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Vixen Polaris motor controler and ST4 mod

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#1 Fred76

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Posted 17 May 2021 - 11:38 AM

Hello

 

I own an antic Vixen Polaris. It is equiped with a MD-5 motor and a MD-5 quartz driver. 

 

I want to add a ST4 port to the driver to be able to dither between photos.

 

Does anyone have a link for that kind of modification ?

 

Note that there is a jack plug in the driver, maybe is this the ST4 port already, but I can't find any documentation except that one in german that doesn't say much on that controler : http://www.amateuras...ualvixen80L.pdf (see page 13).

 

 

All the best

 

Fred


Edited by Fred76, 17 May 2021 - 11:48 AM.


#2 BlueMoon

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Posted 17 May 2021 - 12:02 PM

It would be very difficult. The motor is simply too old to be modified for what you want. The MD-5 is a simple DC controlled directional motor and would have to be extensively modified to accommodate being controlled via an ST4 port.  I have a Vixen Polaris myself and know the hardware quite well.

 

My advice would be to look for a more recent (modern) mount with the required ST4 port, controller and software.

 

Clear skies and best of luck.



#3 Fred76

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Posted 17 May 2021 - 12:57 PM

The "MD-5 quartz driver" does not drive a DC motor but a stepper one.

 

I opened the quartz driver and found a Toshiba binary counter TC40103BP. That kind of component was used to control stepper motors. So I also opened the motor box.

 

The motor has 5 wires. Its reference is PF42-48G 100Ω, 90mA per phase, 48 steps/round with a gearbox 1:300 from Nippon Pulse Motor Co. Ltd as mentionned on the label.

 

To control it from ST4, I just need to add some cables to the MD-5 hand controler, but where, that is the question...

 

The hand controler also has a small jack female between the motor cable output and the power supply plug... maybe is it some sort of ST4 port. There are 4 cables connected to it (orange, red, black and green). I will call John McClane grin.gif


Edited by Fred76, 18 May 2021 - 03:56 AM.


#4 BlueMoon

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Posted 17 May 2021 - 01:08 PM

 

t is a 5 wires stepper motor ref PF42-48G 100Ω, 90mA per phase, 48 steps/round with a gearbox 1:300 from Nippon Pulse Motor Co. Ltd as mentionned on the label.

Interesting. Mine was not a stepper. Quartz timed DC with a simple directional and speed control.

 

Clear skies.



#5 photoracer18

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Posted 17 May 2021 - 04:28 PM

How are you going to drive the scope with only an RA motor? ST4 requires dual axis motors or the object will eventually drift out of view without a motor on the DEC to pulse for corrections. You need an SP or GP mount for an ST4 interface. The original ST4 connector was a 15-pin corrector that later was changed to a modular phone type plug. It is possible to dual axis motor the Polaris using the ONstep or EQdrive, it just needs a bracket to allow a motor to connect to the DEC slow-motion gear train.


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#6 Fred76

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Posted 18 May 2021 - 04:04 AM

How are you going to drive the scope with only an RA motor? 

Yes !

 

Many mounts drive the scope in RA only. For example the Star Adventurer, the Astrotrac, the Fornax...

 

Dec is only necessary for second order corrections (like alignment drift, atmospheric refraction...) and Goto.

 

The idea is to add a dithering possibility when I use the Vixen Polaris or any other RA driven mount having ST4 to take photos. That "Dithermeter" would work on any mount having a ST4 port, and it will also serve as an intervalometer to control the DSLR. It is an ongoing project based on Arduino. To date, I will just dither in RA, but I could maybe add dithering in DEC in the future for other mounts. 

 

Note that ST4 is just a simulation of a hand controler. What it does is just simulating pression on "RA+ / RA-" and "DEC+ / DEC-" buttons. This is why all hand controlers can be converted to ST4 ports as long as you know the wiring diagram...

 

By the way, here is an archived post showing the internals of the MD-5 quartz driver : https://www.cloudyni...-voltage-range/


Edited by Fred76, 18 May 2021 - 04:17 AM.


#7 hcf

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Posted 18 May 2021 - 04:11 PM

Have you checked the ST4 mod for the CG-4 mount motors? Might give you hints as to what to do.

 

Although, it might be easier to replace the motor and controller with a newer Stepper/Arduino combo especially if you can find a stepper which fits the mounting bracket.

 

You might also want to search in the AP forums, regarding "banding" caused by RA only dither, as some have reported.



#8 Fred76

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Posted 20 May 2021 - 12:48 AM

I know that RA dithering only is not ideal. But it is better than no dithering at all. And when you have a small mount that only drives in RA you can’t do DEC dithering !

Most people that have banding issues with RA dithering forget that to be effective, this dithering in one single axis shall be very aggressive. Far more than a few pixels. 10-15 pixels amplitude is a good figure to start. And it is more difficult when you image an object more than 60° in dec.

Think about users of Sky Adventurer, Astrotrac, Vixen Polarie, iOptron SkyGuider…

I own an antic Vixen Polaris that only has RA drive. No DEC. And I don’t want to do deep modifications to the mount. Adding a few cables inside the MD-5 quartz drive is OK but replacing everything would be too much.

#9 astrokeith

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Posted 20 May 2021 - 01:05 AM

If you have a hand controller, then it is quite easy to add an opt-isolator. The isolator outputs sit across the direction buttons on the controller, the inputs go to your new ST4 socket.




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