  Today, electric scooter is a trendy personal mobility vehicle. The rising
demand and opportunities attract ride-share services. A common problem of such
services is abandoned e-scooters. An autonomous e-scooter capable of moving to
the charging station is a solution. This paper focuses on maintaining balance
for these riderless e-scooters. The paper presents a nonlinear model for an
e-scooter moving with simultaneously varying speed and steering. A PD and a
feedback-linearized PD controller stabilize the model. The stability analysis
shows that the controllers are ultimately bounded even with parameter
uncertainties and measurement inaccuracy. Simulations on a realistic e-scooter
with a general demanding path to follow verify the ultimate boundedness of the
controllers. In addition, the feedback-linearized PD controller outperforms the
PD controller because it has narrower ultimate bounds. Future work focuses on
experiments using a self-balancing mechanism installed on an e-scooter.
