FreeCAD: Sticker Sketch and Text

Sometimes you need to model a special part like a shift drum for a motorcycle gearbox or something more simple like putting text on your perfectly modelled cup of coffee. While the content of this post does not completely solve any of this problems, it shows an important step forward. I'm doing this because of its similarity with some parts of the sheet metal workbench core.

What it does is to roll around a cylindrical surface a sketch or a text string. Code at the end of the post.

Sketch sticker:

This is a plain sketch tangent to a cylinder, with a random polygon inside:

 

The script rolls the sketch along the cylinder surface. Only straight lines at the moment.

 

Text sticker:

Equal to the previous one but with strings. The font must must be made only of straight lines.

 

It works for any face orientation (but not character length, this will be improved )

Text Sticker Code:

"""
Javier Martinez Garcia  2015  GPL
"Text sticker" script
"""

import Draft
from math import sin, cos, pi

BaseCylinder = Gui.Selection.getSelectionEx()[0].SubObjects[0]

# Cylinder axis:
for edge in BaseCylinder.Edges:
  if str(edge.Curve)[0] == "C":
    AxisPoint = edge.Curve.Center
    AxisDirection = edge.Curve.Axis
    CylinderRadius = edge.Curve.Radius
    break

# For text string:
FaceList = []
SelStrings = Gui.Selection.getSelection()[1].Shape.Wires
wire0 = SelStrings[0]
p1 = wire0.Edges[0].Curve.StartPoint
p2 = wire0.Edges[0].Curve.EndPoint
p3 = wire0.Edges[1].Curve.EndPoint
va = p1 - p2
vb = p3 - p2
SketchNormal = ( va.cross( vb ) ).normalize()
TangencyPoint = AxisPoint + SketchNormal*CylinderRadius
CylRevPlane = ( SketchNormal.cross( AxisDirection ) ).normalize() # perpendicular

for wire in SelStrings:
  def H( n, m ):
    #Hamilton product
    w = n[0]*m[0] - n[1]*m[1] - n[2]*m[2] - n[3]*m[3]
    i = n[0]*m[1] + n[1]*m[0] + n[2]*m[3] - n[3]*m[2]
    j = n[0]*m[2] - n[1]*m[3] + n[2]*m[0] + n[3]*m[1]
    k = n[0]*m[3] + n[1]*m[2] - n[2]*m[1] + n[3]*m[0]
    return ( w, i, j, k )

  def RotateVector( V, Axis, alpha ):
    #Rotate 3d vector with axis and angle using quaternions
    csa2 = cos( alpha / 2.0 )
    ssa2 = sin( alpha / 2.0 )
    R = ( csa2, ssa2*Axis[0], ssa2*Axis[1], ssa2*Axis[2] )
    RT = ( csa2, -ssa2*Axis[0], -ssa2*Axis[1], -ssa2*Axis[2] )
    V = ( 0, V[0], V[1], V[2] )
    RV = H( H( R, V ), RT )
    return ( RV[1], RV[2], RV[3] )

  #projectpointocylinder
  def point2Cyl(p):
    # input p = FreeCAD.Vector( x, y, z )
    L0 = FreeCAD.Vector(p)
    L1 = FreeCAD.Vector(p)
    E_TGL_P0A = L0.projectToPlane( TangencyPoint, CylRevPlane )
    E_TGL_P0B = L1.projectToPlane( TangencyPoint, CylRevPlane ).projectToPlane( AxisPoint, SketchNormal )
    VBA = E_TGL_P0A - E_TGL_P0B 
    VBA_N = (E_TGL_P0A - E_TGL_P0B  ).normalize()
    ARC_RAD = ( p - E_TGL_P0A ).Length / CylinderRadius
    # Turn direction
    Aux_VRotA = FreeCAD.Vector( RotateVector( VBA_N, AxisDirection, ARC_RAD ) )
    Aux_VRotB = FreeCAD.Vector( RotateVector( VBA_N, AxisDirection*-1, ARC_RAD ) )
    if (Aux_VRotA - p ).Length > ( Aux_VRotB - p ).Length:
      VRot =  Aux_VRotB

    else:
      VRot = Aux_VRotA

    RP0 = FreeCAD.Vector(VRot).multiply( CylinderRadius ) + E_TGL_P0B
    return RP0
  
  
  WireBS = []
  for edge in wire.Edges:
    points = []
    for i in range(100):
      p = edge.valueAt( edge.Length*i / 100.0 )
      rp = point2Cyl(p)
      points.append( rp )

    rp = point2Cyl( edge.Curve.EndPoint )
    points.append( rp )

