Students working on Autonomous Programming asked me why the KoP AM14U3 chassis they were using was pulling to one side. After some investigation and parts swapping found the output shaft bearing journal for the R6ZZ bearing was short and the bearing was bottoming out in housing, binding up the Toughbox Mini. I swapped in a narrower bearing instead of having the shaft machining. First time I’ve encountered this issue causing a Toughbox to bind up. AndyMark has been contacted and pictures of the issue sent.
George, thanks for documenting this. We ran into similar binding issues Monday night, students reported it was a similar issue but I, frankly, just assumed it was they’d forgotten to lubricate something.
Now that you’re seeing similar issues I’m concerned that others are too. Which is a shame, otherwise the AM14U3 has seemed pretty solid.
Our team also experienced binding in one of our transmissions. We disassembled, re-assmbled, and wheels spun without much resistance. Have not driven on them yet though, so can’t be sure this problem has been totally resolved (since we didn’t really do anything except re-seat bearings and gears :rolleyes:)
Thanks for bringing your investigation to our attention.
In this case the Tough box Mini housing would not set flush to the rail, so when the housing was tightened, the gear box bound up. The bearing was bottoming out in the bore with the hex bearing and output shaft gear correctly installed.
Thanks for the heads up!:]
We had a TB-mini bind up near the end of build yesterday. We checked the obvious stuff like gears installed backwards (bosses together instead of at bearings), but not this. We just replaced the gearbox with one we had build for the second robot and moved on, and we’ll look at the binding gearbox tomorrow. (no build today.) I’ll be sure we check for this early in the process.
We had a similar problem on a practice base that was constructed for our programming team during our training season. We never looked much into this, its good to know of this issue. Will look into it once the season is over!
Thank you for the heads up. This is great to know as we begin to test our drive base. Would you be willing to link to where we could purchased the thinner bearing?
This should be one source: https://www.bocabearings.com/products/r6-zz-w-2188c-1901
Hope this helps,
Thanks for posting this! Our robot was jerking to the right last night and I was going to begin the investigation today. This is the first place I’ll look.
This bearing is not shielded, but it has the right dimensions. I can’t remember for sure, but I think this bearing is pretty well protected in the gear housing, so I don’t think the shielding should be much of an issue. I’m sure someone will correct me if I’m wrong about that.
I would not risk using an unshielded bearing. If this game is even half as bad as 2014 your steel gears will have a ton of wear by the end of the season, that leads to steel powder in the gearbox, i have no idea what the poweder would due to an open bearing but i would suggest we not find oit. I know that vex has bearings with a 3/8 ID that are shielded that I believe would fit.
I think the Vex bearings that would “fit” are the same thickness as the ones GDG 2337 pointed out above as too thick. You’ll need to find the 0.218" thickness. McMaster-Carr does not have this bearing in shielded form either.
I’m confused…we had several of our new students assemble our kit chassis this week, and I was watching over them quite a bit. I did notice that the bearings are thicker than the machined portion of the hex shaft, as shown in your photo. But we were very careful to assemble the transmissions as the instructions say, and they worked fine, no binding.
I know in the past we’ve had trouble with the gearboxes, when I was not so involved with the assembly (but did help with the diagnosis and reassembly), and we’ve had problems with gears installed backwards causing binding.
I really don’t think that a thinner bearing is needed. But I also did not measure the shaft. Have you compared the dimensions of the questionable shaft, with those on the AM drawing?
As we were trying to free our bound out TB Mini yesterday, I am trying to figure out how too short a journal would cause a problem with seizing, as it does not make contact with the plastic housing in either case. I am even more curious as to how you put a thinner bearing in and did NOT cause the bull gear to rub against the large cluster gear; they are rather close to each other with the stock bearing. This would only be feasible if, rather than the journal being cut too short, the hex part of the shaft is cut too long.
On our TB-mini, the binding is certainly not from the output shaft or bull gear; it occurs from time to time when back-driving the cluster shaft with a 3/8" socket. The binding appears to be due to the large cluster gear rubbing against the output shaft bearing (in the plastic housing). We tried swapping out the large cluster gear (slight improvement?), swapping the two bearings in the housing (no difference), and will try swapping the face plate and plastic housing tomorrow on the suspicion that the bearing holes have the wrong spacing on one or the other.
Guess I’ve done a poor job communicating the issue, a better way would have been as GeeTwo has stated
“This would only be feasible if, rather than the journal being cut too short, the hex part of the shaft is cut too long.”
Or when the round journal was turned on the hex shaft, normally from .520 to .780. It is only turned from .520 to .720, making the bearing extend .60 farther into the Mini housing. Which was corrected by installing a thinner .220 bearing replacing the .280.
OK, that makes sense now!
Our issue wound up being the plastic housing. I did a few measurements which seemed OK, but I did not measure everything. Swapping it out appears to have solved the problem. That housing went to the dumpster Saturday so we don’t use it again.