Bevel Gear

Today we did an exercise to rotate the torso horizontally from left to right (first gear), while the arm with the elbow straight as a stick rotated in Ni Chan (second gear).  The second gear’s rotation was driven by the first gear. The result was like how the train wheel turned, and the rod attached to the wheels moved along the rotation without changing direction.

The torso is attached to the arm in the same way as how a bevel gear works as shown in the diagram above. As the torso rotates, the arm must rotate proportionally. This is the result directly related to how it is set up. In action operation, it is key to start the arm rotation from the armpit. Another important part is that the action must be initiated by the kuas, causing the waist (torso) to rotate, in turn, causing the arm to rotate. When the torso must also be like a solid cylinder, when the waist (bottom part) turns, the shoulders/chest (top part) must turn together. This is said to have one action, while two different parts are moving/rotating in their own designated ways. In the future, there can be more than two gear discs attached together, one action drives many different individual movements. In taiji, this is known as when one part moves, all parts move.

The shoulder is where the split happens. It is the middle that is not involved in either side. No power should be added at the shoulder. This allows the dantian and the fist to be connected. The resulting action is called a "through fist/通拳", it is not a punch in the normal sense.

When observing others performing the same exercise, the following common mistakes are noted:
  1. The torso rotation is limited to above the chest - The arm rotation is only driven by the horizontal chest rotation. The bevel gear is still working in this way, however, it lacks an extra level of indirectness (the vertical distance) created when the kuas initiates the action.
  2. The two gear discs are not attached - The person is independently moving the arm and the torso trying to match the rotations and make them proportionally. The external appearance is almost the same as the intended outcome, but the mechanics are not.
  3. There are no two gear discs at all - When the person rotates the torso, the arm will change the direction that it is pointing at following the torso rotation.
  4. The torso is not one solid cylinder - When the person attempts to rotate from the kuas, the chest adds a separate action and does not follow the action from the kuas. The result is that there is a twist in the torso, the energy leaks at the left shoulder.
  5. The arm is pushed by the shoulder - The person uses power at the shoulder to push the arm out. The torso rotation is not involved, i.e. no bevel gear setup.
  6. Using the arm to punch - The person is using the upper arm to throw a punch.
In taiji, the concept of a bevel gear is very important in understanding how we should connect our various body parts.

The full instructional video can be found at