Simple USB Motorfocuser

[Thalestris24]

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!

Hi Kev

What type of focuser do you have? My motor is on a R+P and it's not easy to move by hand. I observed that the motor just on it's own (unconnected to the focuser) needs a fair bit of effort to rotate it by hand. Mind you, I'm only little and not very strong! I can't see that it would be easy to shift the focus through an accidental small tug on the cable - but I may be wrong! I was quite dismayed as to how short the supplied cable is which is why I bought a longer one: http://www.ebay.co.uk/itm/200553785416  Of course, I'm not actually using it now but may do with a second setup.

There may be some clear time to test the usb controller on some stars later tonight. In any case I'll try it out properly during the day first. I'm hoping it will come into its own when swapping between narrowband filters but I'll need to write custom software for that. Might make a start with Visual Studio today

Louise

[Thalestris24]

I ran the focuser in anger last night I have to say I didn't find it easy to do the focusing! This was largely due to the software being general purpose motor control rather than what would be required for focus adjustment. I did eventually manage it though I used APT's focus aid with a focus plan and focused on 109 Her - a mag 3.85 star in the West. I acquired clear images of the star but collecting images is quite slow compared to Liveview. But Liveview doesn't really work with low brightness stars. I had actually used the focuser earlier (just after sunset) and focused on a distant spire. That seemed quite easy... However, it's much harder in the dark and I really don't like using a laptop trackpad! Anyway, having started close to focus, it's surprisingly easy to inadvertently go way off! Then it takes time to get close again. So the whole process took much longer than I hoped. Perhaps with more practice... However, I quickly realised that custom software is what's required. APT actually has an inbuilt auto-focus tool. Has anyone used it? The trouble is that, as currently implemented, it only works with a stepper motor

I've asked Yoddha (on the APT Forum) whether it might be possible to get hold of the FWHM/HFD values that APT generates. They would be really good to have. In the meantime I'll try and put together some code to implement a single slide control with forward-reverse on the same control. Actually, two sliders - one coarse, one fine. A similar history graph to that which APT creates would be useful - needs to be a lot bigger than the APT version!

It's forecast to be mostly cloudy for the next 5 days so this little project will keep me busy!

Louise

[kev]

Sw 2"/1.25" on my 8" newt.

Ive found my longer cable, its helped a lot. 8-)

Sent from my iPhone so excuse the typos!

[Thalestris24]

Quick update! I've been working on the custom software (on and off - more off, lol) and have had the focuser running ok on the ST-80 . So far, it's only been with a console app just to check the functionality. One thing I've observed is that the response for a given speed setting varies according to the battery condition. I've only been using a cheap PP3s which get used up pretty quick when testing a lot! At some point I'll get a much better battery. It's obviously a limitation that all batteries run down. I'm not sure whether it might be better to run the motor from a 12V supply which might also be a battery but which won't discharge very quickly during a normal session. On the other hand, when in use, and once focused, the focuser won't get used so frequently as when testing so maybe a PP3 battery will still be ok.

Anyway, next step is to create a user-friendly Windows app. I've had to teach myself Visual Studio/ C#/ WPF which are all new to me but I'm getting there . Will update again with pretty screenshots when I've got an alpha of the app

Louise

[Jonk]

My stepper motor arrived yesterday, just waiting for the arduino.

I'll keep an eye on your progress.

[Thalestris24]

My stepper motor arrived yesterday, just waiting for the arduino.

I'll keep an eye on your progress.

I have wondered whether a stepper motor might be better... But I wanted to start with something I knew worked and which I could easily fit. So I bought the Skywatcher. It does work! So adding the usb controller was simple and the software isn't complicated (though I'm slow at writing it!). Good luck with yours!

Louise

[Shelster1973]

Not wanting to hijack or derail, but have a similar thread on here about usb controlled focusers which are for Newts.

Is linked in there to another few threads were another member on here has taken and run with the idea and come up with a working device.

Have still yet to get one going for myself as other events haved taken priority over this, but is still on my list of things to get hold of and make

http://stargazerslounge.com/topic/224836-windows-driven-stepper-motor-focuser/

[Thalestris24]

Not wanting to hijack or derail, but have a similar thread on here about usb controlled focusers which are for Newts.

Is linked in there to another few threads were another member on here has taken and run with the idea and come up with a working device.

Have still yet to get one going for myself as other events haved taken priority over this, but is still on my list of things to get hold of and make

http://stargazerslounge.com/topic/224836-windows-driven-stepper-motor-focuser/

That's ok. Yeah have seen that. The motor controller I have comes from PC Control too But I'd got the SW Autofocuser first and only fell in after that it was a DC (non-stepper) motor. But at least I have the fittings with it. It seems to work quite well on my ST80 test bed. The basic software I've written is straightforward but I've been trying to interface it to APT to get the fwhm/hfd values but not managed it yet. Ivo kindly made a version of APT for me that broadcasts the values as Windows Messages. Hopefully, I'll figure it out eventually!

