Telescope Leadscrew Advice

[duncan webster 1Participant @duncanwebster1]

Here’s a typical example https://www.omc-stepperonline.com/geared-stepper-motor?srsltid=AfmBOop8RgE418gb-pWmfiGDQoUZnDSn4ZOe5Y2R3ZR6Z7CMpAhO6gKU

[SillyOldDufferModerator @sillyoldduffer]

I am green with jealousy!  25 years ago, I very much wanted a big Meade and putting one on a Dobsonian mount kept the cost down: people liked them for quick resetting and stability too.  Disadvantage is Dobsonian’s don’t track or provide fine adjustment, the latter issue being tackled by Dr_GMJN here.

Never happened!  At the time family commitments meant no space for a big telescope, and no time to use it.   Viewing is obstructed too, and the UK is usually under a cloud.   I compromised on a 6″ reflector on a stand – still too big, and though plenty of interest in the sky, it was rarely used.   Not getting enough sleep is bad for me!

I wondered what Meade sell today: telescopes and accessories have moved on considerably, what with GPS, star-finders, better lenses, tracking stands, digital cameras and whatnot.   Unfortunately Meade get my award for the world’s worst website.   Instead of telling me what their product range is and providing technical detail, it’s full of corporate puff.  When someone is interested in Astronomy, likely knowing that equipment can easily cost several thousands, I don’t care for the likes of:

The Meade Expert Team provides high-quality telescopes and accessories for amateur astronomers. Their products enable stargazers to explore the night sky.

I’d put up with it if the site eventually led to the technical detail I wanted, but this one doesn’t.   Meade’s official site only mentions two cheap entry level telescopes, with no sign of anything else.  Very odd, almost as if Meade don’t want to sell telescopes!    My guess is they first outsourced production to China (successfully), and have since outsourced design as well.   Possibly Meade in the US don’t have any techies, have become a sales outlet, and lost touch with customer needs.   Their site is competent, but the content is focused wrongly.   Searching retailer sites provided technical info showing that Meade still sell high-end telescopes, so someone in their team knows what’s what.   Perhaps Meade’s Sales Department and Board believe technology is a minor detail, and they have a box-shifter mindset.   If so, bad attitude for a technology company to have.

9:15AM, so no more Model Engineering for me today.  Family visiting, and if I don’t shave, tidy the house and put on a brave face, they’ll put me in a care home.

Dave

 

[John HaineParticipant @johnhaine32865]

If you poke around online there are a number of telescope controllers using Arduinos and steppers. Probably also with coordinated motion for a Dobsonian. Once you can control the telescope with a processor if you fitted a ccd sensor you could observe from indoors in the comfort of an armchair!

[SillyOldDuffer]

On SillyOldDuffer Said:

I am green with jealousy!  25 years ago, I very much wanted a big Meade and […]

This is probably more to your taste, Dave:

https://www.orionoptics.co.uk/

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Being a Luddite, for a fine adjustment, why not use a ME 40 thread?

40 tpi from 1/8 up to 1/2″ or 32 tpi from 5/16″ to 1/2″

Howard

[Howard LewisParticipant @howardlewis46836]

Since you have Metric thrust bearings, if you went the ME route, you will need to make some carriers to sit them on the Imperial adjusting shaft

[duncan webster 1]

On duncan webster 1 Said:

You can set a stepper controller to do microstepping,which as its name suggests means it does a lot less then 1/200 of a rev every time it gets an input  pulse from the arduino. I’m not sure how well it would stand still doing that, you can also get gearboxes to bolt straight onto stepper motors.ivd gog one somewhere,ill dig it out and take a picture. For something this simple,where you at a minimum only need clockwise or anticlockwise, continuous or jog you could actually do it with something like a 555 and some push buttons, although I’d use a processor as you are bound to want to add functionality. I always do.

Thanks Duncan.

I’m doing some calcs, and I think a 5:1 or 10:1 gearbox would do the trick for azimuth The backlash of 0.5 deg. looks acceptable too once the gear ratio of the slew ring:drive is accounted for. The motor/gearbox combinations you posted look good – I’d hate to have to build one for that kind of money…

The altitude drive would be direct.

I’m on an astronomy forum where they’re into all sorts of diy tracking projects, and I’m sure if I can get the jog functions working well, I could then adapt it to track for an hour or so, and ultimately try some long exposure photography. The Equatorial Platform is surprisingly great, and seems very insensitive to initial setup.

I’ll be using two rotary encoders on a flying lead to control the axes. One will have a push function so I can centre the altitude nut quickly when I run out of movement.

 

[John Haine]

On John Haine Said:

If you poke around online there are a number of telescope controllers using Arduinos and steppers. Probably also with coordinated motion for a Dobsonian. Once you can control the telescope with a processor if you fitted a ccd sensor you could observe from indoors in the comfort of an armchair!

That’s the ultimate goal I guess – I didn’t intend to go down the powered axis route at all, but a stepper motor for azimuth is so much easier (I think!) than a mechanical knob, quick-release and locking mechanism.

If I’m powering one axis, it would be rude not to power the other, and then why not use a stepper for the platform drive too?

It’s all escalated very quickly.

[Howard Lewis]

On Howard Lewis Said:

Being a Luddite, for a fine adjustment, why not use a ME 40 thread?

40 tpi from 1/8 up to 1/2″ or 32 tpi from 5/16″ to 1/2″

Howard

Thanks Howard – I got the M8 x 0.75 tap and die today, so that’s that.

[Dr_GMJNParticipant @dr_gmjn]

It’s now complete and works smoothly. Just need a clear night to test it for real. Thanks.

 

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