Hi SirHi Guys,
I'm having some problems on my ROV designs. How do you seal the motor casing with the cables? Do you use underwater cable connectors? Is there other alternatives? I uses cable gland with the cables inserted through a metal pipe that can give the cable gland a good seal.
Next, I'm using 4 x 24VDC reversible motors, can a high speed motor (without gearbox) run well rather than to use a high torque motor?
I have been looking into small rov design for several months now and came across thris thread on a google search re thruster seals.
I must confess, the thruster seal (to me) is the greatest problem, the rest seems quite straight forward (he said hopefully lol
Re cable seals -
here are my thoughts. Where the cable enters the housing, the seal should be a solid type. ie, fixed in epoxy with polysulphide sealant injected into the cable via hypodermic syringe etc. use a flying lead with a plug on, also sealed. the join is then made at the plug on the flying lead with silicone grease packed into the plug / socket and a ltex or similar rubber type sleeve fitted over it. Should be fine. A cable glad treated with epoxy or polysulphide (Sikaflex 291 etc) should surfice. Keeping the critical connection external should help with most problems rather than trying to make a removable seal at the pressure housing.
Regarding housings, consider small fire extinguishers !. tested to around 20 to 20 Bar, perfect size for housings and motor units (for the motor units consider the 500 gms or 600 gms unis, or the Paintball gun cartridges as a base for the housing.. why re-invent the wheel lol ?
The biggest problem for me is to seal the motor shaft.
Re high speed motors as opposed to low speed, the problem you come up against is the shaft rpm making sailing more difficult, a slower shaft speed with larger prop is the way to go IMHO.
For the motors, the best apporach seems to be BLDC motors as used in rc flight or cars. could even be run in oil (one area I am considering) but I would prefer dry housings. bldc reversible speed controllers are so cheap now as to negate the expense of building your own controller.