Jump to content


Photo

New mirror cell incl. focusing

  • Please log in to reply
23 replies to this topic

#1 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 29 December 2012 - 04:42 PM

Hi all

Working hard on the design of my new scope before the optics arrives, a Royce 10” f/6.

I’m planning on building the mirror cell from aluminium, pretty much like so many other
primary cells. I was going for 4 mm. thick aluminium, but some test points to 8mm. thick
aluminium for the part that hold the mirror.

Overview
Posted Image

For some time remote collimation has been on my wish list, so I’ve tried to incorporate that
into the design. Aha what is the next logical step, instead of two motors? Why not three
motors and voila now I have focusing as well. If this can be done, it would a great
advantage for my needs for attaching instruments at the focus plane, now more flex from
focuser etc.

I’ve have currently three types of motors.
1- Normal stepper motor with a worm gear that turns the “collimation” bolts
2- A Linear Stepper Motor with threaded motor shaft , <0.01mm steps
3- A Linear Stepper Motor with non threaded motor shaft, <0.01mm steps

Some links
http://en.nanotec.co...ve_lowcost.html
http://nipponpulse.c...-stepper-motors

For the f/6 mirror I’ve calculated a focus depth of 0.08 mm. and I’m going for resolution
better than 0.02 mm.

A solution with motor #1 should be fairly simple, just add a worm gear and it’s ready to go.
But will the accuracy three motors/worm gears assemblies be good enough. Maybe there will be
to drift just like we know it from our mounts?

With motor #2 the linear accuracy should be good enough and repeatable, but the shaft is one
affordable motors only 3 – 3.5 mm in dia. If that solid enough for a 6.3 Lbs. , 10” mirror at
say 30 dr. angle.

Motor #3 solution would be with a threaded shaft that move the mirror holder up and down when
the shaft rotates. (Not illustrated) A threaded hole on the mirror holder should do it, but
I’m not sure if the steps will be fine enough.

What do you think, can it be done?

Some drawings.

Posted Image
Worm gear solution

Posted Image
Linear stepper with spring load

Posted Image
Linear stepper with Belleville Washers

Posted Image
Just a linear stepper

All the electronics, drivers for ASCOM, collimation program etc. is ready. So now the next step
is the hardware design and tests.

#2 Sean Cunneen

Sean Cunneen

    Let Me Think

  • *****
  • Posts: 3256
  • Joined: 01 Aug 2007
  • Loc: Blue Island Illinois

Posted 29 December 2012 - 05:49 PM

From a technology/building standpoint that is a really neat idea. I think if I were building, I would keep the focusing assembly separate from the collimation assembly because each deals with movements of many different magnitudes. The fact you wouldn't have to buy a focuser is intriguing.

The question remains, what would you do with your hands while observing?

#3 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 29 December 2012 - 05:58 PM

Hi Sean

Good point. So maybe some kind of manual coarse collimation system? Then focusing and fine collimation in one assembly?

What I'll do with my hands. I should keep this as a secret, but I'm pretty close in finishing a telescope control system that's wearable. More to follow in the coming month, but basically a observing Vest or Jacket that you wear and then become integrated with the telescope.

#4 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 812
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 30 December 2012 - 07:02 PM

Here is my moving mirror focusing system I built for a C14. The mirror is held by a central arbor similar to the Royce mounting only hollow with 2" opening. The collimation is separate from focusing that uses no springs and includes a collimation locking mechanism. Collimation is done from the outside rear of the C14. Only one leadscrew is used and therefore only one motor is needed for focusing.

Don

Posted Image

Posted Image

Posted Image

Posted Image
Posted Image

Posted Image

Posted Image

#5 piaras

piaras

    Viking 1

  • -----
  • Posts: 820
  • Joined: 26 Jan 2009
  • Loc: Niagara Region

Posted 30 December 2012 - 07:47 PM

Curious why you do not use something like this, instead of saw cutting the threaded shafts?
Pierre

Attached Files



#6 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 812
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 30 December 2012 - 08:14 PM

Curious why you do not use something like this, instead of saw cutting the threaded shafts?
Pierre


Basically the same idea except I cut the slots myself into a 3/8" diameter SS allen socket head set screw and machined the flat at the end. Also the mechanism I built differs from the spiral cut motor coupling wrt axial rigidity. My mechanism is rigid in the axial direction while allowing for tip/tilt. BTW here is a video of my mill cutting the slots with a slitting saw in a similar part as shown complete with Nick Mason vocals from the Meddle album “One of these days I’m going to cut you into little pieces”. Hear the echoes of Dr Who?

