@mptak said:
You might try changing the worldscale in the sketchy physics settings. I'm nowhere near a current sketchup installation or I would try it and tell you the outcome.
YES mptaK , you are right.
I changed the world scale in SP and now it works great . 
One more question for you all.
Why the function ICON applied to a small object ( a hinge or a spring) remain so huge and always have to resize it . Any tips to modify the scale of it too ??
T.I.A.
Red
Hi BOX,
I know some tips and tricks about SP learned from you all ( the experts)and watching some tutorial video from you-tube.
What I found is something weird, not reported anywhere !!!! 
Red
Hi TIG,
what I'm sayng here is that I applied the motor function to a small cylinder rotating horizontally ( it's 5 mm thick and 30 mm in diameter) , I discovered that it remains stationary till I resized it to over 100 mm in diameter .
See the attachment.
Red
It looks like SP doesn't work on small object.
Is there any known limit dimension to work with ?
Moving a circle under 30 millimeter of diameter seems doesn't work for me.
Am I doing something wrong ?
Red
OK , I got it .... 
I was just playing with sketchyphysics plugin because I am planning to make a simple automata using a piston like structure (FOLLOWER) and a rotary hinge ( CAM).
How to connect the follower moving vertically to the rotating circle .
Can anybody help me please.
T.I.A.
Red
