A DC motor is configured so that, while either one of a pair of power feeding brushes makes contact with two commutator segments, the other makes contact with only one of two commutator segments. The DC motor is further provided with: a plurality of coils; a filter unit; and a calculation unit. The number of turns of a predetermined coil among the plurality of coils is different from the numbers of turns of the other coils. The filter unit allows the passing of the waveform of current generated on the basis of the fact that the numbers of turns are different from each other, and interrupts the waveform of current generated at the switching of the states of the contacts of the power feeding brushes to the commutator segments. The calculation unit calculates a rotational speed from the waveform passed through the filter unit.

A DC motor is configured so that, while either one of a pair of power feeding brushes makes contact with two commutator segments, the other makes contact with only one of two commutator segments. The DC motor is further provided with: a plurality of coils; a filter unit; and a calculation unit. The number of turns of a predetermined coil among the plurality of coils is different from the numbers of turns of the other coils. The filter unit allows the passing of the waveform of current generated on the basis of the fact that the numbers of turns are different from each other, and interrupts the waveform of current generated at the switching of the states of the contacts of the power feeding brushes to the commutator segments. The calculation unit calculates a rotational speed from the waveform passed through the filter unit.

An electric tool includes an output member, a motor, and a housing. The motor includes a rotor shaft, a rotor core, and a stator component. The rotor shaft is configured to rotate around a first axis. The stator component includes a coil winding. The stator component surrounds the first axis to separate the accommodation cavity into a first space and a second space. The first space includes a first end and a second end. The motor further includes a first end cover and a second end cover. The first end cover is disposed at the first end of the first space. The second end cover is disposed at the second end of the first space. A passage is formed between the second end cover and a structure surrounding the first space, and the passage is configured to place the first space into communication with the second space.

A method of manufacturing a rotor of an electric motor or an electric generator includes positioning a plurality of amortisseur bars and using additive manufacturing to place electrically conductive material. More specifically, positioning the amortisseur bars may include circumferentially positioning the bars around a rotor stack and using additive manufacturing to place electrically conductive material may include forming a non-solid pattern of electrically conductive material, such as a pattern of electrically conductive traces, across opposite axial ends of the rotor stack to electrically interconnect an amortisseur circuit.

A method of manufacturing a rotor of an electric motor or an electric generator includes positioning a plurality of amortisseur bars and using additive manufacturing to place electrically conductive material. More specifically, positioning the amortisseur bars may include circumferentially positioning the bars around a rotor stack and using additive manufacturing to place electrically conductive material may include forming a non-solid pattern of electrically conductive material, such as a pattern of electrically conductive traces, across opposite axial ends of the rotor stack to electrically interconnect an amortisseur circuit.

A DC motor is configured so that, while either one of a pair of power feeding brushes makes contact with two commutator segments, the other makes contact with only one of two commutator segments. The DC motor is further provided with: a plurality of coils; a filter unit; and a calculation unit. The number of turns of a predetermined coil among the plurality of coils is different from the numbers of turns of the other coils. The filter unit allows the passing of the waveform of current generated on the basis of the fact that the numbers of turns are different from each other, and interrupts the waveform of current generated at the switching of the states of the contacts of the power feeding brushes to the commutator segments. The calculation unit calculates a rotational speed from the waveform passed through the filter unit.

A DC motor is configured so that, while either one of a pair of power feeding brushes makes contact with two commutator segments, the other makes contact with only one of two commutator segments. The DC motor is further provided with: a plurality of coils; a filter unit; and a calculation unit. The number of turns of a predetermined coil among the plurality of coils is different from the numbers of turns of the other coils. The filter unit allows the passing of the waveform of current generated on the basis of the fact that the numbers of turns are different from each other, and interrupts the waveform of current generated at the switching of the states of the contacts of the power feeding brushes to the commutator segments. The calculation unit calculates a rotational speed from the waveform passed through the filter unit.

A brush motor includes a stator and a rotor. The rotor includes a rotary shaft with a rotor core and commutator fixed thereto. The commutator includes an insulating base and commutator segments fixed to the insulating base. The stator includes 2P stator poles, where P is an integer greater than 1. The rotor comprises m teeth, where 4P>m>2P, and 2m is an integral multiple of P. The rotor includes a rotor winding, which is a concentrated winding having m first elements and m second elements. Each tooth is wound with one of the first elements and one of the second elements. the m first elements form a plurality of element groups, each having n first elements connected in series, and being connected only to corresponding commutator segments at both ends thereof, where Pn2. Both ends of each second element are connected to corresponding commutator segments.

A brush motor includes a stator and a rotor. The rotor includes a rotary shaft with a rotor core and commutator fixed thereto. The commutator includes an insulating base and commutator segments fixed to the insulating base. The stator includes 2P stator poles, where P is an integer greater than 1. The rotor comprises m teeth, where 4P>m>2P, and 2m is an integral multiple of P. The rotor includes a rotor winding, which is a concentrated winding having m first elements and m second elements. Each tooth is wound with one of the first elements and one of the second elements. the m first elements form a plurality of element groups, each having n first elements connected in series, and being connected only to corresponding commutator segments at both ends thereof, where Pn2. Both ends of each second element are connected to corresponding commutator segments.