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Robert Brown's "MyFocuserPro2" build


JamesF
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Regarding the required torque, I wonder if it is valid to say that if your kit plus the weight of the draw tube is, say, 4kg, and the centre of the spindle for moving the draw tube is 1.5cm from the rack, then the torque required (in Ncm) is 4 x g x 1.5 ?  Presumably that would be a maximum, given that friction will take care of some of the work?  For a Crayford I assume the required torque might be much smaller because the spindle is much closer to the drawtube.  Perhaps 3mm?  So in that case the maximum torque might be 4 x g x 0.3?

James

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1 hour ago, Gina said:

I use 28BYJ-48 gearbox stepper motors for all my focusers (lenses and telescopes) modified to run off A4988 driver modules as per my blog

as soon as I read your comment I looked through my "bazarbox" and lo and behold I have one of these gathering dust. I was quite stunned by the size difference but when I tried to rotate the shaft on that little guy, I had to exert a LOT of pressure just to move it a little :) I did not know that those small motors were gearbox stepper motors!

StepperCompare.jpg.e78d7d4fa5a8a9facb8c17605b8b46c9.jpg

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Focussing doesn't need much power if you use the 10:1 reduction drive on a telescope focuser.  The gearbox on the 28BYJ-48 holds focus even with a heavy camera hanging off the focuser.

Note that my mod converts a 5v stepper into a 12v one though you could use the 12v version unmodified with the driver often supplied with it (the sketch is a bit more complicated though).

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3 minutes ago, Gina said:

Focussing doesn't need much power if you use the 10:1 reduction drive on a telescope focuser.  The gearbox on the 28BYJ-48 holds focus even with a heavy camera hanging off the focuser.

Note that my mod converts a 5v stepper into a 12v one though you could use the 12v version unmodified with the driver often supplied with it (the sketch is a bit more complicated though).

Sorry I don't understand what you mean by : "the sketch is a bit more complicated" ?

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47 minutes ago, Gina said:

A4988 drivers only want step and direction whereas the ULN2003 driver needs the phases of the motor driven separately.

I bought a Waveshare HAT for the RPI4 and it has built in DRV8825 Motor controller it seems that the DRV8825 is equivalent to the A4988 with minor differences, so it should work.

http://qqtrading.com.my/blog/key-differences-between-the-drv8825-and-a4988

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If you use the Accelstepper library to drive either ,Uln2003 or A498, its a lot simpler and you have the added bonus of acceleration/decelaration motion.

e.g.

#include <AccelStepper.h>

// Define Constants
 
// Define step constants
#define FULLSTEP 4
#define HALFSTEP 8
 
// Define Motor Pins (2 Motors used)
 
#define motorPin1  D5     // Blue   - 28BYJ48 pin 1
#define motorPin2  D4     // Pink   - 28BYJ48 pin 2
#define motorPin3  D0    // Yellow - 28BYJ48 pin 3
#define motorPin4  D2    // Orange - 28BYJ48 pin 4
                        
                       
 
// Define two motor objects
// The sequence 1-3-2-4 is required for proper sequencing of 28BYJ48
AccelStepper stepper(HALFSTEP, motorPin1, motorPin3, motorPin2, motorPin4);

=============================

And to drive DRV8825 or A498 

============================

#include <ESP8266WiFi.h>
#include <WiFiUDP.h>
#include <AccelStepper.h>

// Define Constants
 
// Define step constants
#define FULLSTEP 4
#define HALFSTEP 8
 

AccelStepper stepper(1,D7,D6);

===================================

D7 and D6 are pins on whatever processor used for DIR and Step

 

Both the above "bits" taken from working Focuser's based on Arduino type processors.

Not sure if that Library is available for Python code (C++ etc)  ?? ( I know a port did exist at one time) which I guess you will probably use for RPI HAT driven Steppers

But if going Arduino IMO its the best stepper library available. https://www.airspayce.com/mikem/arduino/AccelStepper/

 

Original coding was based on Projets DIY (http://www.projetsdiy.fr) (Moonlite) and Robert's excellent own MyfocuserPro - later being heavily modified to use AccelStepper library and remove what I didn't use/need .

