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Subject: RE: [Tutor] How to go about a simple object grabbing in python (given coordinates of arms and objects)
Date: Mon, 24 Jun 2024 17:57:00 -0400
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Marc,

Several people have supplied feedback on whether your request is a good =
fit for here. Ultimately it is up to the owner/moderator. In particular, =
your request to the Tutor List may not fit the purpose and be a bit =
complex  and to the main Python List also outside some common usage =
whether it is about a specific module or product you are using, or =
asking about algorithms in a very general way.

You question has evolved to being about algorithms, more than about =
Python as a basic language or even commonly used modules.

So, I suggest you simplify your model and then maybe bring it in-line =
with the module(s) you showed us you were using. Some of what you ask =
sounds like it would be extremely commonly done in things like robotics, =
or even just machines with moving parts.

Consider the somewhat related concept often seen of how you get from one =
place to another in parts of Manhattan where most of the streets run =
either in one direction or the orthogonal direction. How do you get from =
say East 14th Street at 1st Avenue to West 28th Street and 11th Avenue? =
This is a slight imitation of how to move a robotic arm that can mainly =
either go one way or another but not both at once. And, in the real =
world, parts of Manhattan are more complex with streets ending or =
renaming or running more diagonally or huge voids like Central Park.

The number of solutions is huge for walking, and smaller for driving as =
some streets are one way. But assuming you avoid wasteful paths (except =
when roads are closed for endless purposes) and you do not take a path =
through Brooklyn, Queens and The Bronx and back to Manhattan as in the =
NY Marathon that also touches another borough, the solutions mainly look =
like this:

Go as far horizontally as you need and then as far vertically.
Or, do vertical, then horizontal.
Or lots of combined versions such as climbing stairs by doing a block or =
three one way then some in the other and repeat.

The above is referred to as Manhattan Distance, as compared to other =
measures like Euclidean distance.

So back to your robot arm, you can see a set of simple solutions where =
you make a sort of triangle with the direct Euclidean arm being a =
hypoteneuse and the  X and Y movements are the other two sides. You can =
then break up your problem as heading one way and pausing and turning =
the other way and stopping just short of the object you want. If there =
are no obstacles, you can do that in either order. Or, you could =
alternate in smaller amounts and get to the same destination.=20

Grabbing it would be something else I will not address except to say =
that depending on what is grabbing and how it is shaped, you may need to =
aim not for the object, but the appropriate distance and direction so =
that when you stop moving, the "grasper" can close on it, again, =
avoiding existing obstacles. And note, speed is a consideration as many =
things need to be approached slowly and gently.

Next, consider what it would mean if you could have a combined motion =
based on both operations allowed at the same time. Consider a robot that =
is on wheels that can move horizontally while also having a "lift" =
component that lifts the part with the graspers vertically. Both could =
be programmed to run in tandem at appropriate speeds so the graspers are =
traveling along the hypotenuse I mention and are going the shortest =
path. This might be faster and more economical in other ways but can be =
more complex. And, it may be the robot does not have power or computing =
ability to do both at the same time. Your design is beyond vague.

Both of the approaches above make a plan and carry it out. But in the =
real world, many algorithms must adjust and work somewhat =
probabilistically. One algorithm for say catching a moving object, =
especially one that can change speed and direction a bit, like a running =
dog or a kite flying in the wind, is to locate where the object seems to =
be now, perhaps just a direction and a guess at distance, and maybe with =
some observation make a guess at where it might be at some time in the =
future that is approximately when you might move the robot near there. =
Then, use a technique like above (or completely different) that perhaps =
aims to get you something like halfway there. Monitor along the way to =
update your position and the newest destination position (if it is =
moving) and re-evaluate and adjust for the next round and maybe evaluate =
again as you approach halfway or so, again. Eventually, if you are =
close, slow down and gradually try to come to a stop where you can grab. =
If the object reacts to your attempting to go after it, it can be =
complex. And, you may overshoot and sort of circle back.

Now, expand the problem more if needed. What does the robot look like. =
How many places can it bend? For example, can it have something like two =
or more elbows, perhaps one allowing twisting of up to 30 degrees and =
one moving forward and backward and another allowing movement side to =
side, up to some number of degrees. Are all these degrees of freedom =
absolute or are there constraints? For example, to turn beyond some =
number of combined degrees may not be allowed, and instead of turning =
400 degrees clockwise, you simply move forward or back to a 40 degree =
angle from some baseline. Perhaps bending certain ways while carrying =
some kind of weight, can cause it to topple. There can be an amazing =
number of considerations that cannot be anticipated and depend on =
specific choices in making a robot. A longer arm, for example, requires =
fewer degrees of turn to move some known amount.

