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Simple USB Motorfocuser


Thalestris24

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I bought a SW 'Autofocuser' just before Christmas and with a view to adding a usb interface to it. First I installed the motor on my ST80 and checked that everything was working ok (just in daytime test mode). It doesn't come with a battery, by the way - you have to supply a PP3.

Next job was to undo the 'Control Box' to see how it worked. You might think there was some complicated electronics inside... It's actually nothing more than a variable voltage regulator based on the LM317. So combined with the pot for speed control and the two press switches which simply switch the circuit on - that's it really!

I'd originally planned to try and figure out a way to add a usb interface to the SW pcb. However, that would take too much time and effort and not worth it for the SW controller. So I looked around on the net and found a number of different motor controllers with usb. (The SW motor appears to be a brushless geared DC motor. Maybe a servo would be better...)

Anyway, I found this board - the Motorbee control board. https://www.pc-control.co.uk/control/products/boards/motorbee.php This has everything needed plus a few value added features which could potentially be used in the future. It also has the advantage of coming with Windows software plus dll for custom coding. I like that! It's based on a PIC processor.

Here is an image of the Motorbee with the SW pcb next to it:

post-33532-0-33387300-1420135386_thumb.j

Oh, I also bought a longer cable to go with the SW - the supplied one is pathetically short!

Installing the Motorbee software was straightforward. I've only put it on my 32 Win 7 so far. It will have to run on my 64 bit Win 8.1 laptop. I have faith there will be no problems...

Connecting up the Motorbee is also quite straightforward. It requires a PP3 battery + connector with flying leads. The board has screw terminals - so one for the red lead (+ve) and one for the black (Gnd).

I had to snip the RJ connector off one end of the SW supplied 4p4c 'phone' cable. This is 4 colour - black, red, green and yellow. On the SW board the green and yellow are soldered together. Likewise the red and black. I did the same with the stripped back leads. They are quite thin wires so soldering the ends makes for a better connection to the screw terminals. For bidirectional control of a single motor I connected the green/yellow to OP1 on the screw terminal block. Red/black to OP2. Et voila! You have a basic usb controlled motor focuser! The software is fairly simple to use. Sliders control motor speed. Speed control is via PWM, rather than the crude voltage level used on the SW, so much more efficient. You select forward or reverse via a tick box and the motor will keep going in whatever direction until you untick the box. But that's it really - simple and relatively cheap (with VAT and postage Motorbee was £37.80). The software could be improved so I might have a go at writing a more 'focus-friendly' custom version - one day!

Other things I need to do:

Get a small box from Maplin tomorrow, to put the board in.

Add a on/off power switch

Add power-on led

Add led(s) to indicate forward/reverse

I also need to test it out properly. If it goes ok I'll get a second board for controlling the 150pds. I might look into getting an alternative motor - similar ones to the SW seem quite cheap.

In the long term I might look at adding some bells and whistles such as optical switches to prevent movement of the focuser going too far. The Motorbee has optional digital inputs as well as servo control connections.

Anyway, I thought I'd share this in case anybody else might also like to have a go.

Happy New Year!

Louise

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Hi Andy

Oh well, sorry I didn't do this earlier! I'd been pondering getting some autofocusers for quite a while. I wanted computer control but didn't want to pay lots for it. The main thing is having a suitable motor and a way of mounting it. So went for the Skywatcher even though it's quite expensive for what it is... Still, it's enabled me to put together something that's a lot better! :)

Happy New Year, and New Moon too!

Louise

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Thanks Gina! It's pretty simple for a DIY project but thought I'd share it anyway. Once I can get it put in a box etc. I'll do some stills showing the connections and maybe also a video of it working in test mode :) Early indications are that it will do the job :) Then I'll see about putting one together for the Crayford on my 150pds. I might see if I can find a motor that can be fitted in place of the SW and save some money! I'll also have to see if I can get my head around writing some software - I'm very rusty in the coding department...

