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home brew clock drive?

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#1 Don Trinko

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Posted 12 June 2010 - 12:52 PM

I'm getting a used tescope with an EQ mount without clock drive. (Carton supernova mount I think) Has anyone adapted other drives or home made a clock drive for their EQ mount?
From the photos it looks like the slow motion cable has 2 ends and one is available to hook up to. thanks; Don t.

#2 DAVIDG

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Posted 12 June 2010 - 05:53 PM

All you have to do is count the teeth of the RA drive gear and then divide that result by 1440, the result is the RPM of the motor you need. The common tooth counts are 144 and 96. The 144 tooth gear would require a 1/10 RPM motor (6 Rev/hour) and the 96 a 1/15 (4 rev/Hour). Many times you can find these motors as surplus for under $10. New ones can be purchased from Herbach and Redmann http://www.herbach.com/ for under $20. Check out the Classic Telescope section, since this has been discussed a number of times and there are a number of examples there.

- Dave

#3 Gene7

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Posted 12 June 2010 - 08:39 PM

Do incorporate a $20 Wagan inverter driven by 12V. Available from JR Music. Attached is the circuit modification to make it adjustable speed. Quite stable. Otherwise you will drive yourself nuts trying to do mechanical match speed adjustments. Gene
I successfully identified the timing resistor and capacitor in the Wagan inverter. It uses a AZ7500BP-E1 16 DIP I.C. The circuit is listed on-line. Pin 5 is the timing Capacitor, and Pin 6 is the timing resistor just to the right of it. Both are blue metalized film low temperature drift components. See the attached pictures below. The yellow wire is attached to the top of the timing resistor and pin 5 of the I.C. The green wire is attached to the ground, as is the other end of the resistor. Note that the P.C. board conducting strips for these components do a 45 degree jog to the left next to the I.C.

http://www.PhotoShar...seup0232102.jpg

http://www.PhotoShar...seup0264784.jpg

As received the inverter produces a frequency of 57.5 Hz. I connected a 1.5 meg. resistor in parallel across the 135.K timing resistor. This increased the frequency to 61.5 Hz. I suggest that a parallel resistance of 1 meg. in series with a 5 meg. pot would give a reasonable frequency adjustment of a few cycles above and below 60 Hz. Another unit may have a different range and thus require different resistors.

Do the necessary preparation before trying to attach these wires. See detailed section below.



DETAILED SUGGESTIONS

I removed the black front cover of the inverter by applying slight pressure. Seems to have been solvent bonded to the light colored body, but not very well. A couple small screws removed the USB connector from the front cover. One screw allowed the body to come apart and the rear power supply connection removed from the body. Although the circuit board is crowded, it is the conventional through soldered component type and not surface mount, thank goodness.

I saw an A27500BP-E1 integrated circuit, which is a DIP- 16 pin I.C. A first real clue was 4 blue resistors and a small blue capacitor. Blue components are metal film and temperature stable, an indication that they may be timing components. Google told me the I.C. is a pulse width modulation control, and gave me a circuit diagram. Sure enough, pin 5 is the timing capacitor and pin 6 is the timing resistor, both blue components. The capacitor is .1 uF and the resistor is 135 K ohms.

Go about attaching the lead wires in a methodical manor. I used a large self supporting magnifying glass. #28 stranded wire is suggested, as well as a point tip heat controlled iron, a can of flux, and small wire solder. I am unsteady so I used some holding aids to position the wires. Secure the P.C. board so it does not skate around. A block of wood can help steady the iron. After the pictures I placed a small gob of clear epoxy over the solder joints to prevent breaking during wire flexing. #28 wire is hard to find even on-line. One source is for strain gage wiring.

Perhaps a more trouble free method would be to cut the resistor lead at the top of the resistor and remove both halves. Replace with a like value blue metalized film resistor. Let both lead ends extend perhaps a 1/4 inch to give room for lead attachment. Insulate and secure ends with epoxy when bent down. Gene Smith

#4 ccs_hello

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Posted 14 June 2010 - 12:40 AM

Gene,

Welcome to Cloudy Nights!

Your mod should be very useful for many.

Clear Skies!

ccs_hello

#5 skywolf856

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Posted 14 June 2010 - 07:10 PM

Here is a pix of a homemade clock drive I built using small sterling products aluminum gears. It was driven with a 1 rpm Hurst synchronus motor. I didn't have slow motion, but a friction clutch on the worm gear.

