FreeCAD
In this project, the model was created from dimensions scaled from photos of a commercial step ladder as shown in the following screen shot. All parts are in the same file, each of which were created from modified carbon copies of the top level master sketch. In this manner it is possible to articulate the moving parts of the model by changing one constraint defined in the master sketch. All of the moving parts follow the action of the master sketch.
- The model tree includes all the individual parts, standard fasteners, merged parts from a file defining a generic rivet with variable length, and Assembly4 model containing all of the rivets.
Standard fasteners from the Fasteners workbench were attached to appropriate edges in the completed model which is not always the best approach since their position can change if any of the model features are modified due to the topological naming problem. It is more robust to add circles at vertices in the master sketch which can then be used to locate the fasteners. Or, more recently, use the fastener tool in Assembly4 workbench similar to what was done in the below referenced second project. - Picture1.png (315.67 KiB) Viewed 1266 times
- This is the master sketch used to capture the design intent, main dimensions, and a constraint (opening) that can be changed to articulate the sketch. The sketch was created and constrained at an arbitrary opening. It is important at this point to exercise the sketch in small steps through the complete range of the variable to verify that the sketch solution is valid for all positions.
Note that the support brace on the left of the sketch was fixed by locating it at the origin and constraining it with a fixed angle in order to simplify the sketch as much as possible for the solver.
All bodies were created by starting with a Edit>Duplicate of a carbon copy of this master sketch toggled to construction geometry. Construction geometry is added and constrained to the appropriate edges and vertices of the carbon copy. It is important that each feature of the body is somehow related to the carbon copy construction geometry. No external references are required with this method. - Picture2.png (260.9 KiB) Viewed 1266 times
- There are four different lengths of rivets in the model. These were generated by merging a parametric model into a part container from an external file and changing the length as required for each.
Assembly4 workbench was used to attach LCS's for each rivet to the master sketch vertices. These were then offset to their proper position using the LCS Attachment Offset property. - Picture3.png (155.29 KiB) Viewed 1266 times
- The model can be checked at all positions by changing the "opening" constraint of the master sketch in the model tree as shown. It takes about 18 seconds for the sketch solver to reposition all of the moving parts with a I7-2.5 GHz, 16 GB machine.
- step_ladder2.gif (353.56 KiB) Viewed 1266 times
- This locking mechanism was probably the most difficult to model since it is attached to a moving part. It sometimes takes some ingenuity to reference the construction geometry of the master sketch carbon copy. The alternative is to put more detail in the master sketch in the beginning. The master sketch needs to be simple but not too simple. One must carefully think through the modelling of each body at the master sketch stage with the top down approach.
- Picture5.png (417.84 KiB) Viewed 1266 times
I can place the 4.8 MB file on Dropbox for anyone interested. Please contact me via Private Message.
Zolko has recently added several improvements to the Assembly4 workbench that facilitate top down design including fasteners which I used in another project https://forum.freecadweb.org/viewtopic. ... 30#p349238 that was built from detail drawings. This workbench is evolving nicely, at least for my purposes. Kudos to the developer
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.18719 (Git)
Build type: Release
Branch: master
Hash: c021ff70debb106b27d03ed1707f4b05fcf385a6
Python version: 3.6.7
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)
