In this paper, we first derive Hamel s variational integrators for open-chain manipulators in the framework of geometric mechanics, where the roots of Hamel' s variational integrators are found by feedback control. Next, we use the above algorithm to solve a forward dynamics problem in reaction planning. As a result, the gyroscopic force is introduced to replace the repulsive force, thus avoiding the local minima dilemma of the artificial potential method, and realizing real-time obstacle avoidance for the whole manipulator. Finally, the effectiveness of the proposed algorithm is illustrated via two numerical examples.