Mechanical seal for ROV thruster

[Ruddles]

Hi 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?

Hi Sir
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.

Joe.

 

[Aquasky]

Hi Joe,

Thanks for replying. I'm quite confused from the ways the sealing of the cables you describe.

So far, I been experimenting two glues, 1) RT Resin and 2) Aquaseal. I tried to seal the cables with these two types of glues and place the cable in a moulding, both form a nice cylindrical shape. However, the RT Resin dry up too fast, before I can seal the internal gaps of the cable properly, it dry up. The aquaseal was a better choice, and since it cannot stick with metal, my mould was made from a brass rod. Cut into half and drill the desire diameter I needed for the cable gland holding thickness. The aquaseal pass the water-proofing, but I had yet put it for a pressure chamber test.

I tested my reversible motors, found that the brushless reversible motor keep stalling in water, even when the torque haven't reach its peak. Still trying to find out the problem.

 

[Ruddles]

Hi Joe,

Thanks for replying. I'm quite confused from the ways the sealing of the cables you describe.

So far, I been experimenting two glues, 1) RT Resin and 2) Aquaseal. I tried to seal the cables with these two types of glues and place the cable in a moulding, both form a nice cylindrical shape. However, the RT Resin dry up too fast, before I can seal the internal gaps of the cable properly, it dry up. The aquaseal was a better choice, and since it cannot stick with metal, my mould was made from a brass rod. Cut into half and drill the desire diameter I needed for the cable gland holding thickness. The aquaseal pass the water-proofing, but I had yet put it for a pressure chamber test.

I tested my reversible motors, found that the brushless reversible motor keep stalling in water, even when the torque haven't reach its peak. Still trying to find out the problem.

try to get hold of a marine sealant called Sikaflex 291, buy the small toothpaste sized tube, you don't need a lot. apply this to the cables, remove the outer cover if multi core - insert this into the gland housing, fill with 291, let it cure for 24 hours - important as otherwise it will shrink ! - then apply the locking or compression nut to the gland - when the sika cures it makes a superb flexible gasket.. ways of sealing individual cables are by using smalll amounts of cyano acrylate (super glue) down the sheath, or a product called captain trolleys creeping crack cure.. or something similar lol, both the sikaflex and the crack cure are used on boats. for a more solid fitting use 3m 5200, but that will not be removed easilly !.

re the problems with the motors (BLDC) some of these units expect to run at an appreciable rpm, maybe a gearbox is in order, what motor are you using ? and what kind of speed controller ?
Joe

 

[Aquasky]

try to get hold of a marine sealant called Sikaflex 291, buy the small toothpaste sized tube, you don't need a lot. apply this to the cables, remove the outer cover if multi core - insert this into the gland housing, fill with 291, let it cure for 24 hours - important as otherwise it will shrink ! - then apply the locking or compression nut to the gland - when the sika cures it makes a superb flexible gasket.. ways of sealing individual cables are by using smalll amounts of cyano acrylate (super glue) down the sheath, or a product called captain trolleys creeping crack cure.. or something similar lol, both the sikaflex and the crack cure are used on boats. for a more solid fitting use 3m 5200, but that will not be removed easilly !.

re the problems with the motors (BLDC) some of these units expect to run at an appreciable rpm, maybe a gearbox is in order, what motor are you using ? and what kind of speed controller ?
Joe

Hi Joe,

Can the glue be able to hold at 100m depth?

The motors that I used were BLDC motors & Stepper motors from Oriental Motor, the BLDC motor model is BLHM5100K-A. I bought it without gearbox, it came with its controller.

 

[Ruddles]

Hi Joe,

Can the glue be able to hold at 100m depth?

The motors that I used were BLDC motors & Stepper motors from Oriental Motor, the BLDC motor model is BLHM5100K-A. I bought it without gearbox, it came with its controller.

Hi
No problem with depth, what it does is form into the shape and sets, but remains semi flexible. If the plug of sikaflex that you make is then compressed in the gland fitting or similar, you should have no worries.
It is a lot firmer than silicone, and has adhesive properties, where silicone really doesnt.

Me gads on the motors lol :).. musta cost a fortune !.. it may be that the starting torque is just being overcome by the water on the prop..
I was talking more of -
http://www.huntersystems.co.uk/acatalog/Electronic_Speed_Control.html

look at the - Genesis Hydra 15 - Brushless Speed Controller Combo

or ebay http://cgi.ebay.co.uk/Esky-Brushless-Motor-EK5-0006-25A-ESC-King-2-Belt-CP_W0QQitemZ300271273805QQihZ020QQcategoryZ123849QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[Ruddles]

Hi Joe,

Can the glue be able to hold at 100m depth?

