Page 166 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

Chapter 6: Radio-Controlled Systems and Telemetr y 145

Channel Name Position Pulse width (ms) Remarks
Aileron Full left 1.897 22-ms pulse rate
Full right 1.117
Centered 1.499
Rudder Full left 1.891 22-ms pulse rate
Full right 1.105
Centered 1.499
Gear 0 1.580 22-ms pulse rate
1 1.462
Aux 1 (labeled as 0 1.855 22-ms pulse rate
FLAP on DX-8) 1 1.462
2 1.113
Aux 2 0 1.899 22-ms pulse rate
1 1.505
2 1.112
Aux 3 Fully CCW 1.899 22-ms pulse rate
Center 1.500 DX-8 chirps as the knob is rotated
Fully CW 1.112 through the center position.

Table 6.3 Test Results for Remaining AR8000 Channels

experience as an acoustics engineer, it is not an unusual occurrence to have a second
harmonic as the loudest component in an audio spectrum. Of course, the audio noise would
become much louder, and the components would change when a propeller is attached to the
running motor.
I conducted another pulse-width test on the elevator R/C channel. The DX-8 elevator
control stick is on the right side and is spring loaded to stay in a center position. I measured
the pulse width to be 1.5 ms when the stick was centered. I then pushed the throttle all the
way up, and the width changed to 1.9 ms. Pushing it all the way down produced a 1.1-ms
pulse width. The pulses also repeated at a 22-ms rate, which is exactly the same as the throttle
control pulses.
The next portion of my experiment was to determine how the rest of the main AR8000
receiver channels functioned with regard to the pulses generated. I tested the remaining
channels with the USB oscilloscope and recorded the results as shown in Table 6.3.

Measuring R/C Channel Pulse Width and Rate with the BOE
I realize that most readers will not have the sophisticated USB oscilloscope that I used and
may not even have a regular oscilloscope. I highly recommend that you get one if you want
to modify your quadcopter or simply to conduct experiments. Many highly capable two-
channel units are on the market with a few at, or even below, $400. Readers lacking an
oscilloscope can use the following programs written and executed on the BOE to measure
both pulse widths and rates. Remarkably, these two programs report measurements that
match very closely to those achieved with the USB oscilloscope.
The BOE simply uses a normal servo cable to plug into the selected R/C receiver channel,
as shown in Figure 6.20.