Not sure if all the bullets are correct, but I'm trying to get all my thoughts down before deciding which route to go. Thrusters seem to be the hardest item to decide on. I'm using an old cheap Equinox video camera housing as the main hull for electronics. Plenty of room for batteries etc if needed.

500-750GPH bilge pump cartridge

• Limited in depth - Depth makes it wear out faster due to more friction with the seal
• Not too powerful
• Requires relay board (4xDPDT for reverse operation?)
• Good price for an all inclusive package, just add propeller
• Can use 12v sealed lead acid batts

DC motor in housing

• Motor can overheat
• Needs seal on custom housing
• Requires relay board
• Very cheap
• Simple connections
• Can use 12v sealed lead acid batts
• Heatsink can be added with sealed fins sticking out of housing

Brushless outrunner motor in housing

• Needs seal on custom housing
• Heating issues
• Requires ESC (with reverse) which also has heat issues
• No heatsink since the outside spins - inrunners are too fast and too espensive
• No need for relays
• Can use LiPo (ok at pressure?)

Brushless outrunner motor out in the open (like openROV decided to go)

• Corrosion issues

  coating possible without disrupting electromagnetic fields?
  Swap out stock bearings to bushings, sealed bearings or ceramic ones?

• Easiest to put together
• No cooling issue with motor
• Can use LiPo (ok at pressure?)

Magnetic couple drive

• Has to be completely custom made
• May be possible to use parts from an eheim pump etc.

As for seals, would these bearings work well for an ROV at 100 feet salt water?

I ordered the underwater robotics book and hopefully will be here soon and help also

One thing that is in your bullets is the batteries, the fact is you can use any battery chemistry with any motor, brushless motors are quite happy to run on SLA's and visa-versa brushed motors can run on Li-po.

On the subject of the "heating Issues" if the motor and prop are correctly matched to each other then this should be a non issue, also an outrunner attached to an aluminium bulkhead in contact with the water will have all the cooling it needs.

I would be inclined to use ESCs for motor control regardless of motor as well, relays are an on-off no control of power and probably no cheaper than an ESC.

Nick

Thanks Nick, I guess I was confused about the different battery techs.

I was concerned about the heating since my multirotor motors get extremely hot and that's with a lot of airflow over them. I'll make sure to use a metal bulkhead.

I had forgotten all about the brushed ESCs. So these can just connect right to the 2A bilge pumps? I have always seen them using relays or transistor looking regulators so didn't think about ESCs.

Also to use SLA batteries would the ESCs need to be 4S capable bc/ of the voltage?

A 3 cell Lipo has a fully charged voltage of 12.6 volts I've used 3s ESC's on SLA's and usually the 3S are also 10 cell Ni-XX which have a higher than 12 volt fully charged voltage as well.

Those ESCs will work fine they are forward only though.

Thing with a aircraft is everything is pushed to the limit due to needing to be as light as possible for the power, a water vehicle this is much less a concern so things are relatively beefier for the power required.

Nick