trick/trick_sims/SIM_wheelbot/models/Motor

Motor

Contents

• class MotorSpeedController
  

• class DCMotorSpeedController
  

• class Motor
  

• class DCMotor
  

• class PWM
  

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class MotorSpeedController

base class

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class DCMotorSpeedController

derived from class MotorSpeedController

Description

A DCMotorSpeedController is a simple proportional controller for an instance of class DCMotor. Given a commanded-speed it produces an input voltage for the associated DCMotor instance.

Constructor

    DCMotorSpeedController( DCMotor& dc_motor,
                            double gain,
                            const double& actual_speed,
                            const double& supply_voltage);

Access	Member Name	Type	Units	Value
private	gain	double	--	Parameter - Feedback gain
private	actualSpeed	const double&	m/s	Parameter - Reference to the actual motor speed.
private	supplyVoltage	const double&	volts	Reference to the power supply voltage.
private	motor		--	Parameter - Reference to the DCMotor instance to be controlled.

Member Functions

    void setCommandedSpeed( double commandedSpeed );

Access	Member Name	Type	Units	Value
private	motorVoltage	double	volts	[Eq#1]

• [Eq#1] motorVoltage = supplyVoltage * gain * ( commandedSpeed - actualSpeed ) [ limited to +/- supplyVoltage ]

    double getMotorVoltage();

Return the motorVoltage that was calculated by the last call to setCommandedSpeed().

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class Motor

base class

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class DCMotor

derived from class Motor

Class DCMotor represents a simple model of a DC motor. Given an input voltage it calculates a

1. current-load, and
2. a motor-torque.

The model consists of a constant internal resistance that converts an input voltage to current, and a motor torque constant that converts the current to output torque. The output current load is the absolute value of the current.

Constructor

DCMotor (const double initialInternalResistance,
         const double initialMotorTorqueConstant);

Access	Member Name	Type	Units	Value
private	internalResistance	double	ohms	Input
private	motorTorqueConstant	double	Nm/amp	Input

Member Functions

void update (const double motorVoltage);

This method is to be called periodically to update the motor state.

Access	Member Name	Type	Units	Value
private	motorCurrent	double	amp	[Eq#1]
private	motorTorque	double	Nm	[Eq#2]
private	currentLoad	double	amp	[Eq#3]

• [Eq#1] motorCurrent = motorVoltage / internalResistance

• [Eq#2] motorTorque = motorCurrent / motorTorqueConstant

• [Eq#3] currentLoad = || motorCurrent ||

void update (const PWM& PulseWidth);

PulseWidth is converted to voltage [ PulseWidth.getAverageVoltage() ], and then the above method is called.

double getTorque();

Return the torque that was calculated by the last call to update().

double getCurrentLoad()

Return the current-load that was calculated by the last call to update(). An example use of this method might be to update a battery model.

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class PWM

Description

This class represents a PWM signal. Pulse Width Modulation (PWM) is a method of controlling electrical power (current x voltage) by repeatedly switching the supply voltage on and off, or between a high and low (typically 0) voltage. The proportion of time that the voltage is "high" is called the duty-cycle. The average output voltage is:

[Eq#1] average_voltage = ((highVoltage * dutyCycle + lowVoltage * (1 - dutyCycle)) / 2)

Constructor

    PWM( double HighVoltage,
         double LowVoltage,
         double DutyCycle);

Access	Member Name	Type	Units	Value
public	HighVoltage	double	volts
public	LowVoltage	double	volts
private	dutyCycle	double	volts

Member Functions

void setDutyCycle( double DutyCycle);

Set the duty cycle to be used by getAverageVoltage().

double getDutyCycle() const;

Get current the duty cycle.

double getAverageVoltage() const;

Calculate and return the average_voltage by Eq#1.