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Stepper motor focus control version 2


ncjunk

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Blimey, Suddenly a great deal of interest.

Neil, glad to hear you managed to get the stepper working. Did the info help. I think that unipolar motors are generally more common. Looking on ebay you can pick up stepper motors relatively cheaply. Some thought should be spent on how the motor is connected. This effects the size and accuracy (step size) of the motor. This might mean that a step down motor gearbox would be preferable (I picked one of these up from RS a little while ago) Robofocus generally uses a drive belt, Other use a direct coupler. As regards having the motor energised all the time, this shouldn't be a problem as stepper are generally designed for this. Fitting a clutch would be possible however further adds to cost and complexity.

For the coding experts out there, the Robofocus ASCOM driver is open source and fairly well documented (if you understand coding which I don't really). Download (via the ASCOM website) and install the driver (select install source file option). File can be in c:\Program files\ common files\ASCOM\focuser. Many thanks to the Robofocus team for allowing (even encouraging) the use of their code.

Sorry I haven't been too much help this weekend, family commitments, but let me know if help is needed

Rob

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I'd like to replace my servo with a stepper but I'd like to provide functionality for both in the focuser code. I'd like it geared so that the positioning is absolute.

I'm probably missing something but I can't seem to get the robofocus source code to show me any dialog boxes apart from the setup dialog :/

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Have you thought about using Meccano? Readily available, cheap and easily bent into whatever shape you want :D

Just an idea :)

Thanks for the input George, it's been many years since I've laid eyes on a piece of meccano, but yes, it would be good for the task.

I'm also using aluminium stock to make brackets, it's just that I gave all my tools to my son when we moved house, so now all I have is the standard battery-powered drill, some screwdrivers and a rusty file or two! Doesn't do much for looks or accuracy.

I'm pretty ignorant of both servo and stepper techniques, so decided to at least start out with what I was familiar with. I bought a miniature 12vdc geared motor with shaft 2 ppr encoder on Ebay for about 18 pounds, and plan on playing with that using PWM for my focuser prototype, as I'd like to have a position indication function. I'd change to stepper or servo if it made sense.

Cheers,

Mike

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The Stepper code in the Arduino covers both Unipolar and Bipolar. I coded it all manually and then realised there was a pre-configured function that does it (no laughing at the back) so have redone it for that.

The preconfigured function lets you set number of steps required for a full revolution and also lets you use 2 or 4 outputs to control it.

Problem is my L293 is getting warm as it isn´t the correct current rating for my stepper (whats 0.2 amongst friends?) so ordered another one on 2 day delivery.

Mecano seems a good idea I have no idea where I am getting a bracket for at the moment......

I will finish a first revision of the specification by sunday and let you all review it and add to the requirements. I will buy a servo and a unipolar as well (I am getting addicted to playing...don´t tell the missus).

Didn´t realise how cheap the steppers were on ebay....

Probably should start a more specific thread as the title on this one is totally incorrect now...

Neil C

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Neil,

As regards brackets I can probably sort them out, just let me know what you need.

If I remember correctly then L293 chips can run a little hot as they are pushing a reasonable amount of current. Obviously matching the stepper better would help. By the way I've got bids on a couple of ebay stepper motors Stepper motor 24v 9 Ohm on eBay (end time 10-Sep-09 19:16:53 BST) and Teco Stepper motor 24V 0.35A on eBay (end time 10-Sep-09 19:16:53 BST). Both are 24volt but should work at lower voltages. Don't bid against me, I've only bought then to geek with, so if they will help and I win them I can always send them to you

I would certainly be keen to see your spec and perhaps the code, currently I feel your doing all the work and perhaps I should be helping more

Cheers

Rob

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Rob,

the Arduino stepper stuff is easy it is standard that is why I am playing with that, it seems like you are doing loads when really you haven´t done much. The ASCOM stuff is more of a pain because I don´t know it so I am having to read all the notes on the site and figure out what to install.

Trust me Rob I will do the spec and play abit more this weekend and will then run out of steam with probably no idea how to do the ASCOM stuff! The main thing will be to get the list of what we what sorted out and then everyone can add information to it as they solve/find it.

Don´t worry I won´t bid against you I think I have seen the ones you are on about. I am in spain and can´t seem to find the same quantity of steppers available to buy.

Neil

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Perfect Rob, He has examples attached (in VB which is good for me) and an email address to ask permission for use so no problems there.

I have started a Yahoo group called SGL Observatory Automation can someone tell me if this is ok? If not I will delete it again. I think it would be a good common place to put all the code and for everyone to upload their ideas.

Let me know what you all think.

Neil C

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Neil

A yahoo group seems like a good idea (unless the SGL team can provide a common place here) and yes better get it checked out.

