DIY Fork Mount for Widefield Imaging Rig

[happy-kat]

I'd go for practical and get something done and working, otherwise winter will pass and it will still be in tweak mode.

 

[Gina]

16 minutes ago, Dr_Ju_ju said:

Hmmm, methinks the design starts to look like a Mesu , especially if you're planning on automating each axis of movement

In what way do you think it starts to look like a Mesu?  Mesu are GEM mine is a fork.

[Dr_Ju_ju]

All the large diameter wheels, and yes I appreciate its a fork mount....

[Gina]

Right!  Practical it is.  Single imaging rig relying on accurate PA rather than guiding.  This stands a chance of working with the shorter FL lenses if less so with 200mm.  I do have the EQ8 as a more accurate mount anyway.

[Davey-T]

33 minutes ago, Gina said:

In what way do you think it starts to look like a Mesu?  Mesu are GEM mine is a fork.

Latest ones are a sort of fork without the fork, no flipping flipping

Dave

[Gina]

My current WF imaging rig which fits on the EQ8 has provision for turning the camera for best framing.  I've been looking at possibly doing this for the new rig but it's problematic.  Also, unless I motorise it for remote control it violates the totally remote principle.  In fact with the high resolution of the ASI1600MM, the image can be cropped a lot before too much data is lost so frame orientation is not that important.  This means the camera and EFW can be orientated to suit the construction.

[Davey-T]

How are you planning to balance it ? before fitting drive belts ?

Dave

[Gina]

That is something I need to sort out.

[lux eterna]

It´s interesting to read your creative ideas, Gina. I am curious about how remote this will be, and what kind of place will be hosting this mini observatory ? Since you opt for remote PA, I guess it will either be very far away or the ground support may vary a bit from time to time. Otherwise manual PA would be good enough (?)

BTW, I have experimented a bit with 28BYJ-48 steppers and I can tell that there are (at least) two different models out there. They look the same but one is 64:1 and the other just a tad different. I used it for a barn door tracker, but I found out a limiting factor being the cogs on the output shaft did not engage enough, which produced a too big PE (no problem for you as you will not use it for tracking). So now I am in the process of building something better - and it´s great fun. Since retirement I have the time, and with small steps forward each day I will eventually get there. And write a separate thread about it. One thing I have learned is don´t go too fast, because new and better ideas often spoil a lot of work done and materials used (I am reminded each time I look in the waste bin of my small workshop) 😏

Ragnar

[Gina]

Ah yes I know only too well what you mean.

The imaging system will be housed in a micro observatory - either dome or clamshell - haven't decided yet.  This will be something like 400mm diameter.  I run imaging remotely from my living room.  The pier is a Skywatcher Pier Mount sitting on three concrete blocks.  Not far away but I don't want to take a laptop outdoors to see the effect of PA adjustment.  And since I could arrange remote PA adjustment, I did.

[Gina]

Single imaging rig.

Edited December 17, 2019 by Gina

[Gina]

If I were to go for no guiding I don't need the pixel resolution in the DEC axis since this will only be used for initial image framing.  So I could have one less reduction stage resulting in around a 6 pixel resolution.  This will simplify the DEC drive.  I can use a NEMA 11 stepper motor to reduce weight.

[Gina]

Just checked and found the NEMA 11 - size is 28mm x 28mm x 28mm.  A lot smaller and lighter than the 17 size.

[Gina]

NEMA 11 and timing pulley added.  That completes the DEC drive apart from timing belts.  Intermediate shaft wants shortening, I know.

[Gina]

This shows a 450mm dome added to the model.

[Gina]

First attempt at RA drive box design.  It sticks out too far for my liking.  The casing can be combined with the RA axle bearing pillow block as shown but a bit differently.  Overall view, closeup of RA drive and the insides of the RA drive box.

[Gina]

Next try at the design of the RA drive box.  I don't want the small pulley too close to the big one otherwise the belt doesn't mesh with as many teeth on the small pulley.  This is without the top cover on the box.

Edited December 18, 2019 by Gina

[Davey-T]

Do you have any way to adjust belt tension in mind ?

Dave

[Gina]

A couple of ideas - idler wheels of move the bearings.

[markse68]

On 16/12/2019 at 12:07, Gina said:

PA Elevation adjustment.

Not sure what your total load will be but will the stepper bearings take that kind of axial load?

[Gina]

Yes.  This arrangement is frequently used for the Z axis of 3D printers where the loading is more.

Edited December 18, 2019 by Gina

[Gina]

Came to the conclusion that putting the timing pulleys and belts in a closed box made things too complicated and too difficult to assemble so have changed to a skeleton approach.  The bearings for the axles will be held by capping pieces, screwed on, as with the DEC main axle.

I thought the plain parts were rather difficult to separate in the screenshot view so I've coloured them.  Hope this makes it clearer.

 

 

Edited December 18, 2019 by Gina

[Gina]

RA drive bearings modelled and added.

[lux eterna]

Good thinking with the skeleton / capping pieces solution. Now waiting to see how the dome can be operated. A real thriller...😏

Ragnar

[Gina]

Yes, the dome will be next.  Probably be a clamshell design.  Easier to operate.  I did create a true dome a while back but it's too small and I had trouble working out how to motorise the shutter.