How to add rubber belt to a model

How to add rubber belt to a model
I’m making a model in MLCad (3.40 if that would matter) and I need a rubber belt in it.

It is just a simple use: a Technic bush 1/2 (#4365a) placed on an old 9V motor (#2838c01) and connected with a belt to Technic wedge belt wheel (#4185) directly above it. And I find it really difficult to get the position and size right.

I found here thread titled “Rubber bands” in which most important (for me) was another link to page “Modeling rubber belts”. The page indeed helped by providing radius of the Technic parts so now at least I knew what to enter for “R1” and “R2” in “Rubber Belt Generator”.

But how should I know what the dimensions (“X” and “Y”) are? Luckily X is 0 in my case. But the other? How do I know on which height an axle/hole is within Technic brick? How do I know on which height motor axle is placed? I guess that to the difference between centers of those axles I should also add both radius to have the height?

Then after solving that how do I know on which position to place that rubber belt so that it aligns well with the Technic parts?

Is there any software to just point two parts (likely limited to some small set of supported parts) and have a rubber belt connecting them generated?

What I find disturbing is that this is entered not as a “Part” but “Belt”. Is it something specific for MLCad? Will other software be able to “understand” that?

Are there any “predefined” values (in particular for rubber belt thickness) of the “standard” LEGO rubber belts like K3 and so on?

And since I’m already here I expect to have similar questions about pneumatics and electrical cables. Any solutions here?
Re: How to add rubber belt to a model
You can try taking measurements using the attached file I use constantly.

Attached Files
.dat   axis32x.dat (Size: 894 bytes / Downloads: 4)
Re: How to add rubber belt to a model
I assume you are looking for LSynth (

You can do funny things with that, but I can not be of great help on this Sad

That is for any bendable part. If you read how it works, you know what to do.

Please see also the really good tutorial from holly-wood (
Re: How to add rubber belt to a model
rubber belts, pneumatic hoses, cables:
indeed, it's lsynth you're looking for.

mlcad supports it natively.

it is very simple to use: you just put "constraints" into your model, ie. placeholders
at certain places where your cable/rubberbelt/hose should "go through".
then you simply hit a button, and the tool will generate the 3d data like a "connect the points"
drawing, using the 3d sweep technique, ie., by repeating a small 3d object along the path given by your constraints.

my setup is that I've put all lsynth parts into a dedicated folder ldraw/lsynth,
and have added this folder to mlcad.ini and to ldview (use the "file" menu).
now both tools can use them, and mlcad can run lsynth from its gui.
Re: How to add rubber belt to a model
Indeed LSynth did it! Bellow I will describe the process in MLCad for those who will get here while looking for similar info. (Keep in mind that the holly-wood tutorial – – covers mostly hoses rather than belts and bands.)

  1. From menu Extras / LSynth select item Add Command...
  2. A dialog shows, select there “23 – RUBBER BENT” or “24 – RUBBER BELT”.
  3. This will add three COMMENT items to the model: “SYNTH BEGIN RUBBER_BAND 16”, “SYNTH SHOW”, “SYNTH END”.
  4. Between “SYNTH SHOW” and “SYNTH END” add parts on which the rubber bent/belt is to be mounted. Bushes, wheels and so one. There are a few supported parts. It is important that you have to add those parts twice. Once in the model normally, as you build. And for the second part between the LSynth commands. Those second ones will be hidden in the process so in the end you will see just one of them.
  5. At this point you will still see nothing since you just entered commands for LSynth to process – but it didn’t process the yet.
  6. Now from menu Extras / LSynth select item Run LSynth. This will process the commands and add actual parts so you will now see the rubber bent/belt. This will also hide (but not remove!) the parts that were added between LSynth commands.

But I still have some more questions.

I think that what I don’t like mostly about this approach is that I have to have the extra parts for LSynth to process. So if I will modify the original part I have to remember about modifying the second (hidden) one. And then also rerunning LSynth.

I considered using those dedicated parts as actual model parts so there are no copies. But it requires showing them again after running LSynth. And also it means that most likely at least one of the parts will be a lot “out of order” in model build sequence.

Also how is this better from Rubber Belt Generator in MLCad? Sure it seems somewhat simpler by avoiding manual calculations (although those “manual calculations” could be done be a more user friendly user interface!). But you get lots of parts rather then a single one. (Obviously I limit here myself to belts/bands over two parts – over that Rubber Belt Generator is no longer an option...)
Re: How to add rubber belt to a model
In my upcoming 1.3 version of LDCad you can generate any kind of multiwheel band without segment dependencies. Those bands will show up as static parts in any LDraw renderer so you could go back to MLCad afterwards.

See also the attachment of this post:
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