g = 9.8 k = 0.01 r = 0.006 R = 0.002 W = 6*2*Pi a = 3 s = NDSolve[{v'[t] == r*g*k*Cos[ Arg[W*R - w[t]*r*Cos[x[t]] - I*(v[t] + w[t]*r*Sin[x[t]])]] (Tan[ Arg[W*R - w[t]*r*Cos[x[t]] - I*(v[t] + w[t]*r*Sin[x[t]])]] - Tan[x[t]]), w'[t] == g*k*Cos[Arg[ W*R - w[t]*r*Cos[x[t]] - I*(v[t] + w[t]*r*Sin[x[t]])] - x[t]]/r, x'[t] == g*k*Sin[Arg[ W*R - w[t]*r*Cos[x[t]] - I*(v[t] + w[t]*r*Sin[x[t]])] - x[t]]/(r*w[t]), x[0] == Pi/4, w[0] == 10, v[0] == -0.01}, {x, w, v}, {t, a}, Method -> Automatic]
“I used arctan instead of Arg but it caused problem like 135= -45(degree). So I changed arctan to Arg but I got the error. Can someone help me?”
NDSolve::ndinid: Initial condition 0.712979 -0.701185 I is not in the range specified by the discrete variable NDSolve`s$ 60824. NDSolve::ndinid: Initial condition 0.712979 -0.701185 I is not in the range specified by the discrete variable NDSolve`s$ 60837.