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Author Topic: Problem with stepper motors (have looked through archives)  (Read 13665 times)

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Offline Jeff_Birt

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Re: Problem with stepper motors (have looked through archives)
« Reply #10 on: April 13, 2009, 11:33:08 AM »
The speed you can drive a stepper motor at is directly proportional to applied voltage. With very slow step rates you can use a lower voltage. As you try to increase in speed the motors inductance prevents quick build up in current needed. The way to over come this is to use a higher driving voltage and then limit the current delivered to the motor once the desired phase current is obtained. This can be done with big resistors which is very inefficient or by current modulation (which is how most newer drives work.)

Happy machining , Jeff Birt
 
Re: Problem with stepper motors (have looked through archives)
« Reply #11 on: April 14, 2009, 04:22:59 PM »
I HATE WINDOWS.

The system did a complete flake today for reasons unknown. I am currently rebuilding it and getting everything re-installed including Mach3 (Keeping notes outside the box can never be beaten).

Will update on progress.

Michael
Re: Problem with stepper motors (have looked through archives)
« Reply #12 on: April 18, 2009, 05:54:53 AM »
Okay, Here is what I have going on with the motors and the system:

23HS8603 which from Stepperworld are said to be 190 oz-in 6.75V 1.5A Unipolar six wire Motors. The information from Motion King (the firm which produces them matches with the exception of them being 140 Ncm motors. The webpage with technical info is: http://www.motionking.com/Products/Hybrid_Stepper_Motors/23HS_Stepper_Motor_57mm_1.8degree.htm .

The Drivers/Breakout board is a Stepperworld FET3 Dynamo using the power supply that comes with it (a computer PSU 650W) and set up with twelve volt and running inline 1.5 Ohm 50W resistors with one per centre tap (two total/motor). It has an indepedent 5V wired to the board from PSU for logic. Schematic can be seen at the file that i loaded of it awhile ago to the site (look for uploads by me as it is the only one there). Information on it can be had at: http://stepperworld.com/FET3dynamo.htm .

The Router is a World of CNC (Marchant Dice) MDL-2-TR-UN. Which can be seen here:http://www.worldofcnc.com/products.asp?recnumber=194 . One item that I would mention is that a tighting order was not sent with the unit (an order with which it is prefered to tighten the bolts down for truing the unit after shipping). This cost me a good bit of time in getting the unit fully true.

I am using Mach3 and have had good response via both laptop and Desk top units (until Windows ate its lunch on the Desk top and been using the laptop currently) Setting are:

PIN2 = X Direction
PIN3 = X Step
PIN4 = Y Direction
PIN5 = Y Step
PIN6 = Z Direction
PIN7 = Z Step
PIN14 = Enable 1
PIN16 = Enable 2
PIN17 = Enable 3

E Stop is emulated at present

Motors are running at between 135 to 148 steps per unit speed is running from 225 on Z, 300 on X, to 550 on Y mm/Min as stable. This is in half step mode. High Torque is very choppy at these setting and Wave will not move at these setting except Y which goes very choppy. Acceleration is 4 to 5mm/sec/sec last two setting on Mach3 tuning page are 0,0. Tunig was done using and rechecking Mach3 tuner for the steps per unit. Units are mm.

When starting up must start Mach3 before starting break out board or won't see all the motors. Yet if I turn of driver?BOB and do any hardware changes (change from step to one of the other two settings) it will drop one or more motors. Current pulses are set at 25K.

Currently even on a cold start up it is not always picking up all three motors. The clicking sound when it was running all three motors but not stepping X at all was coming from the X motor and I could assist it by hand to turn in the direction of motion it needed to go. This has me believing that the motors maybe be used or not of high quality or just plain not functioning properly.

Items Looking at:

   1. Has the motors crapped out (even though I bough them less than six months ago)? I have put less than 10 hours of run time on them.
   2. Do I need to increase the Pulse rate to give a better signal to the system and therefore allow better control of the motors?
   3. Do I need to go to a dedicated PSU that has 12V or 24V power output available? (the system is rated for 12V I know. I don't know if it will handle higher without finding a way to cool the FET's)
   4. Changing the BOB which entails a whole mess in and of itself (and is not really wanted ATM, but will be done in the hopefully near future, contract first, upgrades second)

Hopefully all this detail will help those of you who can help me get this thing corrected and on line.

Michael
« Last Edit: April 18, 2009, 05:57:44 AM by m.marino »

BClemens

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Re: Problem with stepper motors (have looked through archives)
« Reply #13 on: April 18, 2009, 07:46:57 AM »
Look to be sure that your step and/or direction signals from the computer are not inverted - set to active high. That will do very much as you describe....the trigger edge is on the wrong side of the pulse so the drive is basically backwards and some logic functions of the drive board will not function at all. The S & D pulses should be set 'active low' from Mach 3.

Sometimes the simple things are overlooked....

Bill C.

Offline simpson36

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Re: Problem with stepper motors (have looked through archives)
« Reply #14 on: April 21, 2009, 05:02:28 AM »
Marino,

Something that stands out is that you are trying to run a 6.75 v stepper on 5v.

Stepper ratings are completely unlike what one would expect for a normal electric motor, both in their voltage and torque specs.  According to www.geckodrives.com ( and many other reliable sources) they should be run on a minumum of 4 times their rated voltage and up to 20 times (or more) the voltage. Gecko states that with less than 4 times, the steppers will not run right and over 20  . . too much heat. It is worth a read.

I could not get your link to work for the brand of router you are using, but 190 oz-in is a tiny stepper, and steppers fall off very quickly in torque the faster they run. You may want to consider larger motors.

