Physics#

rc.physics

BWSI Autonomous RACECAR Course Racecar Neo LTS

File Name: physics.py File Description: Defines the interface of the Physics module of the racecar_core library

class physics.Physics#

Returns the linear acceleration and angular velocity measured by the IMU.

abstractmethod get_angular_velocity() → NDArray#

Returns a 3D vector containing the car’s angular velocity.

Returns:: The average angular velocity of the car along the (x, y, z) axes during the last frame in rad/s.

Note

— In the Simulator — The x-axis (pitch) points out of the right of the car. The y-axis (yaw) points directly up (perpendicular to the ground). The z-axis (roll) points out of the front of the car. Rotation sign uses the right hand rule. For example, when the car turns to the left, it has a positive angular velocity along the y axis.

— In the Physical RACECAR — The x-axis (roll) points out of the front of the car. The y-axis (pitch) points out of the right of the car. The z-axis (yaw) points directly up (perpendicular to the ground).

Example:

# ang_vel stores the average angular velocity over the previous frame
ang_vel = rc.physics.get_angular_velocity()

# yaw stores the yaw of the car, which is positive when it turns to the left
# and negative when it turns to the right.
yaw = ang_vel[1]

abstractmethod get_battery_current() → float#

Returns the battery current measured by the NEO-PIT power sensor.

Returns:: The current draw in amps (INA226 sensor).

Note

— In the Simulator — This function returns 0.0 (there is no power sensor in simulation).

— In the Physical RACECAR — The value comes from the /battery/current topic.

Example:

# current stores the battery draw in amps
current = rc.physics.get_battery_current()

abstractmethod get_battery_voltage() → float#

Returns the battery bus voltage measured by the NEO-PIT power sensor.

Returns:: The bus voltage in volts (INA226 sensor).

Note

— In the Simulator — This function returns 0.0 (there is no power sensor in simulation).

— In the Physical RACECAR — The value comes from the /battery/voltage topic.

Example:

# voltage stores the battery voltage in volts
voltage = rc.physics.get_battery_voltage()

abstractmethod get_encoder_speed() → float#

Returns the car’s forward speed measured by the drive encoder.

Returns:: The average forward speed of the car over the last frame in m/s, derived from the NEO-PIT hall encoder (the Teensy applies the gear ratios and wheel circumference). Positive is forward.

Note

— In the Simulator — This function returns 0.0 (there is no drive encoder in simulation).

— In the Physical RACECAR — The value comes from the /encoder/speed topic.

Example:

# speed stores the car's forward speed in m/s
speed = rc.physics.get_encoder_speed()

abstractmethod get_linear_acceleration() → NDArray#

Returns a 3D vector containing the car’s linear acceleration.

Returns:: The average linear acceleration of the car along the (x, y, z) axes during the last frame in m/s^2.

Note

— In the Simulator — The x-axis points out of the right of the car. The y-axis points directly up (perpendicular to the ground). The z-axis points out of the front of the car.

— In the Physical RACECAR — The x-axis points out of the front of the car. The y-axis points out of the right of the car. The z-axis points directly up (perpendicular to the ground).

Example:

# accel stores the average acceleration over the previous frame
accel = rc.physics.get_linear_acceleration()

# forward accel stores acceleration in the forward direction.  This will be
# positive when the car accelerates, and negative when it decelerates.
forward_accel = accel[2]

abstractmethod get_magnetic_field() → NDArray#

Returns a 3D vector containing the car’s magnetic field measurements.

Returns:: The average magnetic field measurements from the magnetometer along the (x, y, z) axis during the last frame in Teslas.

Note

— In the Simulator — This function does not exist.

— In the Physcial RACECAR — The x-axis points towards the back of the car. The y-axis points towards the right of the car. The z-axis points directly up (perpendicular to the ground).

abstractmethod get_rc_channels() → NDArray#

Returns the eight FlySky RC transmitter channels.

Returns:

An array of eight values, each in the range [-1, 1] (0 at the channel’s center or with no transmitter signal). Channel map on the FlySky iA6B (verified on hardware):

[0] right stick X (steering) [4] switch A [1] right stick Y [5] switch B [2] left stick Y (throttle) [6] switch C [3] left stick X [7] switch D

The firmware drives steering from channel 0 and throttle from channel 2.

Note

— In the Simulator — This function returns eight zeros (there is no RC receiver in simulation).

— In the Physical RACECAR — The values come from the /rc/channels topic, normalized by the firmware pulse widths.

Example:

# channels stores the eight RC channels in [-1, 1]
channels = rc.physics.get_rc_channels()
steering = channels[0]