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Adding a Drive to a ATM Mount?

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#1 DarkSkys

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Posted 07 March 2013 - 03:06 AM

Anyone on here done it? I keep thinking how nice it would be to have Tracking on my GEM mount. I'm a Visual Observer with no plans of Astrophotography, so Close enough is good enough for me.

My Mount uses Solid Steel shafts 1.25" in diameter, I have never weighed My scope, But I don't think I have much more than 10-15lbs of scope and counter weight, It's only got a 6" Newt on it.

I have a bunch of old printers, I Wonder if the stepper motors from that would be powerful enough to drive it.

It seems like a stepper motor with a adjustable Drive contoller would be the easiest way to do this, might not even need a worm gear?

What say Ye, members of the ATM Section?

#2 polaraligned

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Posted 07 March 2013 - 07:08 AM

I have a Mel Bartels stepper driver that I never used and will sell cheap. The software is Windows 98 and no longer supported, but it is available from Mel's website for free download. It is listed on the other Mart site if you are interested.

#3 Dick Jacobson

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Posted 07 March 2013 - 08:57 AM

I've built fork mounts with tracking, not German Equatorials. I use DC motors with a potentiometer to control the speed and they work very well although vibration can be a problem. I haven't used steppers but I know they can be noisy and vibrate a lot.

I've used motors from Servo City and Herbach & Rademan, gears from sdp-si.com. I understand that a lot of ATMs use the Celestron Astromaster drive, adapted as necessary.

#4 Arjan

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Posted 07 March 2013 - 11:18 AM

Anyone on here done it? I keep thinking how nice it would be to have Tracking on my GEM mount.

Yes, on my Vixen Polaris. See here.
You can also buy simple DC motors which are good enough for visual use.

#5 Bill Kocken

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Posted 07 March 2013 - 11:32 AM

I haven't used steppers but I know they can be noisy and vibrate a lot.

Hey Dick, don't judge steppers based on what you saw mine do. My first try at it was a noisy, vibrating mess :o, but my latest iteration is pretty good. At least it's good enough for my equatorial platform with no vibration noticed in the eyepiece. I'm sure it could be improved even more by someone more skilled in electronics than I am.

#6 Lynnblac

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Posted 07 March 2013 - 11:53 AM

You can solve all this stepper motor/electronics mess by getting a drive from Orion Telescopes and then adapting it to your mount. Orion sells several different drives for GEMs.

#7 Geo.

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Posted 07 March 2013 - 12:56 PM

Certainly, a drive based on your basic synchronous clock motor is the most straight forward approach. Not a lot of torque, but they are generally are at the end of a very high gear reduction ratio. For reasons never explained to me, my dad couldn't seem to pass up a bargain on clock motors. So I inherited quite a collection in various output ratios. So there are lots of gearing options. Celestron used a lot of 1 revolution per hour outputs to drive the original C8 spur gears. IIRC the output gear is 12 teeth (tooth?). So for a solar day of 1440 minutes and 12 teeth/hour we need 12 * 24 = 288 teeth on the main gear. Oddly, the RA/AZ gears used on the Nexstar goto mount also had 288 teeth. Meade used worm gears in most of their mount early mounts. A 180 tooth worm wheel was the most common. With a simple clock motor rotating the worm at 0.125 RPM or once per every 8 minutes (8 * 1800 = 1440) you get your solar day. The rarer 360 tooth wheel used a 4 rotation/minute worm. Celestron sold about 20,000 mounts with Byers worm gears including a few with clock motors. The Byers wheel had 359 teeth, which when driven by a 0.0625 (1/16th) RPM motor gets you a sidereal day (1436 minutes). I gave these worm gear sets available for sale.

The speed of synchronous motors can be controlled to a limited extent by changing the frequency of the AC line signal. Autoguiding is possible with the proper circuitry. See: code.google.com/p/ultima8drivecorrector/

Stepper motors seem to come in and out of favor. It is no longer true that a stepper setup need be noisy of create vibration. The latest Synta EQ-6 uses steppers. Steppers came into favor for precise motion control earlier than servo motors as the electronics needed to control them were somewhat simpler. As processors got more powerful servo motors in closed loop control systems became the norm. Now with even more powerful processors steppers are getting a second look. Running microprocessors at higher frequencies permits finer micro-stepping that greatly smooths out a stepper. The PICgoto Yahoo group (Picgotogroup@yahoogroups.com) has several PIC microprocessor based stepper driver designs developed by members. The drivers are controlled by a WinPC with freeware from the group. The freeware has been ported to other platforms.

The Roboscope Yahoo groups specializes in adapting the Meade Autostar goto system to other mounts. Autostar is a closed loop servo-motor system controlled by two or more networked microprocessors. It's great advantage is that it's fairly cheap and easy to adapt to other mounts.