Just by way of example, I am running 425oz-in steppers rated at 4v on a 36v power supply geared 2:1 (so I have 850oz in at the ball screw). I have to limit speed to 60in/min otherwise the steppers can stall reversing direction. If I set the accelleration low enough to use a higer speed, then the CV suffers.

Have a look at the torque curve of whatever stepper you plan to use. The meaningful number is the torque available at the speed you plan to run your axis.

EDIT: I just came across this in another thread . . . scroll down to torque curves for various steppers at different voltages. http://mcsupplyco.com/uploads/images/drawings/pdf1/md808.pdf
Note that the 200oz-in stepper has only 100oz-in left at 20RPS  .  and then only 50oz-in at 40RPS and that's at 30V. That's a loss of 75% of the initial torqe. Punch up to 60 or 72V and you get 160 - 170 @ 20RPS  . . interesting info, yes?


ANd incidentally, I replaced a 640oz-in 4v stepper on the Z axis with a  900 oz-in 2v stepper running on the same 36v source. That's 18 times voltage. It is noticeably more 'enthusiastic' than the 4v stepper, although not as smooth running. It does not stall like the 4v motor and it does not seem to get any warmer.

For your 6.75v steppers, I would suggest you consider getting a 72v power supply.

« Last Edit: April 21, 2009, 05:35:37 AM by simpson36 »

BClemens

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Re: Problem with stepper motors (have looked through archives)
« Reply #15 on: April 21, 2009, 05:27:25 AM »
Simpson,

You require a schematic for the circuit to hook up an optic sensor? What sensor? What BOB? What supply is available? Hard to help with nothing to relate to....

I would almost be afraid to help anyhow, it could possibly steer you wrong and I would feel really bad about that. But, you'll need to provide some better information about what you need. Facts are facts.


Bill C.

Offline simpson36

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Re: Problem with stepper motors (have looked through archives)
« Reply #16 on: April 21, 2009, 05:50:07 AM »
OK, Bill, gimme a break. I said I was sorry  :-*   . . but I guess I did have it coming  . .  :-[

Actually I started a new thread on this and posted most of the info you asked for. My bad for mentioning it again in another thread.

Anyway, this is the device I was thinking about:

http://www.nteinc.com/specs/3100to3199/pdf/nte3100.pdf

Available from Mouser for about 8 bucks.

I now have two breakout boards.

http://www.cnc4pc.com/Store/osc/product_info.php?cPath=33&products_id=49

And a new design MB-02 v1.0 from Homann Designs (I don't think this one is generally avaiable and the manual is not available yet).

For power I have a PC power supply which has the usual + 5 -5 +12 -12 available. I use the +5 to feed the BOB and the +12 to power relays (motor reversing, etc.) I *think* that it is OK to use the +12 and -12 to get 24v for a limit switch loop, but this is where I get nervous and imagine expensive smoke. Just because it seems logical to me doesn't mean it is going to work.

Let me know if you need anything else. Appreciate the help.

Thanks!














« Last Edit: April 21, 2009, 06:01:35 AM by simpson36 »

BClemens

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Re: Problem with stepper motors (have looked through archives)
« Reply #17 on: April 21, 2009, 06:19:53 AM »
You don't need to be sorry for a thing! Just let's get on with this if I may help you out.

You do realize that the manufacturer's web site has all the info on the device that you could possibly need? They usually will also provide suggestions and circuits for hook-up of the device.

I'll look at the CNC4PC BOB.

One more item - but just an opinion.... These machines are not clean, meaning a very bad environment for an optic sensor, or hall sensor for that matter. There are proximity sensors that are used for milling machines that do well and...there are applications where the optic interrupter have been successful but special provisions must be provided for housing the device to eliminate stray interruptions from FOD. And there's plenty of FOD on a milling machine!

Bill C.

Offline simpson36

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Re: Problem with stepper motors (have looked through archives)
« Reply #18 on: April 21, 2009, 06:35:08 AM »
Chips get on the stops and rollers, not to mention the connectors, for the mechanical switches as well, so I think the issue you point to needs to be addressed no mater what form of switch is used. I'm looking for accuracy and from what I read in many places, photointerruptors are best for that.

The device I noted is used on my spindle for indexing and it gets it's fair share of chips, oil and generla nastiness and so far it has not been a problem.

Information on manufacturers websites is useful to someone who knows how to use the information.

In the realm of electronics, I'm not one of those people . . . 
« Last Edit: April 21, 2009, 06:38:15 AM by simpson36 »

BClemens

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Re: Problem with stepper motors (have looked through archives)
« Reply #19 on: April 21, 2009, 07:11:48 AM »
Yes, mechanical switches are not trouble free either, just a tiny bit easier to deal with...(opinion again!)

The CNC4PC BOB is totally working at TTL levels meaning as you probably noted - 5 volts, and you must provide that supply. The four connections to the device are: top left supply voltage to the IR emittor and the pin below "E" is ground. The top right is the detector output to the BOB through the appropriate resistor noted on the datasheet for the BOB. So, tie the two +'s together to the 12 -16V supply that has a common ground with the BOB and the supply then the "D" (detector) will have a series resistor of 1.5Meg Ohm for a 12 Volt supply. This output will connect to the BOB at #'s 10, 11, 12, or 13 and you can use 15 as well....Only use 5 V to the BOB supply but the Opto Device requires a higher voltage. Just keep the grounds together and use three conductor shielded wire to the device.

Clear as muddy water? I will make you a drawing if needed.....

Bill C.