OH SNAP! Belt failures 2014

[kevincrispie]

Everyone with belt questions/issues should look at this thread and this thread. Also, I wrote a post in the first thread (long I know) about what 971 has learned about belts.

I summary: use Gates GT2 and not the Vex HTD. It's my experience that they are better in terms of manufacturing quality and usefulness for FRC applications. Also, look up Gates/other companies documentation. There is quite a bit of information out there if you know where to look (I linked some in my original post). Knowing what a properly tensioned belt is is important, and knowing the signs of an undertensioned or overtensioned belt can save you many headaches in the future.

Andrew,
One question I have for your belt failures is how high is your center of gravity? 971 speculates that having a high cg could affect the failure of drivetrain belts. (see my post for more details)

If you post pictures of your belt failure, I or someone else might be able to help you diagnose what happened.

[instantcake]

We used gates gt2 belt on our shooter when we had a motorpolt, however this happened:

after we killed the first belt, we switched to chain. user error probably killed the belt, as we were hard stopping the shooter while still running the belt. The belts were driven by 2 cim's and 2 775's geared 5.33:1 at the section that sheared. We did not break the pulleys, but the belt was dead. The belts we use on our drivetrain, however, are still in good shape after two regionals. We used VEXpro 9mm Timing Belts (two of them are attached to two cims each, and two to a cim and a minicim each), and they have held up great.

Originally Posted by kevincrispie

Andrew,
One question I have for your belt failures is how high is your center of gravity? 971 speculates that having a high cg could affect the failure of drivetrain belts. (see my post for more details)

If you post pictures of your belt failure, I or someone else might be able to help you diagnose what happened.

Kevin, Our center of gravity this year was about 8-9 inches off of the floor. I don't have pictures, unfortunately, but I plan on stopping by your pit at champs and asking about your drive, if you have the time.

[kevincrispie]

Originally Posted by Andrew Lawrence

Kevin, Our center of gravity this year was about 8-9 inches off of the floor. I don't have pictures, unfortunately, but I plan on stopping by your pit at champs and asking about your drive, if you have the time.

Please do. We might be able to give you more detailed information in person.

[Thad House]

Originally Posted by kevincrispie

Please do. We might be able to give you more detailed information in person.

I might have to stop by and take a look as well. Your robot is incredible.

[kevincrispie]

Originally Posted by instantcake

We used gates gt2 belt on our shooter when we had a motorpolt, however this happened:

after we killed the first belt, we switched to chain. user error probably killed the belt, as we were hard stopping the shooter while still running the belt. The belts were driven by 2 cim's and 2 775's geared 5.33:1 at the section that sheared. We did not break the pulleys, but the belt was dead. The belts we use on our drivetrain, however, are still in good shape after two regionals. We used VEXpro 9mm Timing Belts (two of them are attached to two cims each, and two to a cim and a minicim each), and they have held up great.

It looks like the teeth are coming off this belt, which means that it is likely undertensioned. Teeth coming off belts is a pretty common failure for undertensioning.

Originally Posted by Thad House

I found a picture of our first break. This was the belt on the practice bot. The competition ones were not quite as diagonal of a cut, but they were still really jagged.

It looks like these belts might have been overtensioned. Just because all the teeth line up fine doesn't mean you can't overtension belts. Also, excessive wear is a telltale sign that you've been overtensioning. Most teams running belts are actually overtensioning belts without realizing it. Taught is too tight when it comes to these belts.

[instantcake]

Originally Posted by kevincrispie

It looks like the teeth are coming off this belt, which means that it is likely undertensioned. Teeth coming off belts is a pretty common failure for undertensioning.

Although that could be a reason that our belt sheared teeth, it was overtensioned if anything (it was extremely difficult to get on), and made the nice tension'd sound. The cause of failure was the sheer force put on the belt.

[kevincrispie]

Originally Posted by instantcake

Although that could be a reason that our belt sheared teeth, it was overtensioned if anything (it was extremely difficult to get on), and made the nice tension'd sound. The cause of failure was the sheer force put on the belt.

Interesting. But it was possible to get on without detensioning before? Do you have a tensioner on your drivetrain that you use to get your belts on? Are these gt2 or vex belts? What brand of pulleys did you use?

[Pretzel]

Team 1619 used a tank tread style design this year that used two belts wrapped around four pulleys each to propel our robot. We had our right belt snap in quarterfinals match 1-1 in the Utah regional. This occurred because the belts were the same we had used with a two cim drivetrain in years prior, while this year we had used a four cim drivetrain with a two speed transmission, which gave the belts a bit more abuse (along with the rough gameplay).

We did design to be prepared for a belt failure however, and we back up and running within five minutes. All we needed to do was remove our side panel, slide the belt off, and then slide a new one back on since our design had the side panel acting as the second point of support for the pivots. As soon as the new belt was on, we merely had to slide the side panel back in place and tighten the screws again.

It turns out that the belt had failed at its weld point. The failure itself actually occurred when we were pushed sideways for an extended period of time and one of our guesses as to what happened is that the tread, with it's square edges, had its edge hang up on the carpet. This would allow the best to twist and increase the tension on the belt, which could lead to a snapped belt.

At any rate, our team came out of Utah with a learning experience behind us. We ordered some new belts before the Colorado regional, with twice the steel fiber content, and went back out to compete with no further problems.