FRC Bearing Load Ratings (Climber Winch)
 

There was a thread last year that talked about the RPM ratings for hex bearings, but it doesn't appear that either primary supplier of FRC hex bearings followed through with posting load ratings on their product pages. While those numbers may once again come into play for flywheel shooter designs, I'm interested in the load ratings for bearings for purposes of climber design. Particularly the hex bearings, which seem to be of a less standardized nature compared to the round bearings (which are closer matches to what are found in industry). With many of the winch-based climber designs, many teams are going to be supporting the weight of their robot with two bearings. While hex bearings have been used for supporting drivetrain loads, that robot weight has been split among four or more axles and eight or more bearings. I'm curious if teams are going to be getting themselves into trouble with bearing loads on their climber winches.

In terms of round bearings, this Amazon listing has FR8ZZ bearings listed as having a static radial load rating of 2.4kN (~540lb), which pushes it beyond all but the most extreme shock loading conditions on a climber. Anyone have any data for the hex version of this bearing?

Re: FRC Bearing Load Ratings (Climber Winch)
 

Going off the load ratings for the 6800 bearings (10x19x5), which have smaller balls (like the larger inner race hex bearings) I would estimate them to have at the very minimum 200lbs static load or 400lbs dynamic load, which should be more than suitable for FRC considering that climbing is at its highest force during the climb/dynamic rate and that you're using two bearings. Plus, those ratings are for 1 million cycles, which I doubt any climber will see.
That doesn't take into account the stress concentrations on the hex, but it also doesn't account for the increased width or anything.

Re: FRC Bearing Load Ratings (Climber Winch)
 

I also do not know the load ratings. However, this would be a situation where Thunderhex is ideal. The thunderhex bearings are round so you are far less likely to crack the inner bearing race upon high/impact loading while maintaining hex shaft functionality.

Cheers, Bryan

Re: FRC Bearing Load Ratings (Climber Winch)
 

We're planning to support weight with a 2" to 3" diameter tube, riding in some sort of plain bearing (bushing), are we doing something wrong?

Re: FRC Bearing Load Ratings (Climber Winch)
 

As long as your bearings are rated for 154lbs plus a factor of safety at the RPM you're using them at and the tube has a sufficient wall thickness that it will not bend under load, then you should be fine.

Re: FRC Bearing Load Ratings (Climber Winch)
 

Is the bushing itself going to be 2-3" ID? McMaster's rating for a 1" ID, 1" long Delrin bearing is 400lbs @ 25 rpm. Bronze bearings will have much higher ratings. So you definitely don't have to worry about too much load. You may have to be careful about the speed rating, though. Too fast and too much load can cause galling and extremely rapid failure. You should be able to find max P(ressure), V(elocity) and PV values for any bearing you get, and calculate out what your actual values for that are.

Re: FRC Bearing Load Ratings (Climber Winch)
 

This seems like a far more mechanically durable / safe solution than using a hex shaft for climbing, if your team has the design and manufacturing "chops" to do it. Bushings are in general far stronger than bearings in terms of peak loading, and the rotational losses just aren't a big deal on a high power mechanism like this. A tight, crappy bushing might even help with backdriving a little.

I would be quite nervous about supporting the weight of your robot on an aluminum hex shaft this year, depending on the implementation. Have spares ready, at the very least.

Re: FRC Bearing Load Ratings (Climber Winch)
 

I agree with the request/focus on bearing ratings, but I'd be less concerned about bearings on a simply-supported climber shaft failing than I would a wheel bearing, particularly in a WCD-type application. The climber shaft should see very low (if any?) dynamic loading, where-as the drivetrain bearings will often see a wide variety of dynamic loadings... even if the climber never falls and the robot lands on its wheels. ;-) Additionally, the drivetrain bearings experience a lot more cycles/use given that they're used almost continuously during the match and are often turning at higher speeds.

Regardless, it'd be good to use more than experience from other applications!

Re: FRC Bearing Load Ratings (Climber Winch)
 

Just to clarify, our "bearing" will be either a hole in a piece of wood, or a chunk of plastic if the wood doesn't work out. At 1 or 2 revs/second, and a total of under 5 turns per use, I think we'll be OK :)

Re: FRC Bearing Load Ratings (Climber Winch)
 

This.... sounds like a lot of friction.

Re: FRC Bearing Load Ratings (Climber Winch)
 

-nevermind-

Re: FRC Bearing Load Ratings (Climber Winch)
 

yes....but will it be enough to prevent backdriving? we can only hope

Re: FRC Bearing Load Ratings (Climber Winch)
 

:ahh:

For the sake of your climbing speed I really hope not...

Though in general I think a plain bearing could be a robust solution to this problem. Especially if it was coupled with a dry-film lubricant.

Re: FRC Bearing Load Ratings (Climber Winch)
 

The trick is to balance the friction right where it needs to be....there should be about 7 times as much torque available, as needed to climb (stall torque vs the torque at design climbing speed), so I think we'll be ok.

Re: FRC Bearing Load Ratings (Climber Winch)
 

To be clear, with the proposed climber design that inspired this comment for my team, we were planning on use 1215 steel hex, not aluminum (including Thunderhex). Given that compression of balls in our intake caused deformation in a ~24" piece of Thunderhex last year, I am definitely shying away from Thunderhex and any aluminum shafts as a primary weight bearing piece of our climbing mechanism.

Turning down the corners of the steel to fit into a Thunderhex bearing is a possibility, as is hex broaching a larger round bushing to fit the hex.