My students and I ran your  "particle in a crossed E and B field" simulation  today.  It appears that the axes shown in the applet are not the axes the program reads. For example, if I click and drag the velocity vector to a point along the +x axis, the program does not show (+vx, 0, 0) as expected. Please could you check into this and contact me?
A physics teacher sent me the above email message.
I am sorry that I did not write it clearly about how to change the initial velocity in the above applet.
Because I want user to be able to change initial velocity in 3D. However, the screen is 2D.
So user can use mouse to change the initial velocity either in the X-Y(Vz=0), Y-Z(Vx=0) or Z-X(Vy=0) plane.
Please see the attached file to find out how to switch between the above 3 different planes (Click in different region to switch between plane).