 

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I had a sort through all my boxes of components tonight and ordered what I don't have (enough of) to build two focuser controllers.  I already had the stepper motors ordered and I have a couple of Nanos left over from my dew controller builds (I ordered a box of five).  Mostly I just needed diodes (including LEDs), the electrolytic capacitor, buzzer and buttons.  Oh, and the 1.2k resistors.  I'd run out of those.  Somewhat to my surprise I found a few 9-pin D-sub plugs and sockets complete with shells for the plugs.  For reasons that I'm not entirely sure of I have piles of the 25-pin versions.  Perhaps one day I might find a use for them.

James

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I think all the parts have arrived now, so I need to get on with laying out the stripboard.  I found what looks to be quite a handy tool for doing that last night (it's probably simple enough to do by hand, but having something else check my work is always welcome) called VeroRoute.  It appears to be intended for more general PCB layout, but can do stripboard as well and can check for sections that should be connected but aren't, or vice-versa.

Unfortunately work has been getting in the way quite a lot this week, so I've made little other progress :(

James

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In the end I couldn't find a single application that would do what I wanted, so I just decided to start cutting tracks and see where I ended up :)

rb-focuser-controller-03.jpg

This evening I have spent a happy hour or two soldering in all the headers,

rb-focuser-controller-04.jpg

and then adding all the string to join the various bits of track together.

rb-focuser-controller-05.jpg

Oh, I put the two capacitors in for the voltage regulator too.

Now I think I'll do a bit of testing to make sure I don't have any bridged tracks where I don't want them.  There is actually one place where I deliberately bridged the tracks with a lump of solder.  The DRV8825 "sleep" and "reset" pins are next to each other and both clamped to the 5V output of the Nano, so I just dragged a lump of solder across the tracks they use.

Once I've checked the soldering over there's not a lot left to do -- the resistor network for the pushbuttons, current-limiting resistor for the buzzer, two resistors and a diode for the supply voltage sensing, another couple of diodes, a capacitor and the voltage regulator and I think I'm done.  I may need to break a few more tracks to fit all of those in, but that's not a problem.

James

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On 30/01/2020 at 20:40, Vox45 said:

Yes I am planning on changing my focuser to a Baader steeltrack with a built in pulley between the 2 knobs (coarse and fine) I find this very elegant, placing the motor underneath the focuser instead of sticking out on the side.

steeltrack.JPG.13fdea0a1f2e56a12a0f48a64e853294.JPG

Good luck finding a corresponding motor pulley. I could not find anything with the same belt profile, correct number of teeth and pre-bored to an appropriate diameter for available motor shafts. In the end I put my own pulley in place of the other knob. Very frustrating and believe me I really looked hard. Almost like Baader wanted you to use their own unit!

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26 minutes ago, IanL said:

Good luck finding a corresponding motor pulley.

@Vox45 I use a BST and found appropriate pullies and belts from hereI also had to buy a sleeve/insert to match the pulley bore to the motor shaft.  The HTD belt fits perfectly on the Baader pulley. I subsequently discovered the same things are available from Amazon but not the same range/choice. The black motor mount was custom 3D printed.

I use a SW dc motor with HitecAstro controller and it works a treat on my ED80DS-Pro. I rotate my ED80 so the focusser is 'on top' but it would work just as well in the more usual configuration.

HTH

Adrian

IMG_9962.thumb.JPG.a3df1724fb8b0f05daef6398fe8a171c.JPGIMG_9963.thumb.JPG.7d6838e3be0816fb8c46d5e868480390.JPGIMG_9964.thumb.JPG.f9aea1c11b4b379332a512618aa80f86.JPG

 

Edited by Adreneline
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Not a whole lot more done so far this week mostly thanks to work stuff going on, but I have now got almost all the components in place.

spacer.png

The large diode at the top left wasn't in the original plan I worked from.  That's the reverse voltage protection diode.  Obviously no-one, least of all me, is ever going to connect the power the wrong way around anyhow, are they?  The leads on this diode were larger than the hole diameter, so I ended up buying some small diameter drills from Amazon and enlarging two of the holes to about 1.5mm so it would fit.

The top right I had to reorganise a little.  Fitted around the top of the header for the Nano is the diode that protects the voltage regulator.  The two resistors and the third diode form the voltage sensing circuit that means the Nano won't try to drive the motors unless 12V power is connected.  To make that all work I had to move one of the capacitors for the voltage regulator and make another cut in the track feeding the Vin pin on the Nano (which is bridged by the diode).

All that remains now is the voltage regulator itself, which will fit at the top on the very right hand edge.

