MinitaurLeg Class Reference

Class for coordinating two parallel coaxial motors in the Minitaur config. More...

#include <MinitaurLeg.h>

Detailed Description

Class for coordinating two parallel coaxial motors in the Minitaur config.

Link lengths can be set, and kinematics are implemented. The user can choose to use meters for the extension, or a nonlinear mapping from 0 (folded up) to pi (all the way extended)

This class is derived from AbstractMotor, in particular it coordinates two motors together in a parallel five-bar configuration.

Kinematics

The kinematics of the leg can be found in http://kodlab.seas.upenn.edu/Gavin/IROS15. In particular, Fig. 1 (borrowed from the paper and included below) will be helpful to follow this help page.

The end-effector coordinates (first argument to MinitaurLeg::setOpenLoop(), MinitaurLeg::setGain(), and MinitaurLeg::setPosition()) are EXTENSION and ANGLE. Assuming the inidividual motor zeros are set when the upper links are pointing vertically up, and the motor directions are set so the positions increase as the motors sweep down (this is the default of Minitaur),

• The ANGLE coordinate always refers to α - π in radians (where the front of the robot is to the right in the figure above). I.e., when the leg is vertically pointing down, ANGLE is 0, if it sweeps back, ANGLE is positive, etc.
• When MinitaurLeg::useLengths is false (this is default), the EXTENSION coordinate either refers to β in radians from 0 (fully retracted) to π (fully extended)
• When MinitaurLeg::useLengths is true, the EXTENSION coordinate refers to r in meters.

Usage

To use a MinitaurLeg in your code, follow the usage steps in the AbstractMotor help page. Additionally,

1. Set MinitaurLeg::useLengths to true if you would like to use the r coordinate instead of β for the leg extension
2. Set the upper link length MinitaurLeg::l1 (default is 0.1 m) and the lower link length MinitaurLeg::l2 (default is 0.2 m)
3. You can call MinitaurLeg::getSpeed() to get a body speed estimate if you supply the body pitch (leaning forward is assumed to be positive pitch).
4. To get proprioceptive torque estimates, you can still use Motor::getTorque() as long as Motor::setTorqueEstParams() has been called.

Example

#include <Motor.h>
#include <MinitaurLeg.h>

// Uncomment the lines corresponding to your board
// MBLC 0.5
const int NMOT = 10;
const uint8_t outPin[] = {PE9, PE11, PE13, PE14, PA0, PD4, PD7, PD6, PB4, PB5};
const uint8_t inPin[] = {PD12, PD13, PD14, PD15, PC6, PC7, PC8, PC9, PE2, PE3};
// // Mainboard v1.1
// const int NMOT = 8;
// const uint8_t outPin[] = {PA0, PA11, PA2, PA3, PB0, PB8, PA14, PA1};
// const uint8_t inPin[] = {PA6, PB5, PB6, PB7, PB1, PB9, PA15, PA5};
// // Mainboard v2
// const int NMOT = 8;
// const uint8_t outPin[] = {PA3, PA2, PA0, PA1, PB0, PB1, PA6, PB5};
// const uint8_t inPin[] = {PB8, PB9, PB3, PA8, PA11, PA15, PB14, PB15};


const int CONTROL_RATE = 1000;
BlCon34 M[NMOT];
MinitaurLeg leg0(&M[1], &M[0]);
const float motZeros[NMOT] = {0,0,0,0,0,0,0,0,0,0};

void controlLoop() {
  leg0.update();
}

void setup() {
  Serial1.begin(115200);

  Motor::updateRate = CONTROL_RATE;
  Motor::velSmooth = 0.55;

