I'm kinda curious as to whether or not the motors as found in disk drives, vcr's etc are suitable for use in constructing a rudimentary drive system for a homemade dob mount. It's only for a 3 inch scope so not much by way of weight it needs to contend with
They are VERY suitable :-)
Just make sure you are taking them from older style 5 1/4" floppy drives.
The newer ones are very hard to use due to mechanical design, and the the torque is not sufficient.
Hi James
I agree with Bojan's comments and perhaps I can add the following comments as not so long ago I adapted an older type hard drive stepper motor to drive a simple mount through a gearbox.
Firstly, you have to obtain or make up a stepper motor driver which is basically a circuit driven by an oscillator to provide through other interface electronics the correct drive to the stepper motor to obtain the required motion and speed.
As well as Bojan's comments there is another thing to look out for. Stepper motors come with four wire (the most common) or five wire connections to the driver coils. You must make sure you get the right driver circuit for the stepper motor you have recovered.
I obtained my stepper motor driver kit from Oatley Electronics in Sydney
(Google them). Since mine was a 5 wire motor I got their kit number
K142D, but I see from their on-line catalogue that they also have a kit
K142B for four wire stepper motors. (See Complete Kit List page 3).
Cost of each of these units is about $27 plus postage which is good value. I also see that they have kits to allow control from a PC.
Having made the driver kit you then have to decide how to connect it to the four or five wires. This can be a bit of a puzzle but with a multimeter
to separate the two groups of windings and a bit of patience in systematically trying out connection combinations you can then find the one that drives the stepper motor correctly. You will also find straps/connections that allow you to stop/start and reverse the direction of travel. Also you may will find a strap that allows you to select the internal oscillator or connect to an external drive source. With the internal
oscillator the speed of the stepper motor will depend on using the inbuilt components or changing say the capacitor in the oscillator circuit to run the motor at different speeds. Note that if you try to run a stepper motor too fast it will stall due to a lag in current build up in the stepper motor coils at high clocking rates. Also small stepper motors have very low torque so you may need an external gearbox to adapt (eg in my case to the 10min cycle of the worm on my mount).
So, although the above kits are easy to make up a bit of electronics expertise and fiddling will be required to match the stepper motor to your desired application.
Whoa---this explanation turned out longer than I anticipated but it may be helpful to you and perhaps others who may wish to embark on this little adventure!
Cheers Peter
Thx for the advice. Had a quick look thru Jaycar as well and it seems they have that sort of kit available as well so may well look into that. At this point I'd be happy to just get it so I can control the speed inthe appropriate directions so as to be able to do some astrophotography, i.e. to track the object I aim at. Tho later I'd likely update and make it a full pc driven job
Thx for the advice. Had a quick look thru Jaycar as well and it seems they have that sort of kit available as well so may well look into that. At this point I'd be happy to just get it so I can control the speed inthe appropriate directions so as to be able to do some astrophotography, i.e. to track the object I aim at. Tho later I'd likely update and make it a full pc driven job
James
Just beware of Jaycar steppers, they behave in very strange manner, as the steps are not equal. I suspect what they sell is not stepper motor, it seems to be asynchronous 2-phase low-voltage motor.
It will step, though..
The best approach for you would be to download Mel Bartels software, and to build the stepper motor driver (it is very simple really, just 4 transistors per motor and one buffer IC. The transistors do not have to be that big as suggested, as he wanted this driver to work with wider range of motor sizes).
The link for Mel's webpage is below. http://www.bbastrodesigns.com/BBAstr...ted_Telescopes
The other approach is to build the small stand-alone stepper driver.. there are numerous designs availabe on the web (with PIC processors, many of them have even input for guiding). Also I can help here as I have number of PCB's (http://www.iceinspace.com.au/forum/s...ad.php?t=45079) and you can have one, no probs.. The processor (old Motorola 68HC705KICS, i have a few leftovers) has to be programmed specifically for your mount, though, while Mel's software is configurable (however, it runs on DOS..)
I built a stepper motor drive using the stepper motors out of old 20 MB MFM hard drives. I used the Silicon Chip driver board (I think it may still be available). It works from the parallel port of a computer (sadly not on modern computers).
I will attach a zip file with the program and a photo of the box with steppers. The stepper ratio is set in the ASTEPSIT.DAT file to suit the numder of steps required for 360 degrees azimuth and 90 degrees Altitude (other location info is also set in the same file).
The box with the board as described by Silicon Chip is attached to the motors (5 wire type) and to a computer parallel port. The program can then be run from ASTEPDRV.EXE the ASTEPDRW.EXE is automatically chained. It also has an inbuilt two star alignment routine, Messier, NGC and IC catalogues, comet and planet calculators and the Meade alignment stars.
Thx Barry. Mine don't have a parallel port. However I went searching for diy pc motor control and came upon the following site which seems quite useful
Thx Barry. Mine don't have a parallel port. However I went searching for diy pc motor control and came upon the following site which seems quite useful
James,
This is OK..
However, one day (sooner than you think at this moment) you will want full control over your scope (GoTo, etc).
