"Do you plan to have some sort of self navigation whilst underwater ? Using ultrasonic s or something to do a sort of underwater location system. I guess one of the problems I face (maybe you don't ) is where ever I want to use my underwater ROV I…"

"Interestingly enough as you only need the odd low speed burst under water the motors seem to handle it fine.
A good bit of water cooling obviously helps. I would still suggest getting the lowest RPM motors you can though that will still give you…"

"Very nice thanks for the link. Please don't take this the wrong way as it's a very nicely built project you've got, However It hasn't cracked the real problem though or at least the video doesn't show it has. To be able to go on the surface (in air)…"

"You wouldn't even need a wire. Bluetooth doesn't go very far under water but would be good enough to go through a plastic hull of a ROV...and have a receiver in side."

"interestingly that site doesn't actually mention the copters going in water...."

"The temp difference isn't as important as the amount of moisture in the air in the enclosure. A few things you can do about this are:-
1,Put the craft (or camera housing) in the fridge and get is super cold before sealing it up. This will force the…"

"Ah yes I see the four props and thus the craft is vertical in flight then drops down to horizontal for under water. You would only be able to control depth whilst moving forward or backwards but maybe some applications would be happy with that. You…"

"Do you mean a standard type quad setup with the X and then rotating the pitch of the props or rotating the motor prop assembly ?"

"Wow that would be something but $1.5 million just for the water version I think it may be slightly out of my play list bracket.. :)
A word of warning to anyone that reads this and thinks model ducted fans would be ideal for a ROV. The ducted fans…"

"I agree , that's  why you don't turn them at the same RPM. You need a brush less outboard that is capable of slow speeds, Many can't but some can..."

"ah yes good point unless you step up to high voltages ect but that adds another level of complexity. With the craft being near neutral buoyancy the batteries can be in the craft with no real loss to anything.. maybe a small one in the float to run…"

"The flight ones will work fine for the up and down element (z axis)  of a near neutrally buoyant craft so if you don't want to vector these some how to give X,Y control then (minimally) you only need one other motor with forward/reverse and a…"

"well sort of that's what you'll end up with but by sharing the batteries, (possibly motors) and the control gear you will save a good bit of weight and unnecessary doubling up on the gear...The bit left on the surface (ie the float) can have the…"

"if you are in fresh water , don't bother water proofing. If in salt water then rinse well with clean water after each dive and just be prepared to change the motors every now and then. Changing the motors is probably less hassle and cheaper than…"

"As long as the water is pretty clear of minerals or salt it is surprising how long those brush less last. I must have used one for at least 20 hours under water doing tests etc and it still runs great, all I do is rinse the thing off and leave it in…"

"you can make low frequency RF links its not that difficult but the antennae lengths start getting ridiculous to get any reasonable distance. Again though you set up a perfect 300 hz RF link with a county length antennae and you still wont get the…"