pic: Stripped VexPro gear

[TheModMaster8]

Originally Posted by Mechvet

We blew every tooth off of two of the VexPro 14tooth 3/8 hex gears.

Turns out aluminum gears just aren't quite rated to the level of impact we were subjecting them to.

those gears are made out of 7075 Aluminum which is as strong as many types of steel, thats one impressive feet lol

[Mechvet]

Originally Posted by TheModMaster8

those gears are made out of 7075 Aluminum which is as strong as many types of steel, thats one impressive feet lol

"Strong" is a rather non-precise word for material descriptions.

Steel and 7075 may have similar load capability and shear strength, but when it comes to a sudden impact (ie a 145lb robot at ~12fps slamming into a barrier), the more brittle aluminum gear doesn't stand a chance.

[pilleya]

Originally Posted by TheModMaster8

those gears are made out of 7075 Aluminum which is as strong as many types of steel, thats one impressive feet lol

In comparison with 4140( normal steel gear material) it has a higher yield strength, but a lower ultimate tensile strength. It also has a much lower %elongation. The percentage elongation means that it can't bend and deform as much before it fails

http://www.wcproducts.net/how-to-gears/

[s_forbes]

The material of the gear is not the end-all deciding factor in whether or not it's strong enough for the job. If you stick enough torque on it, you can break anything!

Each stage of gear reduction adds up fast. Whenever we need a gearbox that needs more than 3 stages of spur gear reduction, I start to get a little paranoid. We underdesigned the 3rd stage of our stacking mechanism last year and separated several gears from their teeth when operating it with the braking mechanism engaged.

Always make sure each stage can handle the maximum torque the motor can output, and add however much cushion you think you need. (Then test test test... break it at your shop so you don't have to break it at competition)

[waialua359]

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.

We found out the hard way losing in the Hawaii regional this year.
Our 14T aluminum hex gear and another of our aluminum VEXPro gear lost teeth in one of our trans. Could not swap out the trans in time for the next semis match.
In the past we always used steel and could see noticeable wear after running our robot for a lot of practice and real matches.
I guess with the aluminum ones, they just break teeth. :/

[pfreivald]

Originally Posted by waialua359

We found out the hard way losing in the Hawaii regional this year.
Our 14T aluminum hex gear and another of our aluminum VEXPro gear lost teeth in one of our trans. Could not swap out the trans in time for the next semis match.

This is exactly why we lost the quarterfinals at Tech Valley; we saw that the gear was starting to strip, but the repair/swap would take too long. We hoped to survive through the tournament and would have made the semifinals if we could have driven ten more feet--but alas, it gave up the ghost on the wrong side of the (open) Sally Port.

We switched to toughboxes with aggressively-lightened steel gears for FLR and had no drivetrain issues throughout.

[CJ_Elliott]

Originally Posted by waialua359

We found out the hard way losing in the Hawaii regional this year.
Our 14T aluminum hex gear and another of our aluminum VEXPro gear lost teeth in one of our trans. Could not swap out the trans in time for the next semis match.
In the past we always used steel and could see noticeable wear after running our robot for a lot of practice and real matches.
I guess with the aluminum ones, they just break teeth. :/

It's ok. We too lost teeth in semis and couldn't run at 10k... after having already replaced the 14 tooth gears in both gearboxes during quals. I feel like this whole 14 tooth aluminum gears thing is an issue.

[Chris is me]

Personally I wish that VexPro would make all of their pinion gears (say 14-24T) available in steel as well as aluminum. They are a higher quality gear than AndyMark in terms of tooth profile, manufacturing tolerances, and quality in general, but being stuck with aluminum pinions can be somewhat limiting when you don't have the ability to compensate for the loss in strength in other ways (ie doubling the face width, different DP of gear, etc).

