Power Supply Segmentation

by Web FishJul 11, 2013 @ 10:31am

For the last couple of months we've been trying to make our mind on power system segmentation. On one hand having separate circuits for the navionics package and the main propulsion seems like a no-brainer - less interference from the powerful brushed motors and speed controllers, separate management of consumption leaving the central microprocessor powered even during deep drain of the propulsion battery bank, being able to store and run at different voltages, etc. On the other hand, the main propulsion bank offers 160+ Watt-hour of capacity which comes at a cost - total SLA battery weight (without the water-tight enclosures) is 8.5 lb. Adding extra capacity as SLA cells adds more weight, adding extra solar panels adds either more weight (glass crystalline) or cost (thin film plastic) to the project. In addition, we have built excellent redundancy with the 4 SLA cells and 4 solar panels which will now need to be replicated on the navionics side (at lower power level / capacity). On top of that the Iridium sat-com modem can draw upwards of 2A on its 12V bus for nearly 60 seconds, so we still need plenty of juice on the navionics segment for normal operation.

For now we will be powering the main electronics from the 4.4V SLA bank through a separate voltage regulator and see if we can work out a good capacity meter to be able to throttle down / cut-off propulsion at a predictable residual level and potentially further adjust comm-link session frequency to save power. This will allow the vessel to drift in case extended periods of low solar harvest rates (weather, panel damage) without completely loosing telemetry and control. Testing will tell if this is the right way of handling it - we still have space on the deck frame for 2x5W auxiliary panels on each side. But we can definitely live without the extra 4 lb of weight...

PilotFish Navionics - Block Diagram

by Web FishJan 1, 2013 @ 10:55am

In a series of articles over the next few weeks we'll cover the various components of the on-board electronics driving the PilotFish vessel. Many components are still in flux, so expect changes as the project develops. As sub-modules and connection paths / interface points get solidified, those will be marked as finalized in future revisions of the diagram.

Here is a quick summary of the navionics sub-systems (click image for full size):

 

 

  • Central Processor: The main control unit. Runs the custom software which makes things move (and find their way)
  • Comm uplink: Telemetry uplink (current position, system status and sensor data reporting)
  • GPS receiver: Current position tracking
  • Compass: Current bearing and acceleration;
  • Aux navigation sensors: additional sensors needed for proper orientation and navigation
  • Additional sensors: environmental and other sensors not directly related to navigation;
  • Image acquisition: live video / snapshots of surroundings
  • Motor controller: accepting control input from CPU and converting it to high-power electric current control
  • Propulsion motors: electric drive motors and propellers
  • Rudder control: directional control
  • Propulsion solar panels: high-power solar harvesting, dedicated to powering main drive motors
  • Propulsion battery bank: high-capacity energy storage dedicated to powering main drive motors in the absence of sufficient solar power
  • Aux solar panels: additional solar harvesting capacity dedicated to powering navionics 
  • Navionics battery bank: navionics battery back-up