r sqrt(X^2+Y^2) ""
dr airgap/2 ""
Bphi (-rmm.BX*Y+rmm.BY*X)/r ""
Br (rmm.BX*X+rmm.BY*Y)/r ""
T_arkkio intop_torque(r*L*Br*Bphi/mu0_const/dr) "Arkkio's torque method"