I don't think we want to express it in otherframe, but rather, use the provided definitions; e.g.
```
>>> A.ang_vel_in(N)
u1 * e_N_x
>>> B.ang_vel_in(A)
u2 * e_A_y
>>> B.ang_vel_in(N)
u1 * e_N_x + u2 * e_A_y
```