How exactly segway works

The Segway personal transporter is a device that transports one person at relatively low speeds. The low-speed (limited to approximately 20 kmph) operation combined with its electric propulsion system makes the Segway a candidate for providing short-distance transportation on city streets, sidewalks, and inside buildings. When a Segway is in use, the device is driven by two wheels that are placed side-by-side, rather than the standard in-line configuration of a bicycle or a motorcycle. When the operator leans forward, the wheels turn in unison in the same direction to provide forward motion. In order to stop, the wheels must accelerate forward to get out in front of the system's centre of mass and then apply a deceleration torque to slow the system down without causing the operator to fall forward off the device. These operating principles are reversed to allow the system to move backward.

            In order to turn, the wheels rotate at unequal speeds causing the system to travel in an arc. If the system is not translating forward or backward, then the wheels can rotate in opposite directions to turn the machine in place.However,it is not possible for the human operator to balance the device, as they can with a human-powered inverted pendulum such as a unicycle. The sensors in the device must constantly be measuring the state of the machine and feeding this information to the computer controller. The controller then uses this feedback signal to adjust the wheel speed so that the forward/backward (pitch) falling motion is maintained within an acceptable envelope so that device and rider do not fall over. Note that under many operating conditions, the system is mechanically stable in the side-to-side (roll) direction. Therefore, the computer does not attempt to control the roll motion. Assuming wheel-ground rolling stiction, the system is also stable in the yaw direction.However, the computer must change the yaw rate in order to turn the machine in 10 response to the operator input. It also limits the turning rate to a maximum value.

Fig1 Segway

  A Segway is often used to transport a user across mid range distances in urban environments. It has more degrees of freedom than car/bike and is faster than pedestrian. However a navigation system designed for it has not been researched. The existing navigation systems are adapted for car drivers or pedestrians. Using such systems on the Segway can increase the driver's cognitive workload and generate safety risks.

Physics Behind Segway

The physics behind segway:

The Segway is a uniquely sophisticated machine that uses on-board computers working with multiple sensors and redundant physical systems to sense the motions of the rider, and to react to those motions. The “Stand up Scooter” requires the rider to learn how the machine will respond to the throttle and brake, while physically holding on to the machine to counter the unbalanced forces of acceleration and deceleration.

Fig1 Forces acting on segway rider

Diagram A, on the left shows person standing, with gravity and the Segway reaction force in balance. In diagram B Person has leaned forward to start moving. The purple arrow is gravity/weight.The magenta arrow is the reaction force of person against the Segway. The dashed blue line is the vector sum of the two. If the Segway doesn’t respond person will fall forward as the Segway is pushed backward. Diagram C shows the response of the Segway as it senses the tilt of the Segway platform as person leans forward. The computers order the motors to power the wheels and accelerate the Segway. The force of acceleration is the red arrow, and the reaction force of the Segway to person is the orange arrow. The dashed yellow line is the vector sum of the two. Diagram D shows that the sum of the forces in diagrams B and C are in balance. The vector sums run through each other and the rider, so there are no unbalanced forces or torque. The on-board computers adjust the power to the wheels to keep the forces balanced through the rider. This is what makes the Segway unique.

Fig 2: Segway Balances the Forces on the Rider in All Phases of Riding

Fig 2 shows how the Segway keeps the rider in balance during all phases of a ride: stationary, accelerating, cruising at 6 mph, and decelerating. This continuous balancing of forces is what makes riding the Segway possible. There are no unbalanced forces to topple the rider off the Segway, which is why many people with diseases or injuries which result in muscular weakness, such as Muscular Dystrophy or Multiple Sclerosis, can safely ride a Segway. They do not have to compensate for unbalanced forces with their own strength - the Segway does it for them.

On a Segway you initiate moving forward by leaning forward. The Segway senses your leaning and accelerates forward, balancing the forces, and you are underway. This is the process shown in Fig 2 above. The beauty of this is that the Segway is controlled by same set of reflexes and reactions that control basic human locomotion. Even if you can’t walk due to physical limitations, you retain these reflexes and reactions.