Gear motors or gearbox motors were designed to deliver reliability and precision for DC motor applications. Miniature DC motors used in the gear motors are often slot wound iron core drives and are paired with planetary gear heads.

Standard DC gear motors are made in a wide variety of diameters and gear motor length. Some companies provide custom gearbox motors or DC gear motors. Micro-Drive DC gear motors offer high performance at low costs. ISL products can help you source a standard DC gear motor or micro-drive DC gear motor or help you develop a custom gearbox motor to suit your needs.

Many applications call for a high start-up torque. The D.C. motor, by it svery nature, has a high torque vs. falling speed characteristic and this enables it to deal with high starting torques and to absorb sudden rises in load easily. The speed of the motor adjusts to the load. Furthermore, the D.C. motor is an ideal way of achieving the miniaturisation designers are constantly seeking because the efficiency it gives is high compared with other designs.

The stator is formed by a metal carcass and one or more magnets that
create a permanent magnetic field inside the stator. At the rear of the
stator are the brush mountings and the brush gear which provide
electrical contact with the rotor.
The rotor is itself formed by a metal carcass carrying coils which are
interconnected at the commutator at the rear of the rotor.
The commutator and brush assembly then select the coil through which
the electric current passes in the opposite direction.

Principle of operation
Whatever the complexity of the rotor coil windings, once they are
energized, they may be represented in the form of a ferromagnetic
cylinder with a solenoid wrapped around it.
The wire of the solenoid is in practice the wire bundle located in each
groove of the rotor. The rotor, when energized, then acts as an
electromagnet, the magnetic field following the axis separating the wires
of the solenoid in the direction of the current which flows through them.

The motor, therefore, consists of fixed permanent magnets (the stator) a
moving magnet (the rotor) and a metal carcass to concentrate the flux
(the motor body).
By the attraction of opposite poles and repulsion of like poles, a torque
then acts on the rotor and makes it turn. This torque is at a maximum
when the axis between the poles of the rotor is perpendicular to the axis
of the poles of the stator.

As soon the rotor begins to turn, the fixed brushes make and break
contact with the rotating commutator segments in turn.
The rotor coils are then energized and de-energized in such a way that
as the rotor turns, the axis of a new pole of the rotor is always
perpendicular to that of the stator. Because of the way the commutator
is arranged, the rotor is in constant motion, no matter what its position.
Fluctuation of the resultant torque is reduced by increasing the number
of commutator segments, thereby giving smoother rotation.

By reversing the power supply to the motor, the current in the rotor coils,
and therefore the north and south poles, is reversed. The torque which
acts on the rotor is thus reversed and the motor changes its direction of
rotation. By its very nature, the DC motor is a motor with a reversible
direction of rotation.

The torque generated by the motor, and its speed of rotation, are
dependent on each other.
This is a basic characteristic of the motor ; it is a linear relationship and
is used to calculate the no-load speed and the start-up torque of the motor.

The curve for the output power of the motor is deduced from the graph
of torque versus speed.

The torque vs. speed and output power curves depend on the supply
voltage

The torque vs. speed and output power curves depend on the supply
voltage to the motor.
The supply voltage to the motor assumes continuous running of the
motor at an ambient temperature of 20ËšC in nominal operational
conditions.

It is possible to supply the motor with a different voltage (normally
between -50% and + 100% of the recommended supply voltage).
If a lower voltage is used compared to the recommended supply the
motor will be less powerful. If a higher voltage is used, the motor will have a higher output power but
will run hotter (intermittent operation is recommended).

For variations in supply voltage between approximately – 25% to + 50%,
the new torque vs. speed graph will remain parallel to the previous one.
Its start-up torque and no-load speed will vary by the same percentage
(n%) as the variation in supply voltage. The maximum output power is
multiplied by (1 + n%)2.

Example : For a 20% increase in supply voltage

Start-up torque increases by 20% ( x 1.2)

No-load speed increases by 20% ( x 1.2)

Output power increases by 44% ( x 1.44)

The temperature rise of a motor is due to the difference between the

absorbed power and the output power of the motor. This difference is

the power loss.

Temperature rise is also related to the fact that power loss, in the form

of heat from the motor, is not rapidly absorbed by the ambient air

(thermal resistance). The thermal resistance of the motor can be greatly

reduced by ventilation.

Important

The nominal operating characteristics correspond to the voltagetorque-

speed characteristics required for continuous operation at

an ambient temperature of 20˚ C. Only intermittent duty is possible

outside these operating conditions : without exception, all checks

concerning extreme operating conditions must be performed in

the actual customer application conditions in order to ensure safe

operation.

In DC motors of 0.1 horsepower (74.60 watts) or less, a permanent magnet field is most useful. Comparing motors below 1.25″ in diameter, permanent magnet motors run cooler than wound field types because no power is expended to maintain a magnetic field.

The permanent magnet field functions perfectly for thousands of hours of operation and lasts indefinitely on the shelf.

Permanent magnet motors are easily reversed by changing the polarity of the voltage applied to the connecting terminals. They are capable of high-stall torque and function perfectly in long-duty cycle applications.

Dynamic braking is easily obtained by merely applying a short circuit to the motor terminals after voltage is removed. With ISL Products International LTD permanent magnet motors, this usually results in C less than 20 armature revolutions coast.

Figure 1 illustrates a speed-torque/current-torque curve for a permanent magnet motor. Each curve is a theoretical straight line since the permanent magnet field and armature winding are constant in a given motor. Current varies in proportion to torque, and the slope of this curve is a torque constant (K_T) in oz. in./amp.

Figure 2 shows that with the permanent magnet motor, no load speed varies inversely with field strength and stall torque varies directly with field strength. In this illustration, curve “a” is the lowest value, curve “b” is the nominal and curve “c” is the maximum value of field strength.

Figure 3 indicates the result of changing the applied voltage to a permanent magnet motor. No load speed changes proportionally to voltage, resulting in a family of parallel speed-torque curves. Remember that voltage determines speed, and only torque will determine current.