Louise

[Thalestris24]

Finally got an opportunity late last night to test out the 'alpha' software live

Here are a couple of screen photos:

I can say the software functioned as expected I just used it in manual mode as 'autofocus' isn't properly implemented yet. Having used it live I think maybe its window is a bit big at the moment so will rearrange things and reduce the window size. The bright white window background is rather harsh! So might see if I can shade it.

One problem that became obvious is the variability of the focus values from moment to moment. For example, fwhm can jump from 1.23, say, to 3.46 just because of the atmosphere. Hmm... I can't do anything about the atmosphere but maybe I could take an average. However, how would I know what the 'true' value is? I suppose the true value has to take into account atmospheric variability so is not necessarily the minimum possible fwhm? I guess the 'best' value would be an average of maybe 4 or 5 exposures. The trouble with that is that it would make the process a bit long-winded but needs must!

Still, it's a much better way to focus compared to twiddling the knobs with my fingers!

I have a second SW autofocuser now so will try and fit it to the 150pds today

Louise

[Thalestris24]

Fitted the second AF to the 150pds. Daytime test with my software ok. Hope to have a live test later - if the clouds clear!

[brown_rb]

Have been reading with interest, congrats on your implementation

APT works with an ASCOM based focuser, so it can work with a DC motor version (if that has an ASCOM driver).

For a DC based version that works with most DC motors, and it comes with an ASCOM driver that was tested with APT, as well as a Windows application, you might want to take a look at 

http://sourceforge.net/projects/mydcfocuserrelativedcfocuser/

cheers

Robert

[Thalestris24]

Have been reading with interest, congrats on your implementation

APT works with an ASCOM based focuser, so it can work with a DC motor version (if that has an ASCOM driver).

For a DC based version that works with most DC motors, and it comes with an ASCOM driver that was tested with APT, as well as a Windows application, you might want to take a look at 

http://sourceforge.net/projects/mydcfocuserrelativedcfocuser/

cheers

Robert

Hi Robert

Thanks. Yeah, I know APT supports Ascom focusers  - I just wanted to do my own for the fun of it! I'm quite pleased with the results so far. Since I have a custom version of APT that will automatically pass fwhm and hfd values to my application, that's sufficient. I used it with my 150pds last night and that went well. My software would benefit from a few tweaks but everything performed ok. 

Louise

[Astroboffin]

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:

SWandMotorbee.jpg

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

Hi Louise,

Could you just clarify for me please, the cable that comes with the Skywatcher focuser, has 4 cables, are only two of these used, for + and - connections, but they do this by connecting the four cables in two groups of two, to make the two connection cables? Of so which colour goes with which?

But the other end that connects to the motor, still has four connections, so would they be connected together inside the motor housing?

The reason for asking is that I have an meade LX90 with the APM909 module and wonderd if I could control the skywatcher focuser through that the same as the mead, but the meade only has a two connection jack plug, but what you say now makes sense, I got confused because the meade uses two cables, but the skywatcher seemed to use four.

Regards

AB

[Thalestris24]

Hi Louise,

Could you just clarify for me please, the cable that comes with the Skywatcher focuser, has 4 cables, are only two of these used, for + and - connections, but they do this by connecting the four cables in two groups of two, to make the two connection cables? Of so which colour goes with which?

But the other end that connects to the motor, still has four connections, so would they be connected together inside the motor housing?

The reason for asking is that I have an meade LX90 with the APM909 module and wonderd if I could control the skywatcher focuser through that the same as the mead, but the meade only has a two connection jack plug, but what you say now makes sense, I got confused because the meade uses two cables, but the skywatcher seemed to use four.

Regards

AB

Hi AB

As above "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". The motor is a simple DC motor, not a stepper motor, so just has + and - connections. I don't know why they make it with a 4-core cable and connector! I don't know what goes on inside the motor housing but if the wires are paired at one end then they are electrically paired at the other. However, an autofocuser would really be better made with a stepper motor. Having said that, the SW motor works quite well.

Hope that's clear

Louise

[Astroboffin]

Hi AB

As above "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". The motor is a simple DC motor, not a stepper motor, so just has + and - connections. I don't know why they make it with a 4-core cable and connector! I don't know what goes on inside the motor housing but if the wires are paired at one end then they are electrically paired at the other. However, an autofocuser would really be better made with a stepper motor. Having said that, the SW motor works quite well.

Hope that's clear

Louise

So if I put a mono jack plug on the end of the skywatcher cable, then there is no reason why it would not work with my meade APM909 module and then I can control through the autostar handset as I do with the the meade focuser.

Thanks for that

AB

[Thalestris24]

So if I put a mono jack plug on the end of the skywatcher cable, then there is no reason why it would not work with my meade APM909 module and then I can control through the autostar handset as I do with the the meade focuser.

Thanks for that

AB

Hi

I'm not familiar with the Meade hardware but the SW control box just uses press to make switches to turn the motor on and at a speed set by the potentiometer which just varies the voltage. My DIY version with the Motorbee allows usb control usim pwm rather than a simple DC level. Both operate from 9V PP3 batteries. Both facilitate selective bidirectional travel. If that sounds compatible then you should be ok - but at your own risk!

Good luck

Louise