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So my birthday just past so money to splash on astro stuff , i will have my 1000D modded by juan at cheapastrophotography and also have ordered an autofocuser from deepsky dad https://deepskydad.com/autofocuser i know they can be done DIY but this is a neat package and costs about the same as a SW autofocuser and a hitechastro focusmaster and i`m no electronic wizard and pavel seems to have a good product and works with ascom and confirmed it works with APT i will update in a few weeks time when hopefully i will have received and tried out .
I have a Helios 200p (identical to the Skywatcher) mounted on an EQ3-2.
I know it is overloaded but I find it OK for visual provided I give it a couple of seconds to settle down at high powers.
I intend to motorise the mount using stepper motors & an Arduino. It will be tracking for visual only with a possible upgrade path to GoTo.
Since I dont need fantastic precision and having read the relevant threads on this forum, I propose to drive the RA worm directly & the DEC with a simple belt drive. By avoiding a step-down gear set I will still be able to use the manual slo-mo controls without disconnecting the motors. I think that centering the target with the slo-mo's & then switching on the tracking will be nicer than using fast-forward & fast-reverse controls.
But no step-down means no torque amplification. So how much torque do you need to drive an overloaded EQ3-2. I decided to do some quick & dirty tests.
200p with 25mm Plossl & 9 X 50 Finder, payload about 9kg.
EQ3-2 with 10kg of counterweights
Improvised wooden pulley, effective radius 0.375 inch
2 X 1kg barbell weights
piece of string
For each axis ,with the clutches locked, a 1kg & then 2kg load was hung from the pulley & released. This was repeated for the opposite direction of rotation.
DEC 1kg Torque 13.5 oz.inch Rotated smoothly at about 90 degree/minute
DEC 2kg Torque 27 oz.inch Rotated quickly at about 300 degree/minute +
RA 1kg Torque 13.5 oz.inch Did not rotate
RA 2kg Torque 27 oz.inch Rotated smoothly at about 90 degree/minute
The required torque for RA would be on the limit for a (cheap, ungeared) NEMA 14 stepper but a NEMA 17 motor with a torque of 84 oz.inch should be up to it.
So now all I have to do is order the bits & learn how to use an Arduino.
Repairing a Tal MT3A Mount STEPPER MOTOR Help...
Before anyone says "why bother" let me just answer because I'm not ready to pick up a Losmandy at the moment...
So I have a Tal 200K which I have enjoyed quite a lot. I have always known that the single motor MT3A mount was less than ideal but it works and if nothing else, an 8" Russian made Kletsov catadioptric scope on a super solid peer mount is a pretty good conversation starter, and some of the views I've seen of Jupiter, especially with a 16mm Nagler - well they were amazing...
So a few months ago the mount stopped tracking and slewing at a star party. I could hear that the motor was spinning or making noise, but the mount was definitely not moving under the motor control. I might have just waited and bought something else, but I've had some major expenses plus I'm expecting another due to a large move about to take place so I can't justify spending the money at the moment, BUT I would really like to have a working mount for the Mars opposition in July. So I decided to tear it down and take a good look.
I was able to pull the mount casing apart ... and kept going, largely thanks to the PDF AndyH so kindly shared with me that had all the great teardown photos .. despite the native German which apparently translates into comical English with Google Translate ("Loosen the maggot whisk and the grub screws..." is that right??? )
The part that took me some time was realizng after removing the screws holding the case together and removing the setting circles and springs, that it was pretty difficult to unscrew the collar holding the drive shaft in the mount casing. For that I had to use a long screw placed into a hole in the collar as a kind of spoke to get some leverage to unscrew it. Once it started it was easy. Next I was more apprehensive about the drive shaft- The shaft fits through 2 bearings that had not seen freedom in 15 years, so I had to wack the shaft pretty darn hard from one end to break it free. I did this (again thanks to the photo in the pdf) using a block of wood over the end of the sharft - hitting the wood with a small hammer, and then a larger hammer. Like the collar once it was freed up it was easy to slide it through.