As may be gathered from the above some precision and control system is the norm for mount drives. Running a low voltage DC motor with a simple resistance control is not going to get you any precise speed. Speeds will vary a lot with changing loads, temperature, etc. Even simple voltage control systems like Meade's LX-10 and ETX90-RA aren't suitable for any extensive tracking. The Celestron Logic drive mentioned has a better system that may serve you needs. I've diagramed the circuit and built a working clone that I'm still experimenting with. To work with this you'll need a 6-24vDC motor with a reducing gear head. This one from Marlin P. Jones & Assoc. Inc. should work; http://www.mpja.com/...p?r=340400&s=39

Here's a couple of drawing I made of the logic drive circuit. Upper is the original PCB the lower is my layout on Veroboard. I omitted the reversing and on-off switches. My layout measures about 1.5 by 1.25" when finished.

Attached Files



#8 Geo.

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Posted 07 March 2013 - 12:57 PM

Here's the working cicuit:

Attached Files



#9 Dick Jacobson

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Posted 07 March 2013 - 04:31 PM

What are the power requirements of the various options? To me, low power consumption is the most important consideration. Accuracy is good but extreme accuracy is not necessary for visual observing. Low vibration/noise, low cost, reliability are also desirable.

A 12V DC motor that I have used consumes only 45 milliamps. I should be able to run it for almost 50 hours on a charge using a small 2.1 amp-hour lead acid battery. The motor has way more power than needed for most drives and I can get the speed accurate to one percent with a potentiometer.

#10 DarkSkys

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Posted 07 March 2013 - 08:47 PM

Certainly, a drive based on your basic synchronous clock motor is the most straight forward approach. Not a lot of torque, but they are generally are at the end of a very high gear reduction ratio. For reasons never explained to me, my dad couldn't seem to pass up a bargain on clock motors. So I inherited quite a collection in various output ratios. So there are lots of gearing options. Celestron used a lot of 1 revolution per hour outputs to drive the original C8 spur gears. IIRC the output gear is 12 teeth (tooth?). So for a solar day of 1440 minutes and 12 teeth/hour we need 12 * 24 = 288 teeth on the main gear. Oddly, the RA/AZ gears used on the Nexstar goto mount also had 288 teeth. Meade used worm gears in most of their mount early mounts. A 180 tooth worm wheel was the most common. With a simple clock motor rotating the worm at 0.125 RPM or once per every 8 minutes (8 * 1800 = 1440) you get your solar day. The rarer 360 tooth wheel used a 4 rotation/minute worm. Celestron sold about 20,000 mounts with Byers worm gears including a few with clock motors. The Byers wheel had 359 teeth, which when driven by a 0.0625 (1/16th) RPM motor gets you a sidereal day (1436 minutes). I gave these worm gear sets available for sale.


Digging around in my Junk storage yesterday, I came across a INGRAHAM Series 80 3W clock motor. It doesnt say What RPM/RPH it is, so I'll have to do some experimenting on that front.
If i'm understanding that last sentance right, Whats the cost for a Worm gear Set?


The speed of synchronous motors can be controlled to a limited extent by changing the frequency of the AC line signal. Autoguiding is possible with the proper circuitry. See: code.google.com/p/ultima8drivecorrector/

Stepper motors seem to come in and out of favor. It is no longer true that a stepper setup need be noisy of create vibration. The latest Synta EQ-6 uses steppers. Steppers came into favor for precise motion control earlier than servo motors as the electronics needed to control them were somewhat simpler. As processors got more powerful servo motors in closed loop control systems became the norm. Now with even more powerful processors steppers are getting a second look. Running microprocessors at higher frequencies permits finer micro-stepping that greatly smooths out a stepper. The PICgoto Yahoo group (Picgotogroup@yahoogroups.com) has several PIC microprocessor based stepper driver designs developed by members. The drivers are controlled by a WinPC with freeware from the group. The freeware has been ported to other platforms.

The Roboscope Yahoo groups specializes in adapting the Meade Autostar goto system to other mounts. Autostar is a closed loop servo-motor system controlled by two or more networked microprocessors. It's great advantage is that it's fairly cheap and easy to adapt to other mounts.

As may be gathered from the above some precision and control system is the norm for mount drives. Running a low voltage DC motor with a simple resistance control is not going to get you any precise speed. Speeds will vary a lot with changing loads, temperature, etc. Even simple voltage control systems like Meade's LX-10 and ETX90-RA aren't suitable for any extensive tracking. The Celestron Logic drive mentioned has a better system that may serve you needs. I've diagramed the circuit and built a working clone that I'm still experimenting with. To work with this you'll need a 6-24vDC motor with a reducing gear head. This one from Marlin P. Jones & Assoc. Inc. should work; http://www.mpja.com/...p?r=340400&s=39

Here's a couple of drawing I made of the logic drive circuit. Upper is the original PCB the lower is my layout on Veroboard. I omitted the reversing and on-off switches. My layout measures about 1.5 by 1.25" when finished.


Thank you for all the info and the picture.

#11 avarakin

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Posted 07 March 2013 - 09:47 PM

EBay is full of arduino boards for $8 and stepper motors for $5. I am working on replacing Servo Motor drive of my CG3 with such setup. Let me know if you need more info, I can post eBay links.
Alex

#12 Arjan

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Posted 08 March 2013 - 04:22 AM

A little further down on the linked Marlin page is a very nice 200step/rev stepper including gearhead. Seems ideal for the application...

