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Electronics PC controlled motors?

Discussion in 'Modding' started by OneSeventeen, 28 Mar 2005.

  1. OneSeventeen

    OneSeventeen Oooh Shiny!

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    I want to be able to hook up a few motors to my telescope and use my computer to controll the positioning instead of turning the knobs by hand.

    It will be crazy easy to make the adapter to mount the motors, but what I'm not sure of is how to hook up a motor to my PC. Would I want to use the serial port, parallel port, or just jump in and go PCI?

    I want it to be able to make either very small movements, or just very smooth ones (and gear it to be small movements), but either way, I'd like it accurate. So if I told it to move up a bit 20 times, then go down a bit 20 times, I'd like it to be in the same place.

    Any ideas? Or suggestions on what type of motors I should use, and a general concept?

    Like, should I be using independently powered motors and have the computer just tell it when to move, and how much to move, or do I make the PC send it power for certain amounts of time?

    I'd also like this to be as cheap as possible, I plan on using a simple web-cam in the eyepeace, so we don't need anything uber fancy. (that will come once I get this working and buy a professional-grade telescope.)
     
  2. TheAnimus

    TheAnimus Banned

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    well how far away is the motor from the computer, that will be the deciding manner as there is no need for a PCI/ISA card for this project.

    if its just a few (<5) meters away, the parports easyest, if your going longer than that a serial interface would be better (using a PIC probably).

    for controlling the motors, google h-bridge, heck you might be able to find something about hooking em straight upto the parport.

    and Hbridge is needed to allow you to control the DC motor, both forwards and backwards.
     
  3. Pballer98c

    Pballer98c Minimodder

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    hmm well hope this doesnt sound like an advertisement but my dad runs a website for computer controlled motors.
    http://www.hobbycnc.com
    stuff is fairly inexpensive and if nothing else, browse the links section :)
     
  4. cpemma

    cpemma Ecky thump

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    Geared-down stepper motors, or any motors with a rotary encoder on the shaft AFAIKS. Then with a bit of programming you can dial in the directions and orft u go.

    full guided tour.
     
  5. ConKbot of Doom

    ConKbot of Doom Minimodder

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    I would think that steppers would be the way to go here. Because with DC-brush motors, you would have to gear them down a bit, and that would introduce a bit of backlash into the setup.

    And people familair with CNC stuff are probably better off to help you, doing computer controlled stepper motors allready, just a different application, and different software.
     
  6. pears0

    pears0 What's a Dremel?

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    if you use a seperate power supply for the motors and a controller cicuit (which would use a PIC) you could make this a wireless sytem. The pic can interface between the motors and the wirless reciver easily (or a USB port if you dont want to go wireless). Not sure how to do this myself as I haven't looked this indepth with PIC's, but I know it can be done. a web site called the PIC list would b a good starting point if your intresed in going down this route. I personally think this would b a better option as you could potentially make a system that works either wirelessly or via USB, and I would also find a greater sence of achive ment than just a simple program t control them throu the serial port. But thats just me and this is just an idea. Also note that this would be more time consuming and more expensive.
     
  7. TheAnimus

    TheAnimus Banned

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    Hmm DC motor vrs stepper.

    I'd say go for a standard DC motor because of the cost, but its worth looking at both.

    making a servo style system with a PIC isn't hard at all.
     
  8. h_2_o

    h_2_o What's a Dremel?

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    go with steppers, you can get small ones pretty cheap plus microstepping a telescope with steppers is becomming more and more common.


    gl
     
  9. nick01

    nick01 What's a Dremel?

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    With a stepper you don't need an encoder. Instead run the motor into a limit switch and count from there. If you think you lost position run it into the switch again. I'm no expert on telescopes. Could you mount two glow-in-the dark dots in your yard and use those as fixed targets for calibration? It would take some image processing for the computer to find them.

    You should use a serial connection. The telescope won't move fast, so - unlike CNC - speed is not an issue (trade off serial vs. DC).

    Here is another stepper board http://www.eggertelectronics.com/ssc1binfo.htm . I used an earlier version and it worked fine. I liked it because you can add more boards on the same serial port. Download the manual to learn more.

    Look around for cheap stepper motors (200 steps/turn, 3 to 12V, <1.5A). Sometimes you find them in surplus as low as $10.
     
  10. OneSeventeen

    OneSeventeen Oooh Shiny!

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    Hmmm....
    I think I'm going to have to look around for a while... ~$50/motor looks more than I was hoping for. I was hoping to go closer to $10 or $15 (yes, I'm that cheap :p )

    This is all good info though. If it winds up costing too much, I may just have to use a new telescope with all the features built-in. (motorized telescopes start around $300, and the $700 range includes GPS built-in, so you just plug it in and it points to the north star)

    But I think I should still be able to do this fairly cheaply using my computer and the links you've provided, so hopefully in the next few months (I'm a procrastinator) I'll have more questions as I'm working on it!
     
  11. Etacovda

    Etacovda What's a Dremel?

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    Or butcher some old photocopiers/printers motors, they're stepper iirc.
     
  12. Pballer98c

    Pballer98c Minimodder

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    floppy drives have small steppers in them :)
    their toque is quite low though.
     
  13. zz300

    zz300 What's a Dremel?

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    Inexpensive stepper motors from MPJA
     
  14. Mr. Beta

    Mr. Beta Minimodder

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    I'm interested in the same thing. Well the motors at least. Still don't know how to build a stepper control interface.
    I'm gonna have to subscribe and see if I can learn anything.
     

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