After a particularly long dive (7+ hours) we were decontaminating the BROV2 and heard some rattles. Loose objects rolling around somewhere in the ROV. Weird. We thought it was debris, but the unit was otherwise clean.
After rolling, shaking, etc to find the culprit we took an end cap off a vertical thruster and a shaft collar was laying in the housing. No biggie, at least it wasn’t lost.
After checking, five of the eight had fallen off. We couldn’t be certain, but there didn’t appear to be any thread locker on the setscrews. We replaced them all, and set the shaft axial play at about 0.5mm. The bushings all felt ok.
We will add a prop free play check to our preflight list, but wondering if this is just an anomaly? Any suggestions for more or less play?
This is not normal, and and should not be happening easily. How exactly the ROV was being run and transported may have had something to do with it, but we have not seen this happen commonly. The setscrews are not thread locked, as we found this risk stripping the screws when removed for maintenance/cleaning.
Just a bit of free play like you describe is appropriate. I usually say just enough for some play to exist, but no more than that. The play is there the ensure there isn’t excessive friction on the bearing flanges. 0.50 mm is on the upper limit of what we normally allow, but won’t harm anything.
These thrusters are only a couple of weeks in service, so not a lot of transport or other hangar rash. We will get the play adjusted a little tighter.
By the way, we use Henkel Loctite MS222 (purple), which is much better for high vibration application on smaller fasteners. Works great, and much less risk to remove. Yes, 242 would be a bit much.
