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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
New mirror cell incl. focusing new
      #5594705 - 12/29/12 04:42 PM

Hi all

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

Iím 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


For some time remote collimation has been on my wish list, so Iíve 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.

Iíve have currently three types of motors.
1- Normal stepper motor with a worm gear that turns the ďcollimationĒ 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.com/linearactuating_drive_lowcost.html
http://nipponpulse.com/products/overview/linear-stepper-motors

For the f/6 mirror Iíve calculated a focus depth of 0.08 mm. and Iím going for resolution
better than 0.02 mm.

A solution with motor #1 should be fairly simple, just add a worm gear and itís 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 Ė 3.5 mm in dia. If that solid enough for a 6.3 Lbs. , 10Ē 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
Iím not sure if the steps will be fine enough.

What do you think, can it be done?

Some drawings.


Worm gear solution


Linear stepper with spring load


Linear stepper with Belleville Washers


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.

Edited by ZielkeNightsky (12/29/12 05:09 PM)


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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5594783 - 12/29/12 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?


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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
Re: New mirror cell incl. focusing new [Re: Sean Cunneen]
      #5594797 - 12/29/12 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.

Edited by ZielkeNightsky (12/29/12 09:53 PM)


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don clement
Vendor (Clement Focuser)


Reged: 02/02/11

Loc: Running Springs, California
Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5596748 - 12/30/12 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














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piaras
scholastic sledgehammer


Reged: 01/26/09

Loc: Niagara Region
Re: New mirror cell incl. focusing new [Re: don clement]
      #5596829 - 12/30/12 07:47 PM Attachment (47 downloads)

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


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don clement
Vendor (Clement Focuser)


Reged: 02/02/11

Loc: Running Springs, California
Re: New mirror cell incl. focusing new [Re: piaras]
      #5596872 - 12/30/12 08:14 PM

Quote:

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 ďOne of these days Iím going to cut you into little piecesĒ. Hear the echoes of Dr Who?



http://s72.beta.photobucket.com/user/miltons_stuff/media/100_3185.mp4.html


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piaras
scholastic sledgehammer


Reged: 01/26/09

Loc: Niagara Region
Re: New mirror cell incl. focusing new [Re: don clement]
      #5597040 - 12/30/12 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


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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
Re: New mirror cell incl. focusing new [Re: piaras]
      #5599174 - 01/01/13 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.


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5599412 - 01/01/13 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

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don clement
Vendor (Clement Focuser)


Reged: 02/02/11

Loc: Running Springs, California
Re: New mirror cell incl. focusing new [Re: Pinbout]
      #5600550 - 01/01/13 11:42 PM

What is the function of the springs?

Don


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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
Re: New mirror cell incl. focusing new [Re: don clement]
      #5601111 - 01/02/13 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.


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5601188 - 01/02/13 12:39 PM

Quote:

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


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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
Re: New mirror cell incl. focusing new [Re: dan_h]
      #5601303 - 01/02/13 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.



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Gene7
scholastic sledgehammer


Reged: 06/10/10

Loc: Mid Ohio, USA
Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5601353 - 01/02/13 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


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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
Re: New mirror cell incl. focusing new [Re: Gene7]
      #5601379 - 01/02/13 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.


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bremms
Carpal Tunnel
*****

Reged: 08/31/12

Loc: SC
Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5601434 - 01/02/13 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.

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: New mirror cell incl. focusing [Re: bremms]
      #5601465 - 01/02/13 03:48 PM

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



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ZielkeNightsky
Carpal Tunnel
*****

Reged: 10/01/06

Loc: Denmark
Re: New mirror cell incl. focusing -Mirror arrived new [Re: Pinbout]
      #5626378 - 01/16/13 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

The finger print belongs to the customs officer


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


The Pololu A4988 stepperdrivers

Edited by ZielkeNightsky (01/16/13 03:18 PM)


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polaraligned
professor emeritus


Reged: 12/26/08

Re: New mirror cell incl. focusing new [Re: ZielkeNightsky]
      #5627727 - 01/17/13 10:02 AM

Quote:


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...


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don clement
Vendor (Clement Focuser)


Reged: 02/02/11

Loc: Running Springs, California
Re: New mirror cell incl. focusing new [Re: polaraligned]
      #5628153 - 01/17/13 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


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