors used (2 volts for Unipolar, 4 volts for Bipolar Drivers)
i = current in circuit
Rmotor = resistance of single motor coil
Rlimit = current limiting power resistor

The objective is to find Rlimit that satisfies the desired current rating i

For example, Using a power supply of 12 volts, what current limiting resistor should be chosen to deliver 1 amp of current to a motor with a coil resistance of 5 ohms? Assume 2 volt drop due to the transistors.

12v = 2v + (1 amp * 5 ohm) + (1 amp * Rlimit)

12v = 2v + (5v) + (1 amp * Rlimit)

5v = 1 amp * Rlimit

Rlimit = 5v / 1 amp = 5 ohm

What will the voltage be across this resistor? 5v
What current will flow through this resistor? 1a
What power rating should this resistor be? 5v * 1a = 5 watt, minimum

This calculation is for determining the current in a single coil. Most motors and stepper circuits are rated in terms of this coil rating - amps per phase. If the hi-torque, or half-step sequence is to be used, then more than 1 coil will be activated, thus more current will be required of the power supply.

Ideally, two matched current limiting resistors should be used, one in series with each of the 2 motor coils. (The Unipolar driver can get away with sharing a single power resistor, with the center taps tied together.) Here is the configuration for the Bipolar Controller...




Current Limiting with Bipolar Controller

jcc3inc
04-13-2004, 11:24 AM
Dear Sir:

If I am not mistaken, you can convert your motors (assuming they are 6 wire) to 8 wire by removing an endcap or possibly some connection plate. It is important that you do NOT REMOVE THE ROTOR or the unit will be damaged. As it it now connected, you have the equivalent of two center tapped coils; you need to find this center tap on each coil and separate the coils resulting in 4 individual coils which have no connection to each other. Thus you can have the full torque which the motor can produce.

My experience with Geckos has been quite positive. The microstepping adds considerable smoothness.

Regards,
Jack C.

balsaman
04-13-2004, 12:16 PM
www.e-zflight.com/files/stepcalc102.zip

:)

m1911bldr
04-21-2004, 12:44 PM
I think Hans Wedemeyer's board will do all you wnat done. It's a "start from scratch" board but I've seen a couple in use and hey kick butt for very few dollars, once you get the boards etched. http://hans-w.com/