    SPL = Part.BSplineCurve()
    SPL.interpolate( points )
    SPL = SPL.toShape()
    WireBS.append( SPL )
  
  Face = Part.makeFilledFace( WireBS )
  FaceList.append( Face )


Compound = Part.Compound( FaceList )
Part.show( Compound )

To use it,  create a cylinder, place a string tangent to it; select the cylindrical surface and the text; run the script. Is very important that the font type of the text is made from straight lines, otherwise it will fail. The font I've used for testing is "UASquare".

Next step is to get it to work with circular edges.

UPDATE 1


The script for sketches is almost working, some screenshots:

Top view of the generated frame:

Generated frame:

This is the step that I'm trying to automatize:

Create faces from edges, create shell from faces, create solid from shell.


Bye!!

FreeCAD: Shell Ecomarathon Prototype Cover

 ... or FreeCAD to the real world without 3d printing, but a 3 meters CNC mill:

 

Updated ( because we won!! :D )

Prototype Dátil 15 wins the European SEM on Ethanol

 

UPDATED: 

The result: 

On the news

 The story:

I am member of the UMH Team, a group of students that build a prototype car to race at the Shell Ecomarathon, an event that this year takes place at Rotterdam. Currently, we are in the first position of the spanish championship, leading it in the combustion category, with a fuel consumption of 1223 kilometers / litre of ethanol. In the European competition, we have been at the top ten, but past edition we finished 13th at combustion category and 3rd on ethanol.

This year we are building a completely new car that we hope bring us to the podium.

What I am showing here is the cover of the new prototype, that I designed using FreeCAD, simulated using SolidWorks, and later converted to CNC code using Hypermill. Special thanks go to Volund Group for their help and support.

The FreeCAD part:

The cover is designed using already existing tools, basically is a loft going through several sketches that I placed using a simple script.

This is the first one I did, just to test if FreeCAD was able to acomplish this work.

The car frame was made with Autodesk Inventor and imported as IGES, then I started to create the sketch-ribs and finally a loft through all them. I adjusted the sketches to obtain the desired shape. Once happy with it, I made the windows and a basic visibility test to ensure we are compliance with the rules of the race.

The rules specify that a pilot must be able to see a polar array of cylinders that are around the car with an angle of 30 degrees between each one.

Thanks to FreeCADs perspective view, I could check window sizes and do some optimization.

 

This is the pilot's point of view

Simulation:

The covering was simulated using SolidWorks, resulting in a Cx of 0.33.

 

Milling:

Once we performed another tests and confirmed that everything was ready, we started to machine a foam block to create a positive mould. We have used a medium-sized CNC milling center (Volund Group) that can handle the 3000 mm of length of this car:

Raw block:

 

Rough pass:

Smoothing pass:

 

The smoothing pass is finishing as I write this. What we are doing next is to epoxy and fiberglass it to create the negative mould and then, do the carboon fiber cover. I will edit this post to upload finished pictures.

I hope this serves an example of real world usage of FreeCAD, beyond 3D printing.

Maybe I do a tutorial to show how to model surfaces like this prototype cover, stay tuned. 

Bye!

FreeCAD: Mechanical 3D scanner using Arduino

Scanning 3d objects mostly relies on several cameras and complex software, so it is not a low budget project. But I want to show you this quick idea I got to virtualize real models using scrap parts, Arduino and FreeCAD:

A 3 degrees of freedom arm that knows its position by the variable resistors that form its joints.
The arduino reads this resistors and prints the code by serial, where a python script running inside FreeCAD waits for the data.

I'm impressed with its accuracy because it recreates the real world objects with some kind of precision, in spite of being poorly built.

This photo is an example:

The propeller seen in the first picture:

With a better built arm, I'm sure this can improve enough to be usable.