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Remote control collimation - ideas please


Rick Foust
 

My 16" Newt is a pain to collimate.  I need a ladder to reach the secondary mirror screws.  I would like to be able to make on-the-fly colllmation tweaks, with camera installed, from my warm room, like I tweak focus.  I am planning to install a small geared stepper motor (28BYJ) on each of the 3 secondary mirror adjustment screws.  I see two options for the controller.  I could create a duplicate of my MKS Gen L ONSTEP controller and use three focuser configs to run the steppers.  This would require running 12 wires to the steppers.  Or I could build a controller that is small enough to mount on the secondary mirror support along with the steppers (in the shadow of the 4" secondary mirror).  That would only require 2 wires (power) instead of 12.

Or, instead of a second ONSTEP controller, maybe I could use a small CNC controller?

Any thoughts?   


George Cushing
 

Sounds like something an Arguino Nano could do. The stepper only needs 5V.

Maybe you can cut down on the wiring by having a second Arduino act as a server to an on mirror client that can switch among the drivers or L293s.
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All you'd need is a switch box to adjust the secondary. Do you really need control of all three adjusters. I'd think two should do like the early Meade 2080.





Alexander Varakin
 

CNC controller sounds like a great idea:
1. Use CNC shield or MKS GEN L for electronics
2. Install appropriate grbl firmware
3. Use Universal Gcode Sender on PC
4. Control it using UI or joystick

Another idea is to change your scope to use hexapod design, so collimation can be achieved by twisting the truss poles


Khalid Baheyeldin
 

Rick,

I remember your scope. It is one of the largest mounts that run OnStep.

Some thoughts:

- Do you really need to change the secondary that often? When I had a 10" Newtonian,
I did not need to do the secondary at all, but the primary did need collimation, and the
3 screws on it did the trick. If you tighten up the secondary, would that eliminate the
need to fiddle with it often?

- The R32 + CNC V3 is about the smallest footprint an OnStep board has. Maybe it would
fit in the shadow of the secondary? If so, it has Axis3 and Axis4 as focuser/rotator. That way
you don't need to write any software, and use out of the box OnStep.
Can you keep one screw fixed, and move only the other two via motors? It has built in Bluetooth,
so maybe a USB connection would not be needed (but you need your phone with the app
close to the scope).

- Of course, you can use any 3 axis board but with custom firmware, as OnStep would not
allow you to have a board without Axis1 or Axis2.


Martin Bonfiore
 

Are you concerned about having active (read: giving off heat) electronics in the scope tube?  I am not sure it is on much concern but I would guess heat (electronics, driving the motors) would generate some turbulence...how significan an effect on viewing, I don't have a clue.  That said, once collimation is finished, you could power off the electronics/motor (probably don't need holding torque on motors???)... I guess you could always model this with a power resistor located where you would mount the electronics...give it a blast and see if the seeing is disturbed.  Way more mechanically complex would be to place the motors and the electronics outside of the tube and move the tube to spider anchor points...or possibly mount the spider through the tube on to a ring external to the tube to decouple the spider/secondary from the tube...sort of like a halo with relief  holes cut in the tube around the spider legs to allow movement...like I said...way more mechanically complex...but fun to think about.  Interesting project.


Rick Foust
 

Hey guys.  I appreciate the ideas.  I am leaning toward R32 + CNC V3.  Thank you Khalid for pointing that out.  I missed that addition to the Wiki (my Onstep is running so well that I haven't had to keep up with the latest new stuff).  I am sure it will fit in the shadow, although I may have to mount it in line with the OTA axis (on edge, so to speak).  And I think it will do everything that I want if I can make the secondary adjustable with only 2 screws.  I am thinking 2 screws/steppers will be enough if I drill out one screw hole and install a spring in place of the screw.  Then it would work like a common finder scope that has 2 adjustment screws and a spring.  The spring will have to be fairly stout to provide enough preload to prevent vibration or shifting.  There is quite a lot of leverage created by the cantilevered mirror and its holder.

In answer to some questions.  I really do need to fiddle with the secondary.  The primary stays rock solid and never needs adjustment.  No matter how well I collimate, it is never quite right once I install the camera.   I know it sounds a bit crazy.  I have 6", 8" and 10" Newts that don't have this problem.  It is a curse of the tube design combined the size.  I have made numerous modifications to stiffen the tube.  But they have not been enough. 

I plan to keep the motors de-energized when not adjusting.  Otherwise, I suspect that the heat would cause too much turbulence.  A fun experiment is to use night vision instead of an eyepiece.  Then, with the scope way out of focus on a bright star, hold your hand in front of the OTA.  You can clearly see the heat plume coming off your hand.

If I fail to make the 2 screw idea work, I will give the grbl firmware a try.  Thank you Alexander for suggesting that.  I was wondering which CNC firmware to consider.  Gcode and hexapod are new to me.  I will have to check them out.

If none of the above works out, I will go old school with switches and DC servo motors.  Might even be the best option.  Simplicity has its advantages.

Anyways.  Thanks again.  And if you have further ideas, I am all ears.


George Cushing
 

I just got a couple of these for experimentation. $6

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They will drive a small stepper. The remote is a clone of a Sony car stereo unit.



Rick Foust
 

That might be just the ticket George. Does it use IR or RF?  RF would be better for me because I need to control from within a room.  I have been thinking along the same lines with this thiscontroller  to drive DC gear motors.  Your find has built in stepper drivers though.  And for $6!  I couldn't resist.  I ordered a couple.

In the mean time, my R32 and CNC V3 arrived.  So I am going to play with them for a bit.