The paper deals with expandable motors for power assist wheelchairs. Significant part of the users of such wheelchairs are the persons, who are highly motivated to use their wheelchairs applying as much of their own muscle power as possible, so that the rate of assistance may vary from zero to maximal power. On the other hand, the maximal power itself may be different. In the case of wheelchair use for rehabilitation purpose, it decreases, requiring less powerful motor of smaller weight and size. On the other hand, in the case of progressive disability it may increase. In both cases, it would be practical to use the same wheelchair with alternative motor. These two tendencies indicate the need in a motor, which maximal power and torque could be corrected, providing less weighty and bulky solutions for less powerful occasions. In the considered research, the above stated problem is solved with a help of arc shaped motor, varying the number of arc shaped modules for variable maximal power. There are several possible configurations of such motors. These configurations are evaluated in the given report from the point of view of their weight, size, cost and requirements for the corresponding electronic drivers.