Vespa Front Lantern

An old design? Rust… Steel… And heavy. But for me elegant, classy and stylish. An old design full of spice and adventure ready. I remember going up a hill with my wife and at the middle the motor bike was struggling. Fortunately my wife improvised dismounted and run up the hill to saddle in again, what a funny moment.

Vespa 50s Round Front lantern
Vespa 50s Round Front lantern

Are you more curious? Take a look at Wikipedia Vespa in https://en.wikipedia.org/wiki/Vespa

Vespa front wheel

When we look at a vehicle being a car, a motor bike, they have wheels. Typically these vehicles have a suspension but even if they don’t have visually they will have some sort of elastic support and dampening effects even if coming from the structure.

Vespa_50s_scooter_front_wheel close up
Vespa 50s scooter front wheel close up

My vespa suspension performance is very bad, I really need to fix it. If I ride the bike with a second occupant the suspension gets fully loaded.

Going back to my school memories what concept simplifications would represent a wheel system?

Mass_Spring_Damper_for_Vespa

Sun bench Reloaded

Independent of the structures boundary conditions, shape… stresses tend to be smooth when the structure is subjected to a specific load, considering also there are no stress concentration zones. The sun bench structure works no differently. An interesting point is that the angled leg is weaker compared to the vertical part of the leg.

This work was done in FreeCAD from the geometry design to the FEM setup. Material data used was a simple isotropic ABS from FreeCAD database. The load considered was for a 100Kg load. Supports used were fixation lines at the profile bottom borders.

Sunbench stresses
Sun bench stresses
Sun bench
Sun bench

HandleBar model discoveries

Finally I get to see if FreeCAD is of any use.

Previously I described the problem which was to discover why Brompton bikes updated the handlebar design. I got curious to know if the top elbow would or not bend first and if the length between the two would make a great distance. All of this resorting to many assumptions and simplifications. (I am doing this for fun)

First off all I have a Brompton! I am one happy user.

Brompton handlebar
Brompton handlebar

Now The issue was the design differences, which you can checkout the new here:

2017 Brompton handlebar
2017 Brompton handlebar

And the old design here:

2015 Brompton handlebar
2015 Brompton handlebar

Our hands are positioned on the blue top zone and the handlebar is fixed on the blue bottom element.

I considered lower force justo to get an ideia, many direction could have been studied.

HandleBar model constraints
HandleBar model constraints

Then I selected my simulation package which in this case I opted for FreeCAD. And started meshing wright a way with Gmsh.

Handlebar mesh
Handlebar mesh

And now finally I got to the results part.

Handlebar bending result
Handlebar bending result for the version bellow 2017 model

From the image it seems that the lower elbow until the fixed support will take much of the stress. The bar height being bigger will increase torque which will increase the reaction force at the supports. Reducing the central bar between the lower and top elbow will increase handlebar strength. The only thing I can see that made them go for the previous geometry for the bellow 2017 model is design or manufacturing technical difficulties. Maybe it is harder to bend the single shaft with such low central support at each handlebar side.

FreeCAD works as expected… Good work open source comunity!

HandleBar model constraints: The Model & assumptions

I started showing two handlebar model versions (before and after 2017 model). Introduced my constraints into the handlebar, fixation and load location. But now what? The objective!!!! I wanted to know where was the weak spot of the handlebar. It has two elbows at each side. Where will the cracks start preferebly? I could just say 50% chance on any of the elbows but that would be to easy.

So why not Build the simulation model???? First check my previous posts:

Handlebar model constraints

Handlebar model case II

Handlebar mesh
Handlebar mesh

Forgetting about model accuracy I am just looking for the stress field.

My assumptions:

  • Isotropic material
  • No transient effects

Making the mesh was straight forward with FreeCAD. The two meshers in FreeCAD behaved differently in Gmsh I could not use the default values. I had to use max 1.8mm and min 0.8mm mesh size. On NetGen I used the default without any issues.

I am not saying that it was easy to setup things… I got many installation issue however in the end everything worked. Fortunatelly FreeCAD has a great forum that can help when in need.

FreeCAD forum post

On a next post I will look at the results…

Salome-Meca 2017 Is out

It looks like finally the CodeAster powered version of Salome is out… Hopefully it will introduce the much awaited improved GUI additions with support for adding constraints, loads, … everything needed for the simulation model. Salome-Meca 2016 failed in this field.

http://www.code-aster.org/spip.php?article303

Nostalgia, Bridges, Sirs and Madams

Today I got nostalgic… Traveling is the thing I most like to do!!! To plan and live intensely every possible experience in that specific place, city or moment in time. One of my last adventures was in London, It wasn’t the first time I have been there, but it looked as it was, for the tremendously fun moment’s I had. But the biggest memory I took home wasn’t a fridge magnet!! Well I fell in love for a bike and just not any bike. A Brompton bike. And I just had to bring it home…

The London Bridge
The London Bridge

Vespa in the hood

We see every day things that have really great designs, other which are terrible for our taste, others memorable in any time and age that are transversal to age, gender, location, …. Good old designs that were imagined with pencils and paper.

I still keep wondering how would those brains design with today’s tools??? How would they reimagine things with CAD (Computer Aided Design), CAE (Computer Aided Engineering), and CAM (Computer Aided Manufacturing).

Vespa In The Hood
Vespa In The Hood

Salome 8.2 Geometry

I read a lot of information about salome as a pre processor and post processor. Basically you can make a geometry create a mesh and then view results.

The GUI is quite simple at start.

Salome 8 Menu and Toolbar
Salome 8 Menu and Toolbar

As we start diving into this program we start to see it’s complexity. If we make a new project and open the geometry pane we see myrad of tools.

Salome 8 Geometry
Salome 8 Geometry

Although the way we manipulate sketches and solids is way easyier in spaceclaim or RS Mechanical 2 Salome is good enough to make parts. I also think FreeCad isn’t the perfect environment since it also has it’s gaps, however between one and the other I am starting to prefer Salome for its interface looks more clean. A good plus in Salome is that I can define veriables and use them when I create features. Then if I want to change anything it’s plain simple, however if I don’t create the variable and link it there is no other way to change it. This point for me could be improved in the future. Since if we need to change something after it’s done its not that friendly to do it with the GUI.

Salome 8_2 Geometry Table
Salome 8_2 Geometry Table

All in all it is a solid CAD modeler that is very usefull and in my opinion far better then design modeler from Ansys and on par with FreeCAD but way behind payed CAD packages like Unigraphics, Solidworks, Creo, Spaceclaim, … Although not as good as these professional packages I think that there is no shame on using it since it is sufficiently powerfull to build and anlyse models and I also question if it is necessary all the power of those heavy weight tools. Maybe if I was allowed to ask something I would ask for more natural part building and part manipulation and selection.

Improving Rendering in DS Mechanical 2.0

Some time ago I was noticing some rendering quality degradation on my screen. I noticed that maybe my customization values had change. In order to have nice graphics one just needs to change on the options menu the following.

Improving Rendering In Design Spark
Improving Rendering In Design Spark