import sympy as sm
import sympy.physics.mechanics as me
me.init_vprinting(use_latex='mathjax')

l = sm.symbols('l')
q1, q2, u1, u2 = me.dynamicsymbols('q1, q2, u1, u2')

N = me.ReferenceFrame('N')
A = me.ReferenceFrame('A')
B = me.ReferenceFrame('B')

A.orient_axis(N, q1, N.z)
B.orient_axis(N, q2, N.z)

O = me.Point('O')
P1 = me.Point('P1')
P2 = me.Point('P2')

O.set_vel(N, 0)

P1.set_pos(O, -l*A.y)
P2.set_pos(P1, -l*B.y)

P1.v2pt_theory(O, N, A)
P2.v2pt_theory(P1, N, B)

print(P1.vel(N).express(N))