in normal code of 3D drawing
the forces line are drawn correctly with the arrow head pointing in the direction correctly.

but in 3D Java the forces arrow head is pointing opposite to the size.
probably the variable "sign2" flip the size of Y is making the 3D java inaccurately display?

the source file is here Ejs Open Source Direct Current Electrical Motor Model Java Applet ( DC Motor )
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266.msg4902#msg4902