Featured is a controller for a motor that is ultra-compact, with a power density of at least about 20 watts per cubic cm (W/cm.sup.3). The controller utilizes a common ground for power circuitry, which energizes the windings of the motor, and the signal circuitry, which controls this energization responsive to signals from one or more sensors. Also, the ground is held at a stable potential without galvanic isolation. The circuits, their components and connectors are sized and located to minimize their inductance and heat is dissipated by conduction to the controller's exterior such as by a thermally conductive and electrically insulating material (e.g., potable epoxy). The controller uses a single current sensor for plural windings and preferably a single heat sensor within the controller. The body of the controller can also function as the sole plug connector.