Re: Digest for pydy@googlegroups.com - 1 Message in 1 Topic

[Luke]

Alberto,
Could you post the rest of your code? From what you show, things
look correct, but my guess is that the way you obtained q1 might not
be correct.
~Luke

On Sun, Dec 6, 2009 at 11:22 AM, <py...@googlegroups.com> wrote:
>   Today's Topic Summary
>
> Group: http://groups.google.com/group/pydy/topics
>
> Starting with PyDy [1 Update]
>
>  Topic: Starting with PyDy
>
> Albertus <icem...@wanadoo.es> Dec 06 12:55AM +0100
>
> Hi to all!
>
> I'm an engineering student from Spain. I'm working in a project (the
> design of an Stirling's engine) and I'm trying to use PyDy to get the
> motion equations to calculate forces, etc.
> I'm very new to Python and also to PyDy.
> I'm trying to define a solid who rotates around the y axis of the
> newtonian reference with this sentence:
>
>
> C = N.rotate("C", 2, q1, I=(Ixc, Iyc, Izc, Jxyc, Jyzc, Jxzc))
>
> But I get an error message:
>
> Traceback (most recent call last):
> File "motor.py", line 17, in <module>
> C = N.rotate("C", 2, q1, I=(Ixc, Iyc, Izc, Jxyc, Jyzc, Jxzc))
> File "/media/AL_USB/Documentos/ENGLOBE_Stirling/python/pydy.py", line
> 1298, in rotate
> length 3")
> NotImplementedError: angle must be a list/tuple
> of length 3
>
>
> What's wrong? I don't understand this error because I have seen in the
> examples a lot of similar expressions.
> I hope you could help me.
>
> Thank You very much.
>
> Alberto
>
>
>
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[Iceman_5]

Here is the code:

# coding=utf8



#from sympy import *

from pydy import *



# Create a Newtonian reference frame

N = NewtonianReferenceFrame('N')



# Declare parameters, coordinates, and speeds

R, l4, l6, Ixc, Iyc, Izc, Jxyc, Jxzc, Jyzc, Ixd, Iyd, Izd, Jyzd, mc,
md, lgd, betta, F=\

N.declare_parameters('R l4 l6 Ixc Iyc Izc Jxyc Jxzc Jyzc Ixd Iyd Izd
Jyzd mc md lgd betta F')

q1, qd1 = N.declare_coords('q', 1)

u1, ud1 = N.declare_speeds('u', 1)



# Orient the three rigid bodies, assign inertias

#Definimos el solido cigüeñal

C = N.rotate("C", 2, q1, I=(Ixc, Iyc, Izc, Jxyc, Jyzc, Jxzc))

#Definimos un sistema de referencia auxiliar en el cigueñal
correspondiente al brazo girado

Caux = N.rotate("Caux", 2, q1+betta)

#Definimos el solido disco 1

D1 = N.rotate('D1', 2, -q1, I=(Ixd, Iyd, Izd, 0, Jyzd, 0))

#Definimos el solido disco 2

D2aux=N.rotate('D2aux', 3, pi)

D2 = D2aux.rotate('D2', 2, -q1-betta, I=(Ixd, Iyd, Izd, 0, Jyzd, 0))



#locate mass centers and assign masses

CG = N.O.locate('CG', 0, C, mc)

D1G= CG.locate('D1G', (-l6/2-l4-lgd)*C[2] + (R/2)*C[3], D1, md)

D2G= CG.locate('D1G', (l6/2+l4-lgd)*Caux[2] + (R/2)*Caux[3], D2, md)



#locate the force application points P and P2

P= D1G.locate('P', -lgd*D1[2] + (R/2)*D1[3], D1, force=F*cos(q1))

P2= D2G.locate('P', -lgd*D2[2] + (R/2)*D2[3], D2, force=-F*sin(q1))

On 6 dic, 23:46, Luke <hazelnu...@gmail.com> wrote:
> Alberto,
>   Could you post the rest of your code?  From what you show, things
> look correct, but my guess is that the way you obtained q1 might not
> be correct.
> ~Luke
>
> On Sun, Dec 6, 2009 at 11:22 AM,  <py...@googlegroups.com> wrote:
> >   Today's Topic Summary
>
> > Group:http://groups.google.com/group/pydy/topics
>
> > Starting with PyDy [1 Update]
>
> >  Topic: Starting with PyDy
>

> > Albertus <icema...@wanadoo.es> Dec 06 12:55AM +0100

[Luke]

The default behavior of the declare_coords and declare speeds methods
are to return lists. So in the case of a single coordinate (q1) in
your case, this method is returning two lists, each of length 1. This
is useful if you have lots of coordinates and you want to have a
single list which can be used to index each of the generalized
coordinates or generalized speeds (or their time derivatives). If you
change these:

q1, qd1 = N.declare_coords('q', 1)
u1, ud1 = N.declare_speeds('u', 1)

to this:
(q1,), (qd1,) = N.declare_coords('q', 1)
(u1,), (ud1,) = N.declare_speeds('u', 1)

Then, your code should run fine.

I know this seems a little annoying to have to do, but for any system
with 2 or more coordinates, you would just do:
q, qd = N.declare_coords('q', 500)
u, ud = N.declare_speeds('u', 500)

and then you could access the 300th generalized coordinate by:
q[299]
which is easier than having to type out each of the 500 coordinates.

Let me know if this make more sense now.

Thanks,
~Luke