  // Arguments are pwmPin, pulsePin, zero(rad), direction(+/- 1)
  for (int i=0; i<NMOT; ++i)
    M[i].init(outPin[i], inPin[i], motZeros[i], 1);

  attachTimerInterrupt(0, controlLoop, CONTROL_RATE);
}

void loop() {
  leg0.enable(true);
  // These commands are similar to Motor commands, except with an added first argument
  leg0.setGain(ANGLE, 0.3);
  leg0.setPosition(ANGLE, 0);

  leg0.setOpenLoop(EXTENSION, 0.1);
}

Public Member Functions
	MinitaurLeg (Motor *M0, Motor *M1)
	Declare the leg based on the consituent motors.
float	getSpeed (float bodyPitch)
	Return forward speed. More...
void	getToeForce (float &ur, float &uth)
	Get force at the toe. More...
void	getToeForceXZ (float bodyPitch, bool bRight, float &ux, float &uz)
	Get toe forces in N in absolute coords. More...
Public Member Functions inherited from AbstractMotor< 2 >
virtual void	physicalToAbstract (const float in[N], float out[N])=0
	Transformation for forces at the toe to joint torques. More...
virtual void	abstractToPhysical (const float in[N], float out[N])=0
	Forward kinematics. More...
void	enable (bool flag)
	Enables all the motors in this "leg". More...
float	getPosition (int i)
	Returns the ith toe position coordinate. More...
virtual float	getPosition ()
	Get position of 0th coordinate. More...
float	getVelocity (int i)
	Returns the ith toe coordinate velocity. More...
virtual float	getVelocity ()
	Get velocity of 0th coordinate. More...
float	getOpenLoop (int i)
	Get the openloop value for the ith coordinate; useful when using setPosition(int, float) More...
virtual float	getOpenLoop ()
	Get open loop value of 0th coordinate. More...
void	setOpenLoop (int i, float val)
	Set open loop command to coordinate i. More...
virtual void	setOpenLoop (float val)
	Set open loop value for 0th coordinate. More...
void	setGain (int i, float Kp, float Kd)
	Set PD gains for coordinate i. More...
void	setPosition (int i, float setpoint)
	Set position setpoint for coordinate i, and change to position control mode. More...
virtual void	setPosition (float pos)
	Set position for 0th coordinate. More...
void	update ()
	This should be called at a more or less fixed rate (once per iteration) More...

Static Public Attributes
static bool	useLengths = false
	If true, use the exact leg kinematics, and the extension coordinate is in length units. If false, use the mean angle as a proxy for extension (between 0 and PI).
static float	l1 = 0.1
	Upper and lower link lengths. More...

Inherits AbstractMotor< 2 >.

Member Function Documentation

float MinitaurLeg::getSpeed

(

float

bodyPitch

)

Return forward speed.

Parameters

bodyPitch

Pitch angle of the body (required to figure out absolute leg angle)

Returns

Speed in m/s

void MinitaurLeg::getToeForce	(	float &	ur,
		float &	uth
	)

Get force at the toe.

The lengths MinitaurLeg::l1 and MinitaurLeg::l2 need to be correct, and also Motor::setTorqueEstParams needs to have be called for this to work.

Parameters

ur	Radial force in N. This is an output parameter (declare before this function)
uth	Tangential torque in N-m. This is an output parameter (declare before this function)

void MinitaurLeg::getToeForceXZ	(	float	bodyPitch,
		bool	bRight,
		float &	ux,
		float &	uz
	)

Get toe forces in N in absolute coords.

The lengths MinitaurLeg::l1 and MinitaurLeg::l2 need to be correct, and also Motor::setTorqueEstParams needs to have be called for this to work.

Parameters

bodyPitch	pitch such that > 0 when leaned forward
bRight	true if this is a right leg
ux	Returns horizontal force in N. It is >0 if leg is pushed "back"
uz	Returns vertical force in N. It is >0 if leg is pushed "up"

Member Data Documentation

float MinitaurLeg::l1 = 0.1

static

Upper and lower link lengths.

Copyright (C) Ghost Robotics - All Rights Reserved Unauthorized copying of this file, via any medium is strictly prohibited Proprietary and confidential Written by Avik De avik@.nosp@m.ghos.nosp@m.trobo.nosp@m.tics.nosp@m..io

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

• MinitaurLeg.h
• MinitaurLeg.cpp