User Manual

Table Of Contents

Trapezoidal Switching

Advanced Digital Motor Controller User Manual 97

The number must be entered using the Number of Pole Pairs menus in the in the Roborun

PC utility..

Or by sending the conﬁguration command:

^BPOL channel nn

See “BPOL” in the command reference section for details. This parameter is not need-

ed for basic trapezoidal motor operation with Hall Sensor feedback and can be left at its

default value. It is needed if accurate speed reporting is required or to operate in Closed

Loop Speed or Position modes . The number of pole pairs is a critical conﬁguration in sinu-

soidal mode.

Entering a negative number of pole pairs will reverse the measured speed and the count

direction. It is useful when operating the motor in closed loop speed mode and if other-

wise a negative speed is measured when the motor is moved in the positive direction.

Trapezoidal Switching

In trapezoidal switching, the controller applies current to two of the 3 motor wires, in turn

and in alternating direction. A total of 6 combinations of current ﬂow are possible, result-

ing in the rotor getting a changing magnetic ﬁeld every 60 degrees of electrical rotation.

The controller must therefore know where the rotor is in relation to the electromagnets so

that current can be applied to the correct winding at any given point in time. The simplest

and most reliable method is to use three Hall sensors inside the motor. The diagram be-

low shows the direction of the current in each of the motor’s windings depending on the

state of the 3 hall sensors.

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Hall

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FIGURE 8-2. Hall sensors sequence