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Stepper Focuser

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#1 Charlie Hein

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Posted 01 July 2012 - 04:59 PM

Stepper Focuser

By John Pearson

#2 rsraney

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Posted 09 July 2012 - 10:14 AM

Thank you, I was about to dive into building something close to this for my own small OTA. And have been testing the Adafruit motoshield with the same stepper.

Would it be possible to have a link higher resolution image of your schematic drawing? Specifically the FocuserSchematic86.gif? the 800x600 does not do it justice.

A few small questions:

1) I have the same stepper motor, the adafru.it/324. But the wiring for the bipolar stepper may be different. The version I have is grouped with (yellow, red) and (green,brown). In your image of the motor shield you have the pairs, (blue, green) and (red, yellow). I and guessing your steppers do not have Grn, and its just the common ground, or did you solder common ground to the stepper case?

2) Do you find it makes a difference in how you have the stepper coil pairs arranged in the adafruit motorshield? I currently have them as follows:

M1 (yellow, red)
M2 (green, brown).

Again, Thank you for the great build and make!

- Shane

#3 Arctic_Eddie

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Posted 10 July 2012 - 12:59 PM

The stepper motors appear to have no consistency in the wire colors. I bought a second motor for my AT80EDTA and the colors were the same but the rotation direction was reversed. The best way to reverse direction is to swap the two wires going to M1 or the ones going to M2. In your case, make it:

M1 (red, yellow)
M2 (green, brown)

or

M1 (yellow, red)
M2 (brown, green)

Be sure to measure the leads with an ohmmeter to identify the two pairs. Either pair can go to M1 and the other to M2. It also makes no difference, other than rotation direction, whether the two wires within a pair are reversed. Reversing within one pair is the way to get the rotation in the direction you want.

If you have a motor with five or six wires then the odd ones, which are often center taps, are connected to the center ground terminal on the motor strip.

#4 allyman

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Posted 13 February 2013 - 02:31 PM

An Abolutely brilliant article. Can I also request a clearer copy of the schematic although the rest is fine.

Regards
Graham.

#5 ccs_hello

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Posted 16 February 2013 - 11:00 AM

I would suggest adding a LCD module to show the absolute position. That will add the value significantly.

P.S. it can easily add a thermal couple temperature probe to do the focuser temp compensation.

Clear Skies!

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#6 Arctic_Eddie

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Posted 19 February 2013 - 09:07 AM

I'll try to get a better schematic but it will likely be a screen capture in BMP format. The file will be large. If I can't send it to you directly then it will go on my website.

A four digit display will easily show position but you will lose the absolute part at power down. I see no way of easily adding a position encoder to the internal focusing mechanism.

Temperature compensation is likely too dependent on the individual scope. Calibration would also be a problem. The focusing action is so smooth and easy to use that I will not likely add any more accessories. It solved my problem of not having to touch the scope.

PS
I did a screen capture of the schematic in KiCAD, cropped out the extra part, and put the BMP image in a ZIP file. It will unpack to about 3MB. Download the included attachment.



#7 Arctic_Eddie

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Posted 19 February 2013 - 09:31 AM

The attachment apparently did not get included. Here it is again.

Attached Files



#8 allyman

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Posted 19 February 2013 - 03:18 PM

Hi John,

Many thanks indeed for making your schematic clearer. Your project is an excellent one and worthy of copying. I'll be studying it very carefully over the next few days.

Well done and many thanks again.

Best Regards,
Graham.






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