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Breaded Electronics / Embedded » Mechatronics » 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:
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).
Program:
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:
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 |