Home made remote controlled focussing system

[Gina]

This is taken from my Obsy Build thread as I want to make some improvements and having this information in the middle of the Obsy thread was a mistake on my part - it should have had a thread of it's own before. Anyway, it's having one now

Before I get to the pictures, here is info on some of the parts.

The motor/gearbox came from Maplin Model SN36P :- Multi Ratio Motorgearboxes : Motors & Gearboxes : Maplin Electronics

Pulley and belt bought from Technobots

Pulley used two of these back to back :- Plastic Pulley 30/25 2.9mm

Belt was :- Pulley Belt 2.5mm x 70mm ID

The shaft on the motor/gearbox is 3.0mm so the 2.9mm hole in the pulley makes a good tight fit. These were the only pulleys shown that had this size hole - nearest otherwise would be loose on the shaft and didn't have a grub screw to tighten it. They only represent half a pulley (like railway wheels) so needed two back to back.

These photos show the focus motor mounted on the scope mounting bar (using the bolts used to stop the scope sliding right off if the fastening knobs are undone), from various angles and ending with a photo showing how it's fixed on. More pics to follow plus further info.

[Gina]

This is the Mk.2 circuit for the focussing control box circuit. The pot varies the output voltage from 1.2 to 6.6 volts but the speed range available with this has proved insufficient, so I shall be producing a Mk3 soon. This will probably use a variable pulse width control instead of analogue voltage.

The following images show the circuit for the present focus control. I've also included a circuit diagram of the circuit showing two versions - the ideal using two SPDT push button switches and my alternative using a DPDT biassed centre-off toggle switch. The final image shows the outside of the control box with the speed control knob and rocker to move focus in or out.

[bluemarkus]

really cool focuser, love thecolorful appeal to it. now u need a bahtinov mask, its also a DIY object. (if u dont have one yet).

[JamesF]

Something about that focuser just makes me think childhood days lost playing with Meccano, Gina

Nice to see it done from scratch. I've just been out testing the motor focuser on my Mak, but that's all built from existing electronics. I shall certainly be following this with a view to using the ideas on other scopes.

James

[Gina]

Thank you for all your comments Meccano was great stuff when it was all metal.

[JamesF]

It was. I had lots of the "blue and yellow" era metal Meccano when I was a child combined with hand-me-down "red and green" era stuff from my dad. It's all in a large box in the cellar now. I guess it's about time we got it out for my children...

James

[Gina]

The gears etc. were particularly hard wearing and I remember them being used in test rigs for life tests on things in the 1960s. Millions of rotations or back and forth movements produced no noticeable wear on on the Meccano bits! Now that's what I would call durability!

[jon1000]

Looks good

[bluemarkus]

in germany we have "märklin" and "lego" and "fischer technik". its meant for kids to learn technology and build their own stuff but some of that stuff is really useful for adults as well...

[cabby]

I made a focuser for mine and actually pinched a few bits of my son's Meccano to build it!!

[pel]

Very clever Gina, does it slip at all though?

[Gina]

Very clever Gina, does it slip at all though?

Thabk you No the reduction radio from the fine focussing knob holds the focuser alright.

[Gina]

I'm working on a new control system with a wider range of control using PWM (Pulse Width Modulation) this provides better motor speed control at lower speeds. At the same time I'm thinking of computer control. I'm working on a combined interface for both focussing and filter wheel control.

Both can easily be handled by the Velleman USB Interface card K8055 which I bought some time ago. These have 2 analogue inputs, 5 digital inputs, 2 counters, 2 analogue outputs or PWM, and 8 digital outputs. The outputs are capable of handling 100mA sink current @ up to 30v.

[Gina]

Here's an alternative using only one relay and using the PWM set to zero in the software as the off/stop state. In the diagram above there are two relays with one on or the other on for IN or OUT focussing motion and both off for STOP. In this latest version, the single relay switches the polarity of power to the motor. A switch counts revolutions of the motor to determine the focus position.

I've included just the focussing part of the interface here.

[bluemarkus]

since i saw gina lisas thread, i thought i might cook something up myself. just built me an EQ platform which after 15 days of work now is about finished, and modded me a toUcam so i can start photography. now what i needed is a focuser. hmm so why not use some lego ? my brother has this 10yr old "lego robotics invention system 2.0" thing lieing around in his room. it is a bundle to build simple robots that can drive around, and do simple tasks. i didnt need the light sensors or contact sensors, just 1 motor, the handcontroller (put new batteries in it still worked like a charm), and a simple gearbox consisting of only 1 wormwheel on the motorshaft, and 2 small gearwheels. then 3 layers of old bicycle tube onto the focuser wheel to create anough friction, and VOILÁ...

now i only need to make the cable like 5m long so i can sit lazy inside and take pictures while my homemade EQ platform does the tracking, my homemade focuser focuses and my homemade toUcam takes pictures. then i get homemade astropictures that i can edit with my not homemade astropicture-processing software...

greetings to Avalon from Krautland

Mark

PS: now the only thing that might suck is my brother might throw a temper tantrum when he sees i used his lego (my famly always does), but i hope its not gonna happen.

my super focuser 2.bmp