KISA
14-06-2006, 07:29 PM
Hi All,
After attending the star party in Lostock I learnt that trying to do digital planetary capture using manual focus was a nightmare. Nothing more frustrating that trying to focus the planet by hand, waiting for it to stop bouncing around on the laptop screen and then wondering if it was actually an improvement :doh:
So my mission was to build a motorised focuser out of whatever I had lying around at minimal cost.
Things I found at home included an old remote control car controller and servos (no car), some circuit board, 555 timer, voltage reg, resistors, wire, screws, a small plastic enclosures and some sheet steel.
Things I had to acquire included, gears, another small plastic enclosure, power connector and a short length of steel rod. The gears I got out of a scanner I picked up from Aussie junk for $3, the enclosure from Jaycar for about $3, power connector from Jaycar for about $1 and the steel rod from a metal distributor, free scrap.
My plan was to connect the servo motor to my focuser and control it using the lever off my remote control controller.
First I had to modify the servo so that it could continue to rotate in any direction and not return back to the neutral position. This required the removal of the internal end stops and replacing the internal variable resistor (used to provide the neutral position voltage) with a resistor voltage divider so the servo always thought it was in the neutral position and therefore stay where it stopped. At that stage I also connected the small gear to the servo motor.
Next I constructed a circuit that would produce the necessary pulses to control the servo motor, used a simple 555 timer. I also added a 5V regulator so I could use my standard 12V connector to power both the circuit and the servo motor (trying to keep consistent on my scope). To set and vary the pulse width to the servo motor (pulse width controls the direction and speed of the servo motor) I needed to select particular resistor values for the 555 timer and include a variable resistor to provide the control. It just so happens that the controlling levers on the remote control controller is purely a variable resistor, so after removing it from the controller, measuring the resistance and adding additional resistor to make up the correct value for the 555 timer I had my means of control. And to include it into the 555 circuit I just wired it in using about 5m of wire, which allowed me to stand away from the scope when controlling it.
Next I pulled apart the original focuser and replaced the adjusting rod with the one I bought attached the other gear (hot glue is great stuff), then I cut out the steel plate attached the circuit to one side and the servo motor to the other and screwed it to the focuser base, using one of the original screw holes and tapping an additional hole in for better stability.
And there you have it, one motorised focuser controlled remotely with a small lever, which gives both directions and variable speed depending on how far you push the lever. Total cost < $10 and due to the gear ratio I used the minor adjustment is small enough to allow for precise focusing.
The only glitch I seem to have at the moment is the servo occasionally sticks at very slow speed, but moves on with a bit of persuasion. I'm pretty sure a replacement of the internal grease will fix that, just need to determine the best type to use.
My long term plans are to build a circuit that will allow control from the serial port, so I can site at my PC for all control of movement and capture, all I need is time :)
Thanks for reading my spiel and I hope this may spark some ideas for someone out there and hopefully make life that little bit easier. If youi have any questions please ask.
Cheers
KISA
After attending the star party in Lostock I learnt that trying to do digital planetary capture using manual focus was a nightmare. Nothing more frustrating that trying to focus the planet by hand, waiting for it to stop bouncing around on the laptop screen and then wondering if it was actually an improvement :doh:
So my mission was to build a motorised focuser out of whatever I had lying around at minimal cost.
Things I found at home included an old remote control car controller and servos (no car), some circuit board, 555 timer, voltage reg, resistors, wire, screws, a small plastic enclosures and some sheet steel.
Things I had to acquire included, gears, another small plastic enclosure, power connector and a short length of steel rod. The gears I got out of a scanner I picked up from Aussie junk for $3, the enclosure from Jaycar for about $3, power connector from Jaycar for about $1 and the steel rod from a metal distributor, free scrap.
My plan was to connect the servo motor to my focuser and control it using the lever off my remote control controller.
First I had to modify the servo so that it could continue to rotate in any direction and not return back to the neutral position. This required the removal of the internal end stops and replacing the internal variable resistor (used to provide the neutral position voltage) with a resistor voltage divider so the servo always thought it was in the neutral position and therefore stay where it stopped. At that stage I also connected the small gear to the servo motor.
Next I constructed a circuit that would produce the necessary pulses to control the servo motor, used a simple 555 timer. I also added a 5V regulator so I could use my standard 12V connector to power both the circuit and the servo motor (trying to keep consistent on my scope). To set and vary the pulse width to the servo motor (pulse width controls the direction and speed of the servo motor) I needed to select particular resistor values for the 555 timer and include a variable resistor to provide the control. It just so happens that the controlling levers on the remote control controller is purely a variable resistor, so after removing it from the controller, measuring the resistance and adding additional resistor to make up the correct value for the 555 timer I had my means of control. And to include it into the 555 circuit I just wired it in using about 5m of wire, which allowed me to stand away from the scope when controlling it.
Next I pulled apart the original focuser and replaced the adjusting rod with the one I bought attached the other gear (hot glue is great stuff), then I cut out the steel plate attached the circuit to one side and the servo motor to the other and screwed it to the focuser base, using one of the original screw holes and tapping an additional hole in for better stability.
And there you have it, one motorised focuser controlled remotely with a small lever, which gives both directions and variable speed depending on how far you push the lever. Total cost < $10 and due to the gear ratio I used the minor adjustment is small enough to allow for precise focusing.
The only glitch I seem to have at the moment is the servo occasionally sticks at very slow speed, but moves on with a bit of persuasion. I'm pretty sure a replacement of the internal grease will fix that, just need to determine the best type to use.
My long term plans are to build a circuit that will allow control from the serial port, so I can site at my PC for all control of movement and capture, all I need is time :)
Thanks for reading my spiel and I hope this may spark some ideas for someone out there and hopefully make life that little bit easier. If youi have any questions please ask.
Cheers
KISA