Robot Coordinate Frames and Motion Direction
This page describes the conventions that CLARAty uses for coordinate frames for rover and manipulators, motion directions, and Mars Yard coordinate frames. CLARAty follows the surface vehicle (SAE J670E) standard for vehicle coordinate frame and rotation direction definitions.
World Coordinate Frame
World-fixed coordinate frame (X, Y, Z) is a right-hand orthogonal axis system fixed on the earth. The trajectory of the vehicle is described with respect to this earth-fixed axis system. The X and Y-axis are in a horizontal plane and the Z-axis is directed downward. The figure below shows the world coordinate frame relative to the Earth's North direction. It also shows the Rocky 7 and Rocky 8 vehicle frames relative to the world coordinate frame
Vehicle Coordinate Frame
This system is a right-hand orthogonal axis system fixed in a vehicle. The direction of the axes are as follows:
- +x axis forward
- +y axis to the right
- +z axis down
The origin for this coordinate system changes from one vehicle to another.
- x-y origin is in the center of the middle wheels (for 6-wheeled vehicles)
- x-y origin is in the centroid of all non-steerable wheels configuration
- z origin is on the center of rotation of the wheels when the vehicle is on flat ground.
The orientation of the vehicle axis system (x, y, z) with respect to the earth-fixed axis system (X, Y, Z) is given by a sequence of three angular rotations. The following sequence of rotations (see Note 6), starting from a condition in which the two sets of axis are initially aligned, is defined to be the standard:
- A yaw rotation, Y, about the aligned z and Z-axis.
- A pitch rotation, q, about the vehicle y-axis.
- A roll rotation, f, about the vehicle x-axis.
Absolute Heading Angle (Y) - The angle between the trace on the X-Y plane of the vehicle x-axis and the X-axis of the earth-fixed axis system. (See Figure 2.)
Sideslip Angle (Attitude Angle) (b) is the angle between the traces on the X-Y plane of the vehicle x-axis and the vehicle velocity vector at some specified point in the vehicle. Sideslip angle is shown in Figure 2 as a negative angle.
Course Angle (n) is the angle between the trace of the vehicle velocity vector on the X-Y plane and X-axis of the earth-fixed axis system. A positive course angle is shown in Figure 2. Course angle is the sum of heading angle and sideslip angle (v = 41 + 0).
Vehicle Roll Angle: The angle between the vehicle y-axis and the ground plane.
Vehicle Pitch Angle: The angle between the vehicle x-axis and the ground plane.
For drive wheels, a positive wheel rotation results in a clockwise rotation along the motor shaft (right-hand rule) or a counter- clockwise motion when facing the wheel (mirror image)
For steering, a positive steering angle results in a clockwise rotation when looking from the top