The final design (tentatively)

7 02 2007

The final design is in! Now that we’re in possession of all SubjuGator’s components, we can accurately plan for the weight distribution, space consumption, and any other limitations of said components. After weeks of each department (electrical, mechanical, and computer engineering) putting in their two cents, everyone agreed on this design:

sub1.jpg

The aluminum hull dissipates heat build up from the internal electronics. Also, stronger than Lexan, SubjuGator will be able to dive deeper sans worried engineers. An external aluminum “cage” supports the hull on dry land and also acts as mounting point for external sensors such as cameras. Since aluminum lacks the transparency of Lexan, the cage must support the cameras.

sub2.jpg

The DVL rests at the center of the turning axis to avoid unnecessary coordinate changes when only changing heading. One thruster adorns each endcap and each side of the sub. Additionally, a strafing thruster is positioned in the center of the hull, just above the DVL. All wetplug connections conveniently interface the sub below the sub, at the DVL enclosure. Past designs have had the disadvantage of a wetplugs protruding from one endcap.

sub8.jpg

The hull has a certain added complexity from years past. Much more planning and machining goes into a design such as this one than into a tube plugged at both ends. However, given the current team of engineers, I am alright with this.





A potential design (but not really)

21 01 2007

Here are four different angles of the original CAD mock-up for SubjuGator:

right side

bottom

front view from top left

left side, nose facing down

 

The original idea called for two tubes, connected by a series of wet plugs, mounted to a metal frame. The DVL would hang below a strafing thruster. When we designed this version, our goal was a compartmentalized submersible with a diverse range of motion. One compartment would house all the electronics while the other carried the batteries (which add significant amounts of weight to smaller subs). The metal frame, somewhat incomplete in these drawings, would support both the sub (while on land), and it would also act as a mounting point for the various sensors we forsaw ourselves possibly using in the future.

Needless to say, this design exhibited some unignorable problems. Firstly, it’s a bad idea to mount thrusters to removable endcaps. No one wants to disconnect and reconnect the thruster every time they require access to the sub’s innards. Next, two tubes spells added complexity, more circuity, and a mess of external cables. Each motor is attached via wet plug/cable combo and each tube must be wired to the next in order to transfer power and/or data. Apart from the mess of external lines to each thruster and submersible sensor, the conversion plugs required inside each tube wastes valuable space. Furthermore, we based the design on the assumption that the DVL unit (sans power supply) was fully submersible and should hang from the center of the turning radius (so turning in place yields no acceleration). It turns out that the DVL must rest partly in a dry hull.

So now, the trend has returned to a healthy, one-tube design. Though, this year, SubjuGator will be longer, stronger, and more capable.





Sensor overload

19 01 2007

This year, SubjuGator, in addition to a complete software overhaul, will undergo a body transplant. The traditional Lexan-crafted, cylindrical shell has been traded in for a mroe cost-effective and heat-dispersive aluminum shell. Lexan’s primary advantage is transparency– you can manually check for leaks, place dry cameras internally, and display onboard debug information easily from within the dry hull. The material also offers a good amount of durability (proportional to wall thickness) compared to other transparent materials. Aluminum, though it lacks the transparency and the lightness of Lexan, boasts durability, good heat-dispersion, and low cost. I had originally pushed for an aluminum endcap since our batteries would shut down after the sub had run for an extended period in the sun. It looks like the mechanical engineers brought it up a notch.

SubjuGator will also sport a variety of new sensors come competition time. The main feature is a new DVL, donated by one of our sponsors. Despite the $15000 price tage and the five additional pounds, it should be worth the navigational enhancement. The sub also finally graduated from web cameras as its primary vision source. In addition to two high-quality USB cams, several students are working on both ranging and imaging sonar devices. I am skeptical of the usefulness-versus-overhead ratio of the imaging sonar. The ranging sonar, however, will help us determine the location of the walls in SPAWAR‘s TRANSDEC, and possibly obtacles in our path. The hydrophones have not changed since last year, and similarly, most of the custom board designs will be the same.