[Solved] Draft/PathArray--Expected Behavior?

[ppemawm]

Chrisb might be on to something with his approach. I'll try that again with different combinations of sprocket radii and no. of teeth.

Not to beat a dead horse but wanted to let Chrisb know that his approach works closely enough for my purpose. This picture shows the result of using Draft->PathArray with an offset path for roller chain objects that include links, rollers, and pins:

Detail at the tangency point where the roller leaves the sprocket pitch line. Offset path shown in white.

roller_chain3.jpg (83.57 KiB) Viewed 930 times

It should be noted that although the links, rollers, and pins can be exactly aligned in the sprockets using this approach, there is a small misalignment in the straight sections as shown below in a simplified set of sketches:

Detail showing alignment/misalignment of links and pins located on the offset path. Red circles indicate the pins.

links&pins.jpg (126.85 KiB) Viewed 930 times

Note that the error will be larger for smaller diameter sprockets and/or longer pitch links.

The PathArray path is offset from the required path by using constraints related to the pitch length of the links:

The offset path (green) is created using only constraints and the link pitch length (15 mm). The offset path is constrained tangent to the line representing the link pitch length with its endpoints constrained to the required path (blue). The PathArray objects are located at the global origin. The link is centered on the origin and the pin offset is pitch/2.

Offset_Path.jpg (42.57 KiB) Viewed 930 times

links&pins.FCStd

(58.89 KiB) Downloaded 46 times

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6706 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: f86a4e411ff7848dea98d7242f43b7774bee8fa0
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17

[chrisb]

Not to beat a dead horse but wanted to let Chrisb know that his approach works closely enough for my purpose.

Good to hear.
You cannot stay on the inner circle when it comes to the change into the straight. I am not yet sure where and how to move to the outer (blue construction) line. I will think about it, but it may take a couple of days.

[ppemawm]

I am not yet sure where and how to move to the outer (blue construction) line.

The only thing I have come up with so far is to downgrade each PathArray twice (PathArray->Compound->Solid) to isolate the individual solids. The solids on the straight portions and those at the tangency points can then be moved or rotated into place (tediously) using Placement properties.

This may not be so bad because the link PathArray has to be downgraded to individual solids so that half of them can be moved axially to separate the links anyway. Each half can then be re-compounded, copied, and moved to the opposite side of the roller to complete the chain.