I and Daniel were talking about the reason why there are bounce and roll coupling, and the bounce should be the local gravity axis versus the arm angle.
I looked at old DCC document (T980044) and found that Y arm is almost parallel to the vertex local Y axis while X arm is almost parallel to the X end local X axis.
Below is a table of angle deviation from pi/2 between the relevant arm and the local vertical defined by the gravity. Deviation=0 means that the arm is orthogonal to the local gravity. FYI, the difference in the local gravity angle over 4km is about 2*pi*4km/40000km = 628 urad.
| EX (X end vertical VS global X) | EY (Y end vertical VS global Y) | IX (Vertex vertical VS global X) | IY (Vertex vertical VS global Y) | |
| LHO | 8 urad | 639 urad | -619 urad | 12 urad |
| LLO | 315 urad | 19 urad | -312 urad | -611 urad |
The bounce coupling is directl proportional to these numbers.
LHO EY is 80 times worse than LHO EX. At LLO EX is worse than EY, but LLO EX should be a factor of 2 better than LHO EY.
By Keita.
Roll mode:
If the roll motion happens in the plane that bisects the angle formed by the HR surface and AR surface, there's some coupling to length because of the wedge angle.
If that's the mechanism, the coupling depends on the centering on the mass.
By Keita