The million dollar question for me is regarding the CDF…
It sounds to me from reading the CDF comments in the Palmetto thread, that the CDF’s were repaired around match 10-20 or so by adding a piece of steel to the under-side of each Lexan board/teeter-totter. Is that correct? Did it resolve the CDF-demolition problems at Palmetto?
I don’t really see that particular fix addressed in Team Update 14… should we expect more broken CDF’s in Week 1?
The fix that was implemented at Palmetto did appear to mitigate the demolition issue. After they made the change, the CDF was in play for the rest of the event.
The CDFs are all being modified for week 1, though I don’t recall the specifics on the change. I’ll let you know in a few hours when we start making the change for the Lake Superior and Northern Lights regionals.
That’s the change to GE-16028 and GE-16178. A countersink in the plastic with a flat head screw was replaced with a counterbore with a button head cap screw.
A steel plate was used at Palmetto but does not appear to be the permanent solution.
I saw that change… I don’t know anything about the exact failures seen on the CDF’s at Palmetto, but I have a hard time imagining that using a BHCS in a counterbore vs a flat head screw in a countersink is significant enough to prevent CDF’s from breaking consistently (as the unmodified ones did at Palmetto).
Can a mod please move posts 37, 41, 43, and 45 to a new thread on CDF revision? This topic deserves its own, separate discussion.
Done!
Since this thread has been split off, here’s the update this is referring to: https://firstfrc.blob.core.windows.net/frc2016manuals/TeamUpdates/14.pdf
Whatever the fix(es) were, based on the follow-up webinar for scorekeepers last night, the CDF has a permanent fix and FTAs know what they are. Beyond that I don’t know as I haven’t asked any FTAs.
That being said, if it’s safe to post, if an FTA would be willing to post details, it would be very interesting. If not, well, those at week one, it’s time to play “spot the difference”.
This is second-hand but apparently, the countersunk screws were being overtightened when the CDFs were originally assembled.
This started stress cracks in the polycarb that were then aggravated by robots smashing into them.
The damage to the CDF occurred along the stress cracks.
The counter bore replacement of the countersink seems to have eliminated the stress cracks.
I can’t confirm they were countersunk (because I wasn’t paying attention to that), but I can confirm that screws overtightened in manufacturing were labeled the root cause in Myrtle Beach.
When the only tool you have is an air-powered impact wrench, everything looks like a lug nut.
:shudder:
Reminds me of the time (ca 1995) that I pulled on the shoulder of I-10 for a tiny little shimmy that started suddenly. By the time I came to a stop, three of the five lugs on my right front tire had sheared clean off. I was probably a few seconds from using a pine tree as a brake. I don’t know what tool they used to tighten the lugs at the shop, but it obviously wasn’t the right one. I never used that shop again.
Edit (especially as off-topic):
I believe they were; curious as to the connection between these two. The dealer where I had the jeep towed told me they had been over-tightened. I ran the same vehicle and wheels for another 10 years without the problem recurring.
Were they cast aluminum wheels?
OK. My favorite description of this years game so far!
I expect to hear that description from the game announcer at NYC…
Here’s Frank’s description (http://www.firstinspires.org/robotics/frc/blog/week-0.5)
Cheval de Frise
The Cheval de Frise defenses didn’t hold up well during the event, often breaking when hit by robots. This breakage was not revealed during our testing here at FIRST HQ or during the Week Zero scrimmage, and we know why. Turns out, we assembled the defenses we tested using hand tools, but when we got into production mode, we started using power drills to secure the bolts. These drills put more torque on the bolts, stressing on the planks in the defense, make them susceptible to breakage. We’ve redesigned the planks to use a counterbore, rather than a countersink, in the bolt areas. This greatly reduces the stress on the polycarbonate when tightening the bolts, and our new testing here has shown this fix works well. All events will be getting the newly designed Cheval de Frise planks, starting with this week’s events.
Turns out, we assembled the defenses we tested using hand tools, but when we got into production mode, we started using power drills to secure the bolts.
I was joking, but it looks like I wasn’t too far off 
Now that this thread appears to have run its course, I’ll digress into the land of broken lug bolts.
When I first read your post, what came to mind was, “Wonder if this is on a four-wheel drive vehicle”?
When run in four-wheel drive on an interstate, the differential turning of the front wheels can “wind up” the system. The bouncing of rough terrain keeps this from being a problem, as occurs on smooth roads. I’ve seen ALL the lugs on both front wheels snap at the same time because of this. Don’t suppose you had it in four-wheel drive by accident, did you?
Just sayin’!
Off topic:
You know that on civilian vehicles you’re not supposed to use impact guns on the lug nuts either? At least if you’re not using a torque stick (and even then, it’s technically good practice to use a torque wrench afterwards).
Otherwise one risks warped brake rotors/drums an/or broken/bent/stripped lug nuts/studs/bolts. Not to be a so called torque nazi, but impact guns can really mess a lot of things up when used to torque things down. They’re better suited for removing fasteners (especially rusty stuck ones).
No, it was a rear wheel drive 1991 Cherokee.
I did a bit of online research, and it appears that the more likely problem for the wheel was loose nuts. Left side nuts tend to loosen farther and spin off, where right side nuts just don’t provide enough contact force and put lots of shock force on the studs. While I don’t have those studs anymore (though I did find one after I pulled off the road), they had the “beach” look on the sheared face.
As to aluminum, I did find several claims that aluminum wheels were more likely to have this issue than steel, but they were anecdotal or otherwise suspect. Admittedly anecdotal, but I noticed that a few of the aluminum wheels which were thrown happened in snow or had plants without foliage in the background. As aluminum has a higher coefficient of thermal expansion than steel, it seems reasonable that a lug nut tightened on a steel stud against an aluminum wheel in warm weather (or a warm garage) would loosen in cold weather.
I also found quite a few recommendations to re-torque lug nuts after a dozen to a hundred miles after they’re removed/replaced. If the nut was tightened a bit off-center, jostling can loosen them. This is essentially the same reason I often stop about two miles down the road and check cargo straps.