Posted Image

http://s72.beta.phot...0_3185.mp4.html

#7 piaras

piaras

    Viking 1

  • -----
  • Posts: 820
  • Joined: 26 Jan 2009
  • Loc: Niagara Region

Posted 30 December 2012 - 10:23 PM

I am wearing a Dr Who t-shirt right now. Also had a Dr Who marathon Christmas Day.

Yes the coupling will collapse along it length, I see what you are doing in this case.
Pierre

#8 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 01 January 2013 - 08:05 AM

Thanks for the comments and pics.

Some test of designs will now begin. I'll keep you posted when there's progress.

#9 Pinbout

Pinbout

    Cosmos

  • *****
  • Posts: 8039
  • Joined: 22 Feb 2010
  • Loc: nj

Posted 01 January 2013 - 11:35 AM

You don't need to spring load the cell with motors. The motors won't be strong enough to compress them properly and the motor will act as a break anyway

#10 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 812
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 01 January 2013 - 11:42 PM

What is the function of the springs?

Don

#11 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 02 January 2013 - 11:41 AM

I've put it there in case there's some backlash on the linear steppers.

I have some different motors on the way now, so test of different designs can hopefully start soon.

#12 dan_h

dan_h

    Surveyor 1

  • -----
  • Posts: 1981
  • Joined: 10 Dec 2007

Posted 02 January 2013 - 12:39 PM

What do you think, can it be done?


Yes. It should be doable easy enough with steppers. Control each motor individually to achieve collimation. Control all motors simulatneously to control focus.

The bug in the system is in the required travel to focus for various accessories. If you only wish to adjust prime focus for astronomical targets it is easy enough as focus travel will be short. If you add the need to accomodate a Barlow or coma corrector or a range of eyepieces that are not at all parfocal, you may find that an inch or two of focus travel is a more difficult to implement and hold collimation well if focus is done by adjusting the collimation bolts.

dan

#13 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 02 January 2013 - 01:57 PM

Hi

On my current scope I'm using a Moonlight focuser and fairly happy with it, but I sometimes see flex when using my a spectroscopes, filter wheel/barlow combi and other instruments. I comes from both the tube and the focuser.

So my plan is to have an instrument platform with an 2" adapter and all instruments, EP, Barlow etc. must mounted using an adapter, even if it has to be made special for each device.

So I'm actually planning now for only 10mm. focus adjustment and and the rest by adapters.

Here's a rendering of what I have in mind.

Posted Image

#14 Gene7

Gene7

    Viking 1

  • -----
  • Posts: 877
  • Joined: 10 Jun 2010
  • Loc: Mid Ohio, USA

Posted 02 January 2013 - 02:32 PM

I have several folded mirror systems,Maks and Cats. including a Celestron 5 inch. All are junk optics, I believe because of
unstable focusing mirror systems. My $10 Shed 2 inch achromat and 5 and 10 inch Dobs are fine, sharper. Beware you do not create the same. Gene

#15 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 02 January 2013 - 02:48 PM

Hi Gene

My backup plan is to use my Moonlight focuser if it fails and hopefully I can then use the system for collimation.

#16 bremms

bremms

    Mercury-Atlas

  • *****
  • Posts: 2715
  • Joined: 31 Aug 2012
  • Loc: SC

Posted 02 January 2013 - 03:32 PM

I like the idea for collimation but not for focusing. To make it work well it needs to be engineered with the proper materials and freedom of motion, otherwise you will get binding and very quick wear. Never liked the idea of moving the mirror to focus. To do it right takes a lot of work, time and proper design. Not saying it won't work, but to not get shifting and or binding takes a lot of engineering and precision machining.

#17 Pinbout

Pinbout

    Cosmos

  • *****
  • Posts: 8039
  • Joined: 22 Feb 2010
  • Loc: nj

Posted 02 January 2013 - 03:48 PM

I haven't done it yet but this is my plan.
and no batteries... :grin:

Posted Image

#18 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 16 January 2013 - 03:16 PM

Hi all

Today I got my new mirror for the project, a very nice Royce 10" F/6 Conical.

Some stepper drivers from Pololu was also in the mail, so now testing of different design will begin as soon as the mirror cell is ready from the plasma cutter.

