Motion Model

Predicted Behavior

Before collecting data, we created graphs of the expected behavior of our system. We modeled the position and velocity of both the seat and handle through two full strokes, noting the different stages of the drive and recovery.

Position of Seat

For the position of the seat when the user is rowing correctly (black), we anticipate the motion to be smooth throughout the leg extension. During the end of the drive and the beginning of the recovery, we expect to see a stable position because the legs, and therefore, seat shouldn't be moving during that time. The recovery should also look smooth and end in the catch position.

In red, we show the predicted adapted motion of the seat when the user bends their legs too early in the recovery. We anticipate that the seat will rest for a shorter amount of time, as the legs will begin to bend too early. We also predict that the motion won't be smooth through the recovery because as the arms begin to bend, the user's legs and seat would likely slow down to make space for their elbows to bend.

Position of Handle

We anticipate the motion of the handle to behave similarly to the position of the seat. Since both the drive and recovery should be continuous motions, we expect that the position curve will look smooth through both of these sections. Unlike the seat graph, the handle will move throughout the entire drive, so we don't expect to see a rest at the top of the graph.

If the user is rowing incorrectly, we anticipate that the recovery will look less continuous -- as the legs bend without the arms, the motion will likely look slower. During the time the arms and legs move together, we predict that the handle will have a higher velocity, and then even out near the end of the recovery.

Velocity of Seat

When the user is rowing correctly, we anticipate a spike in velocity during the leg extension section of the drive, decreasing to zero velocity while the arms pull and extend. We expect the recovery to look very similar to the drive, creating a negative peak.

If the user begins bending their legs too early, we expect the velocity to start decreasing earlier. We also anticipate a small dip in the recovery as the legs and seat slow down during the arm bend.

Velocity of Handle

The graph of the velocity of the handle was the hardest to predict because the legs, arms and upper body all contribute to its motion. We anticipated that the velocity of the handle would have a bit more of a plateau than the seat because handle is moving all throughout the drive so would have more time to reach its maximum velocity. When Brooke modeled a few practice strokes, they seemed to have a relatively smooth recovery with a sudden stop at the end as they approached the catch. Because of this, we thought the graph might look more triangular.

With an early leg bend (shown in red), we anticipate the velocity of the handle to start slowly as only the legs begin to move, speed up as they move together, slow a little bit once the legs move by themselves again, and finally slow down as the user approaches the catch.

Predicted Frequencies

We predict that each stroke takes around 3.5 seconds to complete, depending on the user's technique and their height, causing our principal frequency to be around 0.28 Hz. We expect that we might also see frequencies that are twice that of the principal frequency for oscillations that occur twice during the stroke (ie. movements that happen both during the drive and the recovery)

Informed Data Collection

We used our motion model to inform how we went about collecting data. We set our sample rate high enough that it would pick up both the macro frequencies of the stroke as well as the smaller motions that are associated with problems in the stroke. In addition, our motion model informed our use of sensors on the seat and handle specifically, as those are the points we considered to be the most significant motion-wise, allowing us to see the cumulative motion of the stroke (handle), the motion of the legs (seat) and the opportunity to see the motion of the arms & back (handle minus seat).