Mountings and Controls For Widefield Imaging Rig

[Gina]

Connecting up completed and now testing.  Rotation fine, imaging fine but focuser not working and no camera power hence cooling not working nor  EFW via camera USB hub.  So a couple of connections not working.  Now to fault-finding...

[Gina]

Focuser motor connections were wrong, put them right (I think) but it still doesn't work.  Checked camera power cable and connections and they were fine - turned out to be plug not properly connecting - fine now.  Cooling now working and also EFW which showed by the captured image being much brighter with L filter than any of the NB ones.  One fault fixed and one still to find...

[Gina]

Checking out the focuser.  Connections fine now, resistance at driver motor coil pins show 55 ohms on each coil when unit powered down.  Ekos sends focus commands as usual but no motor rotation or extra current drawn from bench PSU.  Going to try another stepper motor.

[Gina]

No difference!  Then I replaced the driver module still with the other motor and it worked.  Switched back to proper motor and it didn't!  Changed to separate motor again but that's not working now. 

Time to give it a rest I think and leave it until tomorrow - sleep on it!!

[Gina]

Trouble shooting continued...  Tried putting the stepper driver from the focuser into the socket for the rotator and no rotation or current drawn so after shutdown, replaced the original rotator driver module and rotation worked, so it seems the driver module used for focus has failed. 

Question is - what is causing this?  Do I risk another driver module by trying a new one for the focuser?  Is there something wrong with the focuser motor or its wiring - ohmmeter testing shows correct resistance for both coils and no shorts.

[Gina]

Just to be sure of my facts I put one of the driver modules that appeared to have failed back in the focuser position with the test motor connected and it worked.  So that driver module isn't dead!  Now I'm wondering if the problem is the socket the driver module plugs into.  I'm using DIP chip sockets with the sides separated to provide the 0.5" pin spacing of the driver.  The depth of the sockets is less than the length of the pins - these sockets were designed for the flat pins on a DIP and not the square ones on the driver board.

[tekkydave]

Try these.

[Gina]

Thanks Dave   Yes, I've ordered those in the past - haven't got any left but I've ordered these - two sets giving me sockets for 5 driver boards.  That should keep me going for a while

[Gina]

Oh! - they won't last that long.  3 pairs wanted straight off

Guess I'd better wait for them to arrive rather than try further to get all this working.  Plenty of other things to do and the weather doesn't look like co-operating any time soon!

[Gina]

Had a thought about the middle section that will later become the zoom control.  Apart from that problem also being the sockets, I could try the Astroberry Board driver and see if the GPIO lines change state according to the controls in the Board driver front end.  Don't need a driver board plugged in for that, only the DMM to show the logic state of each GPIO line.

Another sub-project to look at is writing my own INDI drivers.

[Gina]

Just checked the scope focuser and that uses those proper headers

[Gina]

I've removed the sockets and associated solder ready for the headers when they arrive.

[Gina]

Edited and recompiled the Astroberry Board rpi_brd.cpp file to use pins 19,21,23 as were to be used for the zoom stepper motor control and tested the GPIO outputs - all correct.  Power OFF gives +3.3v and Power ON gives 0v - this worked for all three pins.  So I conclude that the RPi is doing what is expected and the previous trouble with stepper driver was bad connections.

[Gina]

Been looking again at my zoom lenses.  Three of them, one M42 Pentax thread and two Canon EF/EFS bayonet.  I have adapters for both sorts to match the ZWO EFW mini and ASI1600MM-Cool.  They are all bigger than the various lenses the current rotation rig takes and will take so it will mean a larger one will be required.  That shouldn't be a problem - just a redesign and print of new parts.  I think the one cage size should be able to take all three though (no not at the same time ).

Here's a photo of the three lenses - 18-55mm, 35-105mm and 75-300mm.

With the two longer lenses the focus sleeve only rotates except for a small in/out movement but the 18-55mm focus sleeve moves in and out with the zoom by nearly 10mm so this will need a long pinion on the stepper motor and allow the gear attached to the focus sleeve to slide up and down it.

Unlike the M42 thread prime lenses the focus sleeves on these zoom lenses turn far less to cover the focussing range (even less for astro focussing) so I might have to re-think this part.  The zoom angle ranges from about 60° to about 90°.

[Gina]

I've checked dimensions of the zoom lenses and the biggest diameter is the middle one but that is still smaller than the body of the camera so I think the same diameter cage will work but it will want to be longer and with different internal mountings.  Plus, of course, an extra "partition" to hold the zoom stepper motor.  Both motor partitions and the lens support will need to be capable of being placed at different positions to suit the different lenses.

[happy-kat]

Have you single image tested each lens for astro optical quality?

[Gina]

No not yet.  I live in hope just as with the weather

[Gina]

I'll probably make up a simple rig for testing before going all the way to making a full rotation rig.

[Gina]

Designing and printing supports for a simple zoom lens rig.

[Gina]

Was hoping the driver headers would arrive today but they didn't   So no progress on the electronics box.  Been trying to get the C compiler to work on my Linux Mint desktop for INDI driver writing but no joy there either   So no progress yet today (except that I did some grocery shopping this morning).

[Gina]

The 8 pin headers have arrived today so I'm continuing work on the electronics box.  Headers soldered on and driver modules plugged in, wired up and secured in box.

[Gina]

Testing...  Focuser works but rotator doesn't quite but I'm not using the same driver module as before so this one might be set at too low a current.  The driver draws current but less than before.

[Gina]

Found the driver module I used before for the rotation and swapped over - both rotator and focuser now work fine   Now to assemble all the hardware and test again.

[Gina]

Still fine

[Gina]

Seems I didn't produce a focus gear for the 135mm lens, which is the one I want to use for imaging next time the opportunity arises, so I've designed one and now 3D printing it.