LDCad tips and tricks

[Philippe Hurbain]

Rather than burrying this kind of questions in LDCad new version announcement threads I figured out it might be interesting to create a specific thread...

[Philippe Hurbain]

What is the best way to align the links of a chain around gears so that the chain bars go between teeth instead of going through them? I tried to rotate the path points, the whole chain then readjusted the path points to center on the gears, no way... of course I could rotate the gears instead, but since they are linked to other parts of the model I'm not keen of doing this!
   

[Philippe Hurbain]

What's the best way to properly rotate the connecting rods in a V-engine such as the one below? (question initially asked to me by Max...). It is relatively easy to come to a good solution using a successive approximation method, but maybe there is an easier way?
   

[Max Martin Richter]

Just a bit off-topic: Finally I made an AutoCAD drawing to solve this. This way took less than 3 minutes to get the exact angles for this problem. The model is finished, but there wasn't enough time to create the b-model, so the upload will take some more time...
Anyway a built-in solution in LDCad would be pretty cool.

/Max

[Merlijn Wissink]

I think there's a very simple solution to make it easier in LDCad: just a few extra shadow-library parts. Altough, I think (I'm still very new to those 'shadow parts') Roland would need to introduce a few extra commands to create this type of connection. SR3D-Builder did have brick-snapping for these engine parts.

Any possibility to sneak this into 1.5?

[Philippe Hurbain]

There are already connectivity files for engine parts (I made them
The problem is that currently LDCad makes a single connexion at a time, so you can't ensure that piston head is centered in engine block AND connected to rod at the same time.

[Milan Vančura]

Exactly - that's another example why I asked for "rotation snap" function. But, you remember, Roland answered he could not know if he would be able to achieve such functionality with current snap functions. So we'll see.

[Roland Melkert]

Chain placement can be very demanding especially if you are a perfectionist and or want to have some exact link count etc.

But it should be possible by playing around with the first control point rotation, control point radius-es and adding one or two extra points to force the chain 'hang', like so:

   

If anyone has an idea on to improve this by e.g. adding extra parameters to the control points or applying some additional magical math I'm open to suggestions.

[Roland Melkert]

Improvement on these kinds of part placement is indeed needed.

But you could probably also solve it by using some helper parts combined with the selection info feature, or maybe I could add some kind of additional helper for it. Thinking about this makes me wonder if this is something a scripted plugin system could be helpful for.

Also a set of templates for groups of 2 cylinders at often used angles would probably be a big difference in most builds.

[Philippe Hurbain]

But it should be possible by playing around with the first control point rotation

I thought so (and it seems quite logical) but I couldn't make it work - maybe I goofed somewhere, I'll try again.

[Milan Vančura]

I made several tests now. It's logical but not intuitive. I hope I found the principle behind:

even when the path is circular (like your chain), it has the beginning and the end. You can see it, for example, if you change the control "point" diameter slightly - there is a place where the circle chain is broken because its length is not dividable by one chain part length. If you rotate the control point where the path beginning/end is, it really moves the chain along the path. The rotation of other control points has no effect.

So, if you know a set of magic constants (control point diameters for usual LEGO gears), set the correct diameter and rotate the correct control point, you should get a nicely fitting result.
EDIT: I assume you use the nested mode, of course.

Which reminds me: Roland, could you add some guide/help about the set of gears diameters, please? I have never known if the correct one for gear24 is 30 or 30.5 or whatever else (for example)...

[Roland Melkert]

even when the path is circular (like your chain), it has the beginning and the end. You can see it, for example, if you change the control "point" diameter slightly - there is a place where the circle chain is broken because its length is not dividable by one chain part length. If you rotate the control point where the path beginning/end is, it really moves the chain along the path. The rotation of other control points has no effect.

Only the first point's rotation matters as it determines the position of the first link.

This got me thinking though, if I add an option to also take the rotation of other circles in account it would be possible to automatically calculate the 'hang' between two wheels and apply that instead of using the straight line it does now use. I have to look into this some more though

Which reminds me: Roland, could you add some guide/help about the set of gears diameters, please? I have never known if the correct one for gear24 is 30 or 30.5 or whatever else (for example)...

I usually set the so they cross about half the tooth's height. But a table for it should be nice indeed, maybe encoded in a new shadow meta.

[Jason Smith]

This is a great thread idea but I think I it would be more beneficial if it just had tips and tricks vs conversation. Seems as though it's already losing its way.

[Philippe Hurbain]

Clearly I goofed somewhere - works perfectly.