[JesseK]

Can anyone confirm, via math, that the steel teeth would have been strong enough to prevent total tooth failure? At the time this happened, we had to move fast to fix it for our first event:

For our tilt motor we ran a BAG -> 100:1 VP -> 20T/40T reduction and kept stripping the teeth on the 20T. This was because of the cantilever on the VP - the shaft would flex just enough to cause a LOT of stress on the teeth, and they'd strip. By the time this happened VEX was out of 20T gears, so we swapped to belts. We also added a plate on the other side of the cantilever with bearings to support it.

We're running WCP gearboxes with an extra 18->36T sprocket reduction (non direct-drive) and they have been flawless this season with no signs of wear on the sprockets. So I don't know that aluminum vs steel is the issue.

[waialua359]

Originally Posted by CJ_Elliott

It's ok. We too lost teeth in semis and couldn't run at 10k... after having already replaced the 14 tooth gears in both gearboxes during quals. I feel like this whole 14 tooth aluminum gears thing is an issue.

Is that really what happened? Holy Moly. Sorry to hear that.....I had wondered what happened to you folks when the backup robot was used.
For our situation, we had hoped to come back in and decided not to bring in the backup bot.

[Chris is me]

Originally Posted by JesseK

Can anyone confirm, via math, that the steel teeth would have been strong enough to prevent total tooth failure? At the time this happened, we had to move fast to fix it for our first event:

For our tilt motor we ran a BAG -> 100:1 VP -> 20T/40T reduction and kept stripping the teeth on the 20T. This was because of the cantilever on the VP - the shaft would flex just enough to cause a LOT of stress on the teeth, and they'd strip. By the time this happened VEX was out of 20T gears, so we swapped to belts. We also added a plate on the other side of the cantilever with bearings to support it.

We're running WCP gearboxes with an extra 18->36T sprocket reduction (non direct-drive) and they have been flawless this season with no signs of wear on the sprockets. So I don't know that aluminum vs steel is the issue.

Gears versus sprockets are apples and oranges comparisons - you can't draw conclusions about material choice for one by looking at the other. Sprocket load is shared by several teeth at once, while gear loads are borne by just a few teeth at a time. Chain also dampens some degree of shock load, to an extent.

[JesseK]

Originally Posted by Chris is me

Gears versus sprockets are apples and oranges comparisons - you can't draw conclusions about material choice for one by looking at the other. Sprocket load is shared by several teeth at once, while gear loads are borne by just a few teeth at a time.

Hmm, fair point.

[CJ_Elliott]

Originally Posted by waialua359

Is that really what happened? Holy Moly. Sorry to hear that.....I had wondered what happened to you folks when the backup robot was used.
For our situation, we had hoped to come back in and decided not to bring in the backup bot.

Yea... 10k was a bit of a cluster. We broke every system on our bot, but we digressed. 3 grenaded drivetrain gears at 1 competition... I think that might be a record.

[Jeffrafa]

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.

We also learned this lesson the hard way on the WCP SS gearbox. Fortunately it first happened during our 6-hour unbag window prior to our first competition, so it didn't cost us any matches. It did cost us 2x 45 minute teardown sessions (1 during unbag, and 1 at the event) to upgrade both competition gearboxes - We were also fortunate to already have the 14T steel gears on-hand, spared for another mechanism.

We also helped get 4469 back up and running with steel gears at PNW DCMP after they stripped the same 14T aluminum gear in the Vex 2-stage SS gearbox.

R.C. - It would be great if these two gearboxes were configurable with steel 14T gears, or even came with them by default for the relevant gear ratios. Currently only aluminum is available when building a gearbox for purchase through Vex or WCP - steel replacements have to be purchased separately.

[R.C.]

Originally Posted by Jeffrafa

R.C. - It would be great if these two gearboxes were configurable with steel 14T gears, or even came with them by default for the relevant gear ratios. Currently only aluminum is available when building a gearbox for purchase through Vex or WCP - steel replacements have to be purchased separately.

Jeff,

I totally agree with you, I thought we made this change over. I will check and get this implemented, also have a few other changes planned.