Final Design

The final design for the project utilized an electronic timing system and a mechanical release system. Important and delicate parts were sealed from the seawater by a white PVC tube housing. One end had a static o-ring seal and a rotary o-ring seal. The other end was intended to be permanently sealed using resin and include a pressure release valve; the valve was not implemented in time so that side was not sealed. The PVC had a diameter of 10cm (exactly 4 inches) so all components fit, and was approximately 30.5 cm (a foot) in length. All internal components of the device were mounted to the end cap on the cam side. Towards the permanently sealed end was the 12V rechargeable lead acid motor battery.  

Figure 1: Prototype timing and release components.

The lead acid battery powered the motor, a 12V high torque DC brushed motor with a gear ratio of 810:1. This high gear ratio allowed for the high torque required to overcome the friction of the rotary seal and most external forces and successfully turning the cam to release the rope. Its movement was controlled by a motor driver. The motor had an encoder so the user and Arduino can assess where the cam was in relation to the starting position and so that the user could input the desired release time.

Timing was performed by an Arduino Pro Mini and a Real Time Clock (RTC) chip. The Arduino was kept in low power or sleep mode for the majority of its time underwater to save power and was powered by 3 AA batteries stored in the device near the motor. The RTC chip enabled greater precision than the Arduino’s in-house timing mechanism as the RTC's error was two orders of magnitude smaller. The chip was powered by a coin cell battery. A motor driver connected the circuit to the motor and allowed the motor to be powered.

Located inside the housing was a reed switch which was operated by an applied magnetic field. By placing a magnet near the reed switch, the CAM was rotated to an angular position, which indicated the set time of release of the buoy, until the magnet was removed. The RPM of the motor was low so the fisherman would have a reasonable amount of precision when making this adjustment. A dial was written onto the cam so that the fisherman could set the desired time until the release of the buoy by turning the cam to the proper location; the arduino recorded this time using an encoder to measure the cam’s rotation.

The peg cap (translucent part in figure 2) is tied to the buoy and line, making it naturally want to float up. The cam was designed such that it would hold the rope around the release cap until the cam rotates to a certain position, wherein the rope would be free to rise up off due to an upwards applied force from the buoy. A rotary seal prevented water from entering the device around the camshaft. The camshaft and end pieces of the design were machined out of Delrin to avoid corrosion in seawater. The peg and peg cap were printed from ABS, which is also resistant to saltwater corrosion, though care must be taken during manufacturing to select the type of ABS that can be exposed to UV light.

Figure 2: Release mechanism in locked (left) and unlocked (right) states.