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Author Topic: Stepper Motor Nightmare!  (Read 1209 times)
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So I am working on a project to create a Split-flap display using a stepper motor, and some laser cut parts.

I am having a night mare about the stepper motors, they are expensive and seem complicted to drive ideally 2+ on a board so I can have multiple characters.

I guess I just need a simple explanation as all these other guides I have found over complicate it or aren't clear. I am by no means a noob but I really find it hard to understand whats going on.

I just need a servo which can accuractly be turned to one of about 40-50 positions in a spindle of characters. I guess I need atleast a 7.8 degree stepper. What can people suggest, you can see the 1st prototype used a modified servo for control.

Here is an example...


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Brunsbüttel, SH, F.Rep.GERM
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hey!

in wikipedia i found this U.S. Patent 3,501,761.

it seems like the split-flap display "knows" at which position it is...
are there any pins, that might say, the code of the current sign? u could drive a normal DC motor with a BJT and stop it as soon as the right code is read...

at an airport i saw a split-flap display, that had many little elements that were either black or white. maybe that is easier to control? maybe with 74hc595 chips?

bye
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-Arne

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Add gearing to get much finer rotation control.
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Sorry, I am happy to do this but the solari displays actually use servos and I would like to as gearing is complicated and yes it will have an encoding system to enable it to detect its location but my original message is asking for help in getting started with how to use steppers and I would like to stick to this topic for the moment if this is okay. I have been struggling to select an appropriate stepper and how to connect it to an arduino, I think i have to use h-bridges?!
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For a look at stepping motors try:-

http://www.thebox.myzen.co.uk/Workshop/Motors_3.html

and

http://www.thebox.myzen.co.uk/Workshop/Motors_4.html
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You are attempting to operate a system where angular position is important using an open loop control system.  The problem is that the system really needs to know where it is at any given time and right now it doesn't.  You can add feedback with either a simple encoder or make a gray scale encoder that is mounted to the side of the rolodex to tell you where you are at any given time.  Another way is to mark the edge of the split flips with either gray scale or simple binary marks and use several IR optos to monitor which is showing.  With a step index you can move the flip cards to which ever one you want.
  for simple understanding of steppers try http://www.stepperworld.com/pgTutorials.htm
« Last Edit: August 24, 2009, 05:34:36 am by Lepton_man » Logged

Lepton Man

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Grumpy_Mike that was excellent your tutorials really helped and I will be reading others on your site too like de-coupling later.

I am sure i need a 4 phase stepper which will be a bit more costly but I can buy one of those control chips and just pulse the motor along, then using some optical wizardry make it detect passing flaps and see what character its on.

Binary time me thinks!

What I need now is advice on where to get these steppers, Rapid have some, and so do RS but RS have only got expensive ones and other sites and eBay have random collections, there is no site it seems with a good catalogue like some have for things like LEDs etc.
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Also where on earth can i get SAA1027 as its not on any of the common places like Maplin, RS, Rapid, Farnel, CPC
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Quote
Also where on earth can i get SAA1027
It is rather old by now, you can look here for modern parts but most of them tend to be surface mount:-
http://uk.farnell.com/jsp/search/results.jsp?N=0&Ntk=gensearch_001&Ntt=steppin+motor+driver&Ntx=&suggestions=false&searchTerm=steppin+motor+driver&_requestid=227030&isGoback=false&isRedirect=false

For a bargin how about these motors at £2.50:-
http://www.motioncontrolproducts.co.uk/index.php?cPath=1048

They also do lots of other motors.

You don't have to have a driver chip the software can generate the signals, see the motor drivers at:-
http://www.arduino.cc/playground/Main/InterfacingWithHardware
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You may or may not need an h-bridge.  If your stepper motor has 6 wires, you will probably not, as generally there will be three wires per coil, a wire from each end and the center tap.  So you can ground the center tap and energize each end with simple single-ended drivers.

If your motor has 4 wires, then there are two wires per coil, and you will need an H-bridge per coil in order to energize with both polarities.

You will only need low speeds for this project, but be aware that if you do try to drive a stepper motor at high speeds you will need to ramp the speed up/down from/to stop, since the motor has mass which gives it significant intertia and it will not folow rapid accelerations.
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I can judge the size of your project by the size of the USB connector, but is seems relatively small, so not a very large stepper needed.
If you don't mind reusing "junk" you can salvage steppers out of old printers, scanners, plotters. In CD-ROM drives sometimes there are geared steppers. Sometimes, if you're lucky, you can find a unipolar stepper and a desolderable darlington array (ULN2003, ULN2803) which is all you need.
I was looking into creating exactly this type of split-flap display, but with only 7 different options - the days of the week. Would you share some of the vector files for the flaps and/or for the side wheels you used for your design?  
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Yeah it is a small project but is the motor in a floppy drive really good enough, they must be the tiniest little things.
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