pic: Toughbox Gear, destroyed

[B - Morris]

loading photo ...

[Kyle Love]

Did you properly lube the gearbox prior to testing?

[AdamHeard]

I've heard of similar experiences with both the 12 and 14T this season.

[Kevin Sevcik]

Related questions that spring to mind are if you checked that the output shaft turned freely before powering the motors, if you were running the motors through an appropriate breaker, if you put the e-clip on the output shaft, etc, etc.

Given the super slippery floor this year, I can't see a freely rotating drivetrain doing this to a toughbox. Nor should you be able to do easily do this with appropriate breaker protection on the drive train.

The only way I can think of for a nice loose drivetrain to do this to a gear is if you have some wicked shock loading on it from your control system going from full forward to full reverse instantly and repeatedly.

[sdcantrell56]

This is kinda scary. We have experienced some tolerance issues with the andymark extended output shafts as well which is slightly disappointing. It seems that the hex portion is slightly not concentric with the 1/2" round portion. We are also using the aluminum cluster gears and it will be interesting to see how they hold up. They should be ok since the forces on the drivetrain in this years game are quite low but only time will tell.

[sanddrag]

You may consider trying the Macro mode on your camera (it usually has an icon that looks like a flower).

Anyhow, we experienced a near identical failure with AndyMark 12 tooth pinions on a CIM motor, mating to an AndyMark 50 tooth gear. We run at +.003" between the theoretical pitch circles. The gearbox rotated freely when assembled, but when running, we noticed wear and steel dust almost immediately. After approximately two hours of running, the teeth were nearly completely gone. Before they wore completely down, they turned to sharp points. We showed several professors of Mechanical Engineering at a local university who were just as shocked and baffled as we were.

It appears the gear tooth profile may not be a true involute curve as it should be. The gear teeth appear to be sliding against one another, rather than more of a rolling contact motion. My best guess is that something is wrong in the gear forming/cutting process, since the application/design we are using these gears in is not different really from any year past, and we have never experienced this accelerated wear before. I'm guessing that the pressure angle is not 14.5 degrees, or the curve is not a true involute.

However, I have not looked at it in too much detail, and there may indeed be something wrong on our end. We plan to hardness test the gears eventually, and perhaps harden new ones.

EDIT: We are trying new gears with grease, per Paul's recommendation. We'll post here again after more testing.

[spc295]

we have had similar tolerence problems from AM products, we had an extended shaft strip the hex part, it must have not been heat treated.

[B - Morris]

Thanks everyone for the feedback.
I didn't assemble the toughboxes, so I can't honestly say whether it was lubed up or not, but the students (with a mentor) that did it, followed the instructions provided. I still can't see how packing it with grease could solve this problem, as it seems like the gear is too soft, but I'm no expert.

PS sorry for the poor quality, the only camera I had available was on my phone.

[Paul Copioli]

B-Morris,

Please listen to this post very carefully:

You must lube this gearbox or you will get the failure shown in your picture!

The Am toughbox uses the same basic gears that was used in the 2005 Kit of Parts. Andy Baker, JVN, and I designed that original gearbox and it also had to be lubricated. They do not need much grease, just put some on the teeth. These gears are plenty hard for our application.

Team 217 has been using these exact gears since 2005 and we have had ZERO problems and we have used them on 3 motor gearboxes and robots with much more power than this year.

By the way, I am an expert as I design gears for industrial robots that have to run 24 / 7 and last for 10 years.

Please, please, please lubricate these gears with grease and you will never have a problem.

Paul

[B - Morris]

Thanks Paul.
We are going to get some replacement gears and make sure our toughboxes are properly greased for the future.
Hopefully this picture will help other teams realize grease is needed before they destroy their gears too.

[MrForbes]

I've worked on cars for years....the gears used in automotive transmissions and differentials are made of very very hard steel, and will last for a very long time with proper lubrication. Without lubrication, they will be destroyed in a matter of miles (I've done it myself by forgetting to add oil to a differential on a car I built).

Use grease! add a little more grease if you aren't sure exactly how much you need.

[gauntletguy]

However you do not want to add so much grease that it goes onto the shafts as our team had learned the hard way. A mentor told some of our students to grease the gears but they greased all of it and the keys on the CIM shafts fell out on all of them almost every time we drove the robot.

They had to be cleaned with rubbing alcohol, but now we have the problem solved.