Attached Files



#6 rwiederrich

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Posted 15 June 2010 - 11:26 AM

Here is a pix of a homemade clock drive I built using small sterling products aluminum gears. It was driven with a 1 rpm Hurst synchronus motor. I didn't have slow motion, but a friction clutch on the worm gear.


That's pretty slick....I have a gear reduction my father built that is very similar to yours. I use a 12v motor now. It originally used a 110v clock motor that has since pooped out.

I tackled the speed control issue with something very out of the ordinary.

I use a model train power pack. It is designed to deliver ample current to drive model trains with heavy loads up steep grades......
High voltage low amps.

I know it sounds goofy...but I can simply control the speed of the 12v motor by turing the speed control know and away we go. No drag or binding. And the best part of it all....My *railpower* was only $10 at a second hand store.

I run the reticle light for my polar alignment scope with it as well......sweet.

And I also have another one...*Railpower* Powerpack (duel control version) that I use for the 12v motor in my focuser on my 10"f/15 and I use the other controller in it for the DEC tangent sector drive as well.

Model rail power is very accurate and very controllable...and is way cheeper and easier to use them most units designed for telescope drives.

Anyway that's my story.

Rob

#7 GilATM

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Posted 05 April 2013 - 02:38 PM

"
That's pretty slick....I have a gear reduction my father built that is very similar to yours. I use a 12v motor now. It originally used a 110v clock motor that has since pooped out.

I tackled the speed control issue with something very out of the ordinary.

I use a model train power pack. It is designed to deliver ample current to drive model trains with heavy loads up steep grades......
High voltage low amps.

I know it sounds goofy...but I can simply control the speed of the 12v motor by turing the speed control know and away we go. No drag or binding. And the best part of it all....My *railpower* was only $10 at a second hand store.

I run the reticle light for my polar alignment scope with it as well......sweet.

And I also have another one...*Railpower* Powerpack (duel control version) that I use for the 12v motor in my focuser on my 10"f/15 and I use the other controller in it for the DEC tangent sector drive as well.

Model rail power is very accurate and very controllable...and is way cheeper and easier to use them most units designed for telescope drives.

Anyway that's my story."


>> so I'm looking at adding a drive to a mount I'm working up, and came across this mention of using train drives - I found this one with two controllers - thinking of using for both axis - any thoughts?
TECH 4 280 DUAL POWER

What reduction in gearing would you suggest?

Gil
Ventura

#8 rwiederrich

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Posted 05 April 2013 - 03:21 PM

I'm not so certain of the gear ratios...but suffice to say..a good reduction so the DC motor is not heavely loaded. Then simply control the motors speed via the train transformer. I use one for both my homemade mounts...for the 6" and the 10" refractors.

#9 idp

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Posted 13 April 2013 - 07:50 AM

Hi Skywolf, that looks like a pretty neat arrangement. May I ask a couple of questions?

I've got an old mount with a dead Hurst, 1/2 RPM. Darn difficult to find a replacement one, but I got a 1 RPM like yours and was thinking of coupling it with a reduction gear to get the 1 RPM I need.

How would you proceed? Where do you find the gears? Is the aluminum you used good enough, compared to bronze?

Thanks,

Ivano

#10 Dick Jacobson

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Posted 13 April 2013 - 01:23 PM

I purchase gears from sdp-si.com.

#11 skywolf856

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Posted 14 April 2013 - 12:27 PM

The spur gears are all aluminum, small pitch.
My worm wheel is bronze with a steel worm driver 100 tooth.
Here are some good sources for gears and small parts:

http://www.wmberg.com/
http://www.sdp-si.com/
http://us.misumi-ec.com/
http://www.mcmaster.com/

#12 don clement

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Posted 14 April 2013 - 08:05 PM

I used passivated SS spur gears from Allied Devices but now available from Pic Design http://www.pic-desig...spur-gears.html in the beggining gear train for my cable drive that I still use BTW http://clementfocuse...Drive_Print.pdf
A really old school 7400 series TTL crystal controlled VFD (I built a few decades ago) is used to drive a Globe 33A603-3600 hysteresis synchronous 1.000 RPM motor so exact gear ratios weren’t needed. Note the nice Deutsch connector of Banning, Ca. on the front panel. http://www.astrex.ne...CFYF7QgodSUYAuQ

Don Clement
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