Discussion in 'General Electronics Chat' started by Berne, Mar 27, 2009.

  1. Berne

    Thread Starter New Member

    Mar 27, 2009
    Hi All,
    Im real new to this site and electronics. Good to have the forum for advice.
    Firstly what board should I post my request for advice on rigging a stepper motor with a long run from controller to unit of c.25 feet?
    I will need quite a bit of detail and patience on this one: type and spec of motor ect to purchase, costs, wiring explanation, general cautionary tips ect. All additional equipment necessary for this stage of my project.


  2. SgtWookie


    Jul 17, 2007
    Hi Berne,
    Welcome to the AAC forums. :)

    This is as good a place as any to start off with, as at this point you're just trying to get some general information about stepper motors, from what it sounds like.

    But in order to help steer you in the right direction, it would help us help you to have a good idea on what your project concept is.

    All we know right now is that you have an idea that your controller needs to be a long ways away from your stepper motor for some reason.

    How much torque do you need to apply/hold? How fast will you need the motor to step, or what is the highest RPM you need for it to turn? Do you have size/cost constraints?

    Or if that is a bit overwhelming, can you just describe what it is that you're trying to do?
  3. hgmjr

    Retired Moderator

    Jan 28, 2005
    In case you have not discovered the free online ebook on electronics, I encourage you to take a peek at its contents at If you already have a grasp of the basics it is a good reference to refresh your knowledge. If you are new to electronics, then it will serve as a good source of the basic electronic concepts.

  4. Berne

    Thread Starter New Member

    Mar 27, 2009
    Hi Again,
    The concept is this, Im building a magnetic loop antenna to transmit SSB phone / CW for the HF radio bands 10-20mtrs, the magloop is made out of copper tubing 28mm and is formed into a circle shape which retains best performance as oppossed to the popular square version. The magloop - desktop run is well over 25feet. The tuning is to be remotely controlled using a stepper controller from my desk, this controller issue is not something I know much about and some guidance on price, setup and operation is requested.
    This reply was sent to me from a ham friend re the motor, I hope it will assist correct choice and particulars of what type ect Stepper Motor and controller I should choose, keeping price in mind:

    1. Any small stepper motor will work to drive a vacuum capacitor. I highly recommend using a stepper motor and a small controller to operate the capacitor. You can control the speed and the direction. It will not “coast” when you turn off the power. A very small value “10 mmfd” will make a large change in the freq of the antenna. The controller has a pulse circuit that can go way down so that you take as little as one step per 5 seconds. In this way you can come right up on the right capacitance. The question is now how fast, but how slow. Small motors have very little torque at very low speeds, that is why at stepper motor is really needed ( End )

    2. Unsure if assistance is possible on this point but anyhow...let me discuss the Vaccume Variable Capacitor which Im using to tune up and down the releavant bands, some say that for my magloop which is a copper circle, with an inside diameter of 3.2 feet, the VVC should be 5kv, this is established...what is not certain though ( even among gurus ) is the picofarad range, some say 5-100pf others say be safe if the larger is not going to effect the performance of the loop then that would be the best option with a max of 200watts output power, but if performance is optimal using only 100pf then perhaps that should be considered? Im open to all good advice on this.

    Bye for now,

    Berne MI0GFU + SWL Ei1544
    Last edited: Apr 2, 2009
  5. loosewire

    AAC Fanatic!

    Apr 25, 2008
    Welcome, Berne ,You could be a typeing coach.
  6. SgtWookie


    Jul 17, 2007
    Well, first you'll need to decide upon your variable capacitor, and then determine how much force it takes to move it. The force required to move it will have a bearing on what kind of force will be needed from a stepper motor.

    You can get small "pancake" type stepper motors for just a couple of dollars, and they can be run from low voltage at low current. You can get increased torque from them by gear or belt drive reduction.

    Jameco has these PF35T-48L4 unipolar steppers for $2.95 each:

    You would want to use a reduction drive, because they are 3.6° per step; that would be a rather coarse adjustment for a trimmer cap with a 90° travel.

    They're rated for 7v, although you can drive them with 5v at lower torque.
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    If there is only 90 degrees of travel, wouldn't an R/C type servo work? Controller could be as simple as a 555 timer, though a bit mroe complicated if automatic very slow adjustment is needed.
  8. SgtWookie


    Jul 17, 2007
    As far as the capacitance required to tune your antenna; you will need to determine that yourself by experimentation. If you're really using it for transmitting from 10 meters to 20 meters, that's one heck of a range of frequencies. I'm not familiar with your antenna design.