Section 2.5 Glossary

Kinematics

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Study of motion without explicitly modeling the forces that cause it.

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Differential Drive

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A drivetrain with independently driven left and right wheels used to control translation and turning.

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Track Width (\(L\))

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Distance between wheel centers in a differential drive robot.

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Linear Velocity

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Forward translational speed of the robot.

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Angular Velocity

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Rotational turning rate of the robot.

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Forward Kinematics

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Computing robot motion from known wheel or joint velocities.

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Inverse Kinematics

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Computing wheel or joint commands needed to achieve a desired robot motion.

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Pose (\(\mathbf{q}\))

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Robot position and orientation, represented as the Pose vector \(\mathbf{q} = [x, y, \theta]^T\text{.}\)

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Global Frame (\(W\))

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A fixed reference frame attached to the room or arena floor, used to express a robot’s absolute pose.

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Robot Body Frame (\(R\))

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A moving reference frame fixed to the robot’s chassis, with its positive \(x\)-axis pointing forward and its positive \(y\)-axis pointing to the robot’s left.

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Wheel Velocity (\(v_L\text{,}\) \(v_R\))

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Left and right wheel surface speeds used in differential-drive motion equations.

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Wheel Radius (\(r\))

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The radius of a drive wheel, used to convert between wheel surface velocity and rotational motor speed.

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Instantaneous Center of Rotation (ICR)

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The fixed point in the plane that a turning differential drive robot rotates around at a given instant.

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Turn Radius / Radius of Curvature (\(R\))

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The distance from the robot’s center to the ICR, computed as \(R = v/\omega\text{.}\)

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Spin-in-Place / Point Turn

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Turning around the robot’s own center point by driving the wheels at equal and opposite speeds (\(v_L = -v_R\)), giving \(R = 0\text{.}\)

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Pivot Turn

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Turning around one stationary wheel by driving only the other wheel (\(v_L = 0\) or \(v_R = 0\)), giving \(R = L/2\text{.}\)

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