yeok-c / stewart_py

Python implementation of stewart platform

Stewart_Py

Python implementation and step-by-step inverse kinematic explanation of stewart platform

Usage: Fork this repo and copy the src folder into your project folder. Import package in python

 from src.stewart_controller import Stewart_Platform

Create object by defining parameters for the stewart platform

 Stewart_Platform(r_B, r_P, lhl, ldl, Psi_B, Psi_P)

Where
r_B = Radius of Base (Bottom)
r_P = Radius of Platform (Top)
lhl = Servo Horn Length
ldl = Rod length
Psi_B = Half of angle between two anchors on the base
Psi_P = Half of angle between two anchors on the platform
For details please refer to my tutorial https://github.com/Yeok-c/Stewart_Py

Call function calculate([translation vector], [rotation vector]) to solve inverse kinematic for rotation angles (Radian) for 6 servos

 servo_angles = platform.calculate( np.array([X,Y,Z), np.array([Pitch, Roll, Yaw]) )

Sources and additional reading

Robert Eisele's Explanation and js implementation: https://www.xarg.org/paper/inverse-kinematics-of-a-stewart-platform/ https://github.com/infusion/Stewart

hbartle's MATLAB implementation https://github.com/hbartle/Stewart_Platform/

Others resources https://github.com/NicHub/stewart-platform-esp32 https://github.com/daniel-s-ingram/stewart https://github.com/felixros2401/Stewart-Platform

stewart_py's Issues

TypeError: __init__() missing 1 required positional argument: 'ref_rotation'

Firstly, thanks for creating and sharing the library, it looks like something that might be really useful to me.

However, I have just tried to use it and the there isn't any documentation around the parameter ref_rotation.

The code states:

    To initialize, pass 6 parameters
    r_B = Radius for circumscribed circle where all the anchor points for servo shaft lie on
    r_P = Radius for circumscribed circle where all anchor points for platform lie on
    lhl = |h| = length of servo horn
    ldl = |d| = length of rod
    alpha_B =
    alpha_P =

Yet the function takes 7 parameters and there is no default for ref_rotation:
def __init__(s, r_B, r_P, lhl, ldl, gamma_B, gamma_P, ref_rotation)

Can you tell me what ref_rotation is and how it should be used please?

Hexapod

Inverse Kinematics

Can you explain why you stated in the Jupiter Notebook at inverse Kinematics with Rotational Servos that:
h = H - B
d = P - H
l = P - B
and after that why the square of the lengths of this is that system? the T is meant to be the transpose matrix?