Center of Mass

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The center of mass (COM) or center of gravity (COG) of a robot is the mean location of all the mass of a robot.

When a robot brakes, the friction between the wheels and the floor rapidly decelerates the robot ( velocity is in the opposite direction of acceleration in this case). This creates a torque around the center of mass of the robot, jerking the back of the robot up. In many cases, the rear wheels lose grip with floor as well.

Example from 6105C Blackout Robotics Tipping Point

To mitigate jerking in opcontrol, reduce the height of the center of mass off the ground or decrease the max acceleration available to the driver. In programming periods, motion profiling and other motor control techniques can be used as well.

The magnitude of the torque is proportional to the height and magnitude of the braking/slowing force.