6.0 Mechanical Aspects
6.1 The Coiled Cable
The team have to redesign the coiled cable so that it can fit inside the body of the buoy. With many of the old designs, the cable is released into the ocean after the anchor. With the cable inside the buoy it will be easier to recover the buoy.
When the first designs were drawn, the coiled cable reel was vertical. This was going to create problems during deployment because the orientation would crate a turning effect of the anchor as it was lowered to the sea floor. The team changed the design of the reel to be horizontal, it this wasn’t changed the anchor would spin with aspect to the vertical axis and this would have caused problems with the tangling of the wire. This was much more
suitable and caused no problems with deployment.
This was the teams first developed design. The three gears connect each other. The first gear connects with handle. A motor can be used to turn the handle to wind/unwind the cable. The second gear connects with the spindle and the coiled cable cylinder. This is the most important part for coiling the cable. The third gear connects with the link which is in-between the gear and entire thread.
Figure 18: Diagram of the coiled cable mechanism.
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When the motor drives the first gear, the second gear will start to turn. This will make the coiled cable cylinder start to turn and the third gear will also turn. Using the slider-crank mechanism, the gear will turn and make the entire thread move around. The purpose of this mechanism is to make sure that the cable evenly distributed on the coiled cable cylinder.
The handle is only for use in emergencies. There will be a cylindrical motor inside the spindle which will turn the gears and therefore move the link and thread.
This coiled cable mechanism had a problem. When the handle was turned once, the coiled cylinder also turned once. Therefore, the entire thread only moved one cycle. This means that
Figure 21: A rendered CAD drawing of the coiled cable mechanism.
Figure 20: Top view of the coiled cable mechanism.
Figure 22: Side view of the coiled cable mechanism.
only one loop was created on the coiled cylinder. This is very inefficient and to combat this the team changed the design.
The slider-crank mechanism converts the rotational motion into linear motion. This is shown in the figure 23 below. When the crank (2) rotates once, the link (3) will make the slider (4) move left and right.
Figure 24 is the team’s second design. Here the three gears are connected to each other, but the slider-crank mechanism was changed to the Geneva mechanism. This means that the entire thread was changed to the rack. Both of these functions are the same. They enable the cable to be evenly distributed on the coiled cable cylinder. However, there are some differences.
Figure 24: The second coiled cable mechanism.
Geneva mechanism
Figure 23: The slider-crank principle.
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Using the Geneva mechanism this enables the the mechanism to have more loops on the coiled cylinder in one turn. The green component is like the gear and the yellow component is like the rack.
Figure 25: The Geneva mechanism.
However, there was problem with this due to the use of the rack. It takes up too much space when the rack moves in one cycle. It would need to have a space double the length of the rack. This would increase the dimensions of the team’s design by two.
Geneva mechanism 2 1
Figure 26: The Geneva mechanism shown on the coiled cable mechanism.
Figure 27 is the team’s final design of the coiled cable mechanism. This is a much simpler way to distribute the cable evenly on the coiled cylinder. This device connects with the motor.
This design resembles a screw thread. As it turns the cable rolls into the spaces between the peaks.
Figure 27: The final coiled cable mechanism.
Type of Motor Advantages Disadvantages
Brushless
Stepper Motion control.
Can be used in steps and can hold
More efficient – if less torque is required current is reduced.
Bigger in order to accommodate the additional heat of operating at maximum current all the time.
AC Robust and sturdy – can last a lifetime. cannot be used for traction and lifting loads.
After looking at the advantages and disadvantages of the two different motors, the team decided that the best motor to use for our application is the AC motor. This is because it is low maintenance, does not produce sparks and can last a lifetime. The motor will be powered by an external source of energy upon recovery. The motor will not be used during deployment. Solar panels produce DC current and would therefore need an inverter. This would create extra weight which is not needed.
The pressure can be released by simply moving the bottom object upward, with the initial impact of the buoy on the waters surface. lead to the pressure on the clamp holding the anchor to disappear allowing the anchor to release and fall safely to the holding latches could be unreliable. Whilst keeping the main design concept of them, it was adapted slightly.
It was decided that the latches would be more reliable if an automatic spring mechanism was built in. This would ensure the release of the anchor to the ocean floor.
The design chosen is shown in figure 31.
Here is is shown that the anchor (green) is attached to the surface buoy (blue) by a latch that is holding the weight due to the direction of force that the anchor contains.
Figure 29: Latch design 1A.
Figure 30: Latch design 1B.
Figure 31: Spring loaded latch design.
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direction of force changes and the anchor is pushed upward causing the surface buoys latches to release the anchor. This process is helped with the use of a spring (yellow) that can ensure that the latch doesn’t return to the previous position. These latches are crucial to ensure to the design of a smaller more compact design as it releases the anchor upon deployment, which was one of the team’s main criteria.
To help spread the weight of the anchor evenly across the bottom of the buoy the latches are equally spaced on the underside of the buoy. This decreases the pressure on each latch in order to hold the heavy anchor in position. To further help distribute the weight of the buoy the latches are screwed into an internal frame (see figure 32 below) that is attached to the underside of the buoy. The material of the frame is cast iron which is a very strong and heavy metal. The frame will have the double purpose of acting as the counter weight for the surface buoy. This will help to keep the buoy in an upright position.
Figure 32: The final latch design.
controlled from distances of up to 6000m. The standard release is motor actuated, alternatively a relay output may be provided to energise an external mechanism.
The battery life of the package is dictated by how often the latches are used. The mechanism only draws power during the attachment and release when the motor is driven.
The transponders have a single-chip microcontroller at their heart for timing and control functions. The transponder remains in a low power sleep mode until commanded by the Transponder Control Unit. This means that the battery life of these mechanisms can last anywhere from three months to ten years depending on the size and use of the attached batteries.
However, as the project team will be using an innovative new coiled cable the remote controlled acoustic release will not be necessary in this design. The team will use mechanical release clips that will function on command by sending an electromagnetic current down to the clips releasing the seismometer from the surface buoy. This is shown in figure 34 below.
Figure 34 shows the coiled cable from the surface buoy attaching to both the anchor and seismometer at the bottom of the ocean. The seismometer will still be connected to the anchor, but won’t have the ability to float away. This relieves the tension between the surface buoy and
Figure 33: An acoustic release.
V = volume of buoy below water (m3) ρ = density of sea water (1025 kg/m3) g = gravity (m/s2)
m = mass of surface buoy (kg)
𝑚 = 1025 × 0.222049832
∴ 𝑚 = 227.6𝑘𝑔
ρ = density of concrete (2300kg/m3) V = volume of anchor (m3)
m = mass of anchor (kg)
𝑚 = ρV
𝑉 = 𝜋 × 0.25 N × 0.4 + 5 × 0.04 N × 𝜋 × 0.1
∴ 𝑉 = 0.08105𝑚R
𝑚 = 0.08105 × 2300
∴ 𝑚 = 186.415𝑘𝑔
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