DIY Spectragraph Phase 1 V2

[NickK]

So my original "Dear Santa" spectrograph design got it's first light...

However it became evident that the design has some serious accessibility flaws, where adjustments often lead to the need to remove components and then realign.. so I took the decision to move away from the cage design. The same internals, but I have mounted them to a piece of wood in a V, and reused the existing alu as a lid:

This still requires the addition of the back - tomorrow, the lens adjustment holes in the lid along with the scope struts. It will be possible to run the scope for alignment without the lid.

I'm still waiting on my FedEx parcel - they delivered it to a rather antisocial neighbour.. who signed for it and hasn't been back to the house since.. in the pack is my flocking and optical wonder cleaning fluid.. grrr.

After SGL I'll look at optimising further but for now getting back into a working state for SGL9 will be a good thing!

[NickK]

Thinking ahead for the scanning mechanism - it's also occurred to me that a DVD drive would have an ideal precision scanning mechanism to hold a couple of mirrors. 

[image from repairfaq.org]

Now being able to control the scan motor, adding a detector switch for each end of the travel, should be all that's required.

[NickK]

Well - I'm back So whilst I'm between jobs, and applying for roles I have a few hours here and there to finish some of the projects I started but then got prioritised.

Firstly - I now have a permanent telescope pier.. second I have made a decent sized work bench in the garage... which leads me neatly to number 3 - the spectrograph!

I've been having a bit of a rethink around the design - chiefly for operational ease of use around focusing and the use of wood V blocks to keep things nicely clamped as the current X-Y scope ring type holders are fiddly and quite difficult to sort out quickly.

One of the things I want todo is make the collecting lens a detachable camera box - so I can, if so wanted, make it a wide field DSO camera in it's own right.

[MattJenko]

You are unstoppable! Hats off. Spectroscopy is something I am gravitating towards quite strongly, so will be following this with interest. 

[NickK]

i've investigated the DVD-Blueray transport design - this is very very good starting point. The blue ray transport has an active lens system controlled by magnets.. but I digress - in this scenario the transport has the same worm operated mechanism.

The down side is my grating has taken a battering.. not bad enough to stop the initial design and setup but I will probably replace it with a higher resolution to up the performance - currently the initial testing was an R6000 0.9A bandwidth result, adding a higher resolution grating would see a jump in performance making it a great scanning solar spectrograph.

I have an audino that could be used but first I need to hack the movement of the blue ray's motor (I will be disconnecting it so that the laser assembly will not be active.

[NickK]

The bluray ROM drive motor is a 2 phase motor to control the position of the head. A 3 phase motor then controls the spinning of the disk and a single phase for the in/out of the tray to the outside world. The fine movement of the heads is through a linear direct drive motor that's minute.. so the lens assembly moves about 3mm on that and the motor controls the coarser major movement.

One option is to make a linear drive but.. that's probably the step after.

I have an arduino motor shield with a 2 phase motor control - this should be perfect for this particular application.

One thing I note about the arduino is that, although it's useful as a prototype (does the idea work?!), it ends up being an arduino for each thing.. not particularly cheap.

I've been looking at ODroid - a multi core ARM design capable of running Ubuntu with performance 200%+ of raspberry pi.. but has a row of 40 GPIO pins. Cost $35. A more powerful version is about $135 with OpenCL capable graphics chip.. I've coded ARM and Blackfin before so it's slightly more interesting to me than arduino..

[NickK]

 

Here's the blueray drive with the stepper motor - note that the stepper is disconnected from the main BD mechanism and the drive is not being powered so there's no laser active.

It's a little coarse but I think it's a good starting point. The idea is to use this as a slit scanner for the spectrograph

[frostynixon]

Very impressive. I hope your project works out well!

[NickK]

I should be making a nice jump forward - my father in law is giving me his old bandsaw so this will help with cutting the pieces

[NickK]

Thinking about this now I have the band saw Thinking of a bit of 18mm plywood as a basis for the MkII .. this will allow me to setup a scanner form in addition to the basic form. Price for plywood is reasonably cheap considering the size of the sheet you get.