Louise

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Only if you have the skills /physical abilities to solder etc.

Not a prob though.

It isn't absolutely necessary to solder for the basic setup I described. There is just the wires in the phone cable that you have to strip the ends off. But it is a DIY project... If you want a ready made usb focuser then you can buy the Shoestring FCUSB from Opticstar which probably has better software - and warranty :)

http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Imagers-Shoestring.asp?p=0_10_5_0_5_40

Edit: or the Hitec Astro version http://www.firstlightoptics.com/astronomy-cables-leads-accessories/hitecastro-dc-focus-controller.html

Louise

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I also want to put something together like this.

You mentioned the supplied software - would it be easy to operate via EQASCOM?

Hi

The supplied Motorbee software is standalone, I'm afraid. It's just a general purpose motor controller that I've adapted to drive the Skywatcher focus motor. However, they provide a dll library to facilitate customisation but that will require a fair bit of coding in Visual C++ or Visual Basic. I believe the Shoestring and Hitec versions have Ascom-compatible drivers. Personally, I don't see a particular need to have Ascom compatibility as a focus motor doesn't have to be visible in other software. I plan to simply use mine manually and in conjunction with the APT focus tool :). It will be a big step forward from focusing (or not!) by hand! Another advantage of a focus motor is that it will aid holding the focus tube in place without using the locking screw. I hate it when I have focus, tighten the screw and consequently lose focus!!

Louise

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The reason I would like eqascom compatibility is so I can use the gamepad option.

But if it works via APT then that sounds good.

I agree on the focus lock...the less touching the better.

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The reason I would like eqascom compatibility is so I can use the gamepad option.

But if it works via APT then that sounds good.

I agree on the focus lock...the less touching the better.

Hi

Just to clarify - it won't work via APT. It's just that when using the APT focus tool (FWHM/HDR), instead of adjusting focus by hand, I'll be able to do it with a mouse :) Simples!

Louise

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My apologies.

I re-read the op and note that soldering is not a necessity.

I like the sound of this now!

The only requirement for soldering is if you want to add leds to show direction. This will also require custom programming. Also, if you want a power led, that would require some soldering. However, you can do without any leds. Maplin do a pp3 battery holder with switch:

http://www.maplin.co.uk/p/1-9v-switched-battery-box-l90an

I just got a standalone toggle switch. I also just bought this box from Maplin:

http://www.maplin.co.uk/p/small-plastic-box-black-114x76x38mm-lh14q

It should hold everything ok - will confirm later. I actually wanted a white one but they were out of stock :) It will be necessary to drill/saw some openings for the cable/usb connector :)

Louise

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I put the Motorbee board in the plastic box today :) Added a switch and led and gave it a test. The board is just held in place with some Velcro. Similarly, I attached the battery to the lid with some Velcro. Drilled a hole for the usb B and cut a small slot for the motor cable.

post-33532-0-57642600-1420225085_thumb.j

Here is a close-up showing connections:

post-33532-0-06728300-1420225323_thumb.j

Finally, a video showing the focuser running in forward and reverse at about 90% max speed:

https://www.youtube.com/watch?v=67yJOJ9TtM4

The software interface leaves a lot to be desired but seems to be just about useable. Having said that, it has automation options that I haven't investigated yet. Still, it looks like the system will be capable of very fine movement. It's very quiet and smooth.

Edit: apologies for not very slick video. It was made with my handheld phone :)

Louise

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I like this. Even using the focus motor with the hand controller i still manage to move it by the pull on the cable.

Sent from my iPhone so excuse the typos!

That's not so good! I've yet to test it properly. I hope it holds focus otherwise I'll have wasted my time :( I have a dslr and filter wheel attached so a fair weight pulling down. There might be a chance to test it tomorrow.

Louise

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Dont panic too much. When im on the steroids (asthma) my hands shake a bit. What would probably help in my case is extending the focus cable lead to the controller.

Sent from my iPhone so excuse the typos!

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