Overview
Closeup |
A brush motor rotates when the brushes and commutator alternate the direction
of the current passing through the armature conductors.
Torque is proportional to the product of the current and the torque constant.
Therefore, to generate a larger torque with the same current, the torque
constant needs to be increased.
However, increasing the torque constant will reduce the rotation speed,
so it is important to understand the torque characteristics of the motor.
This note presents a case study of a 2-pole 3-slot small brush motor with
regard to its Speed-Torque curve and Torque-Current curve. |
Speed-Torque and Torque-Current Curves
| The Speed-Torque curve is shown in Figure 1, and the Torque-Current curve
is shown in Figure 2. The graphs show the speed decreases with toque and
torque is approximately proportional to current. Also, the speed range
controllable in this motor can be seen on the Speed-Torque curve. |
Closeup |
Closeup |
Magnetic Flux Distribution
Closeup |
Figure 3 shows the magnetic flux distribution at the rotation speed of
12000 rpm. The magnetic flux density is particularly high in the regions
circled in red. The magnetic flux from the rotor and the stator are adding
together. When the magnetic flux of the rotor or stator leaks due to the
magnetic saturation and does not interact with the other part, the torque
may be reduced. |
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