Basic Information:
Printer Model: generic
MCU / Printerboard: mostly rp2040
Host / SBC: RPI5 8GB
klippy.log:
klippy.log (203.1 KB)
Fill out above information and in all cases attach your klippy.log file (use zip to compress it, if too big). Pasting your printer.cfg is not needed
Be sure to check our “Knowledge Base” Category first. Most relevant items, e.g. error messages, are covered there
Describe your issue:
Hi,
As a newbie here, i am starting with custom kinematics c helper.
my final goal is scara kinematics, though parallelogram 3-DOF might found it adoptable.
this is what i am working on now, more or less:
// SCARA kinematics stepper pulse time generation
// Copyright (C) 2025 R.Kaeter kaeter@gmail.com
// This file may be distributed under the terms of the GNU GPLv3 license.
#include <math.h> // sqrt, atan2, acos
#include <stddef.h> // offsetof
#include <stdlib.h> // malloc, free
#include <string.h> // memset
#include “compiler.h” // __visible
#include “itersolve.h” // struct stepper_kinematics
#include “trapq.h” // move_get_coord
struct scara_stepper {
struct stepper_kinematics sk;
double arm_a, arm_b;
};
// Inverse kinematics function for the first arm’s stepper (Angle 1)
static double
scara_stepper_calc_angle1(struct stepper_kinematics *sk, struct move m, double move_time)
{
struct scara_stepper ss = container_of(sk, struct scara_stepper, sk);
struct coord c = move_get_coord(m, move_time);
double x = c.x;
double y = c.y;
double r2 = xx + yy;
double r = sqrt(r2);
double alpha = atan2(y, x);
double beta = acos((ss->arm_a * ss->arm_a + r2 - ss->arm_b * ss->arm_b) / (2 * ss->arm_a * r));
double theta1 = alpha + beta;
return theta1;
}
// Inverse kinematics function for the second arm’s stepper (Angle 2)
static double
scara_stepper_calc_angle2(struct stepper_kinematics *sk, struct move m, double move_time)
{
struct scara_stepper ss = container_of(sk, struct scara_stepper, sk);
struct coord c = move_get_coord(m, move_time);
double x = c.x;
double y = c.y;
double r2 = xx + yy;
double theta2 = acos((r2 - ss->arm_a * ss->arm_a - ss->arm_b * ss->arm_b) / (2 * ss->arm_a * ss->arm_b));
return theta2;
}
struct stepper_kinematics * __visible
scara_stepper_alloc(char angle, double arm_a, double arm_b)
{
struct scara_stepper *ss = malloc(sizeof(*ss));
if (!ss)
return NULL;
memset(ss, 0, sizeof(*ss));
ss->arm_a = arm_a;
ss->arm_b = arm_b;
switch(angle) {
case ‘a’:
ss->sk.calc_position_cb = scara_stepper_calc_angle1;
break;
case ‘b’:
ss->sk.calc_position_cb = scara_stepper_calc_angle2;
break;
}
ss->sk.active_flags = AF_X | AF_Y;
return &ss->sk;
}
Please kindly suggest or comment, as i like to fine tune the c helper before move on to the python side. My assumption are the printer kinematics mechanism and printer config can be as general yet generic as possible 
. Thx
Regards,
Kaeter
