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..

Corona DS929MG DIGITAL METAL GEAR MINI SERVO

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).

Program:

  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.

 


Impressions:

 

Impressions
Part Cost Blocked
current
draw
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