GT2 pitch = 2 mm. Pitch diameter = teeth × 2 / π. Belt length is computed
along the pitch line as: L = 2·√(C² − (R−r)²) + π(R+r) + 2(R−r)·asin((R−r)/C).
The belt-teeth count is rounded to the nearest whole tooth — pick a standard
closed-loop belt at or just above this number.