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Chapter 5: Quadcopter Propulsors 109

the BOE’s pin 14 connected to the BEC’s signal lead (usually white or orange) and the ground
leads connected. I attached an oscilloscope lead to the signal lead in order to measure the
waveforms being created by the BOE. I report some key timing measurements in the results
section below.
Note that the BEC’s power lead (usually red) is left unconnected. I did not plug the BEC
connector directly into the BOE’s P14 servo pins because doing so would have tied the
BEC's power into the BOE’s power, which is not a desirable configuration.
A USB serial cable connects a laptop running the Parallax Serial Terminal (PSerT)
program to the BOE. Entering data using the PSerT program is the way you control motor
speed. You just need to enter a single number from 0 to 8, which represent power levels from
0% to 100% respectively. The eight steps mean that increasing each number by one is
equivalent to increasing the power level by 12.5%. It turned out that the maximum level I
could reach was 5, or 62.5% of maximum power. Anything above 5 simply created way too
much vibration and energy in the experimental setup to the point where I felt unsafe in
continuing the operations. However, I did test the motor up to level 8 without a propeller
attached. This was simply to check that the program functioned as expected and to measure
some waveform timing parameters.

Caution: I highly recommend that you place some sturdy barriers around the area where the
propeller is spinning to prevent anyone from inadvertently touching or coming in contact with
the spinning propeller. Remember that the propeller is completely invisible when it is spinning.
Touching a spinning propeller will cause serious injury—no question about it! You might want
to use some large pieces of foam board attached to chairs to fashion a reasonable barrier system. I
am very cautious around propellers, whether they are the small ones discussed here or the large
ones, such as the type I use when flying a light plane. Coming in contact with one of those when
it is spinning would be the last thing you do on this earth.

Figure 5.21 is a screenshot of the PSerT communications screen connected to the BOE
that is running the demo program. You must press the space bar in order to start entering

Figure 5.21 Screenshot of the PSerT connected to the BOE running the demo program.