Remote Focuser For Misers (no engineering degree required)

[EwanV]

One of the biggest problems with being a miser is allocating funds for research and development.  I am, therefore, a big believer in lettings others do the expensive bit and I'll come along afterwards to see if I can cut corners and costs.  The target for today is the MyFocuserPro2 project on Sourceforge. 

 

The idea of my build was to make a motorised focuser that could use ASCOM drivers to remotely and automatically focus my telescope so I could do away with focusing masks and make my rig truly controllable from my sofa (I'm finding the cold, long nights aren't doing me any favours now).  Currently, the mount, camera, guider and such are all controlled by an old laptop which I can access using VNC or TeamViewer remotely.  The focuser I was using (SkyWatcher DC Motor & Hitecastro DC Focus Controller) do not give you a fully automatic means of focusing, so I was still reliant on a bahtinov mask and getting up off my lazy backside to replace and remove the mask every time I wanted to check focus.  There were two options:

 

1. Motorise the mask so it slides in and out of position on its own

2. Stop overthinking everything and steal someone elses work

 

Option 2 it is then!!

 

1,000,001 Choices and no clear path

The MyFocuserPro2 project has grown and grown, with different design options, configurations, depth of software and instruction manuals.  Whilst this makes it a brilliant resource, it also means that navigating it and finding the bits you actually want and need can be tricky.  I know virtually nothing about Arduino programming and have the soldering skills of your average 3 year old.  This meant that what I really needed was a manual written by an idiot for an idiot and working to a budget of "Telling your wife (truthfully) exactly how much you spent".  That manual didn't exist so I decided, like an idiot, I'd write one.

 

Low cost and using spares

Firstly, I decided to base my design around the MyFocuserPro2M - a version of the focuser that you can buy pre-made from the designer, Robert Brown, that he's also given instructions on so you can build your own.  Robert's a clever chap and even this version of the focuser has multiple options.  One design in particular had minimal soldering needed so I decided to work with that and see if I could improve on it.  The cost of the parts once I'd worked my magic was less than £40 if you didn't go for things like a hand controller and even less if you opted not to have the temperature probe (something you can add in later if you want).

 

I wanted to make sure that some parts were things you were likely to have kicking around the house anyway.  I used standard Cat5E network cables for the connection between the motor and controller, as I know they'll handle 12v and you're likely to have some spares as you get given new ones every time you switch internet service providers and they send you a new modem/router.  I made heatshrink wire covers optional, but Lidl often have kits you can pick up.  For those that are confident with a soldering iron, you can switch between Arduino models and wire connection methods if you want.

 

Oops!! I broke something!!

One of the design amendments I wanted to make was to ensure that if one piece of the remote focuser broke, I could replace it without having to:

a. dismantle the entire thing

b. replace unbroken parts that were attached

c. do more soldering than absolutely necessary

 

Additionally, I have more than one telescope.  The best solution would be to have a remote focuser attached to each scope so that if I want to swap from the 72mm refractor to the 203mm newt, I don't have to detach everything but who wants to spend £40 per telescope when they don't have to?  The re-design means all you need to do is make the motor section for each telescope (about £16 plus some 3D printed parts).  The actual controller remains in place so there's no unplugging of USB leads and that means that you don't have to reboot the software when switching to a different telescope. 

 

Testing, Testing, 1, 2...... Clouds

At the time of writing this post and starting the thread, I'm in the testing phase of things.  In other words, the Astronomy gods (they are real) have stepped in and I've had cloud cover since building the focuser.  The manual is half written and I shall be passing it on to my trained monkey (my mate Steve - we're known as "The Idiot Twins" but we're not related) to try out, but I will put together a parts and price list in the next few days.

 

 

[EwanV]

A few photos to keep you updated. 

First image - the motor inside its (designed by me) 3D printed housing using the (designed by Robert Brown) 3D printed mounting plate

 

Second image - The Arduino Uno in its box (3D design from Thingiverse) with wires leading to the exposed motor driver in a box designed by me.

 

Third image - showing the wires connected to the Arduino - no soldering required as I used the Arduino Uno R3

 

Fourth image - Arduino end of the connectors to the motor driver board

 

Fifth image - Motor driver board of the same connectors

 

Sixth image - wires (same colour as on the actual motor) showing wiring connections leading from the motor board to the motor.

 

The only bit of "cut and paste" is cutting a length off each of the wires coming off the motor to use as shown in the 6th photo.  Using the Cat5E connectors I've selected don't need any soldering either!!

[EwanV]

I can't believe I've had to wait so long for a clear evening!! Who's been buying astro gear and summoning the clouds?  Come on; own up!!

 

Tonight is looking to be the first night when I'm going to have the opportunity to test the remote focuser.  I have full confidence in the device working, but I do wonder whether I should consider some kind of gearing to reduce the distance travelled with each step.  The Nema 17 travels 1.8 degrees per step, meaning that it completes one revolution in 200 steps.  I know I can 3D print some gears to give me a 4:1 reduction, so the equivalent of 800 steps per revolution of the focusing "knob", but I'll only do that if absolutely necessary as I don't want to add in anything that's going to have possible tension and lagging issues.

[EwanV]

IT WORKS!!!!! I finally got enough of a gap in the clouds to give the focuser a test run. 

 

I've decided that I'm going to change the motor from direct drive of the focuser to via a 4:1 gear and belt drive.  This will give me 4x finer control over the focusing mechanism for more accurate results.  The belt drive may add a bit of lag to the focuser, but the software for focusing takes care of that for me.

[EwanV]

Update!!  The 4:1 ratio wasn't necessary.  I've found that using a 2 step change in the focuser in NINA works just fine. 

 

Translation: Autofocusing works by the camera taking a picture, looking at the stars, moving the focuser a set amount and then taking another picture.  It does this several times and by giving each of the pictures a score, it works out the best position to be in then moves that number of steps to get there.  You can tell it how many pictures to take and how many steps in between each picture then it does everything for you.  In my case, I've told it to take 2 half steps each time and 4 photos either side of the point it starts at, each of which is 4 seconds long.  This means it takes a total of 8 pictures of 4 seconds each to get me to the point of best focus. 

[len2376]

On 8/24/2021 at 9:37 AM, EwanV said:

Second image - The Arduino Uno in its box (3D design from Thingiverse) with wires leading to the exposed motor driver in a box designed by me.

Why not put all the electronics in one box? Much tidier that way and less chance of wires coming adrift.

 

[EwanV]

7 hours ago, len2376 said:

Why not put all the electronics in one box? Much tidier that way and less chance of wires coming adrift.

 

Hi Len

 

Don't worry - the final design will have everything in one box... well... two boxes if you count the one for the motor!!  During the test phase, I tried out some different motor control boards before settling on the one in the picture, so the box it's in was purely to protect it whilst I made sure everything works (I'd already printed the Arduino box for another project so it was simpler to just use what I had).  I'm getting some decent RJ45 female sockets and they will be incorporated into the design too.  The final thing I am considering is whether to fit a heatsink to the motor and that will mean changing the box that's in too.