Servo - June 2008

A set of PCB parts for two Loki legs/feet (no upper legs).

time. Driving servos into their mechanical stops can damage them. Proceed cautiously. Also be aware that if the battery discharges too far, erratic servo operation can occur. Turn off the power immediately!

Power up either Loki’s controller with ONLY servo #0 connected, or a servo driver (Servo Driver Pro). These servo drivers are reportedly (I don't have one yet) useful in aligning servos during construction of a robot — just what we need!

Turn on the servo power, being careful to hold up Loki by the body, and WATCH your fingers!

Servo Calibration

As mentioned earlier, with the servo horns only allowing rough squaring, we will record and save a calibration value for each centered servo position. This calibration will be dependent upon the controller board and software used. The intent is to be able to send a 1,500 μs (null) position request to all servos and have Loki move to the “left foot forward” posture. This is the “starting” position, and all of the canned move sequences should both start and stop here.

NOTE: Futaba 3004 servos rotate the opposite direction to Hitec HS-475HB servos! Be sure you account for this if you change between the servo brands.

Part 2

Part 2 of this article will discuss the QwikFlash board I used and the software developed to run Loki.

Loki’s Future

A better location for the IR and ultrasonic sensors could be investigated. Maybe rotating sensors! I’ve been contemplating adding some foot sensors, as well. These would be great for keeping Loki from walking off the table! A battery test function would be quite useful. A low dropout voltage regulator to supply the controller board would probably allow Loki to run on just a 6V battery pack. One would have to check to see what current the IR and sonar sensors would need, however. A custom control board for Loki is also envisioned. SV