Design Goals

This page dedicated to resolving the design goals for this project. These will evolve as the design itself progresses.

Performance Envelope Goals:

  • Depth: To 130 m (425 ft) in salt water.  While this is within the open-ocean photic zone (http://en.wikipedia.org/wiki/Photic_zone), it is below the photic zone in the coastal and inland water bodies targeted in this design.  It also allows for off-the-shelf components rated for 200 psi pressure.
  • Range & endurance at 0.5 m/s (1 knot/1.125 mph): 43.2km (26.8 miles)  over 30 hours at 80% duty cycle.  This would allow an operator with two vehicles to launch and recover once per day and achieving full time coverage.
  • Endurance keeping depth (not making way): 5 days.  This mode is envisioned to be used if the vehicle can not be recovered on a given day, and must kept off the surface for one more day with the 20% remaining battery capacity.
  • Operational environments: fresh water, sea water, super-saline lakes & lagoons.

Budgetary Goals:

  • Parts cost: less than $1000
  • Additional scientific sensor part costs: less than $250 each

Operational & Maintenance Goals

  • Air weight: less than 14 kg (31 lb).  This is a common definition of “human portable”.
  • Time to complete battery re-charge: 4 hours or less. This would allow the system to be recovered in the morning, recharged in the afternoon, and stored safely overnight.

Communications Goals:

  • Support 3G, and 4G wireless communications at the surface
  • Be able to operate with only Wifi (IEEE 802.11n) connectivity in a limited area

Sensing Goals:

  • Global Positioning Service (GPS) on the surface
  • AHRS (tilt/roll+compass)
  • Height above the sea/lake/river bed
  • Depth
  • Camera
  • Optical Backcatter/turbidity

 

5 comments on “Design Goals
  1. Thomas Monterey Thomas Monterey says:

    Hey Mike,

    Range and Endurance:
    If we put half the vehicle weight into batteries (15 lbs) and use standard laptop batteries, (4.5 Ah/ 0.7 lbs), we have about 100 Ah. Spread that over 30 hours and you are looking at an average 3 Amp discharge rate. If it is a 15 volt system, we have 45 watts per hour to play with. This is a pretty tight energy budget.

    Depth:
    A 200 psi system is probably pushed past the ragged edge of the COTS items. If we stick to a light weight Schedule 40 CPVC pressure hull, we can go to 220 psi with a 4″ diameter. That seems hard to pack 20 laptop batteries into. ( http://www.engineeringtoolbox.com/cpvc-pipes-pressures-d_240.html ) We can look at 6, or 8 or 10 or even 12 inch pipe but our max pressure starts dropping to 180, 160, 140 and finally 130 psi. Any reason why 140 psi is not “good enough”? That gets us 90+ meters of dive which far exceeds any cheap pumps we might find lying around… BTW, we will need some way to controlling buoyancy at depth if you are serious about loitering submerged for 5 days.

    Operator Interface:
    I don’t see this being described anywhere. Is our user writing hex code on the fly or are we going for something mere mortals can do?

    Thomas

  2. Phil Marcelino says:

    Fair enough.

  3. Mike Godin says:

    The camera support goal was added in recognition that eventually, a number of users will want to take shallow-water imagery. And if the system is not fundamentally designed to support a camera, later integration of a camera is likely to be very difficult, or maybe even deemed impossible. I specifically mention “shallow water” because the baseline design is not likely to result in a “do anything anywhere” vehicle, and the illumination required for deep water imagery can probably be considered outside the scope of the initial design.

    Surely you’ve noticed that when you discuss AUVs with anyone unfamiliar with them, they almost always ask “So it takes pictures underwater?” and then you say “no, it measures underwater properties such as blah blah blah…” and their eyes glaze over. I’m just saying it is probably worth listening to people’s intuitive sense of what makes sense.

  4. Phil Marcelino says:

    How important will it be to have a camera on the system? If the vehicle is designed to go to a depth of 200m how much will a camera be able to record much below 25-30m?

    I don’t know much about the GoPro, but cameras in general are usually power hogs. Well not so much the cameras, but any lighting to support the cameras. Are LED’s strong enough? If so, that may be an option.

    I think it’s going to be a little tricky to support a camera. Like most of the cost is going to come from the sensors, most of the weight is going to come from the batteries, which will make it hard to meet the 31 pound requirement.

  5. James Bellingham says:

    Hi Mike,

    Re location of the mobile phone…surely there must be phone out there that can accommodate external antennas. That would give you a lot more freedom with the design. I’ve always liked the Seaglider ‘stinger’ concept, which (as you say) would not work well with an entire cell phone in the stinger.

    Jim

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