Bartel's software (which is a full-blown control application for both dobson's and EQ's, with unlimited data base of objects and almost totally configurable for a variety of mechanical designs, supports encoders and interface to star chart programs) does not work via USB (neither does Barry's..).
So, as you are building your stepper interface, try to find a cheap old PC with LPT and two RS232 ports (100MHz is enough for Bartlel's application, probably the same applies to Barry's).
James,
This is OK..
However, one day (sooner than you think at this moment) you will want full control over your scope (GoTo, etc).
Bartel's software (which is a full-blown control application for both dobson's and EQ's, with unlimited data base of objects and almost totally configurable for a variety of mechanical designs, supports encoders and interface to star chart programs) does not work via USB (neither does Barry's..).
So, as you are building your stepper interface, try to find a cheap old PC with LPT and two RS232 ports (100MHz is enough for Bartlel's application, probably the same applies to Barry's).
Hi Bojan
I wanted that last week LOL. This is for my current scope which is not that crash hot and so aint gonna go to too much for it. Just to get some basic functionality to be able to get the scope to track the targeted object. As for the goto scope. I'm saving for that
The other approach is to build the small stand-alone stepper driver.. there are numerous designs availabe on the web (with PIC processors, many of them have even input for guiding).
i also suggest a stand alone version. It's allways a problem if you need a PC to get the motors running. Specially then when the needed connectors (LPT) are missing.
I publish a couple nice self constructions projects too
A low cost Version with the possibility of upgrading a display or my newest Project, my little Rolls Royce , that was not that cheap but offers more features then any other controller that I know.
If you need further informations, PCBs etc., on this projects just let me know.
I wanted that last week LOL. This is for my current scope which is not that crash hot and so aint gonna go to too much for it. Just to get some basic functionality to be able to get the scope to track the targeted object. As for the goto scope. I'm saving for that
James
Well, Bartel's software will definitely do it for you, and for free (except motor drivers).
You can easily ignore features that are outside your scope of interest :-)
ups, sorry. Just see you are searching for a Alt/Az controller.
CS
Rajiva
Hi Rajiva
Actually looking to do a lil diy job enough to get the scope to track what I'm aimed at at the time. And possibly later might make it computer controlled. Spotted a circuit to control stepper motors via usb and I have reasonable programming ability so can likely write a program to suit my purpose if/when I take that path
Well, Bartel's software will definitely do it for you, and for free (except motor drivers).
You can easily ignore features that are outside your scope of interest :-)
Thx. I did notice on the site I mentioned a usb control for stepper motors. I think I can adapt that to my current needs/wants
Spotted a circuit to control stepper motors via usb
do not worry to much about USB, any RS232 Device can turn into USB by useing the cheap and easy to get FTDI FT232RL Chip. Even ready made converters are quit cheap.
Just beware of Jaycar steppers, they behave in very strange manner, as the steps are not equal. I suspect what they sell is not stepper motor, it seems to be asynchronous 2-phase low-voltage motor.
It will step, though..
.....
Interesting, will investigate.
Jaycar sells a USB --> RS232 Serial converter and a USB --> Parallel converter. $39.95 each. Cat#'s XC4834 and XC4847 respectively.
Jaycar sells a USB --> RS232 Serial converter and a USB --> Parallel converter. $39.95 each. Cat#'s XC4834 and XC4847 respectively.
Jaycar got a few visits from me recently. I bought a plastic worm gear from them, just to keep the brain ticking about how to drive the scope.
I did look at the jaycar ones a few months ago (steppers). The step was 7.5 degrees. Thought it was a bit too much.
I actually got the idea to buy a USB to RS232 converter, as with the system I bought, it was going to be plugged into a late model laptop.
But I didn't, as I read a webpage about the parallel / serial port wouldn't do well with the conversion.
I haven't tested/tried it, so I can't confirm it, it was on my mind a bit, as I thought it couldn't be that hard, but someone did (by memory it was using a Bartel design stepper system) try it and it failed (or was told it didn't go so well)
I found a great little piece of software to drive the steppers, it's really basic and it works. One of the best and easiest to use, just to get it working.
Though it's limited to about 1 minute of operation until you pay $2.95 .
Got it from www.electronics-diy.com and it's called "Stepper Motor Controller".
It's not DOS, it's a windows GUI.
My project has stalled slightly.
Lack of funds as other priorities tend to take precedence.
House, Car Loans, Bathurst Race trip in Oct, O/S trip that the wife is organising..
Due to the slowdown, no o/t, no increase in wage (not even CPI), some things are on the down low. But I kept my job (err... for the moment).
But I have had a hard time finding a worm gear system to guide the scope, that's within a reasonable budget for functionality. Found a couple of ways, some with no backlash (yay!!!)..Hard searching though.
Whilst the funds are low, it has now led me to do the heathenous thing, of a direct drive as a trial, till the funds get back to a good point.
Direct drive concept is only on my mind, as "can it" work under a digital driver. As per quote "We do it, not because it's easy, but because it's hard". Not expecting 100% accurate results but worth a crack.
Not sure if it's relevant to your project but epoxy molded gears work well for tracking and slewing with steppers. I use them on mine successfully. There are 'how to' guide here:
, that was not that cheap but offers more features then any other controller that I know. 
