Skywatcher Star Adventurer replacement control system Project

[Photosbykev]

I'm looking for some support from other forum members interesting in motor control with encoder feedback to push this little project along ready for the winter season

I've just pushed the button on a Skywatcher Star Adventurer astrophotography mount with a view to replacing the electronics with my own control system so it does what I want rather than doing what it thinks I want

Looking inside the mount there is a single control board with plug and socket connections to the various components on the mount i.e. the motor/encoder, mode dial, Camera snap port, power switch etc.

As supplied the mount works well for astrophotography but is seriously lacking any flexibility or thought when it comes to the timelapse functionality.

This project will replace all of the Skywatcher control board including the motor driver and encoder counter, and incorporate a PID controller for position/speed control

For me, very basic timelapse functionality would include:

1. Manually define left and right limits for a panning timelapse (fast slew to position camera at start and then finish). Report back defined number of degrees and maybe options to preselect a shoot mode based on frame rate required.
2. Manually select the 'framerate' by entering the total number of frames to shoot while the camera traverses the measured angle in a defined time period.
3. Selection of shot mode, either Move Stop Shoot Move or Shoot on the move.
4. Definable start delay to the imaging sequence.


Camera control
This should include:
1. User defined shutter durations
2. User defined shoot intervals
3. HDR options, number of frames, only bulb mode maybe with exposures longer than 0.1 seconds for reliability. Potentially an external signal to a dedicated HDR camera controller I already have.
4. Mirror lockup options
5. Camera wake up trigger to handle long start delay


For astrophotography I would want
1. Standard Sidereal, lunar and solar rates
2. User definable tracking rates within system limitations
3. Plus the user camera control

The 1st step will be to check what control system is in use, I assume PWM and closed loop feedback but need to check that and the nominal motor voltage. The encoder is a 4 wire device so probably power, ground, A & B signals.

Once the existing system has been tested, then I'll add an external 9 pin D type connector to the casing to connect my control system into it.

I would appreciate any thoughts on the best alternative Motor drive board and encoder counting options from other forum users, arduino maybe?

The rest of the project coding is relatively simple once I can accurately control the speed/position of the motor.
 

[Horwig]

Nice mount. I DO like mounts with dc motors and opto encoders, I'm running a Sitech mount with them. As to doing it from scratch, It's beyond my coding prowess, but I think this man has done it successfully on an Arduino.

http://stargazerslounge.com/topic/105383-diy-homemade-telescope-mount-project/?hl=%20diy%20%20mount

http://astro.neutral.org/arduino/arduino-telescope-control.shtml

Best of luck with it

Huw

[Photosbykev]

Nice mount. I DO like mounts with dc motors and opto encoders, I'm running a Sitech mount with them. As to doing it from scratch, It's beyond my coding prowess, but I think this man has done it successfully on an Arduino.

http://stargazerslounge.com/topic/105383-diy-homemade-telescope-mount-project/?hl=%20diy%20%20mount

http://astro.neutral.org/arduino/arduino-telescope-control.shtml

Best of luck with it

Huw

Thank you Huw,

some interesting links there

[Photosbykev]

Further observations from yesterday

Access into the mount is very simple. 4 x socket head cap screws need to be removed and the casing can be split open. Internally there is enough freedom in the wiring loom to allow the top case to be hinged back giving easy access to the main components.

The encoder mounted directly on the rear motor shaft is a 44 slot disk with 4 wires controlling the encoder generating the control pulses. The encoder design is an optical IR? transmitter/receiver pair so only a single pulse from each slot/post pair on the encoder wheel i.e 44 pulses/revolution. At sidereal rate the motor and encoder disc spins at approx 48rpm (stopwatch timed over a minute), giving a pulse rate of (48*44)/60 = 35 pulses per second which is easily within the capability of an arduino. The nominal voltage going to the motor is 5 volts PWM controlled.

The output from the motor goes into a direct coupled gearbox with a 24T brass spur gear on the gearbox output. The 24T spur gear drives a 42T brass idler gear which, in turn, drives a 37T brass spur gear coupled directly to the brass worm. The worm drives a 144T wheel for the primary rotation.

[Horwig]

I was going to query the single optical pickup for the motor, but having thought about it, since this motor is not required to do gotos, the control is very easy, it does not need to reverse, just keep a steady forward speed, in which case, your control electronics should be a whole lot easier.

Best of luck, I'll be watching this thread.

Huw

[Photosbykev]

I was going to query the single optical pickup for the motor, but having thought about it, since this motor is not required to do gotos, the control is very easy, it does not need to reverse, just keep a steady forward speed, in which case, your control electronics should be a whole lot easier.

Best of luck, I'll be watching this thread.

Huw

I agree, it doesn't need an A & B signal as the user manually switches the direction of travel using the N to S hemisphere switch. With a replacement control system the direction control would be computer controlled but still very simple logic change.

[Photosbykev]

Top and bottom views of the encoder board

[Davey-T]

Hi Kev, just wondering if you have made any progress with this project.

The SW SA I  got from FLO was running slow in RA, just got a replacement but not tried it yet, do you know how the motor speed is controlled when it is switched between speeds ?

Dave

[Photosbykev]

Hi Dave the speed control is via a custom pic on the pcb. I haven't looked at it in detail as Im still planning to replace all the control system with an arduino

sent from my Sony Xperia Z2

[Davey-T]

Hi Dave the speed control is via a custom pic on the pcb. I haven't looked at it in detail as Im still planning to replace all the control system with an arduino

sent from my Sony Xperia Z2

No way of adjusting it then, just got a replacement for mine as it was running slow and couldn't keep up with stars in RA for more than 60secs, haven't had a chance to try the new one yet.

Dave

[synfinatic]

Hi Kev,

I was curious how this project was going?  I was comparing the iOptron SkyTracker and Sky-Watcher Star Adventurer and was leaning towards the Star Adventurer since it seems a bit more capable.  While researching them, I came across this thread and thought it would be really cool to extend the Star Adventurer even further.  I've done a couple of Teensy (Arduino compatible, but smaller, cheaper and more powerful) projects, including one astronomy related: http://synfin.net/teensydsc

I'd definitely be interested in helping out.

-Aaron

[Photosbykev]

On the back burner at the moment Aaron work is eating into my spare time.

[zooto68]

So, what is the update with this project please? Did you get it working in the end? 

[Davey-T]

Hi Kev, don't know if you caught this or if it's any use with what you were trying to achieve.

Dave

[Photosbykev]

Hi Kev, don't know if you caught this or if it's any use with what you were trying to achieve.

Dave

At first glance they've put a lot of thought into that upgrade