Library to control a 3DOF robotic leg. Specify an [x,y,z] co-ordinate and the library will solve the inverse kinematic equations to calculate the required servo pulse widths to position the foot at the target location.
Leg.cpp
- Committer:
- eencae
- Date:
- 2015-05-24
- Revision:
- 0:74b4e50e0d15
- Child:
- 5:1190596b8842
File content as of revision 0:74b4e50e0d15:
/* @file Leg.cpp @brief Member functions implementations */ #include "mbed.h" #include "Leg.h" Leg::Leg(PinName coxa_pin, PinName femur_pin, PinName tibia_pin) { // set up pins as required coxa_servo = new PwmOut(coxa_pin); femur_servo = new PwmOut(femur_pin); tibia_servo = new PwmOut(tibia_pin); // PWM objects have 50 Hz frequency by default so shouldn't need to set servo frequency // can do it anyway to be sure. All channels share same period so just need to set one of them coxa_servo->period(1.0/50.0); // servos are typically 50 Hz // setup USB serial for debug/comms serial = new Serial(USBTX,USBRX); } void Leg::solve_inverse_kinematics() { // Equations from Quadrupedal Locomotion - An Introduction to Control of Four-legged Robot // Gonzalez de Santos, Garcia and Estremera, Springer-Verlag London, 2006 coxa_angle_ = atan2(target_.y,target_.x); float A = -target_.z; float E = target_.x*cos(coxa_angle_) + target_.y*sin(coxa_angle_); float B = coxa_length_ - E; float D = (2*coxa_length_*E + tibia_length_*tibia_length_ - femur_length_*femur_length_ - coxa_length_*coxa_length_ - target_.z*target_.z - E*E)/(2*femur_length_); femur_angle_ = -atan2(B,A) + atan2(D,sqrt(A*A+B*B-D*D)); tibia_angle_ = atan2(target_.z - femur_length_*sin(femur_angle_),E-femur_length_*cos(femur_angle_)-coxa_length_) - femur_angle_; //serial->printf("coxa_angle = %f\n",RAD2DEG*coxa_angle_); //serial->printf("femur_angle = %f\n",RAD2DEG*femur_angle_); //serial->printf("tibia_angle = %f\n",RAD2DEG*tibia_angle_); } void Leg::move_to_target() { // formulas to convert angle to pulse-width // these need calibrating for each servo // the base value is the pulse width that aligns the joint along the common normal // the gradient value comes from measuring the pulse that moves the joint to 90 degree // i.e. gradient = (pulse_90 - pulse_normal)/90 // TODO implement calibration over serial float coxa_pulse = 1510.0 + 10.44*coxa_angle_*RAD2DEG; float femur_pulse = 1480.0 + 10.88*femur_angle_*RAD2DEG; float tibia_pulse = 490.0 - 10.33*tibia_angle_*RAD2DEG; //serial.printf("Servo Pulses (us): c = %f f =%f t = %f\n",coxa_pulse,femur_pulse,tibia_pulse); // update servo pulse widths coxa_servo->pulsewidth_us(int(coxa_pulse)); femur_servo->pulsewidth_us(int(femur_pulse)); tibia_servo->pulsewidth_us(int(tibia_pulse)); } void Leg::set_target(float x, float y, float z) { target_.x = x; target_.y = y; target_.z = z; } void Leg::set_link_lengths(float coxa_length, float femur_length, float tibia_length) { coxa_length_ = coxa_length; femur_length_ = femur_length; tibia_length_ = tibia_length; }