AndyMark 8 Inch pneumatic hub fail

All,

We took apart our drivetrain to give it some TLC today and discovered all of our 8 inch pneumatic hubs are failing. Very similar to the rhino tread pulleys.

If you are using them, I suggest you take a close look are your hubs.

I just sent pictures to AndyMark and we awaiting for a reply.

Locktite was just applied, it was not there before about an hour ago.

http://imgur.com/a/DX4OH

http://imgur.com/a/DX4OH

Is that loctite on the nuts? Loctite will destroy the polycarbonate hubs.

What’s the blue stuff all over? Is that loctite? If so, that explains it. Loctite eats polycarbonate, chemically, causing it to become brittle and crack.

They’re failing because you put loctite on your screws.

You shouldn’t have done that for 2 reasons, the first being that loctite will melt the plastic, the second being that it’s pointless because you’re using nylock nuts.

Even have been using these hubs successfully without using any loctite.

It seems like this isn’t Andymark’s fault.

The locktight was just applied to get through the next couple of days!

The damage goes all the way through the hubs.

I highly suggest everyone using these take to a look at your hubs.

You don’t need loctight when you use nylock nuts…
Looking at how much excess loctite is on the hub, that damage could have easily been done by a combination of chemical breakdown and stress on the plastic.

Again, it looks like the failure was caused by the loctite and not the hubs. It causes the polycarbonate to get brittle and crack so I’m not surprised the damage goes through the hub.

Locktite was just applied, it was not there before about an hour ago. After the damage was found a student put the locktite on in an act of desperation.

What did you anticipate loctite helping with that the lock nuts weren’t already doing for you?

Everyone, please read the thread BEFORE responding.
The Locktite was added AFTER the failure. It is NOT the cause of the failure.

I believe the nylock nuts may have actually contributed to the failures.
Some nylock nuts have larger outside dimentions than the comparable regular nuts.
Forcing the larger nut into the hex opening, and over tightening them may crack the polycarbonate.

What screws/nuts are you using?

I’ve got 3 robots I’m working with that are using those hubs and none show anything like that kind of wear.

We did read the thread. He edited his original post to say that it was applied after the damage appeared.

[edit] On closer inspection there are some cracks around the nut cavities that look like they might be consistent with slightly too large of a nut.

Look, I’m not trying to get anything other than the word out to check your hubs.

The locktite was applied after the fact.

We are fixing our issue, just make sure you don’t have the same one.

No argument. Locktite WILL cause this type of failure!

Forcing in nuts that are too large for the opening can crack the polycarbonate too. Just my $.02.

Clint,

We have 8 of the hubs here in our shop if you need them ASAP get someone on the road to Vicksburg if you need them before bag and tag. If not we can bring them to you next Saturday in Oxford.

-Chuck

We added the loctite in an attempt to try and keep things still. Obviously, with a hub that is nearly disintegrating around the bolts, a substance needs to be applied to hold things together until a permanent fix has been applied.

We used the nylock nuts included in the mounting hardware for these hubs, purchased from AndyMark (Wheel Hardware Kit 11: Hub Mount to Pneumatic Wheel - AndyMark, Inc). These are the correct nuts from my understanding.

Sorry for our ignorance. We simply did not know that loctite eats away at polycarbonate. We are currently looking at other options.

EDIT: Another thing. The center hubs (6 wheel 1/8" center drop) were not damaged as much as the outside hubs. We have been stress testing our robot by hitting defenses as much as possible.

No ignorance implied, I was simply curious as to what you thought a thread locking substance was going to achieve there.

How much air pressure did you fill your tires to? Did you check the outsides of the hubs as well (take the tire off and really check)? I would be curious if there was any impact directly to the wheel itself that wasn’t absorbed by the tire due to a low pressure situation.

Thanks for the heads up. I can see the barriers being the main culprit due to the stress on the wheels and not be surprised if that ends up being the case.
We’ve broken plaction wheels before in 2010.
It’s a good thing we decided to machine our own rims.

We did have the pressure below specifications. We did this because we believed using a lower pressure would help absorb shock from ramping over the defenses.