RecursionLimit while forming lagrangian in modeling of spherical pendulum - recursion

Question

I am new to Mathematica and this gives me headache. I was modeling spherical pendulum using rotationary matrices and it gives me reclim exception at forming lagrangian (L=T-V). Any idea where is the recursion and where is the problem? (I studied documentation but i can see nothing helpful there). File: Download
In[55]:= Clear["Global`*"]
p2 = {0, 0, -L}
Out[56]= {0, 0, -L}
In[57]:= R10 = {{Cos[\[Theta][t]], -Sin[\[Theta][t]],
0}, {Sin[\[Theta][t]], Cos[\[Theta][t]], 0}, {0, 0, 1}}
Out[57]= {{Cos[\[Theta][t]], -Sin[\[Theta][t]], 0}, {Sin[\[Theta][t]],
Cos[\[Theta][t]], 0}, {0, 0, 1}}
In[58]:= Grid[R10]
Out[58]= \!\(
TagBox[GridBox[{
{
RowBox[{"Cos", "[",
RowBox[{"\[Theta]", "[", "t", "]"}], "]"}],
RowBox[{"-",
RowBox[{"Sin", "[",
RowBox[{"\[Theta]", "[", "t", "]"}], "]"}]}], "0"},
{
RowBox[{"Sin", "[",
RowBox[{"\[Theta]", "[", "t", "]"}], "]"}],
RowBox[{"Cos", "[",
RowBox[{"\[Theta]", "[", "t", "]"}], "]"}], "0"},
{"0", "0", "1"}
},
AutoDelete->False,
GridBoxItemSize->{
"Columns" -> {{Automatic}}, "ColumnsIndexed" -> {},
"Rows" -> {{Automatic}}, "RowsIndexed" -> {}, "Items" -> {},
"ItemsIndexed" -> {}}],
"Grid"]\)
In[59]:= R21 = {{Cos[\[Phi][t]], 0, -Sin[\[Phi][t]]}, {0, 1,
0}, {Sin[\[Phi][t]], 0, Cos[\[Phi][t]]}}
Out[59]= {{Cos[\[Phi][t]], 0, -Sin[\[Phi][t]]}, {0, 1,
0}, {Sin[\[Phi][t]], 0, Cos[\[Phi][t]]}}
In[60]:= Grid[R21]
Out[60]= \!\(
TagBox[GridBox[{
{
RowBox[{"Cos", "[",
RowBox[{"\[Phi]", "[", "t", "]"}], "]"}], "0",
RowBox[{"-",
RowBox[{"Sin", "[",
RowBox[{"\[Phi]", "[", "t", "]"}], "]"}]}]},
{"0", "1", "0"},
{
RowBox[{"Sin", "[",
RowBox[{"\[Phi]", "[", "t", "]"}], "]"}], "0",
RowBox[{"Cos", "[",
RowBox[{"\[Phi]", "[", "t", "]"}], "]"}]}
},
AutoDelete->False,
GridBoxItemSize->{
"Columns" -> {{Automatic}}, "ColumnsIndexed" -> {},
"Rows" -> {{Automatic}}, "RowsIndexed" -> {}, "Items" -> {},
"ItemsIndexed" -> {}}],
"Grid"]\)
In[61]:= p0 = R10 . R21 . p2
Out[61]= {L Cos[\[Theta][t]] Sin[\[Phi][t]],
L Sin[\[Theta][t]] Sin[\[Phi][t]], -L Cos[\[Phi][t]]}
In[62]:= v0 = D[p0, t]
Out[62]= {-L Sin[\[Theta][t]] Sin[\[Phi][t]] Derivative[1][\[Theta]][
t] + L Cos[\[Theta][t]] Cos[\[Phi][t]] Derivative[1][\[Phi]][t],
L Cos[\[Theta][t]] Sin[\[Phi][t]] Derivative[1][\[Theta]][t] +
L Cos[\[Phi][t]] Sin[\[Theta][t]] Derivative[1][\[Phi]][t],
L Sin[\[Phi][t]] Derivative[1][\[Phi]][t]}
In[63]:= T = 1/2 m v0 . v0 // Simplify
Out[63]= 1/2 L^2 m (Sin[\[Phi][t]]^2 Derivative[1][\[Theta]][t]^2 +
Derivative[1][\[Phi]][t]^2)
In[64]:= V = m {0, 0, g} . p0
Out[64]= -g L m Cos[\[Phi][t]]
In[65]:= L = T - V
During evaluation of In[65]:= $RecursionLimit::reclim: Recursion depth of 1024 exceeded. >>
Out[65]= Hold[g L m Cos[\[Phi][t]]]