Page 148 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

Chapter 5: Quadcopter Propulsors 127

source GCC compiler that the SimpleIDE uses to compile and load the source code. I have
used GCC for many years but never with as much ease as I experienced with the SimpleIDE.
Well done Parallax!

Summary

First, congratulations as you have slogged through this somewhat complex but (I hope)
interesting chapter. I believe you will have gained a substantial appreciation of the Elev-8
propulsor components that should help you understand and evaluate new choices when
(not if) it comes time to modify your quadcopter.
The chapter began with a detailed examination of the highly energetic and somewhat
unusual motors that power quadcopters. These motors are known as outrunners because the
rotors are on the outside of the motor, while the stator is stationary on the inside (a bit
unusual as compared to normal electrical motors). These motors are also multiphasic—they
are driven by dedicated controllers known as electronic speed controllers or ESCs. The motors
are very light and compact but can produce extreme amounts of power for their size, which
is why quadcopters can fly.
The ESC that powers the motor was discussed next with attention drawn to the ATmega8L
microcontroller that controls the ESC. I also explained how the raw battery power is switched
on by a series of power MOSFETs to provide the three-phase power for the motor. ESC
waveforms were shown to help illustrate how the three-phase power technique works.
A lengthy discussion followed regarding an experiment that I designed to show how an
Elev-8 motor functioned with one of the propellers mounted on it. I went through the setup
of the experiment and explained the control circuitry that was centered on the Parallax
Propeller Board of Education (BOE) as the controlling system. The program running in the
BOE was also thoroughly examined later in the chapter.
I discussed all the experiment’s results and used a series of charts to help explain what
caused certain outcomes and why. The results also provided some useful information
regarding power consumed versus available flight time and other operational tradeoffs that
should always be considered
Next came a brief discussion on ESC update rates and how some ESC designers are
concerned about slow updates.
I discussed the battery eliminator circuit (BEC), describing its design and purpose. I also
pointed out some potential issues with BECs that are applicable only in a quadcopter design.
A solution was also offered for those readers so inclined to follow it.
A section on the design and selection of propellers was next. Here I included a handy
table of standard propellers that are commonly used in quadcopter designs. A set of propeller
selection guidelines was also provided to help you choose knowledgeably.
The propulsor discussion ended with a brief introduction to a comprehensive and
interactive website that allows you to conduct a detailed analysis on your quadcopter
design. It is an incredible tool that should be used with care due to the great amount of
information and data presented.
The remaining section of the chapter concerned a detailed analysis and discussion of the
BOE control program that ran the experiment. I discussed the program in two major
divisions, the first being the Spin code and the second, the assembly language code. These
discussions were initiated to further increase your background in the Propeller languages
that began in Chapter 4.
I recognized that the assembly language discussion would be a bit daunting to readers
who are not too conversant in imperative programming. I still wanted to introduce the topic