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Twin Arduino Focuser


smudgeball
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Hi

As I have a single Arduino controlled remote focuser, a friend asked me to make one for him but with two motors.

Just finished the project and thought I would share the images.

All credits to the SGL Arduino Focuser Project Team without whom I would not have completed this.

Kit List

2 x Arduino Nano

2 x Easy Driver Board

2 x AdaFruit 12v Stepper Motor

2 x Model boat couplings

Project box

Various switches and connectors

Usb hub

Cable

Strip of aluminium bar

A steady soldering hand !

Project box with fitted switches and usb hub

post-10504-0-60597300-1423917949_thumb.j

Arduino(s) and Driver Board(s)

post-10504-0-27240100-1423918006_thumb.j

All connected up ( I did tidy it up before putting lid on !!)

post-10504-0-09033600-1423918073_thumb.j

Motors attached to bar

Coupler is 5mm one end, 3mm other to attach to focuser fine control shaft.

It will be a "custom mod" after that to attach to main scope and guide scope.

post-10504-0-65081300-1423918117_thumb.j

The four tiny wires coming from stepper motor were a real concern as there was no strain relief (and none could be fiited)

So I attached four cour cable and secured cable to underside of bar

post-10504-0-76306600-1423918219_thumb.j

Connected up 12v supply and uploaded SGL Focuser sketch.

Worked first time :smiley:

Each motor comes in on a different COM port.

Hope it inspires someone else to try?

Regards

Neil

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just what I'm looking for ,could you do a wiring plan or show a close up of the wiring please ( i can follow this much better than a plan ) also where did you get the ardunio nanos from and stepper boards  

cheers mark

Edited by msh1
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Thanks Gina

Basically I didn't know, so just doubled up on what I knew would work :grin:

The nanos were £3.75 each so it's not too much of an error.

Food for thought for next time (not that there will be a next time !)

Neil

Fair enough Neil :)

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thanks davey-t read all 28 pages i think i have bought the right things i know nothing about the software tho 

mark

Just need to download the Arduino software for your board and Tekkydaves software. I did it so it must be idiot proof  :grin:

Dave

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Any particular reason for using a nano rather than a uno ? Curious as I intend to do one for 2 channels but using model aeroplane etc servo's rather than steppers so bought a uno but may have missed something doing that.

Bit held up at the moment as I need to upgrade my Linux to load the software I need. :sad:  I've just had a hell of a game installing it on a netbook in case I get tempted to try the INDI approach to telescope control.

John

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I was basically guided by the SGL focuser document, so went for the nano.

They're cheap and work for this.

The adafruit 12v steppers are expensive by servo motor standards, but again I went with what I knew would work.

If I ever do the project again, I may look at steppers half the price and maybe run everything off a single arduino ?

Neil

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I'm interested in trying to do it with model aircraft type servo motors but not sure about the torque needed. Not sure on that point with steppers either.  I need to measure it.

From memory steppers are driven by a phased pattern on the 4 wires but I have no idea what the arduino driving boards need so can't comment really. Patterns can be generated by having an array of them and stepping through it at the rate you need to switch at. The processor does have more than one timer that could do that via interrupts or I suppose a simple loop could be used. Has to be from memory as I haven't had an interest in them for a long time.

The servo motors are driven by a square wave and altering the mark space ratio sets the position the arm on them goes to. There is also a type that rotates.  Some people convert the arm type to these, there are details about on the web. The mark space ratio then sets the speed and direction. The control can be directly connect to a pin on the processor. I haven't fully looked at the data on the processor yet and these things need precise timing if they are to stay in position.  The digital ones usually have something like a 2 uSec dead band - any more than that and they will move. The other problem is hooking them up to the focus. I have seen one rated at circa 10 kg for about £9.  If one is firmly hooked up to a focus knob turning it by hand is likely to be hard work. They use small electric motors and a gear cluster. It's also possible to buy servo testers - set them with a knob but they usually have one or two other facilities as well.

:evil: Don't quote me but it's probably possible to take a servo motor apart remove various bits and pieces and just drive the motor - nice compact motor and gearbox set up. I assume the 10kg is at the end of one of the arms they usually fit. Like most things though it's probably an OTT rating and might let the smoke out. All electrical things really work via smoke because once it comes out they don't work any more. On the other hand if used as servo motors they will apply power to maintain position or rotational speed on that type.

John

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Edited by Ajohn
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I use very cheap stepper motors and Arduino control.  Stepper motors used are 28BYJ-48 12v with ULN2003A drivers.  4 phase, 8-beat motor, geared down by a factor of 64. Step angle is 5.625/64 degrees.  28BYJ-48 5v are also available.  This is a triple focuser for my triple imaging rig using SLR camera lenses.   You could also use ready made driver modules often sold as a package together with the stepper motors.

post-13131-0-36313000-1424167769_thumb.j

This shows how I laid out the circuit board.

post-13131-0-99819100-1424167994_thumb.j

Edited by Gina
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D13 goes to the ULN2003A which drives stepper 3.  A link across to the next strip on the stripboard (Veroboard) which goes underneath the USB connector on the Nano  Note also that the wires to the stepper motors are not all in the same order due to the power feeds and arrangement of pins on the UNL2003As.

ULN2003A datasheet

Edited by Gina
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Reading the other thread and noticing mention of timing belt drives I fixed a variable magnification microscope head that used these to move bits about. They used a plastic sector on the end that was being turned and it had broke in places. I removed it and rolled a thin cylinder of epoxy putty, rolled it around the part that was being turned, placed some cling film over it taking care to keep it smooth and then pressed the belt into it and smoothed out the edges with my fingers. When it had gone very firm I removed the belt and cling film. It worked well. I took a bit of care that the belt teeth weren't pushed down hard onto the part that was being turned but found it was difficult to displace all of it which would have weakened it too much.

There's not much chance of making a full diameter timing belt pulley with all of it's teeth like this, just a sector.  I used the epoxy putty that £ shops  sell, a packet with several small rolls of it. Milliput is reckoned to be the best and as they say it can also be drilled and tapped. It's useful stuff to have around. It also sets under water -  :grin: so no need to worry about it getting very wet.

No guarantees etc and perhaps it would be best to try it on something that doesn't matter first. I didn't but me £300 2nd hand head was useless anyway. It now works perfectly. Due to the cling film it more or less turned out shiny. I had the belt on and off several times while pressing it in to see what was going on. Where there is a lot of load it might be best to wrap a slab or something similar of the stuff part way round what is being turned to increase the area that grips. There are other options, maybe even make it and then fix it in place some how.

John

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Edited by Ajohn
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While looking around for some info on something else these popped up

Using a crudely modified servo as a geared motor for focusing - there are plenty of source of information on the crude method

http://emediadesigns.com/focuser/

And a page which I was looking for doing the same thing to a servo but retaining the servo action. I think he is being a bit OTT matching the resistors that accurately.

https://learn.adafruit.com/modifying-servos-for-continuous-rotation/overview

John

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