need advise or help with stepper motor controller box

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VenusAstronomer
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need advise or help with stepper motor controller box

#1

Post by VenusAstronomer »


Hi all -

I have an old-style Newtonian scope (14.5 inches), solid fiberglass tube, on a steel fork equatorial base, set in concrete, in an observatory. I live in Florida - LOTS of dew! The control box (which I have schematic for) was made for a place where there is no dew, so things have shorted out a few times over the years. Well, this time, by golly, I want to not just replace the shorted out capacitor, or whatever, I want to get this thing done right, in a watertight box. This SHOULD be a pretty straightforward thing, for someone who knows what they are doing! (As in - not me!) I have tested both motors (RA is 60 hertz AC; Dec is 12v DC), and when power is applied to them directly they work, so it's just the controls to the wires that are my problem (the accursed controller box). The RA motor, being 60 hertz, tracks along, with the help of fine adjustments, using a timing chip and diode, both of which have shorted out in the past. Fine adjustment centering in RA is done by either speeding this up, or "stalling" it for the appropriate amount of time. Dec centering, with the DC motor, is done by running the motor one way or the other. (I have the schematic for the box.)

Along with the tracking needing to be fixed, the field centering also needs work. The controller for this had been jury-rigged to 2 focuser hand-boxes, taped together. The previous owner used this, but I have just used the slip-clutch feature to manually center things - which is seriously AWFUL, especially with a big, heavy scope! I would like to get field centering control on a paddle type box. Seems like that wouldn't be too much to hope for in 2019!

Any suggestions on who (in Florida) I might be able to get to do this, or if I might be able to get this done myself with a little advise?
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Dec
Dec
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Re: need advise or help with stepper motor controller box

#2

Post by VenusAstronomer »


Dang! I put those pictures on too quickly! (In defense of my insanity - I was in a hurry to get out and find some galaxies with my scope! Picked up some nice 13th mag. NGCs in Pegasus - without a drive motor to keep it in the field, tho.
RA - correction from first post, which is the DEC (ARH!)
RA - correction from first post, which is the DEC (ARH!)
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RA motion motor, housed under the RA gear
RA motion motor, housed under the RA gear
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Re: need advise or help with stepper motor controller box

#3

Post by VenusAstronomer »


OK, one more try with these darn pictures, then I'm outa here - heading for the observatory. Hunting down NGC 7720 tonight!
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Dec motor and gear!
Dec motor and gear!
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Re: need advise or help with stepper motor controller box

#4

Post by KathyNS »


Sorry, I don't know many people in Florida. I could recommend a good aircraft mechanic there, but that might not be helpful. :D

It sounds like you need a new controller. For the DC Dec motor, a reversible PWM module should do the job.

For the AC motor, it's a bit more complicated. What voltage is it? Some RA tracking motors used 120v AC, which would be nasty to try to fiddle with. I am guessing that the original build used a fixed-speed tracking motor, and that the stall-or-speed-up slow motion was an afterthought. It requires a variable-frequency oscillator, which would be ugly enough at low voltage, and really ugly at 120v.

Your subject line mentions stepper motors, but from your description, it doesn't sound like there are any stepper motors there at all. A pity, because replacing the existing motors with stepper motors would be a practical, and likely simpler, solution. Your controller could be an Arduino, and the speed controls could all be implemented in software.

You still need to find someone there who can do the work. Good luck with that.
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Re: need advise or help with stepper motor controller box

#5

Post by VenusAstronomer »


Thanks for the reply, and yes, the RA motor is 120v. Timing chip was in the original build. I'm putting an image of the schematic for the controller box here. This is the part that is not working.
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schematic of control box
schematic of control box
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Re: need advise or help with stepper motor controller box

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Post by KathyNS »


I can see how that works. The RA motor would work fine without the timing unit: it would just run at a constant rate. So all those electronics are just for the fast/slow control.

There are two dozen components there, any one of which could be what is malfunctioning. Someone with basic test equipment could, with some effort, possibly determine which one is the problem and replace it. But generally the effort to identify the problem makes repairing electronics uneconomical.

Good luck with it!
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DSO AP: Orion 200mm f/4 Newtonian Astrograph; ATIK 383L+; EFW2 filter wheel; Astrodon Ha,Oiii,LRGB filters; KWIQ/QHY5 guide scope; Planetary AP: Celestron C-11; ZWO ASI120MC; Portable: Celestron C-8 on HEQ5 pro; C-90 on wedge; 20x80 binos; Etc: Canon 350D; Various EPs, etc. Obs: 8' Exploradome; iOptron CEM60 (pier); Helena Observatory (H2O) Astrobin
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Re: need advise or help with stepper motor controller box

#7

Post by VenusAstronomer »


Thanks for the response. Just FYI, the timing chip allows me to tweak the power so that tracking is more accurate. Towards the upper right corner of the diagram is a "pot" that allows me to do this. The power here fluctuates quite a bit (we are way out in the country) so this come is very handy. I have put this post on this board in hopes of maybe finding someone who can take this diagram and make up a NEMA box with this in it. My husband and I can take the result and hook it up to the motors. We are just too old to have our fingers work well enough to get all those parts soldered up. No problem with paying for the time and materials involved!
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Re: need advise or help with stepper motor controller box

