Building a cheap focuser with BJY48 stepper

[powerlord]

Hi chaps, I see a few old threads about this, but not many details.

I've plenty in my parts bin, so figured I'd knock one up for my skymax 102.

As far as I can see though the bjy48 has a 5 degree full step, the gear box is 64 reduction, so basically I've got 4096 micro steps to play with with 360 which is loads of precision I think ?

I was planning to just wire it up to an arduino nano, and stick a little 4 way joystick on it (fine, fast) and write some code using the existing stepper libraries.

I reckon easiest fit is to directly connect to focus wheel rather than via belts for the skymax ?  Then I'll just CADS design a mount for it and print it out.

However, I'm a lazy [removed word], so don't like redesigning wheels - so thought I'd ask incase any of this has been done before and there's stuff I can steal/reuse 🙂

[theropod]

How do you plan on reversing the unipolar motor? Does your stepper driver reverse the voltage as a feature? This problem is one reason I tend to sick with bipolar steppers. The flexibility in drive options makes it much easier for me to use bipolar motors and simple drive boards like the Easy Driver and Big Easy Driver. These only need a step pulse signal and a direction signal, and the motors respond as expected every time.

[theropod]

You might be interested in my efforts to build a bipolar stepper driven alt/az I built using a joystick input method to make the steppers speed be proportional to joystick input. Below is a link right here on SGL where I document the whole affair. The last post is the most useful version of the Arduino sketch.

 

[powerlord]

thanks - Ill have a look.

I must admit, short of long ago wiring one up and playing with it, I just assumed it was bipolar.

some tutorials seem to also suggest this ? e.g:

https://www.makerguides.com/28byj-48-stepper-motor-arduino-tutorial/

This other post though also suggests it can be made to run CW and CCW ?

https://forum.arduino.cc/index.php?topic=549927.0

Have I embibed some duff info ?

I'll have a look at your project, though obviously the needs for a focuser are a lot simpler. When the skywatcher one is only 57 squid, there's a pretty low bar of complexity before I just buy that one tbh.

Edited March 4, 2021 by powerlord

[BCN_Sean]

With using this motor on a tangent correcting barn door, one thing I can tell you is that it's not a true 4096 step as the gearbox is slightly under 64:1, after testing it, it comes in at 4075.6 steps per rotation (reference : Arduino Forum) so if you're after serious precision then it's something to take in to account, and also the gearbox backlash is quite high.  I didn't use a stepper library for it, instead using an array to step through each state when rolling forwards, and then just subtracting it when it's in reverse.

Here is a bit of the code that I used to work with this motor, it's not been tested as it is, the pins aren't assigned for the drive (ints called drivePin(X)) and the only thing you'd have to do would make something to fix up the way to change the directions (the modes are called FORWARD, REVERSE, STOPPED, stored as ints 0, 1, 2).

Hope this is some use.

Forward_Backward_bjy48.ino.zip

Edited March 4, 2021 by BCN_Sean
Forgot something.

[powerlord]

thanks. the good thing about using it for a focuser (and I mean one controlled by me via buttons, not via PC) is that precision isn't that important. compared the the precision of Stu mk1  hands, it's gonna be massively better surely - if only due to the lack of vibration meaning I can actually see when things are in focus.

stu

[Seelive]

1 hour ago, theropod said:

How do you plan on reversing the unipolar motor? Does your stepper driver reverse the voltage as a feature?

The direction of a unipolar motor is quite simply changed by changing the phase of the drive signals, there's no voltage reversal involved.

[Davey-T]

23 hours ago, powerlord said:

Hi chaps, I see a few old threads about this, but not many details.

Lots of details here

Dave

Arduino Ascom focuser Mark2 - Page 40 - DIY Astronomer - Stargazers Lounge

[powerlord]

@Davey-T awesome - just what I'm looking for. thats my weekend project sorted 🙂

[theropod]

2 minutes ago, Seelive said:

The direction of a unipolar motor is quite simply changed by changing the phase of the drive signals, there's no voltage reversal involved.

Well, I’ve had a misunderstanding about unipolar motors for  a while. Thanks for the info. I’ll go off and educate myself more deeply now.

[BCN_Sean]

8 minutes ago, powerlord said:

thanks. the good thing about using it for a focuser (and I mean one controlled by me via buttons, not via PC) is that precision isn't that important. compared the the precision of Stu mk1  hands, it's gonna be massively better surely - if only due to the lack of vibration meaning I can actually see when things are in focus.

stu

I'll be building one as well in due course, just frustrated with the back-order blues at the moment; but as a simple addition it's worth doing it and as you say, probably more precise than the hands.

[Ibbo!]

2 minutes ago, theropod said:

Well, I’ve had a misunderstanding about unipolar motors for  a while. Thanks for the info. I’ll go off and educate myself more deeply now.

Some info here.

