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RA Motor assembly for EQ5 Goto/GPX DX/SkyView Pro

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#1 ccdmaker

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Posted 30 May 2013 - 06:14 PM

I am in the process of building an EQMOD compatible microstepping drive for my ancient Vixen GP. It is working well but those sloppy gears that are part of the MT-1 motor assembly are producing much high frequency variations in periodic error. I managed to get one motor assembly that is part of the GoTo upgrade kit sold by Skywatcher; Orion sells the same thing (at least the motors look identical) :http://www.telescope.com/catalog/product.jsp?productId=7817&utm_source=channeladvisor&utm_medium=cse&utm_campaign=Channel%2Badvisor.
Unfortunately they will not sell spares unless you bought the whole kit, and I have no use for the rest of the parts.
Now that I know that this will work, I am looking for a DEC motor too.
Could someone enlighten me as to where I can find this part?

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#2 John Carruthers

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Posted 31 May 2013 - 07:50 AM

I fitted the SW eq5 kit to my SP, no I don't know of any SW parts supplier, only the full kit.

If you want to go the whole hog AWR will sell you a goto kit to suit your needs....
http://www.awrtech.co.uk/
They have Vixen compatible (MT1) motors.

#3 Geo.

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Posted 31 May 2013 - 05:48 PM

Cute little buggers, those steppers. Not sure what they are but I've got a couple of these $5 take off NEMA 14s coming from MPJA Online.

MFG: MOTION KING
P/N: 14HY9401
NEMA: 14
COIL: 6.5VDC/.5A/15 ohms/16mH
TYPE: 2 Phase Bi-Polar, 4 lead
STEP ANGLE: 1.8 deg
USED, 5mm Dia. X 1" steel shaft. Four corner M3 mounting holes. 8" leads.
L: 15/16" (Body) SQ: 1-3/8" WT: .22

If you are doing goto and money is no object the iOptron sells a kit for around $500, Meade LXD55/75 systems can be easily adapted to the GP. I needed a extra washer on the Dec to get good gear mesh. The Yahoo PICgoto group has several designs for PC/tablet controlled stepper motor goto.

Here's on I impemented on Veroboard. This is the front end I started a power section but it's too tough to do on Vero. So I'll have make printed circuit.

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#4 ccdmaker

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Posted 01 June 2013 - 01:18 AM

Hi Geo,

I already have stepper control implemented and working well with the MT-1's using a PIC24 board of my own design, and it is also EQMOD/ASCOM compatible. I know that there are several options to go buy ready made stuff like Ioptron, AWR etc., but for me, the fun is in building the electronics myself.

The MT-1s have notoriously bad gear trains, much slop is added before reaching the worm - the result is uneven high frequency modulation of the drive that results in sub optimal PEC & guiding performance. The solution is to build a microstepping drive and uses a much smaller gear ratio - something like 1:5 vs. 1:120. This gives the additional advantage of also being to run high slewing speeds too.

For me the hardest problem is the mechanicals - brackets, gears etc., I neither have the skills nor the tools to build that part; hence I picked the motors from the commercial GoTo kits. Besides I do not want to use the hand paddles with their built in databases - I'd rather run my mount entirely from my PC through Stellarium or Carte Du Ciel, EQMOD through ASCOM.

That said, if you have not yet finalized your stepper drive design, do look into the Pololu website - they have some neat and easy to use microstepping drivers all soldered on to carrier boards, that will easily spin your MPJA motors.
here's the link:
http://www.pololu.co...og/category/120

RK

#5 John Carruthers

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Posted 01 June 2013 - 02:33 AM

If you go the Skywatcher eq5 kit way you get a Synscan handset, add this to a cheap Syntrek eq mount for goto :-) or sell it on. The kit doesn't include brackets, it's a straight bolt on (depending on your mount of course). It does include gears, a little pack of grease and a couple of tools and bolts.
They say 12V supply but they like 14V better.






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