Oh come on. It's trolling down your leg.

I wonder how long it will be before drones are more heavily regulated than firearms.

Indeed, but it's not the average speed that matters, it's the peak. When water funnels between rocks it can end up moving much faster than the average speed, and it also moves faster below the surface than on it. My personal preference would be more pressure than is necessary rather than too little; the concept of one's vehicle dying in the middle of an unpredictable glacial river is rather scary. Then again, I'm a big chicken when it comes to highland river crossings (had to do a bunch about a month ago**) so I probably have an overabundance of caution in this regard ;)

** Word to the wise: When driving in a wilderness location with lots of fords, make sure that your vehicle hasn't accidentally slipped out of 4wd before your first crossing, not after half a dozen nail-biting crossings of slipping along riverbeds while steam rises from your engine compartment. ;)

remember that in American law, anything that is not explicitly forbidden is allowed.

That's not strictly true. There are lots of catch-all laws, like "wanton and reckless conduct," where an act is not explicitly forbidden, but is deemed illegal nonetheless, and they're upheld by the courts all the time.

If he's taking money earned from fossil fuels and putting it toward renewable energy R&D, then that's a net gain. Besides, if they sold the stock, it would just create a buying opportunity for someone else; someone who wouldn't necessarily use any profits for altruistic efforts.

You're forgetting, rivers don't stand still. One can interpret the velocity of the water as relating to the volume of an imaginary water column above the surface, h=v/(2g). So a 10m/s (22mph) flow is equivalent to a 5 meter (197") water column. The force of fast flowing water is a more significant impact than the water depth, at least in a worst case.

I'm not sure what you mean by "at those volumes". Volume is relatively irrelevant in this context, and only really matters for the motor itself anyway (batteries, having no moving parts, can be water sealed on their own easily), and modern electric motors can be pretty tiny versus their power output. What matters is flow rate combined with pressure. The required flow rate in turn is related to the heat output of the motor. A "normal" motor for a vehicle like this a couple meters per second airflow in peak conditions, while a really high power low profile motor like one of the EMRAX ones at peak would need somewhere along the lines of 15m/s airflow at these sort of pressures (average airflow needs being much lower than the peak). Either way, at pressures of only several PSI, you're just looking at a rotary-vane air compressor, nothing like a piston-driven shop compressor or the like.

The other alternative is of course a submarine-style waterproof rotary joint. But it's an extra cost, will cost you some energy, and either way you still need to cool your motor and pack (unless you only ever operate in a very low power regime)

Yeah, try to drive one of those in the sort of lava fields we have here, it'd bottom out before it even gets started. ;) Even on less extreme terrain, its clearance looks like a pretty big flaw - it can hardly drive on a flat slope without nearly bottoming out, let alone uneven terrain. They could raise the center, but then they'd also be raising the CG because not on the driver but the batteries are in that center bit, and on an offroader you really want a low CG.

Seems to me the solution is to put the batteries next to the hub motors. Something right next to the hub should never bottom out, and as they're low so the CG will stay low. It also allows you to reduce or eliminate your in-arm power wiring (esp. good given all of the bending that goes on in those swing arms), thus reducing wire mass, wire cost, and wire resistance. If you fully eliminate the in-arm power wiring you'd have to charge the packs individually, but even if you retain it you could reduce it to smaller wires that only need to be able to handle charging currents and inter-pack charge balancing, not peak discharge currents. Having the batteries next to the hub motors, you could upgrade them to pretty much whatever power level you wanted.

Another problem I see is with the use of hub motors. Everyone loves them until they start messing around with them and then the problems start to become clear. One, they're unsprung mass, which reduces your ride quality. Two, they're harder to cool, which limits performance. And three, you shake them to bits even on normal roads, let alone offroad. I'd prefer each wheel being hooked up to a small high power motor, connected to the wheels via a stubby CV joint (which should lose only a fraction of a percent of the energy transmitted). That way you keep your unsprung mass low, your motors are easy to cool, and they're not shaken to bits.

This thing is underpowered, but with some proper design choices there's really no limit to how high powered it could become.

The last issue I see is, if you're making an offroader, do you really want motors and wiring connections somewhere that they're going to get wet? Do you want to have your wheel drop into a deep puddle and suddenly short out? It seems to be that they really should have the motors (and as per above, battery packs) protected by a cowling. For transmitting the power to outside of the cowling I see two options. One is to use a waterproof rotary joint, like submarines use, although those are somewhat lossy. A better option might be to have the rotor simply penetrate the cowling (with only a small clearance around it) and use your pack / battery air-cooling system to maintain sufficient positive pressure inside to resist water influx - around 5-10 PSI should be enough for unbridged river crossings, while only 1-2PSI would be needed if you only want to be able to handle the occasional puddle. The air ingress to the cooling system would need to be located as high as possible, of course, whatever design one chooses.

(Yeah, this is something I've been thinking about for quite a while, I'd love to build my own go-anywhere electric vehicle some day ;) )