small motor speed control

Discussion in 'General Electronics Chat' started by dougalere, Aug 14, 2015.

  1. dougalere

    Thread Starter Member

    Mar 4, 2015
    i recently built a RC boat which has a small dc motor, i built a speed control based on a 555,
    mark/ space ?

    the problem is that at low speed settings, all i get is a lot of whistles and squeeling and not much else.apparantly this is a problem with this arrangement.
    is there another approach ?
    the motor is a small dc motor taking around half an amp, due to space restrictions i have to use a 9v pp3, instead of a perhaps a better matched 6 volt AA supply.(not ideal but i get nearly half an hour)
    thank you
    Last edited: Aug 14, 2015
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Do you have a schematic?

    You don't "have to" use a PP3 battery for running a motor, and AA are not the only alternative; there are plenty of superior and inexpensive battery options available today that would outperform either of these.
  3. MaxHeadRoom


    Jul 18, 2013
    Unfortunately this is a down side of motor control without feedback of some kind, essentially you are running open loop velocity control and this does not provide the torque at low mean current levels, I assume you mean PWM for mark/space?
    IOW the mean current drops at low rpm but the torque requirement can remain the same.
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    A lower frequency will help, and you can set it very low if it's driving a boat.