# question : about a DC-motor

B

#### bamse

Jan 1, 1970
0
I have a chart that shows the correlation between torque and rotational
speed for a DC-motor:

The chart can be viewed here:

The motor is inside an actuator, which is used to control the pitchangle of
a rotor blad on a wind turbine.

For those who do not know what "pitchangle" is, I can inform that pitching
of a wing just means rotation of
a wing around its length-axis.

My question is:

What is the chart used for? What can you deduce from this chart? And what
relevant information can be deduced when the motors purpose is taken into
consideration?

J

#### John Popelish

Jan 1, 1970
0
bamse said:
I have a chart that shows the correlation between torque and rotational
speed for a DC-motor:

The chart can be viewed here:

The motor is inside an actuator, which is used to control the pitchangle of
a rotor blad on a wind turbine.

For those who do not know what "pitchangle" is, I can inform that pitching
of a wing just means rotation of
a wing around its length-axis.

My question is:

What is the chart used for? What can you deduce from this chart? And what
relevant information can be deduced when the motors purpose is taken into
consideration?

I don't have any information about the torque and speed requirements
of your application, especially, how the motor will be geared, so I
can't tell you how fast the motor will turn, or its efficiency or its
current and power requirements. You need to produce a system curve
that relates torque to speed for your load. In other words, if you
had a way to measure the load's torque as you applied different speeds
of rotation to it, a graph of that relationship would be the system
curve. When you add a trace of that curve over the motor torque speed
line (in red) the point where they cross will show approximately what
speed the motor will operate at, and what torque it will be
producing. Then you draw a vertical line through that common point
through the other curves, to find out what the power requirements and
efficiency of the motor will be, operating at that speed and load.

If that speed is not acceptable, you have several choices. Either you
change the applied voltage (which result in a different set of motor
curves, that are fairly extrapolatable from this set) and repeat the
process, or you change the gear ratio to change the system curve, or
you select a different motor.

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