BLDC motor and battery config for drone boat 2

[mitchellleary1978]

Hi all,

I'm sincerely hoping someone with more knowledge than me in electronics can help me. I've been working on a project for many years now; designing and building an autonomous drone boat, capable of crossing oceans, guided only by GPS and telemetry. There have been many trials and setbacks to overcome but the boat itself and the internal brain etc has been tested and works well.

The one sticking point that has created the biggest issue has always been the power system which will allow the motors to run almost continuously for 4-6 weeks in the case of crossing the Atlantic(and having time to re-adjust following expected navigation issues).
So I've moved back and forth and tested many different ideas including solar panels covering the deck of a 5 metre boat + battery bank but this method wasn't efficient enough and wouldn't last the 4-6 weeks.
I had chosen a large boat simply to accommodate the solar panels and battery bank.

Just as I'm coming to the end of what I can conceive as a solution and close to giving up, I wondered if it would be possible to drive the boat if I reduced its size to maybe 1-2 metres in length and employed high-efficiency motors, maybe normally used in hobby vehicles(boats, quadcopters etc), and then powered them from some long-life vehicle batteries. The batteries would provide balast and if the setup was right, might be capable of providing the continual power for the duration required.

I've attempted to do the calculations to work out if this is possible but don't have a strong electronics background so I'm hoping that someone or different people can help me to get over this stumbling block that's blighted me for so long.

Is there anyone on this forum that can advise, based on their experience whether there is a motor-battery setup capable of achieving what I want to achieve with my 2 motors running continually for around 4-6 weeks?
In my simple mind, I wonder if there could be a large capacity, high efficiency battery out there that is currently used for other purposes that could power 1 x high efficiency(but low power draw) BLDC motor(maybe usually used in hobby vehicles) for 4-6 weeks?
Again, at a basic level, I question for example, how long a car battery could power a small BLDC motor, usually used on hobby drones?
(I understand that to be accurate, I need to know the exact power rating of the proposed motor and battery capacity but I just want to know in a general way, from someone who has experience, if this might be possible because there's no point in me getting my abacus out if it is actually impossible.)

If anyone can help with some advice or knowledge on these questions I have, I would be very grateful for your input. As I say, I've lost alot of hair experimenting to try and find a solution so it would be nice to get some valuable experience-based advice at this stage.

Thanks in advance for you taking the time to read this. I will try and reply to everyone that replies to my thread.

Mitch

 

[imcjoek]

Quick napkin math.

Tesla 100kW*hr battery. Something like 1000lb of mass, so not a tiny boat to fit it in.
1HP of motor, so barely moving your big heavy boat. The tide would probably win.

100Kwhr/746W = 134 hours run time. About 6 days.

Conclusion: High tech battery and a motor way too small to move your boat only lasts about 20% of your intended duration. You need a recharge source or chemical storage.

 

[waross]

Go back to the 5 meter boat. Add a small gasoline or diesel engine driving a battery charging generator. When the solar battery voltage falls behind, automatically start the motor-generator to top up the battery.
Watch your assets when you are negotiating with the Columbians for a payload.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mitchellleary1978]

Thanks @imcjoek for the reply. You may be right.

@waross I always watch my assets You might be right about reverting back to the larger boat + solar again. It just feels like there should be some way of achieving it easier if the correct setup is utilised. I think you're on the right track though by using a variety of different power sources. Thank you.

 

[3DDave]

I prefer the wave-riders, which can make way as long as there are waves. The only power required is for rudder and guidance.

 

[itsmoked]

To do this successfully you really need to know the approximate amount of energy needed to make the trip. Guessing or hoping is just going to lose you some expensive hardware.

The the two easiest ways to do this would be to either 1) Take the boat to a hydro lab either commercial or college (there are a lot of them and they're typically under utilized) or 2) take it out to a pier or choppy lake.

What you need to know is the force required to move the boat at the desired speed. At 1) above they just anchor the model from above, move the water and use a strain gauge on the overhead anchor.

2) Above, you use a winch mounted on a stationary spring scale platform to tow the boat at various velocities.

In the above studies you vary the speed and boat weight so you can understand those parameters as well. You'd also want to find the hull speed so you know what speed to stay away from.

Once you have that fundamental information you can then estimate the thrust and hence power required. THEN you can come up with some valid energy storage numbers.

Until you know the power actually needed this can't work.
Once you have the power number you can add fudge factors for currents and wind, and extra storage.

Tackling this whole project myself I'd approach it differently.

Since this whole thing works or fails based on the propulsion I'd start with that.
I'd set up a system that would use X amount of solar panel and reliably charge a Liion battery pack up in a solar day and also run the propulsion for the same solar day. Then the craft can run on battery overnight with the battery being recharged the next day. Step and repeat. Keep the battery out of the drive circuit during its daily charging.

You then need to add supervisory control to the system so it can recognize things like overcast and adjust its power consumption accordingly with a mind to doing nothing more than station keeping if it must. Trading off miles-made-good for just not losing miles to wind or current.

Once you have a system that does this on land reliably then you know what the craft must carry to propel itself and the craft is then designed to support the propulsion system.

Sounds like fun!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[keyepitts]

Maybe a SAILboat with a trolling motor for backup/maneuvering?

 

[btrueblood]

like these?

https://www.saildrone.com/

 

[3DDave]

https://www.liquid-robotics.com/wave-glider/how-it-works/

https://www.liquid-robotics.com/about-us/company/company-history/