From there I just took stuff apart until I got into the drive gearbox. The small clock-like gear assembly was not difficult to remove and finally I got a good view of the stepper motor. At first I thought the gear was slipping on the shaft but it winds up being more serious. I removed the gear (loosened the 2 grub screws.. or were the maggot whisks?.. ;-) Of course I kept all the little screws in a secure place and tried to keep them attached to their mating parts when possible. But I think I'll be able to reassemble things..
I don't see any broken gears. My idea is to clean them up and lubricate them with a good quality lithium grease.
THE STEPPER MOTOR
I hooked up power and the controller and I clearly saw the drive gear is not slipping, but the motor is slipping, - internally. So I need to either repair the motor which no longer has the torque needed to drive the mechanism, or replace it. There's no way I can get the original motor (Tal is out of the astronomy biz and in Russia), and I don't know the specs about the motor to know how to ID it properly with an equivalent. It may be a type NEMA 17 with 6 leads. They aren't that expensive but will it fit? (looks pretty darn similar) Will the gear fit? Does it take the same signals/control voltages? etc. Alternatively Can the motor be repaired? I don't know much about stepper motors so I have non idea..
I know that stepper motors measure steps in degrees, and I imagine there's a spec that specifies the rate of spin, but I' don't know how to find this out for the motor in the MT3S. I have seen a NEMA 17 stepper motor in Amazon and it's less than $20, has 6 leads and has a 1.8 degree step. I might just take a chance and buy the motor and see if I can figure out the wiring.. if it's the same voltage...??...
I've attached an image of the printing on the motor and a short video showing it's unfortunate behavior.
If anyone has any suggestions how I can move forward I'd really appreciate it.
I've been whiling away my shipping wait for my hardware by watching and reading about Arduino and Stepper Motor control (Specifically). I was watching one rather informative video where the author hit on another library for the Arduino, AccelStepper.
It appears to be a bit simpler than regular Arduino coding, which was attractive to me. But what really brought me running was that it can accelerate and decelerate on either end of the command. Think of it being a Soft Start for a stepper motor running your focuser, or a Filter Wheel. Soft Start?
Yes, a Soft Start, and also a Soft Stop. Making your stepper motor gently begin to move, traveling to your selected point, then slowing the travel so it coasts in to what you requested. Soft Start is becoming quite common for a lot of motor driven devices.
So my thoughts on it were to program my upcoming Arduino projects with my own Soft Start and Soft Stop to bring the focuser to Step XXX and when trying to toy in a best focus, the automatic Soft Start could aid in getting gentler adjustments.
I bounced this idea off of my friend and he said that ramping speed was more for CNC machines and the like. And that tweaking in a focuser was more like around 70 steps to get the human eye to see the difference. I don't know (yet), but it seemed to me making any command gentler on the overall equipment might be a better idea.
Arduino (I've been led to believe) doesn't have this Soft Start - Soft Stop in their library yet. If you would like, Here are the links to this idea:
The Maker Show by Bret Stateham. If you scroll down on this page, there are quick links to the different parts he covers, including the AccelStepper part.
Quick Link to the AccellStepper Part. Or a bit before, where he refers to the Library, and where this software will be if you choose to download it for your Arduino Programming. I did, so it is there when I get my hardware here and actually begin my developing. (I prefer to have things in front of me as I prototype. I'm a hands on kinda guy.)
I searched to see if this had been posted here, but found nothing. So I thought I'd offer it up to anyone who might be interested. OK, back to hammering on my brain. (Think: A BB in a Boxcar.)
Hi all - I'm just about to build a new controller for my old Orion scope on a GEM1 mount - I know getting hold of a controller is near enough impossible now, so I'm going to make one with a microcontroller and an analogue joystick (for variable slewing rate). I'll post the results as I build it, and will make the details available for free - was just wondering how many of these mounts are still out there?