Using Blue Robotics thrusters to propel a diver

Blue Robotics Products Thrusters and Motors
2

Hi @odedezra,

I haven’t used a dive propulsion vehicle before, but that seems to be the best comparison here. I found this list of 12 options for different budgets/performance requirements, and most seem to have a speed of 2-3mph (53-80 m/min), neutral or positive buoyancy, 30-120 minutes of runtime (although that presumably includes some time with the thrusters off/on low).

As an arbitrary example, I found the sub-gravity Ecos+ has a max speed of 220 ft/min (~67m/min), which is with 26.5kg f of thrust. Assuming everything else (mass, shape, drag area, etc) stays constant,

\begin{align} F_{max-thrust} &= C \cdot v_{max}^2\\ \rightarrow C &= \frac{26.5kgf}{(67m/min)^2}\\ &\approx 5.9 \times 10 ^{-3}\frac{kgf}{(m/min)^2} \end{align}

I did the same check for a couple of other options and got an average of about C\approx 5.7 \times 10^{-3}\frac{kgf}{(m/min)^2} (to account for slightly different testing/weight assumptions across manufacturers).

Assuming T200 thrusters powered with a bluerobotics battery, a 4S LiPo battery has an average voltage of ~15.8V (16.8V fully charged, 14.8V nominal - stopping point for optimal lifetime), so the easiest comparison is 5.25kgf Full Throttle @ Nominal 16V from the T200 technical details. Two of those would give you

\begin{align} v_{max} &= \sqrt{\frac{F_{max-thrust}}{C}}\\ &=\sqrt{\frac{2\cdot 5.25}{5.7\times 10^{-3}}}\\ &\approx 42.92\ m/min \end{align}

The nominal capacity of the BR battery is 18Ah, and a T200 full throttle current at 16V is 24A, so 18 Ah/(2\cdot 24A) \approx 22.5 mins of non-stop runtime (for two T200s).

A couple of notes:

  • thrusters near people/marine life should have some form of guard, to protect fingers and other small living things
  • larger thrusters are likely a bit more efficient for this, but with multiple small thrusters you can pretend you’re iron-man :joy:
  • obligatory comment that fast water, fast ascent/descent speeds while diving, batteries, and electronics in water are all potentially dangerous if appropriate precautions aren’t taken.

Hope this breakdown helps. Would be great if someone actually has experience with this kind of system and can chime in with some extra suggestions :slight_smile:

EDIT: updated the runtime calculation to include the number of thrusters (originally forgot to so calculated as though only one thruster would be running).

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