We use our BlueROV2 once or twice a year for short-notice jobs. Every time we pull it out of storage, all of the horizontally oriented thrusters are seized up and require a lot of work to free them up. (The vertically oriented thrusters do not have this problem.)
I’m confident that our thrusters are adequately flushed with fresh water after use.
I know that the standard BlueRobotics answer is “no lubrication is required” on the thrusters. But this approach is not effective for us. I can’t spend 2-3 hours disassembling and cleaning the motors every time we need to use the ROV.
Is there any type of protectant that we can use to prevent the thrusters from corroding while the ROV is in storage? I’m considering using a syringe to inject silicone grease or lanolin into the stators before storing the ROV. Are there any issues with doing that?
Any lubricants can negatively impact the health of the plastic sheave bearings, and the coatings on the motors themselves. That’s before considering that any lubricant you use is going to come blasting off completely when used, and into the ocean (or whatever body of water) - no bueno!
The solution may actually be in the symptom you describe! The horizontal motors, after being rinsed, are stored in an orientation where water can remain pooled in the thruster. After putting it on the shelf, simply orient the vehicle nose down after a day or two - this should give all thrusters a chance to dry out completely! Worth a try at least?
What type of plastic is used in the sheave bearings, and what type of coating is used on the motors? I’d like to look into the chemical compatibility. I assume the motor frame is polycarbonate?
Before resorting to lubricant, here’s something you might want to try:
After flushing the ROV, put it in a big tub of water and let it sit overnight. When it’s in the tub rock it around a bunch to make sure all the air is out of the thrusters. Basically, let any residual salt gradually leach out of the vehicle.
Pull it out the next morning (it’s still a bit unclear to me how long you can leave a Bar30 sensor in the water, but Blue’s info implies that overnight should be fine), and let it drip dry on multiple sides (as Tony White describe above) to get most of the water out of the thrusters.
I suspect this will take care of your issues. But please keep us posted on what you find, and whether you end up using lubricant!
Thanks for the ideas. I’m sure what you describe may help. A two-day decommissioning procedure after every use is a lot…
I feel like slightly larger clearances inside the motor would alleviate some of the propensity for these stators to freeze up from a little salt or sand. Kind of the AK-47 approach to mechanical reliability.
Regardless, I drilled small holes in the front and rear cones of our thrusters and injected them all with a healthy dose of silicone o-ring grease. Then I ran them a little bit to let the grease work in. I’ll report back with my results the next time I use the rov!
Everything is always a tradeoff! A large factor in a brushless motors efficiency is how tight the gap between the rotor magnets and stator is… Blue Robotics R&D efforts to update the motor seek to match or exceed current efficiency, while making corrosion due to coating breakdown a non-issue!
That grease is going to last about 10 seconds before it is blasted away by the turbulence of rotors going at 4000rpm!
A blast of compressed air into each motor post use may be another effective method of clearing out moisture…
