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:
- 2015-05-25
- Revision:
- 5:1190596b8842
- Parent:
- 0:74b4e50e0d15
- Child:
- 6:a91d18a26ba3
File content as of revision 5:1190596b8842:
/* @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); } vector_t Leg::solve_inverse_kinematics(float x, float y, float z) { // Equations from Quadrupedal Locomotion - An Introduction to Control of Four-legged Robot // Gonzalez de Santos, Garcia and Estremera, Springer-Verlag London, 2006 vector_t angles; angles.x = atan2(y,x); // coxa float A = -z; float E = x*cos(angles.x) + y*sin(angles.x); float B = coxa_length_ - E; float D = (2*coxa_length_*E + tibia_length_*tibia_length_ - femur_length_*femur_length_ - coxa_length_*coxa_length_ - z*z - E*E)/(2*femur_length_); angles.y = -atan2(B,A) + atan2(D,sqrt(A*A+B*B-D*D)); angles.z = atan2(z - femur_length_*sin(angles.y),E-femur_length_*cos(angles.y)-coxa_length_) - angles.y; //serial->printf("coxa_angle = %f\n",RAD2DEG*angles.x); //serial->printf("femur_angle = %f\n",RAD2DEG*angles.y); //serial->printf("tibia_angle = %f\n",RAD2DEG*angles.z); return angles; } void Leg::move(vector_t angles) { // 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*angles.x*RAD2DEG; float femur_pulse = 1480.0 + 10.88*angles.y*RAD2DEG; float tibia_pulse = 490.0 - 10.33*angles.z*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_link_lengths(float coxa_length, float femur_length, float tibia_length) { coxa_length_ = coxa_length; femur_length_ = femur_length; tibia_length_ = tibia_length; }