Final Design

An Overview of the Mini Wirewalker

The current Mini Wirewalker has a cam that allows the profiler to descend along a rope using the force of ocean waves. The cam consists of a set of races with rollers that sit inside a set of jaws. The jaws are shaped such that when the races move downwards, they also clamp together on the rope; when the races move upwards, they move apart and allow the rope to move freely. As a wave moves and buoy-wire-weight system down, the Mini Wirewalker descends with it by clamping onto the wire. As the buoy-wire-weight system moves up with the wave, the Mini Wirewalker unclamps from the wire and glides downwards under its own momentum.

In order for the Mini Wirewalker to function properly, the cam mechanism needs to be disengaged at the bottom of the profile to allow the Mini Wirewalker to return to the top of the profile utilizing its own inherent buoyancy. When the Mini Wirewalker reaches the top of the profile, the cam mechanism needs to be engaged again for it to start its descent. In order to disengage and engage the cam mechanism, there is a push rod going through the Mini Wirewalker with a shaft collar on it. When the push rod is pushed up, the shaft collar forces the race to remain permanently in the upward position; when the push rod is pushed down, the shaft collar moves to allow the race to move freely. In order to ensure the push rod is in the correct position at all times, a latch mechanism is used.

Races

The roller races were redesigned to improve the profiling performance of the Mini Wirewalker. The race cam is how the Mini Wirewalker is able to move down despite the Mini Wirewalker’s inherent positive buoyancy. As the buoy-wire-weight system moves down with a wave, the races clamp onto the wire, moving downwards with the system. When the buoy-wire-weight system moves up with a wave, the races unclamp, allowing the Mini Wirewalker to keep gliding downwards with its previous downward momentum. Thus, it is important that the race is capable of clamping and unclamping properly from the wire for maximum efficiency. The new races utilize an alternative assembly method - pins are press-fit into the rollers instead of the race frames. This prevents the warping of the race frames found in the original design due to uneven stresses caused by press-fitting the pins. With the elimination of the warping, the new design allows for more effective clamping on the profiling wire during descents, as well as a smoother profile on the Wirewalker’s ascent.

Current Race Design - notice the off-centered wheels.

Redesigned race compared to original race design.

Left image - original pin-roller assembly (left) vs new pin-roller assembly (right).

Right image - deformation of original design (top) vs deformation of new design (bottom)

Internal Deformation Cam

The mechanism for changing the direction of the profile was changed from a magnetic switch to a constant force cam-spring mechanism. The cam-spring mechanism consists of a cam and follower to lock the Mini Wirewalker in descent or ascent mode as shown in Figure. The cam is fixed to either side of the body of the Mini Wirewalker with the follower sandwiched in between. The follower is rigidly attached to the push rod and has two cantilevered beams that interact with the cam. As the push rod is moved up or down, the follower moves with it, squeezing the two cantilever beams through the cam. The deformation in the follower provides a constant spring force that the force acting on the operator, the threshold force, needs to overcome. This makes it so only at the top and bottom of the profile, when the Mini Wirewalker collides with the surface buoy or the bottom weight, will the direction of travel be switched.

We also had to decouple the motion of the cam-spring mechanism from the motion of the race cam so that switching will be allowed to occur. To do this, compression springs are placed above and below the race around the push rod. When changing from descent to ascent mode, as the follower is pushed upwards, the springs apply a net force opposite the direction of the follower motion until the midpoint of the follower’s travel, keeping the races in the descent configuration. At the midpoint, the springs have no displacement, which means there is no net force from the springs. Once the follower has passed the midpoint, the springs apply a net force upwards, locking the races in the ascent configuration. Changing from ascent to descent mode follows a similar pattern.

The Operator and Angular Displacement Reduction

The operator was modified to be recessed into the nose fairing. The operator would require a modification to the weight and buoy attached to the profiling wire - an extended protruding cone would be necessary in order to correctly interface with the new recessed design. In the up position, the operator would be too large to enter the recess - only direct interaction with the buoy or the weight would reduce the operator’s effective geometry and allow the position to change. With this, the switch would be much less likely to be influenced by the high variation of forces caused by typical ocean dynamics and, therefore, fully change positions. Furthermore, the recessed operator would allow for excess forces to be transferred directly to the body of the Wirewalker as opposed to the more delicate cam and follower mechanism described above.