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Post by OzEclipse »


VenusAstronomer wrote: Fri Sep 27, 2019 3:49 pm Hi all -

I have an old-style Newtonian scope (14.5 inches), solid fiberglass tube, on a steel fork equatorial base, set in concrete, in an observatory. I live in Florida - LOTS of dew! The control box (which I have schematic for) was made for a place where there is no dew, so things have shorted out a few times over the years. Well, this time, by golly, I want to not just replace the shorted out capacitor, or whatever, I want to get this thing done right, in a watertight box. This SHOULD be a pretty straightforward thing, for someone who knows what they are doing! (As in - not me!) I have tested both motors (RA is 60 hertz AC; Dec is 12v DC), and when power is applied to them directly they work, so it's just the controls to the wires that are my problem (the accursed controller box). The RA motor, being 60 hertz, tracks along, with the help of fine adjustments, using a timing chip and diode, both of which have shorted out in the past. Fine adjustment centering in RA is done by either speeding this up, or "stalling" it for the appropriate amount of time. Dec centering, with the DC motor, is done by running the motor one way or the other. (I have the schematic for the box.)

Along with the tracking needing to be fixed, the field centering also needs work. The controller for this had been jury-rigged to 2 focuser hand-boxes, taped together. The previous owner used this, but I have just used the slip-clutch feature to manually center things - which is seriously AWFUL, especially with a big, heavy scope! I would like to get field centering control on a paddle type box. Seems like that wouldn't be too much to hope for in 2019!

Any suggestions on who (in Florida) I might be able to get to do this, or if I might be able to get this done myself with a little advise?

Hi VenusAstronomer,

Nice scope. The control circuit is pretty simple and should be pretty easy for someone with basic electronics skills to diagnose and repair. Because it has mains voltage floating around in there you need to be very careful. If you want to go to the expense of sending it to Australia, I can fix it for you. However, because your RA drive is driven by a synchronous motor, you will never be able to have a high speed slew for centering. Synchronous motors can only be speeded up to about twice their native speed before they start to lose torque and stall and unless they are a special type of synchronous motor, they cannot be reversed.

However, if you want to get a better more useable drive system, I would suggest that you replace both RA and Dec with a dual axis micro stepper motor control or servo motor circuit which will give you high and slow speed slew in RA and Dec on one hand paddle. If you add encoders to a servo system, you could possibly even upgrade to a goto system. There are off-the-shelf systems for doing this however because you have an ATM scope, you will need to do a custom mechanical linkage which will involve a bit of work.

The POT you refer to doesn't tweak the power, it adjusts the frequency of the oscillator circuit. Synchronous motors speeds are only governed by the AC frequency. voltage fluctuations only affect torque not speed. If you run the whole thing off a DC supply, even a DC supply that plugs into AC, then mains fluctuations won't affect the speed or torque. Circuits like that are susceptible to temperature changes.

First things first -

To get your drive system working again in its current function, I can talk you through some easy tests that need no electronics knowledge.

1. Try powering the circuit from both the AC input and the DC input? Does one work and the other not?

2. There are three fuses in the circuit. These are the first thing to check. Disconnect completely from power before removing. If you have a meter you can test them but for a couple of dollars, you can easily replace all three of them. I have coloured them yellow in this schematic. The three fuses may have external screw off access points or they may be mounted in small spring clip brackets on the circuit board.
Scope RA Motor Controller schematic cropped-2.jpg
3. The two transformers are very unlikely to have failed.

4. The 556 timer oscillator (RED) is a very robust circuit. It is possible but very unlikely to have failed in my experience.

_________________________________________________________________________________________________________________
EVERYTHING BELOW THIS POINT WILL NEED SOME BASIC ELECTRONICS KNOWLEDGE TO LOCATE, TEST AND REPLACE.

5. The wires from the handbox to the 556 (PINK) carry the resistances (ALSO PINK) that determine the oscillator speed. Resistors and capacitors in a circuit like this rarely fail. However, if any of those wires have a bad connection, the circuit won't oscillate, no oscillation, no 120vac output.

6. The power amplifier circuit amplifies the oscillator through the output transformer to produce 110v ac. Possible because this is providing the grunt(power) to the transformer it could have failed. if just one of the TIP29C power transistors(BLUE) have failed, the circuit won't work.

So try step 1 first. Then 2.
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Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
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Re: need advise or help with stepper motor controller box

#9

Post by VenusAstronomer »


Thank so much, OzEclipse, for the info, and the offer. Unfortunately you are on the other side of the planet! You have provided a very comprehensive description here. I'm afraid I may have mis-described some things, tho. Some of this my husband and I have looked into. My husband is a radio ham, so he understands electronics, but has reached a "certain age" such that his hands can't do the detailed work, and his eyes can't see very well what he's doing, so we've been hoping to find someone to just make us up a new box, since this one keeps getting dew in it, causing various things to short out every few years. (timing chip one time, capacitor another time) The guys who fixed it these times are now no longer among the living.