The motors that I used were BLDC motors & Stepper motors from Oriental Motor, the BLDC motor model is BLHM5100K-A. I bought it without gearbox, it came with its controller.

By the way Aquasky . What are you intending to use the rov for ?. Perhaps it may help you if I pass on a list of favourites from internet explorer for parts suitable for rovs. ?
You can emal me at captainslarty AT yahoo.co.uk
Perhaps it may save us both reinventing the wheel as we are doing independent research here.

to give you an idea, hows this for a cheap prop unit...

http://www.mtroniks.net/details1.asp/ProductID/261/lockit/true/ductfan68.5.htm

Joe
Joe.

 

[Aquasky]

By the way Aquasky . What are you intending to use the rov for ?. Perhaps it may help you if I pass on a list of favourites from internet explorer for parts suitable for rovs. ?
You can emal me at captainslarty AT yahoo.co.uk
Perhaps it may save us both reinventing the wheel as we are doing independent research here.

to give you an idea, hows this for a cheap prop unit...

http://www.mtroniks.net/details1.asp/ProductID/261/lockit/true/ductfan68.5.htm

Joe
Joe.

Hi Joe,

The links you shown above, seems like RC models parts. I'm not making a ROV for personal or entertainment use. The ROV I'm making now, may require for use in offshore pipeline inspection etc.

 

[Ruddles]

Hi Joe,

The links you shown above, seems like RC models parts. I'm not making a ROV for personal or entertainment use. The ROV I'm making now, may require for use in offshore pipeline inspection etc.

Hi Aquasky, no reason NOT to use available parts. The videoray unit uses simple brushed dc motors and is still agreat comercial product. Mone is also not really intended for personal use. I want a design I can sell to yachtsmen etc.
Joe

 

[Aquasky]

Hi Aquasky, no reason NOT to use available parts. The videoray unit uses simple brushed dc motors and is still agreat comercial product. Mone is also not really intended for personal use. I want a design I can sell to yachtsmen etc.
Joe

Hi Joe,

I had emailed you and attached some of the details. We can share our knowledge.

 

[Ruddles]

Hi Joe,

I had emailed you and attached some of the details. We can share our knowledge.

Excellent Stuff Edwin,
Yes, hopefully we can.
I have mailed you variuos links for you to pursue. I have MANY more items of info.
Including seals for the motor units. Hopefully we CAN share ideas.
The market has a LOT of micro ROV products that are superb, again, the VIDEORAY is probably one of the best.
I do believe the same type of unit can be marketted at under half the price.

I have done LOTS of research into this, am only finalising the actual design at the mo.
My field is embedded microprocessor design and development, so the electronics are no worries. The mechanics are an area I need to contemplate more, but the basic designs are there. I live full time on my yacht, so have constant access to deep water for testing if I need it. I don't work now (retired at 47 years old).. this is just a fun hobby with commercial overtones.
Again, to give you some insight. Using a small commercial fire extinguisher gives you a cheap, readilly available main core pressure housing. I have sources for optical quality domes that can withstand the 100 mtrs pressure you quote, I have designs for the thruster seals, wiring connectors, tether system, video pan tilt and link up, pressure sensors, Fluxgate compass units, leak detectors, etc etc etc.
Anything I can do to help, no worries. If its a two way process, then happy days :).

I also program in VB.net for the application to control the unit.
When you look at Videoray, you can see the development that has gone into this product. It is a case of - they sat, they thought, they played, and then they came back to the simple design that works. They are going about in in an expensive way IMHO, but that can be solved.
Please, yes, let us share ideas and tests.

Joe

 

[Aquasky]

Hi joe,

Nice to know you. Currently, my ROV housings were designed through solidworks and machined by CNC system (CAD/CAM).

maybe we can even joint-venture later.

 

[Ruddles]

Hi joe,

Nice to know you. Currently, my ROV housings were designed through solidworks and machined by CNC system (CAD/CAM).

maybe we can even joint-venture later.

Hello Sir
That would be good,
Please see my personal emails to you.
Look forward to talking more.
Joe, Jayne Molly n Sammy

 

[aurelrica]

hi guys, just ran into this post.
as the rov trusters are in my interest too (since i build a rov) I've came with a few design who i have alredy tested. Did you have made anny progress? are you interested in a collaboration?