Inverse kinematics with the Ergo Junior

In this notebook, we will discover the Inverse Kinematics functionnalities of Pypot + IKPy with an Ergo Jr. You can see this notebook as the starting point to discover Inverse Kinematics, used with a real (or simulated) robot!

Requirements

For this tutorial, you will need :

IKPy installed : installations instructions
The Ergo Jr creature installed : installation instructions
An actual ErgoJr or use the VREP simulator (no hardware required + VREP has a free version)
- Build an ErgoJr
- Install VRep

Setting things up

Some imports first.



In [3]:

    
import matplotlib.pyplot
%matplotlib notebook

ok

First, instantiate your Creature



In [2]:

    
from poppy.creatures import PoppyErgoJr


poppy = PoppyErgoJr(simulator='vrep')

Forward Kinematics

With Forward Kinematics, you can access the 3D position of your robot, from the angles of the motors :

For the Ergo Jr, you will get the 3D position of the tip (the blue dot on the picture above):

To access the Forwards Kinematics of the Ergo Jr :



In [1]:

    
poppy.chain.end_effector









    



---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-1-59c7d659a7b5> in <module>
----> 1 poppy.chain.end_effector

NameError: name 'poppy' is not defined

Plotting



In [4]:

    
zero = [0] * 6

ax = matplotlib.pyplot.figure().add_subplot(111, projection='3d')
poppy.chain.plot(poppy.chain.convert_to_ik_angles(zero), ax)

Inverse Kinematics

More than only accessing the position of the tip of the ErgoJr, you can use Inverse Kinematics to set this position. Simply, you give a desired position in space, and you will get a motor configuration that will move the robot to the target!

The goto function just does this :



In [5]:

    
poppy.chain.goto([-0.00670386, -0.17439168,  0.15083097],2.)



In [6]:

    
from ipywidgets import interact, FloatSlider

poppy.reset_simulation()

c = poppy.chain

x, y, z = c.end_effector
size = 0.3

def goto(x, y, z):
    c.goto((x, y, z), .1)
    
interact(goto, 
         x=FloatSlider(min=x-size, max=x+size, value=x, step=0.01), 
         y=FloatSlider(min=y-size, max=y+size, value=y, step=0.01), 
         z=FloatSlider(min=z-size, max=z+size, value=z, step=0.01))

Here is what you can get :