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

Re: AndyMark 8 Inch pneumatic hub fail
 

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

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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

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

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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

Re: AndyMark 8 Inch pneumatic hub fail
 

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 (http://www.andymark.com/product-p/am-2021.htm). 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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

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.

Re: AndyMark 8 Inch pneumatic hub fail
 

Chuck, thanks for the kind offer!

All, here is situation.

The pressure in the outside wheels was at 15 PSI with the center wheels being at 25 PSI.

We went to add pressure today when we noticed that the frame had a bit of wood from our defenses. Indicating that our tires were compressing enough to allow the wood to contact our frame. Our frame is designed so that the defense can not directly touch the wheel hubs even without a tire on the hub. We have at least a 0.5 inches of aluminum between the hub and any outside contact.

We used the hardware from AndyMark on the Hubs without any locktite.

We drove the heck out of these, thinking we would rather brake it in house that at a competition.

It broke, just not where we thought we were vulnerable.

V/r

Re: AndyMark 8 Inch pneumatic hub fail
 

In my opinion (and I recognize the difference between my opinion and fact) the Loctite was not a factor, unless you poured quarts of it into a container and soaked your hubs in it over the summer. Based on what you said about the failure location, I assume you did not.

You stated that you tested the robot hard, deliberately trying to break it. That is good engineering practice (again, my opinion).

I'm assuming that knowing you were going to do this, your team decided to eliminate as many weak points as possible. Nylock nuts are not 100% nylon, and so, you took advantage of the metal-to-metal contact and added a few drops of Loctite. Pretty sure that did not cause the hubs to fail.

So, you found the weak point in the wheel-hub system that a majority of teams seem to be using this year - the hubs - and you shared it. THANK YOU. This will help a lot of teams.

It seems that this year, more than years past, people are quick to jump on those who post. It's almost painful to read some of the comments when a team posts a CAD rendering of a robot and some of the comments are tantamount to "that looks like 14 gauge wire - don't you know that a CIM requires..."

Come on, people, be grateful when someone shares potentially helpful information - and be helpful with our comments and discussion rather than critical. This is, after all what we're supposed to be doing, right? Setting an example, right?

Re: AndyMark 8 Inch pneumatic hub fail
 

If you've done any serious testing, this may be the root cause. Here is some video of our robot going over defenses. Take a look at the slow motion clips near the middle of the video. See the tires compressing nearly all the way to the rims? This was with tire pressure of 35psi. If you were running at 15 psi on your outer wheels, and hitting your defenses as hard as we have been, I have to think your tires have been fully compressing. I don't think the rims would last long if that were the case.