The aftermath of two of 1678’s matches at Capital City Classic. One of these VEXPro .5" hex bearings sheared its inner race axially, the other radially. I’m glad that this issue will be fixed for the 2015 season.
Where were these bearings used? Any details on the situations that caused them to fail?
It would also be interesting to here how VEX plans on fixing this problem.
since the suppliers of these items are limited, I am not sure what Vex can do about these. However, AM has already put these out for sale.
Both bearings failed as part of the polycarb intake arms. The second one, in particular, was fresh, and failed in its first match. 1678 didn’t have any problems with these bearings throughout the 2014 season.
Where in the polycarb arms were they? Do you know what particularly in the match caused these? It sounds like it was a particular impact or something, rather than a life issue.
I guess I am surprised that after all you put that robot through this season, that you just had 2 failures in close succession.
I am curious as to the details so that we can learn from them for next year.
They were both in the rear arm, on the end opposite the gearbox. (The second replaced the first.) From what I saw from the stands, neither failure was immediately preceded by any sort of contact with another robot.
The failed bearing on the left confuses me.
My experience with hex bearings is that they are hit or miss in terms of quality from all vendors. None of them roll as smoothly as the comparable round bearings, and they have varying degrees of accuracy with runout and hex sizing.
Generally, I’d try to avoid them if it all possible. Even if you think they’re strong enough, dealing with availability and variation between suppliers can be frustrating.
You guys have such fun timing,
These guys will be in stock soon (bigger inner race).
Looks like the weight went down very slightly. What else is different? Smaller balls and more of 'em?
The bearings get used on drive trains without that kind of failure. It seem the drive train would have a higher loading. I am a little hesitant to blame this on bearing quality. Maybe the shaft is bending or severely misaligned which is torquing the bearing rather than a axial load?
Well, larger inner race, so yes, that does mean smaller balls and more of them.
The failure may be due to 1 in a millionth chance that it was manufacturing defect (nothing is perfect) but its not common. In past 4 years we have been using both AndyMark as well as VEX bearings on drive and other systems. Never had this issue. We have 7/8" bent aluminum shaft, 3/16 hollow steel shaft but not the bearing.
Looks like both VEX and AM have/are releasing super-bearings this season. Price will stop me from going to these new super bearings.
The Andymark bearing went up $1 to $6, but the Vex bearing is the same price as before, $5.
I imagine the failure has something to do with the torsional load seen in 1678’s flexible intake arms. Our intake this year had similar flexibility, and when it deformed our intake roller stalled more easily due to the load on the bearings. In a WCD, the load is almost entirely radial, since the double bearing arrangement takes up the torques from the cantilevered wheel and the chain.
EDIT: What Frank said.
Thanks for clarifying, Aren. I could not tell if the inner race was enlarged radially or axially, since there is no pdf on your site yet and I don’t have CAD on my tablet (yet).
I will confess, we should have turned the end of the shaft down to 1/2 round and avoided using a hex bearing in this particular setting. Lessons for next year…
secrets secrets are no fun unless they’re shared with everyone
We wrecked 3 or 4 bearings this year and I had assumed it was due to bad implementation. It probably still was, but it’s nice to know about new and improved hex bearings we can buy to fashion a throne alongside the 3 ft pieces of 1/2" hex shaft y’all sell.
Did one of these bearing failures occur during a chicks in charge match that my team was in against you guys? Those matches were quite aggressive. I think I remember watching the shaft pop out of your polycarb intake when everyone was mashing up on the field. Our intake suffered some damage in those matches with a substantial dent in our intake frame. Actually, now that I think of it, our chicks in charge matches had a lot of intakes hanging outside of frame perimiters, which caused a few tangles.
I can confirm the first failure was during the “Chicks in Charge” matches.
The second failure was shortly after that and might have been there very next match.
Both failures occurred while the pickup was outside the frame perimeter.
Honestly, I am VERY impressed that these failures never happened in all of the matches BECA has played in this year. The torsional load on those bearings when the poly flexes back and forth has to be fairly extreme. That is something these bearings are really not designed for. Maybe a floating bearing setup if something like this is needed in the future? Maybe something like this?
The v2 Hex bearings are now in stock,