Re: Wheel Wear
 

We have not tested our wheels out yet on the Robot but i really, really hope the wheels do not wear down as quick as people say they do. First is expensive enough with out have to have a ref demand you change your wheels out every regional.

Re: Wheel Wear
 

Our experience so far is that little bits of dirt and crud do cause some minor wear of the wheels. This is made worse by the fact that they spin so easily from excessive acceleration. The marks made tend to be along the length of the tread and not the width, but by no means would I say that they wear 'a lot' - just some visible scuffing.

In our tests on the terrazzo floor (in the hallways), waxed vinyl tile floor (in the cafeteria) and a piece of "official" pebbled regolith, the regular floors are almost twice as grippy. We pulled on a 4-wheel test platform weighing about 30 pounds with locked wheels with a spring scale. We found a small (under 20%) difference between sideways pulls and longwise pulls, so those transverse CoF numbers did not pan out for us. Also, the difference between static friction and sliding friction is measurable at about 20% (sliding being less, of course).

The custodial staff was not amused by the scuffs in the school floors the wheels left. We promised to not do it again, and they forgave us.:)

Re: Wheel Wear
 

First time we tested the wheels on a robot and the correct flooring we saw wheel marks left on the FRP. Pretty hard to avoid this when you are doing real testing. Granted, I was trying to show students how easy it was to push robot around when the wheels are spinning. (We could even smell the plastic on wheels at one point)

I guess my suggestion (from the above experience), use caution; do not do extensive testing and learn from others or get extra wheels.

I'm glad we got our 10 wheels prior to them running out. :ahh:

Re: Wheel Wear
 

So, if the inspectors at the regional deem the scrapes on the wheels beyond the normal wear and tear expected, and they want us to change our wheels, will we be responsible for providing the replacements or will they have wheels to give us?

For example, if we think the wheels have gone through normal wear and tear, it is logical that we would not have a full set to replace the robot with. But if an inspector says that they are too damaged, what do they want us to do?

FIRST has not said a point to which the wheels will still be usable, so what should our team expect?

Re: Wheel Wear
 

This might clarify things a bit.

http://forums.usfirst.org/showthread.php?t=11108

Re: Wheel Wear
 

in no way am i saying i will tell my students to push the rules, nor do i intend to wear the wheels down. I dont see anyone on this thread saying "im gonna wear the wheels down" Part of how i was taught was to know everything thats gonna happen and be prepared for it. I just wanted to get others feels on if i should get some extra wheels, and how it may be handeled.

Re: Wheel Wear
 

If you aren't sure your wheels will pass, get extras. If you don't need them, another team (who isn't on CD or reading the Q&A or manual) will.

Re: Wheel Wear
 

I was just looking at that forum post where the "potential for increased traction" will be assessed by the referees. I am not happy with that answer

Here's why-
1. there has been an epidemic of inconsistency in inspections among the regionals and the championships. Since the inspectors/referees are volunteers, often inconsistently trained and always subjective, what is easily allowed in one region may be rejected at another

2. any scratching on the wheels offers a "potential for increased traction" .

3. no recourse is clearly stated for the team who has wheels that are rejected. Are the expected to rip the bot apart on the spot and put on new wheels? Where do these wheels come from? Are the teams expected to put out hundreds of dollars in changeout wheels that they may not be required to use?

We have been driving a nice robot base since last weekend. We prepared a waxed school hallway by sweeping and dry mopping the floor before the robot ever hit it. To the best of my knowledge this is the type of substitute the GDC was proposing if a team didn't have an official practice surface.

Now, after 3 hours of driving around we are noticing scratches and scores from dirt picked up by the wheels. I am sure similar scratches will also happen from metal flakes and such shed by the robot in any situation. Shoes track enough grit to be an issue, especially when we have snow days and salt is all over the place.

So I ask- What is considered NORMAL WEAR? An answer of "the refs will decide" isn't satisfactory.

How about the experts developing a technique for refinishing scratched wheels so they can be used if they experience this "normal wear"? If this traction is such an issue that is the only way I can see that assures that all robots hit the field in the same condition.


WC :cool: :cool:

Re: Wheel Wear
 

Some more food for thought:
I originally thought "no big deal, this won't affect us because we have a large chunk of glassliner." However I was surprised to find out that the wheels wear a noticeable and significant amount even if they spend their entire life on the "regolith".

We've got wheels that have never been driven on anything but a regulation surface, and I'm worried an inspector would dub them "illegal".

Since these wheels were made of delrin I foolishly assumed we would NOT need to replace them. ("Durr... how much could they wear down!? This year we don't need to worry about changing treads!") Maybe we need to tweak our drive a little bit to allow for easier swaps...:rolleyes:

-John

Re: Wheel Wear
 

We've been running our wheels on concrete and they have accumulated a significant amount of dust and grit. However, when we cleaned them with a wet paper towel, they feel as good as new.

Re: Wheel Wear
 

Just from my experience, wiping them down with a rag or paper towel before and after every use keeps them pretty clean

Re: Wheel Wear
 

We have been running our test chassis on some sheet plastic that we think is similar to the official stuff. I'll take a close look today, and see how well the wipe test works, but our wheels have been getting a scuzzy look, kind of like what your mouse will accumulate. No idea if that helps or hurts traction, but it sure is gross!

We have about 10 hours of drive time on those wheels now, hopefully we won't have to go through more than one set before ship. :ahh:

Wetzel

Re: Wheel Wear
 

Update 5 includes a reference to Restoring Damaged Wheels which says that you can clean the wheels with scotchbrite or light sandpaper until your fingernail no longer catches on ridges or burrs.

Re: Wheel Wear
 

Thanks for this info. This will be helpful come competition.

Re: Wheel Wear
 

Our wheels look just like the normal wear and tear picture in the restoring damaged wheels document. A damp napkin went a long way towards restoring it.

Wetzel