DIY Tracking Drive

[samtheeagle]

Could you please give us an update about how your motorized mount has been working, and whether did you make some modifications of your original design. Is it usable to make long exposure photos?

Hi swizzly, I'm afraid I can't give you much of an update on this now. My brother-in-law got all spend happy and purchased an EQ6, and so isn't using the motor drive I made. But I think the work we did shows that the idea is sound, he certainly got the eq3-2 tracking with it. The key things are getting a motor that is powerful enough (torque) to drive the worm gear, securely fastening the motor to the mount and getting the motor shaft coupled to the mount spindle, and finally generating accurate timing steps. Making a strong enough bracket is the bit we struggled with, I just used a thin bit of aluminium which wasn't up to the task. If you can get a bit of steel shaped and drilled to suit you'll be laughing. It's crucial that you get the power of the motor transferred to the worm gear as efficiently as possible.

[swizzly]

Hi skybadger and samtheeagle,

thanks for your answers. I have a (relatively) bigger stepper motor: Phytron ZSS 56mm, that probably has more torque than required. I hooked it up to an Arduino via a Adafruit Motorshield and it worked fine. Now I need to attach the motor to the telescopes spindle shaft and fix it to the mount firmly. I am very curious whether it would work as imagined.

[Epic]

Hi! Anyone still following this?

I am building a rotational decoder for an EQ3/2 mount. I have the original stepper motor and single axis controller. While I have the encoder worked out, I need to understand the motor better.  

I'd like to know more details on the stepper (I think it is a stepper/gear combination) but I don't want to open it. Anyone out there who has done that?

I'd also noticed I can run the motor in microsteps 1/8, so it is much smoother and more compatible with the way I can control the feedback from the encoder. Has anyone tried that? Why isn't that done 'out of the box'?

Cheers

[skybadger]

What is the stepper. It should be fairly obvious How many steps there are.

[Epic]

The total number of 1/8 microsteps seems to be about 46000 +-200. Question is what is the gear ratio, step count. This is not obvious without opening it.

[JamesF]

I've had the motors for my EQ3-2 apart several times.  There are some photos here:

http://www.tanstaafl.co.uk/2012/02/eq3-2-dec-motor-strip-down/

http://www.tanstaafl.co.uk/2012/02/eq3-2-dec-drive-gearbox-stripdown/

The reduction ratio for the gearbox in the motor unit is 120:1, as calculated here:

http://www.tanstaafl.co.uk/2012/10/eq3-2-motor-gearbox-reduction-ratio/

These days though I've abandoned that entire system and gone with AstroEQ using my own motors and mounting brackets.  There's a picture of the completed mod at the end of this page:

http://www.tanstaafl.co.uk/2014/10/astro-eq-conversion-of-eq3-2-part-5/

I'd still like to hear what you're doing with the encoder though.  Sounds like an interesting project.

James

[skybadger]

A gear ratio of 120:1 makes the steppers 43.75 steps per rev - a value i''ve never heard of. 48 would be the nearest.

[Epic]

120:1 makes sense to me, yielding 120 x 8 x 48 =46080 microsteps for single rev. However - James - your motor was the dec motor? I only use RA, so not sure if they are the same. Thanks for that anyway.

On the encoder: I have been working on this for a few months now, building a high-res encoder. My main goal is to come up with something that is low cost and of sufficiently high accuracy to allow  exposures beyond the 15 sec. (Thats what I get out of the EQ3 anyway).

I do have a solution that allows to measure 15''/sec with less than 10% noise. I can improve that with more expensive parts. Not sure if this is good enough, but its a start. Cost in parts (electronics) is about AUD40, plus mechanics. 

The only limitation is the max angular speed, which is rather low, so its unsuitable for fast tracking.

Cheers!

[cjdawson]

Just made a small change to the code posted above... Seems like I had it running in the wrong direction! I got my hands on the mount this weekend, and made a bracket to affix the motor... Using a really nasty bodged coupler made from plastic tube, insulating tape and some cable ties it appears that the motor is happy to move an unladen mount head, albeit with some slippage in the coupler department. I've got a proper one on order from ebay, so that should fix it right up

Fingers crossed it's going to work.

And sods law being what it is, I've just seen a reasonably priced single axis drive for an eq3-2 on astrobuysell! Always the way eh?

I do hope that the code change you did was to allow that to be adjustable.  Playing devils advocate, it not work great for you, but if someone where on the other hemisphere, they'll need the motor to go the opposite way ;-)

[JanH]

I'm building motorized DEG axis for Star Adventurer using parts from Orion EQ1  - worm, worm wheel and stepper motor. I don't expect any spectacular results but wanna give it a try. Some - even bad - correction in deg axis is welcome when guiding. Last night I managed to do polar alignment properly and got considerably long periods with no or minimal guiding and no or unnoticable drift in declination. But I was fidling with it a lot and tiptoeing around. I use Raspberry and Linguider, works great with QHY5mono on HEQ5 and even Phillips SPC880 is running well. It's for short FL not more than around 150mm FF.

How to control the motor? I think I can't use original handbox as it's running at siderical speed when turned ON and the buttons are just 8x forward/backward, stop and 2x forward. Where to solder DEG+ / DEG- wires for ST4?

Is a driver board for stepper motor from ebay a solution?

http://www.nbglin.com/motor.htm

I already ordered this one but now I see it says motor voltage 9-40V. I believe EQ1 motor runs on 6V (doing well on USB too).

If it is usable which conductors shall I use? I need 3 - common, forward, backward. I'd say DIR, ADD, DEC.

I must confess that my "barn" construction is more robust than original eq1 . There is even a thread about people actually using EQ1 (guided in RA) fot AP so the motor and gears can't be useless.

[Epic]

Hi Jan,

I am using an arduino to control the steppermotor with a sparkfun motor driver:  https://www.sparkfun.com/products/12779

Certainly possible to run via raspberry too.

This works well on my EQ3/2.  Not sure if the driver would be suitable to your requirements, but have a look. 

Cheers