Playing with Blender For Artists (Bforartists) - Easier way to learn Blender?

[sorveltaja]

After taking closer look at the bones system, objects are linked to bones, so they just follow their parents. It appears that there doesn't need to be surface reaction related factors involved. Also it seems to provide more accurate movements, when compared to rigid bodies, where there may be some lag between objects.

Although it's very 'clean' way to make objects move, I find rigid body simulation more tempting at this point.

An example, where rotating purple frame is the animated object:

3D files (STL) and instructions for the mechanism that I used, are available at https://www.instructables.com/Antikythera-Orrery-3d-Printed/

[sorveltaja]

I've experimented a bit with rebuilding meshes in Blender, as imported ones are not necessarily that easy to edit.  For example, selecting vertex/edge/face loops or rings is usually impossible with such objects.

Comparison of imported mesh object (2800 vertices) vs rebuilt one (360 vertices):

 [ You are not allowed to view attachments ]  

Imported objects appear to have their origin points at 0,0,0 location (yellow dot on the left):

  [ You are not allowed to view attachments ]  
   
One way to set object's origin or pivot point to a desired location is to select a set of vertices/edges/faces in edit mode.  3D cursor (which acts as a temporary reference point) is then moved to the center/middle of those elements by Shift S → cursor to selected.

Next in the object mode right-click → set origin → origin to 3D cursor:

 [ You are not allowed to view attachments ]     

Some parts of imported mesh may not have so regular structure, though:

  [ You are not allowed to view attachments ]  
                                    
In this case, another way is to use a circular primitive object like UV sphere, which is scaled and moved to find approximate center point:

 [ You are not allowed to view attachments ]  

[sorveltaja]

Off-topic time again:

I remember trying out bones system back in the days in 3D studio max 2.5, but never really got it. In Blender, using bones doesn't seem to be any more straightforward either.

Rigging, or contacting the object(s) to bones or vice versa, and assigning IK (inverse kinematics) constraints when and where needed (like in some mechanisms to work as expected), is where I got totally lost.

In the meantime, this is as far as I got with bones:

No wonder that there are those (although only a few on Tube) who have looked for more easily approachable ways to get certain results by not using the bones system.

One such way is to use 'copy rotation/location'- and 'track to' constraints (not related to ones used with bones).

I've used the usual piston/piston rod/crankshaft combination - as it should have rather predictable behavior - to see how that works out, but stumbled on to one factor, that I never thought before - piston speed/velocity variation vs crankshaft rotation. Can't remember the exact search terms, but I looked on the net about it, and yes, it's a can of worms on its own, having plenty of equations to explain it.
 

[vtsteam]

I ran into the same slight oddity of piston movement when researching Scotch yokes, recently. Apparently a Scotch yoke imparts a true sinusoidal movement to a connecting rod, but not so a conventional crank and conrod.

There's a nice animation somewhere online of two different color pens tracing these alternate versions of movement on top of each other so you can see the difference.

[vtsteam]

&pp

[sorveltaja]

That sure looks strange. So I thought that how about trying to replicate it in Blender, and the resulting curves look pretty similar.

Blue curves are motion paths, which were used to form curves on the top:

  [ You are not allowed to view attachments ]  

[vtsteam]

The conrod is always vertical in a scotch yoke, but at a varying angle to the piston in a crankpin connection. Except at TDC and BDC. So the vertical distance is shorter in between.

[sorveltaja]

Yeah, scotch yoke seems to be easy one to animate/simulate properly, as the location of A (piston/conrod connection point in previous image), can be set to copy B's (yoke) location, by limiting its following behavior to consist only B's Z-axis movement.

To change gears - Although Blender's simulation/physics engine (Bullet) has some major issues with glitches, it can still be used for spotting/avoiding the same (tedious and probably takes too much effort to figure out what seemingly random errors are).

Nevertheless, there may be moments, when simulation runs as expected. An example, where vehicle drives around in circles, having its speed measured:

[sorveltaja]

Some of mesh editing tools in blender have weird ways of working.

So far, most annoying is mirroring an object. The tool itself works as one might expect, but the mirrored object always has a negative scale on mirror axis:

  [ You are not allowed to view attachments ]  

It can be fixed by using 'apply scale' command to reset X, Y and Z scales to positive 1.000.

If the object's scaling is not uniform, it affects modifiers like beveling (which isn't that great in Blender, though). Anyway, I wonder where negative or non-uniform scale can be used without messing things out?

So, once the scale is reset, perhaps because of negative scale value, mirrored object's normals or faces are inverted, which also affects modifiers (such as Boolean operations won't work):

  [ You are not allowed to view attachments ]  

Next thing to do is to select all faces in edit mode, and apply ‘flip’ or ‘recalculate outside’ command.

Same steps have to be repeated over and over every time. It makes otherwise simple operation rather tedious, so I started to look if there are ways to automate previous steps.

One way is to use output of Blender's info window, which shows history of previous actions:

  [ You are not allowed to view attachments ]  

Commands can then be copied to Blender's text editor and executed there as a script. Seems to work quite well, with just one click. But to make a button for it to 3D window instead, I asked ChatGPT - that glorified oracle - how that can be done.

It added some python code to make it happen. Commands included are:

- Duplicate object
- Mirror (in this case in x axis)
- Apply scale
- Enter edit mode
- Selection mode face
- Select all (faces)
- Flip normals
- Enter object mode

Although I'm not much of a programmer, I was able to figure out, what kind of code snippet to add to make a script to an installable add-on:

  [ You are not allowed to view attachments ]  

There are also some other command sequences, that I guess can be handled or 'buttonized' with similar python scripts as well. The script that ChatGPT provided, has comments on what different parts of code does, so it's fairly clear where certain list of commands should be placed.