My offer still stands re brackets and motors. There seem to be a fair few motors on 'fleabay' here in England. If you struggle to source them in Spain let me know and I can bid here and can always send stuff to you.

Biopic sent me the stuff he worked on, using the robofocus ASCOM drivers I'll pm him and see if he can talk me/us through how to talk to ASCOM. Its written in assembly which really is gobblygook to me. If you're interested with what he sent me I can forward it to you although I'd better check with him that that's OK first

Rob

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Rob,

Ask him nicely for any advise. The VB one you posted a link to is creating a class module where, it looks like, the ASCOM commands are configured. The interfacing to the hardware is then done within VB. So there is an interface layer to ASCOM and then we could configure whatever we want underneath.

I suspect ASCOM links to the name of our driver (one is assigned in VB) and the interface becomes something like "drivername.command".

Still trying to find the example files which are meant to exist on the ASCOM install.

I would be interested in a bracket but I have to check. It is to mount to an ED80 but I haven´t had a chance to measure anything.

Neil C

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I have sent a PM asking a couple of the moderators if there is anyone I can ask permission for the Yahoo group.

my head hurts with all this thinking so I am going to go and sit in a dark room for a bit.

Neil C

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Neil, did you select the install source files option when you installed ascom? I've just had a look myself (I did choose the install source files option) and I can't find them either.....

Meh, found where they are, I think.....

go to:

C:\Program Files (x86)\Common Files\ASCOM\.net

and click on:

ASCOMDriverTemplates.vsi

it will install (or reinstall) the templates for you, mine ended up in:

C:\Users\Reggie\Documents\Visual Studio 2008\Templates\ProjectTemplates

with both VC# and VB versions in the respective sub-folders.

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  • 3 weeks later...

Hi George, That's one of the many models that we will use, It depends on whether you are just going to build a single 'module' unit, for instance just a focuser or will you be building a focuser/dew controller unit?

For single module units the model you have chosen will be fine, if you are going to build a multi module unit then I'd prefer if people went for 'Any Arduino with a 328 chip and above' like this:

Freeduino V1.16, with ATMEGA328 - £16.99 : nuelectronics.com, Arduino Freeduino projects

It's only a couple of quid more than the one you are looking at on ebay and the guy also does the LCD Keypad shield which is damned useful for visual feedback at the scope, although I'm a bit gutted they don't do a red LCD version. It'll cost you £3-4 to get both of those shipped, prompt service too.

It's usually the newer duemilanove's that have the 328 chip in them. the reason I would like people to use them is they have double the program space, double ram and double eeprom storage.

There is also an upgrade option, anything that has a 168 chip in it should be able to easily upgrade to a 328, the blank chips are £2.50 each or £5.00 with a bootloader pre-burned onto them.

For even bigger module units I will be using a mega as it has even more program space, ram, eeprom and oodles more IO pins. We've got the 3 possible modules at the moment but I am toying with the idea of getting a camera unit hooked up to an arduino, apart from the obvious of DSO/guiding and being able to autofocus itself(when/if I write the software) I'm wondering what other practical uses it could have? completely standalone autofocus or parfocal autofocus maybe? maybe a cheap option for cloud detection rather than hi-res IR thermopiles.

Regards,

Reggie.

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Thanks Reggie, it would make sense to get the one you have provided a link for as i could convert my manual dew setup to an automated one :o

There's some interesting stuff on this site, stepper motors etc

Stepper Motor High Torque [RKI-1394] - $11.72 : Robokits World, Easy to Use, Versatile Robotics Kits...

Quite reasonably priced too (make sure you set your local currency)

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At the right place you can buy an Arduino mega for £25.00, the focuser should be around £10 for the motor + a driver chip/circuit, as for the dew heater, £12 for the sensors + heater for one tape, £4 per extra tape. Not entirely sure how much the cloud detector will be, and the intervalometer circuit should be about £3 :o

You have to be quite mindful about which arduino to go for depending on how many pins are needed, the LCD takes 6, stepper motor is 4(I think?) the dew heater will be 2 for the ambient, 1 for each device sensor and 1 for each heater + 2 for each extra heater tape. so that's 14 digital pins for a single scope heater + focuser, 16 pins for 2 scopes.

The normal sized arduinos (168/328) have 14 digital pins and 6 analog pins, however we can switch some of the analog pins to digitals, so the arduino 168/328s are compatible with 2 modules. if you are thinking of doing anything else with it then go for a mega.

There are other options, its quite possible that we will be able to make the individual modules fit on an arduino nano so there are cheaper options still, for instance, currently I don't think the intervalometer will play nice with the other modules so would be suited to a nano as its a minimal circuit. I will try and sort it out so that it does gel well with the other modules whatever happens :)

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