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.