There is a little (flashing) red light on the box. It is wired in the diagram where it says, "Neon light." That tells me, by how fast or slow it is flashing, how synched up the motor is to 60hz. This light still comes on, but the motor does not run when powered up.....So, the fuse(s) are ok? Ahh! We just found the schematic for the RA motor, so I'm attaching it here. Also attaching another scan of the controller box wiring, but with some info at the bottom, which is not on the first one. I have a label from the Dec motor that I will have to dig up. I hope I'm not just wasting a lot of your time. Just trying to get my head around this all.

I guess getting the scope to GOTO capability would be nice, but in all the decades that I've been doing serious astronomy, I've never had that. (Actually, I enjoy "the hunt!") I have the documentation on the 110 (RA) motor. I'm attaching it here. We have been told that they are both "stepper motors," but I'm a bit confused here, because they (both) definitely only move the scope VERY slowly. They were installed for photographic tracking centering by the previous owner. (I have exactly zero interest in astrophotography, but I like the wide field views.) I dread to think of yanking motors off (that themselves work) and putting new ones on, probably necessitating drilling new housing screws holes and all.

Hope I'm not driving you nuts here. I can spend hours locating one galaxy and not be frustrated, but I'm SOOO frustrated with this! :(
Attachments
controller schematic with details
controller schematic with details
RA 110v DC motor schematic
RA 110v DC motor schematic
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Re: need advise or help with stepper motor controller box

#10

Post by Sky »


It looks like you need a Meade #43 Varipak DC/AC inverter for 120V RA motor speed control.

Just rip out all that dangerous, old electrical junk on the 120V RA motor and connect a standard 120V power cord/plug to the motor. Now, just plug the RA motor into the back of the Meade Varipak after powering it up with a 12V DC supply and you're set to go with 100% safety. The Varipak has fast and slow buttons along with a knob to fine tune the RA motor speed.

I've used my Varipak to drive the RA AC motors on both my small Criterion mount (1" shafts) and larger Criterion mount (1.5" shafts) that holds an 18" reflector.

Good Luck getting things sorted out ...
Meade-Varipack-43-front.jpg
Meade-Varipak-43-rear.jpg
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Re: need advise or help with stepper motor controller box

#11

Post by VenusAstronomer »


Hmm... Another possible partial solution. I appreciate the suggestion. This would get me back to having tracking, but field centering would only be solved in RA, and by using the same line for centering and tracking, I would have to get the tracking re-set every time I made a centering adjustment. Also, I would have to get a DC power supply, which is now being handled by the defunked controller box. Maybe a good Plan B. Thanks for the info.
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Re: need advise or help with stepper motor controller box

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Post by OzEclipse »


The motor wiring diagram you sent is for many different motors. Your motor could be a Hurst Bipolar stepper motor. It is possible to wire and drive a bipolar motor as a synchronous motor.

http://www.hurst-motors.com/lyg35geared.html

So you may have a bipolar stepper wired as a reversible synch. If this is the case, you may be able to separate the wiring and drive it using a stepper motor drive which might allow higher speed slewing and reversal for fast centering. It's not that simple, you may or may not need to change the gearboxes. I just can't tell from the info presented.

cheers

Joe
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Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
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Re: need advise or help with stepper motor controller box

#13

Post by VenusAstronomer »


I was able to catch up with an old friend yesterday. Haven't seen or heard from him in 3 or 4 years, as health issues took him away from astronomy. He's an electronics expert, who lives a couple hours drive from me, and a long-time ATM. He is going to come up and rescue me in a week or two. (WHEW!) I very seriously appreciate ya'lls trys at helping me here. I suspect that my descriptions of what I have and what's happening are a large part of the problem with trying to work this out remotely, since I have no knowledge of electronics whatsoever. I will add another post here when the situation is resolved and let you all know what the solution turns out to be. Thanks so much everybody! Clear Skies and happy hunting!!!
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Re: need advise or help with stepper motor controller box

#14

Post by Bojan »


This is fabulous telescope....
If I were you, I would seriously consider installing OnStep system... or (older) Bartels..
I am using both, they provide control of the telescope from PC (GoTo, guiding...)

Links are here:
https://onstep.groups.io/g/main/wiki/home
https://www.bbastrodesigns.com/StepperSystem.html
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Re: need advise or help with stepper motor controller box

#15

Post by OzEclipse »


Bojan wrote: Fri Nov 01, 2019 9:11 pm This is fabulous telescope....
If I were you, I would seriously consider installing OnStep system... or (older) Bartels..
I am using both, they provide control of the telescope from PC (GoTo, guiding...)

Links are here:
https://onstep.groups.io/g/main/wiki/home
https://www.bbastrodesigns.com/StepperSystem.html
Hi Bojan,

Nice to see you here.

This is an old post. The owner had minimal electronics skills so building & implementing an onstep was not an option. Also if you read she has a lot of moisture/condensation in the observatory and wants water resistant enclosures for the VFO so she probably doesn't want to add computers etc

Someone local to her has now helped her.

Cheers

Joe
Image
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships Astronomical Association of Queensland; RASNZ Occultations Section; Single Exposure Milky Way Facebook Group (Moderator) (12k members)
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