diffbot::Encoder Class Reference

Decorates the Teensy Encoder Library to read the angular wheel velocity from quadrature wheel encoders. More...

#include <encoder_diffbot.h>

Public Member Functions
double	angularPosition ()
double	angularVelocity ()
	Get the measure the angular joint velocity. More...
	Encoder (ros::NodeHandle &nh, uint8_t pin1, uint8_t pin2, int encoder_resolution)
	Construct a diffbot::Encoder providing access to quadrature encoder ticks and angular joint velocity. More...
int	getRPM ()
	get revolutions per minute More...
JointState	jointState ()
int32_t	read ()
	Read the current encoder tick count. More...
int	resolution ()
	Getter for encoder resolution. More...
void	resolution (int resolution)
	Setter for encoder resolution. More...
double	ticksToAngle (const int &ticks) const
	Convert number of encoder ticks to angle in radians. More...
void	write (int32_t p)
	Set the encoder tick count. More...

Public Attributes
::Encoder	encoder
JointState	joint_state_

Private Attributes
int	encoder_resolution_
ros::NodeHandle &	nh_
long	prev_encoder_ticks_
ros::Time	prev_update_time_

Detailed Description

Decorates the Teensy Encoder Library to read the angular wheel velocity from quadrature wheel encoders.

This class is composed of ::Encoder from https://www.pjrc.com/teensy/td_libs_Encoder.html, which is capable of reading rising and falling edges of two Hall effect signals. This yields the highest possible tick count (encoder resolution) from the encoders. Take the DG01D-E motor/encoder, that has a 6 pole magnetic disk (observed with magnetic paper) and therefore 3 pulses per revolution (ppr). Reading both edges (rising and falling) of both channels in the code, we can observe roughly 542 ticks at the wheel output shaft. Because the DG01D-E motor/encoder has a 48:1 gear ratio (according to its datasheet) we round the tick count up to 576 counts per wheel revolution). So 576 counts / 48:1 gear ratio / 2 channels / 2 edges = 3 pulses per revolution at the motor shaft. Having an encoder with more ppr would increase the encoder resolution. For example let's say we we have an encoder with 7 ppr, then we get the following output resolution at the wheel: 7 ppr (at motor shaft) * 48:1 gear ratio * 2 channels * 2 edges = 1344 ppr (measured at wheel).

Definition at line 35 of file encoder_diffbot.h.

Constructor & Destructor Documentation

Encoder()

diffbot::Encoder::Encoder	(	ros::NodeHandle &	nh,
		uint8_t	pin1,
		uint8_t	pin2,
		int	encoder_resolution
	)

Construct a diffbot::Encoder providing access to quadrature encoder ticks and angular joint velocity.

Parameters

nh	reference to the main ros::NodeHandle to compute the velocity from time and ticks or angle (s = v * t)
pin1	Pin of the first Hall effect sensor
pin2	Pin of the second Hall effect sensor
encoder_resolution	number of tick counts for one full revolution of the wheel (not the motor shaft). Keep track of gear reduction ratio.

Definition at line 4 of file encoder_diffbot.cpp.

Member Function Documentation

angularPosition()

double diffbot::Encoder::angularPosition

(

)

Definition at line 39 of file encoder_diffbot.cpp.

angularVelocity()

double diffbot::Encoder::angularVelocity

(

)

Get the measure the angular joint velocity.

Calculates the angular velocity of the wheel joint using the encoder ticks.

Returns

angular wheel joint velocity (rad/s)

Definition at line 45 of file encoder_diffbot.cpp.

getRPM()

int diffbot::Encoder::getRPM

(

)

get revolutions per minute

Calculates the wheels revolution per minute using the encoder ticks.

Based on https://github.com/linorobot/linorobot/blob/53bc4abf150632fbc6c28cdfcc207caa0f81d2b1/teensy/firmware/lib/encoder/Encoder.h

Returns

revolutions per minute

Definition at line 58 of file encoder_diffbot.cpp.

jointState()

diffbot::JointState diffbot::Encoder::jointState

(

)

Definition at line 14 of file encoder_diffbot.cpp.

read()

int32_t diffbot::Encoder::read ( )

inline

Read the current encoder tick count.

Returns

encoder ticks

Definition at line 89 of file encoder_diffbot.h.

resolution() [1/2]

int diffbot::Encoder::resolution ( )

inline

Getter for encoder resolution.

Returns the currently set encder resolution.

Definition at line 112 of file encoder_diffbot.h.

resolution() [2/2]

void diffbot::Encoder::resolution ( int  resolution )

inline

Setter for encoder resolution.

Used to initialize the encoder with a new resolution, e.g. obtained from the ROS parameter server.

Parameters

resolution

value to which the encoder tick count shoudl be set

Definition at line 106 of file encoder_diffbot.h.

ticksToAngle()

double diffbot::Encoder::ticksToAngle

(

const int &

ticks

)

const

Convert number of encoder ticks to angle in radians.

Calculates the current tick count of the encoder to its absolute angle in radians using the encoder_resolution_.

Parameters

ticks

tick count from an encoder which is converted to a corresponding absolute angle.

Returns

angle corresponding to encoder ticks (rad)

Definition at line 50 of file encoder_diffbot.cpp.

write()

void diffbot::Encoder::write ( int32_t  p )

inline

Set the encoder tick count.

Mainly used to reset the encoder back to zero.

Parameters

p	encoder ticks

Definition at line 97 of file encoder_diffbot.h.

Member Data Documentation

encoder

::Encoder diffbot::Encoder::encoder

Definition at line 39 of file encoder_diffbot.h.

encoder_resolution_

int diffbot::Encoder::encoder_resolution_

private

Definition at line 121 of file encoder_diffbot.h.

joint_state_

JointState diffbot::Encoder::joint_state_

Definition at line 112 of file encoder_diffbot.h.

nh_

ros::NodeHandle& diffbot::Encoder::nh_

private

Definition at line 119 of file encoder_diffbot.h.

prev_encoder_ticks_

long diffbot::Encoder::prev_encoder_ticks_

private

Definition at line 125 of file encoder_diffbot.h.

prev_update_time_

ros::Time diffbot::Encoder::prev_update_time_

private

Definition at line 123 of file encoder_diffbot.h.

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The documentation for this class was generated from the following files:

• encoder_diffbot.h
• encoder_diffbot.cpp