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Prop driving a stepper motor - Page 2 — Parallax Forums

Prop driving a stepper motor



  • NewzedNewzed Posts: 2,503
    edited 2007-10-24 18:20
    Graham, I have an excellentprogram for my superMill if you would like it.· It is not a CNC machine - the Prop gets its instructions from a DAT list that I generate in Excel.

    When the program boots up, you have the option of changing any of the 13 parameters, which includes:

    Set wait time betweem pulses for X, Y and Z.· (Wait time sets axis speed)
    Set backlash compensation for X, Y and Z
    Set ppm for X, Y and Z.· ppm is pulsetrain to travel 100 mils.
    Set hole depth for program drilling
    Set starting positions of X, Y and Z axes.

    There is a menu option to reset the postion of X and Y to 0 on-the-fly.· The program goes to the coordinate entered (or read from the DAT list).· The X, Y and Z positions are stored in the upper limit of the EEPROM so the mill always knows where it stopped when the last command was executed.· When a new command for a particular axis is issued, the Prop computes the travel from where it was, to where it wants to go.

    I used dial gauges to make the initial setups.· For fine tuning, I drilled holes for a 40-pin Prop DIP, then adjusted the X travel until the socket dropped into the holes.· Same for the Y axis except I used a 24-pin DIP socket.


    Yesterday is history, tomorrow is a mystery, and today is a gift.

    That is why they call it the present.

    Don't have VGA?
  • Graham StablerGraham Stabler Posts: 2,507
    edited 2007-10-24 22:59
    Thanks for the offer Sid but I'm happy running my little mill on TurboCNC for now, it suits the kind of stuff I make.

    The propeller stuff was for work in the first instance but I also have interests in unusual machines and the area of motion control itself, I also love the fact that with the propeller I could actually make a matchbox sized controller with SD card for program reading.

    Today I expanded the program beyond a simple demo and now I can move a given distance using arbitrary pins for step and direction, it allows single axis motion on as many pins as you have spare. Movement is still measured in steps and feedrates are in random values based on the counters but I am getting there.

  • Graham StablerGraham Stabler Posts: 2,507
    edited 2007-10-24 23:03

    Keep your eyes on ebay, search for the less obvious things like Daedal, parker, linear stage, thomson and things pop up. The best bargains are those things described really badly, I recently got some massive parker linear stages with brushless servos for a tiny amount, the terrible picture could only be decoded by the enthusiast and the description did not contain the words CNC.

    Another alternative is just to save, then get a taig or a Sherline. You can save by converting yourself.


  • Hello,


    Did you ever finish that code? I didn't see you on the obex. Did you post it on the forum?

    Thank You
  • ...I do have the propeller driving a stepper motor using a counter module in NCO mode, the frequency is updated at regular intervals by the algorithm to implement acceleration, constant speed and decelleration or if the move is short just acceleration and decelleration. All with perfectly lineat frequency increase/decrease. Distance travelled in steps is the frequency applied in each update time period multiplied by that period and the algorithm tweaks appropriately to ensure the wanted distance is acheived.

    ... is based on that of the g-rex motion controller by

    Interesting. Do you also use the PHSA to achieve sub-step resolution? I mean you keep the remainder if FRQA multiplied by the time period does not output a whole number of steps? That reduces staircasing and jitter a lot and runs the motors much smotther.

    BTW, I sell commercial stepper drives and motion controllers for a living. Of course all propeller powered. Here is an example of a machine equipped with my drives:

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