Altitude control using Argo & PIC micro

[kustard (Simon)]

Hi all,

A bit of history first, last year I bought an Orion 14" Go-to Truss Dob. Optics are great but it has suffered from Azimuth drive problems. After back and forth with Orion and local servicing with no complete fix I decided to remove all the controls and turn the scope back into a basic push-to scope with an Argo Navis.

After installing the Argo the scope works flawlessly. The only issue I was having was aligning the scope due to the Altitude axis being quite stiff. Fortunately I still had the altitude motor connected and could move the scope in altitude with a small control that used a variable voltage supply and a toggle switch.

"I can do better than this!" I said to myself. So I contacted Gary at Wildcard and he pointed me to the serial port and SkyComm protocol. I then went and bought some PIC microcontroller SBC's and other bits (LCD's, keypads, a DSO) and a few days of coding later (I've coded PIC controllers before) I have a demonstrable version of a single axis scope controller.

The system connects to the Argo via RS232 @ 19200 baud. The system polls the Argo for guide data and drives the axis motor using a software generated PWM signal. Direction is provided by toggling the output via two relays (SPDT). The system drives the motor at varying speeds based on how much the scope needs to move. The system then "tracks" the object by moving the scope when the object drifts by a small amount. Selecting a new object on the Argo will cause the system to drive the Altitude to the new object. I still have to push the scope in azimuth but I can live with that

I've made it so that you can operate the scope without the Argo connected and if there is any hiccup in data the system returns to a "manual mode" that stops automatic tracking to prevent the scope from driving wild.

I've made a very dodgy video and uploaded it to YouTube and you can check out to see a demonstration of the project. Sorry for my poor video skills

http://youtu.be/BiARNH1eB_s

Please feel free to offer opinions or ask questions.

Cheers,
Simon

[alistairsam]

Very nice work Simon, quite extensive. Would be good to get your Azimuth working as well.
Was there no possibility of modifying the Altitude supports or adding bearings to make it smoother?
Cheers

[kustard (Simon)]

The clutching system and mounting points for the axis are a very strange setup, part of the reason I think the scope didn't perform. Even Gary at Wildcard was scratching his head about their design.

I have an idea for the Azimuth axis, it might require locking the drive and not having it push-to except for some sort of manual disengage.

Cheers,
Simon

[kustard (Simon)]

A bit of an update

The plan was to go out tonight and trial run the system but the weather wasn't as stable as I had hoped. I have managed to put all the electronics into a box (I have no tool shop unfortunately so the skills are a bit poor) and gave it a full test run inside and made sure all modes are working.

Cheers,
Simon