[WIP] 3 link pendulum

[tarzzz]

No description provided.

[moorepants]

A general inertia matrix has 9 entries: three moments of inertia and 6 products of inertia. You are only introducing the moments of inertia about the x and y axes. Where are the other entries? Is the link assumed symmetric? Depending on the symmetry you can reduce the inertia down to the three moments of inertia but since you have no Z inertia at all this seems problematic. I'd prefer you to add all of the inertia tensor entries here and then if you assume symmetry about various planes you can set the appropriate products of inertia equal to zero when you get to the numerical simulation.

[hazelnusse]

Only 6 entries will be unique, inertia matrices are always symmetric (i.e., Ixy == Iyx, Ixz == Izx, Iyz == Izy). If you create a 3x3 with 9 unique entries and somehow you accidentally make it non-symmetric, it won't be representative of an inertia matrix and is probably a mistake. The inertia() function in mechanics may be useful here.

[moorepants]

Why not write a loop to do these three lines?

[moorepants]

Tarun,

The derivation looks correct to me. You'll have to simulated it to see if behaves correctly. Please make a figure (or find a creative commons licensed one) to include and add more detail to the read me.

[tarzzz]

i am rather more aligned on writing some javascripts, for simulation.
it would be nice to see the pendulums in a 3D version ...

On 6/24/13, Jason Moore [email protected] wrote:

Tarun,

The derivation looks correct to me. You'll have to simulated it to see if
behaves correctly. Please make a figure (or find a creative commons licensed
one) to include and add more detail to the read me.

---

Reply to this email directly or view it on GitHub:
#10 (comment)

[moorepants]

The simulation (ode integration) should happen in Python (I don't know of any ode tools in javascript). You don't get any free visualization without simulation.

I think if you do a one-off simulation/visualization for this problem it will be a good exercise in understanding what methods you will need to develop for the final API. So please go ahead a do an example visualization of this more complicated problem. And use what you learn in the process to flesh out the python and javascript api designs that you are working on.

[moorepants]

BTW, I'll merge this example as soon as you add the figure and beef up the readme.

[moorepants]

Oh yeah and one more thing: switch to no loops or loops in the problem derivation so that it is consistent with itself.

Fix those three things and we will merge this in.

[tarzzz]

yes simulation would be in python only. i should have used the word
animation there.
so i will work on this problem + webgl simulation, then it can be
merged. i would also write rough(more specific to this problem)
implementations of functions/methods which are mentioned in this
particular problem, so that we know how things go off.

On 6/24/13, Jason Moore [email protected] wrote:

Oh yeah and one more thing: switch to no loops or loops in the problem
derivation so that it is consistent with itself.

Fix those three things and we will merge this in.

---

Reply to this email directly or view it on GitHub:
#10 (comment)

[tarzzz]

yes simulation would be in python only. i should have used the word
animation there.
so i will work on this problem + webgl Animation(there, i corrected it
:) ), then it can be merged. i would also write rough(more specific to
this problem) implementations of functions/methods which are mentioned
in this particular problem, so that we know how things go off.

On 6/24/13, Jason Moore [email protected] wrote:

Oh yeah and one more thing: switch to no loops or loops in the problem
derivation so that it is consistent with itself.

Fix those three things and we will merge this in.

---

Reply to this email directly or view it on GitHub:
#10 (comment)

[moorepants]

Here are some suggestions for the visualization:

Attach some shape to each bob (dont' use a sphere, make it more general like an ellipsoid). Attach different shapes to each pendulum arm. But also try to attach a shape to a reference frame/point other than the CoM of these objects. Maybe try to attach cubes to your pendulum arm to make it look like a cross. I think making more general choices of shapes and their locations will show you the need for some of the methods we've been talking about on the python side. Make sure that you generate all of the equatiosn necessary to describe the shapes's locations on the python side. Only data should flow into your javascript.

[tarzzz]

noted.
if it is fine i would like to spend some time on this one. two days perhaps.
it basically defines how we proceed with the project.

On 6/24/13, Jason Moore [email protected] wrote:

Here are some suggestions for the visualization:

Attach some shape to each bob (dont' use a sphere, make it more general like
an ellipsoid). Attach different shapes to each pendulum arm. But also try to
attach a shape to a reference frame/point other than the CoM of these
objects. Maybe try to attach cubes to your pendulum arm to make it look like
a cross. I think making more general choices of shapes and their locations
will show you the need for some of the methods we've been talking about on
the python side. Make sure that you generate all of the equatiosn necessary
to describe the shapes's locations on the python side. Only data should flow
into your javascript.

---

Reply to this email directly or view it on GitHub:
#10 (comment)

[moorepants]

I'm fine with that. Like I said, I think doing so will help define your API design. So the goal will be to animation the 3 link conical pendulum and then rework your API design to reflect what was learned. We can discuss the API at that time hopefully coming to a final decision.

[moorepants]

Outstanding issues:

• Add a figure
• More detail in the readme
• Fix the kinematical differential equation definitions so that you get correct EoM

[moorepants]

This needs to be merged into one directory with the stuff in PR #11.