A coil assembly for a flat brushless motor comprises a coil of wire, and a bobbin including a flangeless plate-like portion having a peripheral surface on which the coil is wound with the axis of the coil being normal to opposed major surfaces of the plate-like portion, and with at least a part of the peripheral surface having a profile which deviates from a parallel to the coil axis so as to include sections angled in opposite direction from such parallel to the axis for preventing movement of the coil relative to the bobbin in the direction of the coil axis. The mentioned profile of the peripheral surface may be V-shaped and either outwardly concave or convex, or the peripheral surface may have a ridge extending therealong to define such profile. The opposed major surfaces of the plate-like portion are desirably in the form of triangles with two sides thereof radiating from the motor shaft, and with a support portion of the bobbin extending from the third side of the triangular plate-like portion and being offset therefrom for convenient attachment to a fixed mounting plate of the motor.