As before, there are an amazing number of ways to do such things in any =
language as we are discussing "algorithms."  If the goal is finding A =
WAY, any simpler ones will do. If it is to find an optimum way, we have =
tons you need to learn and consider. If this was a contest and a =
contestant on the other side of the object was supposed to start at the =
same time as you, and the first to grab the object wins, ...

And, if this has machine learning components, which python is in some =
ways well suited to, you may design a robot that moves clumsily and =
almost randomly, at first, and then "learns" from such experiments and =
gradually figures out better and maybe even better ways until it just =
does well at reaching and grasping for any similar enough problems and =
maybe even somewhat different ones. I suspect that is more than you need =
but in real-world robotics, may be part of how to make more =
sophisticated and even general-purpose robots.

But if you want to talk more about python in doing parts of this, there =
are several things to consider. Base python has data structures you can =
use to store and manipulate many things you may need to keep track of, =
or if planning a whole routine in advance, things like lists to hold the =
steps you can then hand over to function. Add-on modules like numpy can =
be very helpful in extending python for some purposes, as an example. =
There are probably many functions that already do things like given two =
points, calculate the slope and distance of a direct line between them, =
or compare two or more approaches and return what is best in some way =
and so on. There ways of running things in parallel while sharing some =
data while making sure to avoid them interfering with each other. You =
can set timers to wake up and recalculate and much more. Then there are =
all kinds of modules that help you with parts. There is a good chance =
that whatever you showed us is just one of many such modules people have =
shared or sold for purposes similar enough to your robot problem.=20

But if your main goal is to do this mainly with the kind of =
functionality you pointed at, since likely none of us have read the =
documentation, nor care to without getting paid a lot, it means you =
should be reading a lot and looking carefully at examples that may apply =
AND finding resources more about that than asking people about "python" =
and especially asking python people how one does things in robotics. =
Mose specific questions such as how to calculate a distance using =
python, will likely get helpful responses, and brief but complete =
examples of code that you want debugged, may also be responded to. But =
asking for complex algorithms in the abstract probably will result in =
silence or ever more elaborate debates till a moderator suggest a halt! =
LOL!

Python, like many languages, is a fairly general purpose language that =
can do many things well, and some less well, and some mainly by standing =
on it's head while including software built in other languages. Your =
project may happen to be in python, but more likely most of it should be =
using functions built-in to whatever add-ons you are using if it is =
designed to do what you want. Your goal is not to create it all from =
scratch, I would think. You may end up using just a little base python =
to glue things together.

Good Luck.


-----Original Message-----
From: Python-list =
<python-list-bounces+avi.e.gross=3Dgmail.com@python.org> On Behalf Of =
marc nicole via Python-list
Sent: Monday, June 24, 2024 5:24 AM
To: Alan Gauld <alan.gauld@yahoo.co.uk>; python-list@python.org; =
Tutor@python.org
Subject: Re: [Tutor] How to go about a simple object grabbing in python =
(given coordinates of arms and objects)

What are the parameters to account for in this type of algorithm? are =
there
some checks to perform the arm moves ? for example angle moves or =
cartesian
moves based on some distance thresholds? Any idea about the
pseudo-algorithm is welcome.

Thanks.

Le dim. 23 juin 2024 =C3=A0 10:33, Alan Gauld via Tutor =
<tutor@python.org> a
=C3=A9crit :

> On 22/06/2024 13:41, marc nicole wrote:
>
> > So, given the x,y,z coordinates of a target object and the offset =
x,y,z
> of
> > arms of a robot, what is a good algorithm to perform to grab the =
object
> > between the hands (either from both sides or from below all using =
both
> > hands).
> >
> > Specifically, my problem is applied to a NAO robot environment where =
I
> > retrieve a target object coordinates using the following code:
>
> This is almost entirely outside the Python domain and all within
> your 3rd party environment. Do they have a user forum or mailing
> list? You will probably get better results asking there?
>
> Another possibility is that you are using a Python wrapper around
> a C (or other language) library and there might be FAQs, fora or
> lists supporting that. If so you should be able to translate
> their examples to your Python code?
>
> In terms of generic solutions the only thing I can suggest that
> might help is to research collision detection algorithms.
> Wikipedia is likely a good starting point.
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
>
> _______________________________________________
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