pic: When things break at the worst possible time - Einstein

[yarden.saa]

[cdm-description=photo]43941[/cdm-description]

[Michael Hill]

Crazy. Are those gear tooth leavin's in that dust?

Did you have 8" wheels on there?

[s_forbes]

Grease your gearboxes folks! Gears need grease, otherwise they kerplode.

This (http://www.mcmaster.com/#1380k35/=13tdd87) costs 6 bucks and will last for at least 4 seasons. It costs less than making 2 buttons per year.

[frcguy]

I see you've one-upped me in the stripped gear game. I commend you.

In all honesty, that's quite impressive. Could you shed any light on how you think this occurred? We ran the same gearbox, and (luckily I guess?) we only stripped the gears in the output stage.

[AlexanderLuke]

In all honesty, that's quite impressive.

I do not even know what to say to this, that's how impressive it is to me.

I am wondering what happened to this gearbox. If there's any insight as to the causes of such wear, you have people listening. There are probably plenty of other people who share similar curiosities to those who have posted. If you could, I would like to see the gears from inside that casing a bit better. I'm interested in seeing some close ups of the extent of the wear, and from what stage the wear was primarily occurring.

Team 696 experienced wear on the 3rd stage reduction of our gearboxes, but nothing to any extreme like this. We were just in that same boat as many other teams this past season in that regard.

[yarden.saa]

I see you've one-upped me in the stripped gear game. I commend you.

In all honesty, that's quite impressive. Could you shed any light on how you think this occurred? We ran the same gearbox, and (luckily I guess?) we only stripped the gears in the output stage.

It's only an assumption - I may be right or wrong:
The failing gearbox was the right one. Our robot design was not 100 precent perfect so if the driver was trying to cross the ramparts a little bit to the right, the robot will stuck and will probably get a strong counterforce as shown in this video (https://www.youtube.com/watch?v=vA-2zZjJxkU).

A better assumption can be that the torqe transferd from the wheels was too high (8" wheels with 9.52:1 gearbox reduction).

Our lesson is that we should have replaced the small aluminium gear with steel gear.


Another photo of the gear http://imgur.com/zBgXDW3

[yarden.saa]

Crazy. Are those gear tooth leavin's in that dust?

Did you have 8" wheels on there?

Yes and yes.

[ratdude747]

It's only an assumption - I may be right or wrong: lesson is that we should have replaced the small aluminium gear with steel gear.


Another photo of the gear http://imgur.com/zBgXDW3

I never have seen the point of Aluminum pinions. They're under so much concentrated load after all.. and they are so small that any gains in weight are too small to be worth the risks (this be case and point).

[Michael Hill]

I never have seen the point of Aluminum pinions. They're under so much concentrated load after all.. and they are so small that any gains in weight are too small to be worth the risks (this be case and point).

This was the reason we went with steel ones in our gearbox. I did the Lewis gear calculations and was terrified. We wanted a 16:1 reduction so I believe we used 12T (CIM, steel) - 50T (Aluminum) - 14T (Steel) - 54T (Aluminum). Using all aluminum gears gave us a very small factor of safety if I remember right, and I just wasn't comfortable with all the dynamic loads from the defenses. I think we had the right decision.

[bigbeezy]

Grease your gearboxes folks! Gears need grease, otherwise they kerplode.


This. That looks like it never was greased.

[yarden.saa]

This. That looks like it never was greased.

We did grease

[s_forbes]

It's only an assumption - I may be right or wrong:
The failing gearbox was the right one. Our robot design was not 100 precent perfect so if the driver was trying to cross the ramparts a little bit to the right, the robot will stuck and will probably get a strong counterforce as shown in this video (https://www.youtube.com/watch?v=vA-2zZjJxkU).

A better assumption can be that the torqe transferd from the wheels was too high (8" wheels with 9.52:1 gearbox reduction).

Our lesson is that we should have replaced the small aluminium gear with steel gear.


Another photo of the gear http://imgur.com/zBgXDW3

It doesn't really look like the gear was too weak from the pictures you've posted. It looks more like wear was the problem. The tooth profile on the large idler gear in that picture is exactly what you'd see if the gears were running in aluminum dust for a while. Clean lubrication keeps that from happening.

If the issue was that the gear itself was too weak to handle the load, I'd expect the failure to look like this: https://www.chiefdelphi.com/media/photos/43700 . Usually if you overload a gear, you'll shear teeth off of it, but if you run a gearbox without enough lubrication then you'll make dust and wear out the teeth like in the photos you posted.

Open gearboxes are great for FRC since you can look at the gears and see if there's not enough grease or if the grease is dirty. That's the only thing I don't really like about the molded vexpro gearboxes, but all of the other benefits make up for it. Watch your gears often and keep them greased!

[jblay]

I can only imagine what might have happened if this gearbox never broke. We were neck and neck with the eventual championship alliance in the first match before you guys broke and then we won match 2 before getting blown out in match 3. If only this gearbox could have held for a few more matches.

I still don't know how you guys got that fixed for match 2. That was one of the most awesome, fast, and crazy repairs I've ever seen. I think there are very few teams in the world that could have fixed that kind of break without missing a match.