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##### Activity
Jason K. Moore
@moorepants
yes they are
they both have th same info
we choose to use the left side when designing mechanics
we could have easily chosen the right side
the basis for the first 3 components and next 3 components are the same
actually they are completely different!
Jason K. Moore
@moorepants
the basis is defined in A
they are the same!
no!
V = [velocity, angular vleocity]
V is spatial veclotiy
V != v + w
V_linVel = v
V_angVel = angular velocity
they are components of tow different vectors
they do not live in R6
but actually in R3cross3
Jason K. Moore
@moorepants
you can write it like SpatialVector(v, w, A) if you want
same thing
which is what I offer
Jason K. Moore
@moorepants
gotta go bye
if you look at attributes, it V.w and V.v
later!
also from the book: "Strictly speaking spatial vectors live in the
R3×R3 space, but for notational simplicity we will treat them as members of the
R6 space."
my point is that spatial velocity is not a sum of angular and linear velocities
yibochallinger
@yibochallinger
is there a good example using pydy.viz?
yibochallinger
@yibochallinger
@moorepants where to find the code to Conical Pendulum Visualization with PyDy? did you generate javascript from python?
@yibochallinger https://github.com/pydy/pydy-tutorial-human-standing works pretty well to show you the ropes on using viz. notebook 8 is on viz.
Jason K. Moore
@moorepants
@yibochallinger the examples are in the examples directory in the pydy repository
yes we generate javascript
extraymond
@extraymond
Sorry for asking a rather vague question:
It stated that it's using pydy, would like to know if there is any more of this.
Jason K. Moore
@moorepants
@extraymond looks interesting, didn't know about it, seems you can't download it without an account on that website
extraymond
@extraymond
@moorepants I've been looking for reference files or citing about this document, but nothing but the one on scribd.com can be found.
yibochallinger
@yibochallinger
I followed pydy tutorial human standing example hoping to create a visualization for a quadcopter but pydy.viz doesn't display any objects.
Renato Marinho
@renatomarinho
This message was deleted
Renato Marinho
@renatomarinho
This message was deleted
Sam Brockie
@brocksam
Hi. What's the simplest way to extract numerical values for Derivative(u, t) from a pydy System object following running System.integrate()? I know System.integrate() returns a np.ndarray with each column corresponding to the vector of q and u states for the system. But if one derives the EoM with auxiliary speeds to bring into evidence noncontributing forces then these can be functions of the time derivatives of the speeds. Or is there a more efficient way to numerically evaluate these noncontributing forces from the auxiliary equations? Many thanks, Sam
Jason K. Moore
@moorepants
The system object currently does not track anything extra. You can lambdify the expressions you want to calculate and then provide the results from system.integrate() to the function generated from lambdify.
extraymond
@extraymond
@yibochallinger If your using jupyter lab, I think the widget is coming out like what it does with jupyter notebook.
Hey guys, I'm very new to PyDy. I was wondering if there are any examples for 1. 3D mechanisms 2. parallel / closed mechanisms? Thanks for your help in advance
Hi everybody, I opened a new issue pydy/pydy#412 I would appreciate if you could help me find a solution. Thanks in advance.
the link to "Inverted pendulum model of a standing human" on this page seems to be broken as I have reported pydy/pydy#413
Hi guys, I would appreciate if you could help me with this question from Kane 1985 book.
nkr0
@nkr0
hello
I noticed this pydy/pydy#55 related to caching.
nkr0
@nkr0

I tried saving forcing_full and mass_matrix_full to a text file using str(trigsimp(*_full)). So that I can start from reading in the matrices, followed by a simpify.

from  basefile import *

with open('matrices.txt', 'r') as kfile:
m = ImmutableMatrix(sympify(kfile.readline()))

Now when I get to the odeint line,

y = odeint(rhs, x0, t, args=(constants_value,))

I get NameError: name 'X' is not defined. Any idea why? X is a Symbol defined in basefile.py

nkr0
@nkr0
rhs = generate_ode_function(f, q, u, constants, mass_matrix=mass)
works without any problem. Somehow inside odeint, X is not defined. X is one of the constants.
nkr0
@nkr0
as an update, I used srepr from sympy instead of str to save the matrices. This is slightly better. Before all variables were not defined. Now only DynamicSymbols are an issue. This is maybe because srepr prints Symbols as Symbol('g') etc. However, DynamicSymbols are printed as Function('omega')(Symbol('t')).