#13 DarkSkys

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Posted 08 March 2013 - 05:53 AM

A little further down on the linked Marlin page is a very nice 200step/rev stepper including gearhead. Seems ideal for the application...


That does look like it could be pretty usefull.

Some thing I'm wondering, I've never had much experience with stepper motors, will the Driver be a stand alone, set it and forget it deal?

#14 Geo.

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Posted 08 March 2013 - 02:16 PM

Steppers are the biggest hogs mainly because they need current to hold them in position when not moving. That said, a NEMA17 only draws about 0.25 amps @ 12v. If you are only interested in a single precise speed, I'd say yes, once you have your pulse frequency set for you desired output speed you will get good tracking accuracy. Over their useful life capacitors can have slight changes in their performance, so a trimmer is valuable to have in the circuit to adjust the value of the resistor that is part of the pulse control. Probably need it to get the precise speed you want anyway.

A stepper driver can be controlled by a 555 timer and dispense with a microprocessor. See:

http://www.techlib.c...cs/stepper.html
http://makeprojects....ee Types of ...

The op-amp circuit shoots 1.2v pulses to the EQ-1 drive when powered by a 9v cell and will run a long time on one battery. The pot gives quite a large range of speeds.

For battery operation, control and guiding this circuit that can be found at Google Project Hosting can be used with a synchronous motor.
http://code.google.c...or/wiki/design2
I repeat a synchro can only operate at slightly different frequencies from its 60 Hz design, so you have to get close with your gearing. This also a fairly easy circuit to build on Veroboard. It does involve buring code to a PICMicro processor.

#15 Arjan

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Posted 09 March 2013 - 02:27 AM

The driver can be stand alone, that's how I use it anyway. You can make a simple one based on a timer (e.g. 555) and some logic that creates the pulse trains. Be sure to add a power driver such as a ULN2803, you cannot directly drive from the logic (like the 74HC74 used in the link by Geo).

I use a PIC driven by a crystal to get stable pulse rate and generate the correct pulse train. You need to program the PIC controller with SW that is right for your application (gearing etc.). An alternative is to make the rate adjustable in some way, but I did not do that for my one-shot implementation. Could be included though, since it has an RS232 interface...

#16 orlyandico

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Posted 09 March 2013 - 03:58 AM

IMHO just buy an EQ-1 motor drive. They are quite cheap.

Now they are built for a 100-tooth worm reduction, so depending on the tooth count of your worm, you will need to change the speed. It's easy, just replace the crystal.

http://orlygoingthir...nt-hacking.html

This has the advantage of being a working system, probably more reliable than anything you can build yourself, and it's cheap. Under $100 for the EQ-1M drive and a couple bucks for the crystal.

#17 DarkSkys

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Posted 09 March 2013 - 05:00 AM

IMHO just buy an EQ-1 motor drive. They are quite cheap.

Now they are built for a 100-tooth worm reduction, so depending on the tooth count of your worm, you will need to change the speed. It's easy, just replace the crystal.

http://orlygoingthir...nt-hacking.html

This has the advantage of being a working system, probably more reliable than anything you can build yourself, and it's cheap. Under $100 for the EQ-1M drive and a couple bucks for the crystal.


I dug out a EQ1 I'm not useing that I could steal the Worm geat train off off .:question:. I would have to be creative with mounting it to the clutch assembly.

One of those EQ1 drives would be powerfull enough for this sized scope? They seem to be available on ebay at a reasonable price.

#18 Geo.

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Posted 09 March 2013 - 10:33 AM

The Synta EQ-1 drive uses the same Chinese bipolar stepper as their other EQ (2, 3 & 4) drives. The motor is a knockoff of the Nippon Pulse Motor stepper used by Vixen on the SP/GP/GP-D line. The early HEQ-5 and 6 (Sirius and Atlas) used a similar system with larger steppers and larger power transistors to drive each channel. The GP-D is rated 30 pound payload. I have several dead Synta controllers, so I don't know how much of a working system it will be :roflmao:

The 8051 microprocessor design dates to 1980. The latest Synta stepper drives I've seen have been ported to a new design.

#19 orlyandico

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Posted 09 March 2013 - 11:26 AM

I'm not sure what sort of motor the EQ-1 uses, I no longer have mine.

The GP uses a Nippon Pulse unipolar stepper; I discovered that the AP 600E QMD uses the same stepper (but with 150:1 ratio instead of the 120:1 of the Vixen GP). So this motor is powerful enough for at least an AP 600E QMD.

You don't need a very powerful motor, so long as the load is balanced. If it's not balanced.. you'd need a huge motor.

#20 Arjan

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Posted 09 March 2013 - 11:52 AM

IMHO just buy an EQ-1 motor drive. They are quite cheap.

... It's easy, just replace the crystal.


I fully agree, but mine doesn't have a crystal: it's a DC motor with some flimsy current driver. Need to change some resistors instead in that case.






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