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Examples
Field-Oriented Drive (FRC)
successful
FIRST Robotics Challenge (FRC)
Y axis (forward-backward), X-axis (strafe), and Z axis (rotating about it's center axis). Each "degree of
freedom" is independent, meaning that the overall robot motion is comprised of a "mix" of motion in
each of the X, Y and Z axes, control of which is easily provided with a 3-degree of freedom joystick. This
resulting maneuverability is quite useful during FRC competitions to avoid other robots, pick up and
place game pieces, line up for shooting to a target, etc.
Yet the driver who remains in a fixed position is now presented a new challenge: when the driving
joystick is pushed forward, the robot does not necessarily move forward with respect to the field – rather
it moves forward with respect to the robot. This forces the driver to develop the skill of "placing their
head in the robot" and performing the angular transformation mentally. This skill can take quite awhile to
develop meaning that rookie drivers face an uphill climb before they can be productive team contributors.
Additionally, the mental energy involved in field-to-robot rotational transformations reduces the driver's
cognitive ability to focus other game-related tactical tasks, as evidenced by drivers who are so intently
focused on driving that their response to their teammates is diminished. Moreover, when the driver does
not have a clear line of sight to the robot, the "head in the robot" becomes even more challenging.
Solving this challenge is conceptually straightforward. First, the current angle (?) of rotation between the
head of the field, and the head of the robot must be measured; secondly, the joystick X/Y coordinates are
transformed by ?, as shown in following pseudo-code:
double rcw = pJoystick->GetTwist();
double forwrd = pJoystick->GetY() * -1; /* Invert stick Y axis */
double strafe = pJoystick->GetX();
float pi = 3.1415926;
/* Adjust Joystick X/Y inputs by navX MXP yaw angle */
double gyro_degrees = ahrs->GetYaw();
float gyro_radians = gyro_degrees * pi/180;
float temp = forwrd * cos(gyro_radians) +
strafe * sin(gyro_radians);
strafe = -forwrd * sin(gyro_radians) +
strafe * cos(gyro_radians);
An easy-to-use, highly-maneuverable drive system is at the heart of a
robot. Omnidirectional drive systems provide motion in the
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