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Tuning Motor Needed

Discussion in 'General Technical Questions and Answers' started by W4KJG, Dec 5, 2018.

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  1. W4KJG

    W4KJG Subscriber QRZ Page

    I'm planning to build another remote controlled antenna tuner. This one will be based on the design starting on page 182 of the ARRL Antenna Compendium Volume 2, and written by W0RPV, Richard Placencia. I had completely forgotten about it (it was published in 1989) when I accidentally ran across it recently.

    For those who don't have a copy of the book, the tuner uses a homemade capacitor formed with a piece of glass from a cheap picture frame, and two 4-1/2 x 4-1/2 inch pieces of aluminum. One is expoxied to one side of the glass. The other slides on the other side of the glass.

    The capacitor uses a medium speed low torque dc motor to turn a 1/4-20 threaded rod through a fixed wing nut expoxied to the glass to move the movable plate. It doesn't use end sensors. Instead, it uses end stops and senses overload current through a resistor to light LEDs when it hits a stop.

    So, I need a motor that turns about 100-200 RPM. I want to keep this simplicity. I don't want to use a stepper. I'm looking at very inexpensive small cordless screwdrivers without a lot of torque.

    Does anybody have other ideas for a motor like this?

  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    W4KJG likes this.
  3. W4KJG

    W4KJG Subscriber QRZ Page


    Thank you. I had dismissed the gear reduction motors because I was afraid their torque may have been too high. After you posted that I did searches on eBay and Amazon.

    I found what I believe will be perfect on Amazon. It appears to be relatively low torque. It is variable from 30-200 RPM depending on voltage. So, for about $15 I get the motor, the mounting bracket, and a coupler. I should have it by the end of this week.


    Thanks again,
    KP4SX likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Nice, I've used a motor just like that for some repair bench test fixtures before. It's really small and good news that you were able to find a shaft adapter for your purposes as the shaft out of that motor assembly is very small.

    Let us know how the project works out, it sounds interesting.
  5. WR2E

    WR2E Ham Member QRZ Page

    Turning a variable cap at 30 RPM? Seems way fast? Or are you planning on gearing it down even further?
  6. N3PM

    N3PM Ham Member QRZ Page

    20 pitch lead screw at 30 rpm - plates move at 1.5 ipm, no?
    Mike N3PM
  7. WR2E

    WR2E Ham Member QRZ Page

    What I get for not reading well! o_O
  8. N8TGQ

    N8TGQ Ham Member QRZ Page

    Reminds me of a capacitor we made for xtal radios for scouts in the early 60's. Made from the celophane and foil from 2 cigarette packs.
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    Electric screwdrivers with dead batteries are available cheap at my local Habitat for Humanity or any other thift shop.

    The screwdriver can be driven (speed controlled and reversing) using an Arduindo pro mini,

    driving one of these H-Bridge modules (with both drivers paralleled):


    I am doing this to make a screwdriver antenna more easy to tune. I am using a momentary, center-off, spring-return, bat-handle switch as a joystick. For the first 5 seconds, the motor is pulsed to start, then PWMed to run slow, after which it runs at full speed to slew to a new band. This makes it much easier to find the SWR null and go from band to band.
  10. AA7QQ

    AA7QQ Ham Member QRZ Page

    I would suggest a stepper motor, with Loftur Johansen's " Automatic loop controller ". Read up on it & you will understand why.


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