Page 43 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

22 Bu il d Y o ur O w n Q u a d c o p t e r

MP1 = T - offset
MP2 = T - offset
MP3 = T + offset
MP4 = T + offset

You should also realize that you could increase the throttle while maintaining a
pitch change, which would result in putting the quadcopter into a normal ascent
versus a straight vertical climb.
Yaw change in a hover state:

Placing the quadcopter in a yaw without changing altitude is similar to a pitch
change except that the lower speed changes are applied to motors controlling the
desired opposite yaw direction. This means that a desired CCW yaw would have
an offset subtracted from both CW motors and the same offset added to both
CCW motors in order to maintain altitude.

MP1 = T + offset
MP2 = T - offset
MP3 = T - offset
MP4 = T + offset

Roll change in a hover state:
Rolling the quadcopter is a matter of increasing the speed of both motors on the
side opposite to the desired roll direction and simultaneously decreasing the speed
of both motors on the other side. Below are the equations for a roll to the left.

MP1 = T + offset
MP2 = T - offset
MP3 = T + offset
MP4 = T - offset

The preceding set of equations is very straightforward and is representative of the
algorithms that the flight-control board implements. However, the quadcopter flight control
is not quite that simple. Automated control of a quadcopter aircraft means that there must
be at least one sensor involved that reports the condition and position of the craft back to the
flight-control board so that the repositioning can stop as desired. The main sensor used in
the HoverflyOPEN board is the Invensense model ITG-3200, MEMS 3-axis gyroscope. Figure
2.11 is a photo of the gyroscope mounted on the HoverflyOPEN board.
This sensor can rapidly detect minute variations in angular velocity changes in all three
of the principal axes discussed earlier. Figure 2.12 shows the three predetermined axes that
the sensor is designed to measure, which makes it critical to align these axes with the three
quadcopter axes. The +Y axis shown on the figure must be aligned with the quadcopter’s
forward direction.
The dot printed on the upper left hand corner of the sensor is the key to proper alignment
on the board. The board itself must also be properly aligned with the quadcopter’s forward