I was thinking about a way of celebrating this events, and last night I saw a .gif image about a flat mechanism at which I could be staring the whole day:
I don't know its exact name, but "double slider mechanism" seems appropriate. It belongs to the family of flat, four bar linkage mechanisms, and, possibly, there is no real use for this one. But it moves very smoothly, with the outer end of the rotating arm drawing some kind of ellipse.
The kinematics of this one are not too difficult (none of the family of four bar linkage mechanism are), and for the animation I have solved it in an analytical way.
# Javier Martinez Garcia August 2015 GPL V2.0 from PySide import QtCore from math import sin, cos, radians # retrieve the objects from the document slider_x = FreeCAD.ActiveDocument.getObject("Pad003002") slider_y = FreeCAD.ActiveDocument.getObject("Pad003001") arm = FreeCAD.ActiveDocument.getObject("Pad002001") # store initial placement (needed to restore initial position) slider_x_placement = slider_x.Placement slider_y_placement = slider_y.Placement arm_placement = arm.Placement # store object placements in a new variable r_slider_x_pl = slider_x.Placement r_slider_y_pl = slider_y.Placement r_arm_pl = arm.Placement def reset(): # function to restore initial position of the objects slider_x.Placement = r_slider_x_pl slider_y.Placement = r_slider_y_pl arm.Placement = r_arm_pl # In this mechanism, "i" represents the angle of the rod in degrees i = 0 # update function calculates object position as f(i) and increases i def update(): global i alpha = radians( i ) x = 150.0*cos( alpha ) y = 150.0*sin( alpha ) slider_x.Placement = FreeCAD.Placement( slider_x_placement.Base + FreeCAD.Vector( 150-x, 0, 0 ), slider_x_placement.Rotation ) slider_y.Placement = FreeCAD.Placement( slider_y_placement.Base + FreeCAD.Vector( 0, y, 0 ), slider_y_placement.Rotation ) arm.Placement = FreeCAD.Placement( arm_placement.Base + FreeCAD.Vector( 0, y, 0 ), FreeCAD.Rotation( FreeCAD.Vector( 0,0,1), i)) # update the scene FreeCAD.Gui.updateGui() # increase mechanism input position i += 1 # create a timer object timer = QtCore.QTimer() # connect timer event to function "update" timer.timeout.connect( update ) # start the timer to trigger "update" every 10 ms timer.start( 10 )
Download the .fcstd model and animation script here, on github.