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DIY controller for Nippon PF42-48 motor specs wanted


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Hi all,

I'm on a diet astronomy budget and have got my hands on an old GP-DX mount with DEC-motor. It's a Nippon PF42-48i3 G. I've found one spec sheet so far (attached) and this motor seems to be controlled from a DD-2 or DD-3 controller, which I don't have, are hard to come by, and pricey.

I do have an Arduino, some stepper controller IC's and all that so it should be easy to get the motor turning. Just wondering if there are more people around doing these things DIY and have more elaborate spec-sheets.

Most important question now is how fast to turn the motor for proper DEC-tracking? It's got an internal 1/120 gear ratio but I don't know the ratio on the mount itself. Not difficult to find out experimentally but maybe someone knows.

Cheers,

Han

npm-pf42-specsheet-1-638.jpg

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Looks like one rotation of the driving shaft on the mount is 10', so I need 1 rotation of the shaft every 10 minutes = 1rev/600sec. For 1/120 gear ratio that makes 1rev/5sec.

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  • 3 weeks later...

Please document the gear train so that there’s a searchable reference for your kit. It might make someone’s life much easier in the future. Also your step frequency to get the drive rate  right would be nice to know. I sure hope you get it sorted as reviving older machines has its own reward.

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Several sites I found state that the DEC and RA gears on the GP-DX have 144 teeth, so 144 rotations of the worm are required to rotate the axis by 360 degrees.  If the motor is driving the axis directly (or via a 1:1 gear ratio) and has an internal reduction of 1:120 then I guess that means the total gear ratio is 17280:1.  That gives a figure of approximately 4.986 seconds per revolution of the motor assuming I've done my maths correctly, which is pretty close to what you have calculated.

James

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Oh, it's almost certainly worth having a look at the AstroEQ project, for inspiration if nothing else (though you could probably borrow a great deal from it).  It uses an Arduino to create a generic mount drive system.  It doesn't get you a handset, but it does provide an EQMOD-compatible interface so it can be plugged into a PC and controlled from a planetarium application there.

James

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