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Needing help with stepper motor selection for a CNC machine — Parallax Forums

Needing help with stepper motor selection for a CNC machine

eagletalontimeagletalontim Posts: 1,399
edited 2008-10-13 02:14 in Robotics
I am in the process of designing my own CNC machine to use at work and at home and am just now learning about stepper motors. At work, we cut gaskets out of all sorts of materials and I am wanting to use a dremel tool to be the cutting device on the CNC. The dremel will be mounted on a wooden brace that will be moved back and forth on an X and Y axis using threaded bars or All Thread and moved up and down on a Z axis with the same principle. The All thread will not support the weight of the dremel on the X and Y axis. I am trying to find what stepper motors I can use that will be strong enough to move the dremel around the grid and be able to push it through thick rubber while it is cutting without missing a step. Hopefully the motors will not be too expensive because I am broke like the rest of the world tongue.gif I did find some on Ebay and am wondering if they might possibly be strong enough. The link is posted below. I would prefer to use a 12v DC source as the power supply since they are easy to come by and i have a few already laying around.

I am using the SX28 as the chip to run the motors instead of getting a driver for them because that will just cost more money. I have a small stepper motor I pulled out of a printer which has 6 wires coming from it. The upper half has a Red, Black and Brown wire and the lower half has Red, Orange, and Yellow wire. I have found that hooking both Red to positive 12vDC and alternating brown and black on the negative terminal will move it one direction, then alternating the Orange and Yellow wires on the negative terminal will rotate it the other direction. I was able to program the SX to step the motor when needed, but it just is not strong enough for my application [noparse]:([/noparse] I do want to keep with the 6 wire design because it is easier for me to run the motor and keep up with the steps. I have another stepper motor that has only 4 wires, but i have to alternate 2 of them between positive and negative to get it to turn. Too much will have to be involved to get that design to work tongue.gif

So, after saying all that, hopefully someone can help me out selecting the right motor. I have heard that you can wire them different to get more torque from the motors, but it all confuses me. Here is the link to the motors on Ebay. I have no idea what i am looking for as in torque specs and all the other specs that the motors say so I really need help picking some out!

cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170269775558

Thanks!

Comments

  • DJSandbergDJSandberg Posts: 56
    edited 2008-10-13 01:45
    There are a lot of factors that determine the power needed to move things, but on my CNC conversion of my mill, I started with 200 oz.·stepper motors and ended up switching to 300 oz. on the X axis.· On my machine, X is the only axis that isn't geared down so one revolution moved the base 1/16".· I found that I has less skipped steps with the 300 oz. vs the 200 oz.·

    I bought all of my stepper motors and controllers on Ebay.· The most I paid for a motor was $22 and the most I paid for a controller was $36.·

    Daryl
  • eagletalontimeagletalontim Posts: 1,399
    edited 2008-10-13 01:58
    do you think it is safe controlling the motors with just an SX chip and some simple circuitry? I am using a VB6 program and sending the data through a serial connection to the chip which tracks the steps and moves the motors. I found the specs on the Nema 23 step motors from the ebay link above here :
    www.homeshopcnc.com/page5.html

    I cannot afford too much so I am hoping to possibly find some decent stepper motors in some kind of electronic device but I am not sure what to look for. That is one reason I want to keep from using a controller if at all possible if I can build my own.

    Edit :
    I keep seeing 3vdc and 6vdc on alot of stepper motors. Is that the max voltage? The one I pulled out of the printer is a very small one and it has been running from 12vdc.
  • DJSandbergDJSandberg Posts: 56
    edited 2008-10-13 02:14
    I don't think there is a really cheap way to drive a stepper motor.

    Take a look at this site. There is a lot of information about what you want to do.

    http://groups.yahoo.com/group/CAD_CAM_EDM_DRO

    Daryl
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