 

[Davey-T]

4 minutes ago, powerlord said:

@Davey-T awesome - just what I'm looking for. thats my weekend project sorted 🙂

I made one as did several others here.

Dave

[powerlord]

on that - maybe should post this, but er.. I use FLO whenever I can (got an adventurer on back order), but last few things Ive got from microglobe.co.uk who, for whatever reason, seem to have everything in stock.

e.g. no one had enhanced motor controller kit for EQ5 in stock - microglobe had, and cheapest. delivered next day.

I checked today for adventurer and they have them in stock too. I'm leaving my back order with FLO, but if yer desperate worth a look ?

dislaimer : I have nowt to do with them or any other company, just a punter.

[powerlord]

2 minutes ago, Davey-T said:

I made one as did several others here.

Dave

If I can do the 102 mak, I'll do my 200p too. and I'd like to do one for my canon 300mm F4 L*

Once I've done one, other than different mounting, it'll be a shoe in - and they are cheap as chips - though as I say, I've got 4 or 5 in the parts bin, plenty arduinos, etc so kinda free (with my warped logic anyhoo).

*ideally that should be possible via regular remote of course - but I don't want to use PC/mac outside, and the only android app I can find that works is qDSLRDashboard - but it's a bit buggy - but it does actually allow remote focus operation all be it, needing to [removed word] around with mobile app.

[powerlord]

Hi chaps, so Ive built the electronics and written the software. It's all working really well.

Next I'll buy 2 gt2 30t pulleys - one 12mm bore for skymax 102 focuser, one 5mm bore for motor, and a 158mm belt. Test it, then cad up the mount for printing.

it all runs off standard USB. I'm gonna put keypad and electronics in a handset, with cable to motor, so motor only thing on scope. Also.. Means I can just plug handset into any other mounts I do - just need to fit motor to then.

I'll share code and cad later. For now, here's rough video.

 

[BCN_Sean]

@powerlord, I built a control system myself for one this morning (rare morning off!!!) using the same setup as you did minus beeper with a pair of interrupting push buttons attached to pins 2 + 3 on the 328 (Uno/Nano).

Here's the code that I've used for it : 

FocusStepper.ino.zip

Now it's just wait until someone gets one of the scopes on my hit list in stock, and then get one built up for it!

Edited March 8, 2021 by BCN_Sean

[powerlord]

Ah, we've taken a bit of a different approach there then - I played about with different libraries and found the AccelStepper one ran really smooth and cool so used that one.

I'll run your code and see how it runs. Mine attached if you want to modify and try mine (my 5 button control is a 1 wire analogue one so you'd need to modify, etc)

stu

 

stu.stepper.ino.zip

[BCN_Sean]

14 minutes ago, powerlord said:

Ah, we've taken a bit of a different approach there then - I played about with different libraries and found the AccelStepper one ran really smooth and cool so used that one.

I'll run your code and see how it runs. Mine attached if you want to modify and try mine (my 5 button control is a 1 wire analogue one so you'd need to modify, etc)

stu

 

stu.stepper.ino.zip 1.73 kB · 0 downloads

Cheers Stu, I'll have a look at it later when I get chance!

[powerlord]

So, all done - here's some photos of the build.

And a video.

I'll probably adjust the speeds as I think giving it 6 different rates was overkill, but works nice.

As you can see from video - lots of 3d CAD and printing, and it fits securely with no screws, etc. And can be fitted with different sized pulleys or belts - though seems to work well with what I have.

Also, added a red led to top of controller to see it dark. I fitted a lithium ion battery and charger so it's self contained, and the controller plugs in to the stepper, so you can have unlimited numbers of steppers on other scopes, cameras and use the same controller.

I'm pretty pleased with the way it turned out tbh. 😃

stu

[powerlord]

Just an update that I'm using it in action for first time tonight - it worked perfectly - getting me a perfect pattern with the bahtinov mask at 10x liveview magnification - before hand trying to adjust focus at that was near impossible! so mission successful! - currently trained on M42 (again) - I'm sort of concentrating on the same target all the time to make sure any improvements I make in process are obvious.

stu

[BCN_Sean]

On 15/03/2021 at 21:00, powerlord said:

Just an update that I'm using it in action for first time tonight - it worked perfectly - getting me a perfect pattern with the bahtinov mask at 10x liveview magnification - before hand trying to adjust focus at that was near impossible! so mission successful! - currently trained on M42 (again) - I'm sort of concentrating on the same target all the time to make sure any improvements I make in process are obvious.

stu

That's good to hear! It's a great feeling when home brew comes together.  Still waiting on my stuff, if I'm lucky it'll be the end of the month, but as there's nothing interesting off the balcony and we're still locked up at night things can wait.

I did make a start getting the head around Astroberry on the Pi and connecting in the focuser, but made the daft mistake of installing Kodi and the other half had a look and decided to put it under the TV, so had to order another Pi... Ah well, it'll keep me amused for a bit longer