pic: Stripped VexPro gear

[EricH]

Originally Posted by pilleya

It only really takes one tooth to break or chip to cause all the teeth to be stripped off the gear, as I believe that the shrapnel causes the next tooth to be clogged and break.

Not quite...

What usually happens is that if one tooth breaks off, the next tooth takes more force than it would ordinarily (fewer points of the same force being applied = more stress as well), plus a chance of shock loading. Then that one takes off... repeat until you're out of gear teeth.

[pilleya]

Originally Posted by EricH

Not quite...

What usually happens is that if one tooth breaks off, the next tooth takes more force than it would ordinarily (fewer points of the same force being applied = more stress as well), plus a chance of shock loading. Then that one takes off... repeat until you're out of gear teeth.

When only a small number of teeth are removed, there is normally a lot of damage to the other teeth. But this damage doesn't seem that it could be all caused by the normal meshing of the other gear. In this case is it the shrapnel that is the cause of this?

[EricH]

Originally Posted by pilleya

When only a small number of teeth are removed, there is normally a lot of damage to the other teeth. But this damage doesn't seem that it could be all caused by the normal meshing of the other gear. In this case is it the shrapnel that is the cause of this?

In that case, yes, it would be any remaining bits. You'll also want to check the mating gear(s) for damage, as damage to metal tends to transfer to any metal of similar softness that it hits... I wouldn't be surprised if there was some "hard whacks" causing damage as well.

[Mechvet]

Originally Posted by R.C.

For the 14T I would personally only use the steel in anything that takes moderate to high load and the aluminum one for low load. Or just use the steel one all the time since the weight difference is minor.

Absolutely. Our fix was to go grab some 3/8 AM hex gears and face them down to the required width. No issues after we switched out the aluminum gears.

Originally Posted by pilleya

<snip>

Also teams are putting much more torque on them than usual, for example if a team normally uses a shifting gearbox with a 11fps low gear on a year with an open field and 4inch or 3.25inch wheels, and then they change to 8inch wheels and a 6fps low gear, then the final stage is experiencing almost 4 times the torque.

This is the differing factor.

However, two years in a row of COTS gearboxes failing us has prompted the decision to return to custom boxes. They're heavier (and a touch more expensive), but they never broke.

[Landonh12]

We had the same thing happen to us on our scaling mechanism. I believe we were using the 60 tooth 1/2 hex bore gear from VexPro. We have a CIM Motor that has 3 stages of AndyMark GEM Planetaries on it, along with a 1:3 gear ratio coming out of it.. totaling up to around 900 ft/lbs of torque. At Bayou, we went out in the quarter finals because we had 4 teeth shear on that gear. We couldn't scale because the robot sagged and got caught in that section of the gear that had stripped.

We ordered a steel gear from McMasterCarr and welded in a 1/2 inch socket. It worked throughout Rocket City flawlessly.