RC Servo

RC Servo's have a geared motor with an internal position sensor.

By feeding a timed pulse ~1 - 2ms the servo knows where to position itself.  Frequency is not important.

ie. 1.45ms pulse = center position.

Frequency ~50Hz is fine.. 8 Hz will be fine asd well I reckon.. (32.768kHZ / 4096)



Jaycar YM2765 metal geared 6v.

Connections are Brown (Gnd), Red (+) and Orange (Signal)

Midpulse is 1500uS, limits are ~600uS & ~2300uS

Holds position when no pulse supplied per last pulse received.


Bought 4 micro servos from dealxtreme:

20023      Mystery 9G Mini Servo with Accessories (1.3kg Torque)       x 1 Shipped         $4.15        -
20087      9g Mini Servo with Gears and Parts (2.1kg Torque)     x 1 Shipped      $4.90      -
31962      Tower Pro MG90S Metal Gear Servos with Parts     x 1 Shipped      $7.12      -
33355      Esky EK2-0508 8g Digital Servo for Esky + 450/250 RC Helicopter     x 1 Shipped      $5.20      -


Additionaly we have some trademe.co.nz sourced parts:

Walkera 22E helicopter servos

3 for NZ$25.00 + postage..


1 for NZ$25.00 + postage ouch.


Test circuit is a PIC16F876 driving the signal pin on the servo.

Servo is powered via it's own 5v 7805 regulator but through a 250mA polyfuse as the larger Jaycar servo above was pulling the main supply down and browning out the PIC16F876 (Supply is 12v 1A).


  1. Steps from 1500 to 600uS and back to 1500uS in 10uS increments with a ~25uS delay between steps
  2. Pauses 1 second at 1500
  3. Steps from 1500 to 2300uS and back to 1500uS in 10uS increments with a ~25uS delay between steps
  4. Pauses 1 second at 1500
  5. Jump back to step 1

Note the delay between steps is approximate as i am outputting to the LCD between each step and I haven't timed that overhead.


Note that I tried driving all the servos below at < 600uS and > 2300uS however they are jerky and inconsistant so we will limit ourselves to the 600-2300uS pulse range.




Part Cost Blocked
Holds position
when no signal?
Consistant return to 1500uS from either direction Action feel
20023 US$4.15 ~500mA No Quite good Smooth
20087 US$4.90 ~400mA No Not so good undershoots A bit rough feeling, perhaps slightly erratic
31962 US$7.12 ~500mA No Not so good, actually overshoots slightly, and then when driven faster quite a bit
33355 US$5.20 ~400mA YES Really good Smooth
Walkera 22E NZ$8.33 ~300mA No Undershoots Smooth
Corona DS929G NZ$25 ~600mA Pretty good Slightly erratic, noisy