A few pics
Posted Image
The finger print belongs to the customs officer :bawling:

Posted Image
The Royce mirror side by side with my Orion Optics 10" F/6.3 1/10PV.
Can't wait to do some comparisons.

Posted Image
The Pololu A4988 stepperdrivers

#19 polaraligned

polaraligned

    Viking 1

  • -----
  • Posts: 691
  • Joined: 26 Dec 2008

Posted 17 January 2013 - 10:02 AM

Why not three
motors and voila now I have focusing as well. If this can be done, it would a great
advantage for my needs for attaching instruments at the focus plane, now more flex from
focuser etc.


I have thought this same thing....Certainly it is very doable, and already done via the secondary on some pro scopes where focus and collimation is controlled via a hexapod. Focus range need not be more that .3" or so for an astrograph. Linear encoders would be ideal to close the loop back to the microprocessor. Care needs to be taken with the placement of steppers or servos, if they are required to supply holding torque, as they will dissipate heat.

It would be interesting if some of the optical guru's here would calculate the kind of tolerances that need to be held when moving the primary to maintain collimation. Again, I am think about only say .3" or so of movement. You could always use different length stationary adapters at the "focucer" to allow for eyepieces, cameras, etc...

#20 don clement

don clement

    Vendor (Clement Focuser)

  • -----
  • Vendors
  • Posts: 812
  • Joined: 02 Feb 2011
  • Loc: Running Springs, California

Posted 17 January 2013 - 02:01 PM

A method I have used to quantitatively measure the tip/tilt of the three-leadscrew focusers I have built was to mount a flat on the focuser and use a calibrated autocollimator.

Don

#21 obin robinson

obin robinson

    Mercury-Atlas

  • *****
  • Posts: 2660
  • Joined: 25 Oct 2012
  • Loc: League City, TX

Posted 30 December 2013 - 12:17 PM

Any updates on this? I am thinking of a similar system using steppers to collimate my Starfinder 10" project.

obin :question:

#22 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 30 December 2013 - 03:14 PM

Hi Obin

I can post an update one of the coming days. After a lot of testing and computer simulations I ended up with system similar to Clements fantastic system, but with build in collimation motors.

The focusing is now totally separated from the collimation system, because tests and simulation showed that the two adjustments can't work as one. All adjustments is still in the same mirror cell.

At the moment I'm doing the assembly and the software is done (Arduino, ASCOM)

It proved rather difficult to produce the parts with DIY tools, so I had to get the parts manufactured on a CNC machine. Sadly I forgot to put all the thread holes in the CNC file, so the assembly takes a lot of time.

Some pics
parts

Drawing

Assembly

#23 obin robinson

obin robinson

    Mercury-Atlas

  • *****
  • Posts: 2660
  • Joined: 25 Oct 2012
  • Loc: League City, TX

Posted 30 December 2013 - 06:56 PM

That looks like a pretty neat setup! You're using an Arduino for focus motor control? Are you using steppers or geared DC motors? When you're done do you mind sharing the motor control sketchup? Right now I'm shopping around for steppers to use for the collimation. Which ones did you settle on?

I like the idea of motorized collimation for multiple reasons. I think that it will help speed up the process a lot.

obin :cool:

#24 ZielkeNightsky

ZielkeNightsky

    Surveyor 1

  • *****
  • Posts: 1511
  • Joined: 01 Oct 2006
  • Loc: Denmark

Posted 30 December 2013 - 09:38 PM

Hi Obin

I use steppers.

For the focusing:
Nema 17 29 oz-in 0.4A Bipolar Stepper Motor Linear Actuator w/ Shaft 12V

For collimation (which has to be tested with some small plastic worm gears) two very small steppers from Pololu:
1204 Stepper Motor: Bipolar, 200 Steps/Rev, 20×30mm, 3.9V, 0.6 A/Phase

The focusing software:
My version of the software from SGL Observatory Automation Yahoo group. You can get the software there, it works very well.

My own version of the Arduino software has extra features like: telescope identification, collimation control, jog wheel focusing, automatic calibration and more.

On the computer side I use the SLG Ascom driver with some modifications. I have almost totally re-written the stand-alone focusing program from the SLG group and currently I'm working on a version the runs on the Processing platform.

More pics...

Electronics box with the stepper
Electronics box and steppers

Here some older screen dumps of the software while testing.
Driver testing

Testing in FireCapture

An older developer version of the client software. As you can see it can iden...

If you need more info just drop me a PM






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics