Newb ROVer - School me on making my first!

electronics
propulsion

#1

Hello everyone,

You guessed it, I’m a newb. I’m looking to get my feet wet building an ROV. I have a couple 3D printers and looking to build an ROV from scratch with a number of parts provided by the OpenROV store.

I’ve already started my research and have a few critical questions I want to clarify in my head of which I’m unable to gain a clear answer to among all the web chatter.

  1. So… the motors (as modified and provided at least by OpenROV) are seriously just in direct contact with the water? Absolutely no protection from the water. :fearful: That’s correct?

  2. The outrunner brushless motors can only be used in this way because it uses magentic force to spin the shaft … inrunner motors not so much? That’s correct?

  3. Ok… I contacted a few hobby stores and they looked at me like I had a squid on my face when I asked if their outrunner brushless motors would work underwater. They said - no.

Let’s translate…

Do they mean “no” as in “yes, but they’ll eventually burn-out as they corrode”?

Or

as in "No… you need to coat it in the rustoleum and that’s what OpenROV has done by default with their motors sold in their store?

In summary of point #3 … can you confirm the following: in theory I can go and buy any (no matter size, power, etc etc) outrunner brushless motor and use it underwater in direct contact with the water with a limited life span (fresh or salt water) and I can use that same motor with a longer life-span duration IF I were to follow the following instructions… http://openrov.dozuki.com/Guide/Waterproofing+2.6+thrusters+for+ocean+use+%28bearing+upgrade+and+motor+coating%29/57 ?

  1. If one were to make an ROV that stayed above 20 ft depths of water, would it still require an air vent to balance pressure as it went down and up? Maybe someone can point me towards a link that could explain why it’s beneficial to have an air vent?

  2. The Marine Epoxy, that stuff is used (as in the ROV instructions) pretty liberally to waterproof cavities and walls. It’s that good? That correct?

Thanks, everyone!


#2

@pdw2732,
Short answer: yes brushless motors will work in both fresh and salt water though their life expectancy will depend on the time spent in the water and the amount of maintenance (pressurized air flushing and lubrication) performed after each dive.
The 2 ton epoxy used to seal the cable pass through and other End Cap cavities is more than adequate for sealing the WTC from the water environment. I was able to maintain a 540 mm Hg vacuum on the WTC for over an hour without any leakage.
As far as the vent goes, it is there to release the air pressure in the WTC when inserting the End Caps which will compress the air in the WTC. That being said, the remaining air pressure in the WTC will increase as the Controller Board heats the air in the WTC which could possibly force the plug from the vent, but I have not seen that happen. The water surrounding the WTC will help to absorb the heat being generated by the Controller Board. Though OROV is recommending that the Controller Board with the new HD Pro Camera be run for 10 minutes or so with the vent plug removed prior to diving to help relieve the buildup of excessive pressure in the WTC.
You might want to take a look at my Hybrid ROV that uses BR T100 thrusters with an OROV WTC/2.8 Controller Board.
Hope this helps.
Regards,
TCIII AVD


#3

Thanks a ton for taking the time (and detail) to respond! That answers my questions well.

You’re Hybrid ROV is awesome. The T-100 thrusters look great.

I’m curious, as you were deciding to build a new ROV why did you decide on the same form factor?

Positioning the question in a different way, if you were to wake up tomorrow not knowing anything about OpenROV’s existence and wanted to build an ROV why wouldn’t you use a submarine like-form? Maybe there’s no “right answer” to this question but I’m interested in learning different insights (not enough room for electronics, etc?) on the decision making for ROV form design.


#4

@pdw2732,
Glad to have been of help.
The configuration of a ROV, IMHO, is dictated by what the ROV will be used for.
If you are just interested in using the ROV for FPV underwater viewing, then a more torpedo shaped submarine configuration might meet your requirements.
However, I plan to attach various tools (grippers/samplers, etc) to my ROV and therefore want a ROV platform that is sturdy and multifunctional which I feel precludes a submarine type of configuration.
However, to each his own.
Regards,
TCIII AVD


#5

Totally, that makes a lot of sense. Thanks again!


#6

Just a comment on recent lessons learned as I am building a unit right now with my own housing. The OpenROV motors are not typical DC 2 wire motors where you reverse the polarity to reverse the rotation. The OpenROV motors use a 3 wire connection and a speed controller to reverse rotation.


#7

Thanks, Jim! Yes, I’ve just now realized ESC programming is an entirely different beast. It was one of the big reasons as to my purchasing of an OpenROV just recently. I hope to learn as much about the software as the mechanics of waterproofing an ROV.