4 hours flight time hydrogen drone

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What’s the cost and what’s the cost of the fuel cell? Also, what’s the power output of the fuel cell?

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If you have to ask, you likely can’t afford it! There’s platinum based nano tech in there…
These fuel cells seem to come in a variety of voltages and currents, depending on the size and number of the internal cells.
you tube has lots of interesting articles on them.

I’m well accustomed to fuel cells, the technology, manufacturers and prices. I’m interested to see what units they used and if another COTS or their own proprietary system.

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Probably A bit of an ask, but could you based on your practical knowledge sketch us an indicator of how much it’s going to be to DIY this? The little hydrogen tank looks like it could rush you a coupla hundy on it’s own, and the cells look to be hard to mass produce out of cheap materials so would I be right in assuming that the 1/2- 3/4 kilowatts version this seems to be, would be in the thousands currently? I’m sure there will be a lot of newbs like myself who have ALWAYS wanted endurance measured in hours, wondering how far out of reach this all is.

I presume you are directing your message to the OP but these things (PEM Fuels, solid oxide, etc) have a rather low efficiency to start with (generally in the 60% range on the high end) so a diy would most likely be even lower given it’s hacked together rather than high efficiency with quality plates in the stack boosting overall system efficiency. Point being that you wouldn’t necessarily see the high overall energy density of the power plant itself if the efficiency is too low and batteries would just make sense.
Interestingly, ICE engines are only in the (approx.) 30% efficiency range but given their maturity, are offered in innumerable shapes and sizes and don’t require the same high psi (aka heavy) pressure vessels that a fuel cell does (few exceptions to that depending on the type of fuel cell but that’s a different conversation). Couple this with better than lipo/li-ion but worse than gas and it’s a hard sell to diy a fuel cell with added complexity, increased hourly cost (direct and indirect) and improved but only marginally flight times.

At the 600-800 watt size, expect 4-$12000 for a system. Larger vehicles start to see the real fuel cell benefit as the power does scale given regulators and required heavy equipment does not (really) need to scale up in weight except pressure vessels.

As for your questions about the pressure vessel itself, these can be DOT approved or not and then even custom made but there are concerns depending on the path taken. DOT ones tend to be heavier but are approved by DOT use so that may be relevant in your CONOPS if commercial use or not. Then there is the class of the vessel. The higher being it’s ability to hold a high pressure so more h2 in the same space and thus higher energy density overall. This easily can be $1000+ to 1000’s depending on the size. Ultimately, liquid hydrogen is the most promising and dense but requires keeping the fuel in a liquid state (cryogenically frozen). It’s been done on drones before but obviously at a substantially increased cost.

Could you diy this? Absolutely. It’s no different than how some of the fuel cell manufacturers started testing these out but at some point you will ascertain what works or could work better and will need to not hack it together for it to make sense in a practical way rather than just power a lightbulb, etc.
It would super cool to see someone diy a fuel cell. I would definitely get behind that!