As I'm not using some of the other features of the focuser controller such as the temperature sensor and the OLED display, there's quite a bit of space free in the middle of the board.  When I make the next one I might move the Nano to the left two or three columns to make a bit more space on the right hand side for the additional components at the top right.

James

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  • 2 weeks later...

Things have got away from me over the last couple of weeks and I've not updated this thread.  Time to do so...

Having finished the circuit board I plugged in the Nano and motor controller and connected it to a USB port (without any other power source connected).  The power LED lit on the Nano, but nothing else happened and I wasn't able to connect to upload a sketch.  Unplugging the Nano from the board allows it to work exactly as expected.  I can upload the "blink" sketch and it runs ok.  Plug the Nano back in and the sketch doesn't start and there's no response when attempting to upload.

I can't find any obvious problems with the circuit or my soldering so far, but I have to assume that either the 12V supply is required in some way that isn't obvious to me or that there must be some issue with my soldering that I just can't see.

As stealing the eyes of a teenager tends to be frowned upon I'm thinking my best option at this point may be to build a second board and test the Nano out at each stage to see what happens.  The only other thing I can think of for the time being is to connect up the 12V supply and check if any magic smoke comes out, but I'm not so keen on that approach whilst there are still other things to try.  I could perhaps attempt to build the circuit on a breadboard, but I'm not convinced there'd be room.

James

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Hi James, As there is not much else in the circuit, and I assume you have removed the Stepper driver to eliminate that? If so and the problem remains its almost certainly the reset circuitry. Try removing those components until the basic Nano works. I did not build the reset/power on cct. in, and my focusser works just fine.  Definitely do not connect 12v up yet!

Good Luck :)

John

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Thanks, John.  I did try removing the stepper driver and it made no difference, so the problem must lie elsewhere.  I didn't include the power on reset stuff bit either, so at least it isn't that.

I think it must be a short somewhere between some of the tracks.  This evening I've built a new one from the ground up, plugged in the same Nano and stepper driver and it's running "blink" fine.  A small part of the layout is slightly different from the first one as I realised I could do it a little more neatly, but the circuit is clearly the same.  I guess I just need to get the big magnifying glass out so I can check things over better.

At least I have something I can continue working with now.

James

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If not already done so, unplug the Nano from the board & connect it to your computer & flash the latest version of the firmware to it, using the Arduino IDE. I use the latest version, 1.8.11, but you have to set Tools \ Programmer - Atmega328p (Old Boot Loader). At least then you'll have more confidence that you at least have a working nano....

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Thanks, Julian.  I'm fairly sure the Nano works ok as it's behaving sanely in the board I built last night.  Updating my IDE might be a good plan though.  I see 1.8.12 has been released now.

However, this morning I grabbed a scribing tool from the workshop and ran it down all the "blank" sections of the stripboard on the first board a few times to try to clear out any tiny drops of solder that might have been bridging tracks.  I also found one place where my soldering might have unintentionally bridged two tracks though I couldn't tell for certain.  If there was a bridge then it would have pulled the RESET (pin 3) input to ground.  As that input is active low I imagine it could well have caused  the behaviour I was seeing, so kudos to fireshipjohn for identifying a possible problem there.  I removed the solder using some braid, cleaned between the tracks and remade the join just to be sure.  I now have a Nano sitting in the socket and behaving as I would expect :)

Now as if it's not enough having to deal with my eyesight not being what it was in my youth, I can't remember where I put my stepper drivers either :D

James

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1 hour ago, JamesF said:

Now as if it's not enough having to deal with my eyesight not being what it was in my youth, I can't remember where I put my stepper drivers either

This is what hampers my DIY projects more than all the other problems put together... 🙄

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1 hour ago, JamesF said:

I also found one place where my soldering might have unintentionally bridged two tracks though I couldn't tell for certain. 

after soldering I normally run along all adjacent breadboard tracks (and isolated sections) with the multimeter in continuity mode waiting for the dreaded 'beep' where there shouldn't be one - like you my eyes wouldn't pick up faint traces... 

Edited by adyj1
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3 minutes ago, adyj1 said:

after soldering I normally run along all adjacent breadboard tracks (and isolated sections) with the multimeter in continuity mode waiting for the dreaded 'beep' where there shouldn't be one - like you my eyes wouldn't pick up faint traces... 

I would have liked to do that, but I get a bit antsy about it once there are polarised components in place just in case reverse voltages turn up in places they shouldn't be.

James

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