AndyMark 8 Inch pneumatic hub fail

[ChuckDickerson]

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

[Landonh12]

Originally Posted by MrBasse

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

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.

Originally Posted by billbo911

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

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.

[MrBasse]

Originally Posted by Landonh12

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.

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.

[waialua359]

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.

[Landonh12]

Originally Posted by MrBasse

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.

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.

[Fusion_Clint]

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

[chapman1]

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?

[ToddF]

Originally Posted by Fusion_Clint

Chuck, thanks for the kind offer!
The pressure in the outside wheels was at 15 PSI with the center wheels being at 25 PSI.
V/r

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.