17-01-2009 19:22

thefro526

Re: pic: Wheel problem.

How exactly did this happen? Did you do it while driving or did you drop the wheel?

17-01-2009 19:40

NorviewsVeteran

Re: pic: Wheel problem.

I suggest finding the "macro" option on your camera. It takes clearer pictures up close.

All of ours are holding up fine, but we haven't driven around yet.

17-01-2009 19:51

Jacob Paikoff

Re: pic: Wheel problem.

We were drifting and the robot went from the Regolith to the wood floor and back on and then we found the plastic cracked when we were checking the robot.

17-01-2009 19:53

ATannahill

Re: pic: Wheel problem.

Forgive the quality, that is what we get with a camera phone, what you may not see are some cracks in the black plastic.

We were driving and when we stopped we found this, supposedly from when we went off of and back onto regolith.

17-01-2009 19:59

kevin.li.rit

Re: pic: Wheel problem.

Where these wheels being driven by some sort of hub? They are the same hub as the previous andymark wheels.

17-01-2009 20:00

gallo26

Re: pic: Wheel problem.

And after i noticed this wheel thanks to our team members, i quickly checked the rest of the wheels. and sure enough the other back wheel is ready to give. The front 2 wheels are cracked but they didn't shatter yet. Could this be a huge issue during competition between the regolith and the carpet?

I'll also try to get you guys some photos of the rest of the wheels. Almost like a before... during... and after stage.

17-01-2009 20:03

gallo26

Re: pic: Wheel problem.

Its just using the bearings provided with the wheels and the wheel was driven by a chained sprocket.

17-01-2009 20:16

bigbeezy

Re: pic: Wheel problem.

were u drifting onto the wood floor? and does the wood floor have a lot more friction? idk maybe the sliding sideways is fine on the regolith but when they go onto something of greater friction the wheels cant take it. i wouldnt think that would cause them to fail but its a possibility

o wait is the hub broke? maybe too much sudden torque like changing directions very quickly

17-01-2009 20:22

NorviewsVeteran

Re: pic: Wheel problem.

It might be a general stress fracture, considering the wheels (hub and tire) have ZERO give when it comes to bumps, such as driving onto a panel. I sure hope it isn't common, and that you guys get replacement wheels soon.

17-01-2009 20:47

Chris Fultz

Re: pic: Wheel problem.

can you post a picture of a wheel "as assembled"?

are you using a plate sprocket, or one with hubs?

if you are using a plate, is there enough clearance between the chain and the wheel material, or is there some rubbing?

We have been driving the new wheels for about 2 weeks on a practice chassis (with #35 chain, KOP bearings, fixed axles and aluminum sprockets) and have not seen any issues at all.

17-01-2009 20:47

germanystudent

Re: pic: Wheel problem.

it might be the shock from the regolith to the wood... kinda like skidding out on ice then sliding onto pavement.

17-01-2009 20:49

dmcguire3006

Re: pic: Wheel problem.

Don't use LocTite on you wheels... It dissolves the plastic. Your picture is what our wheels looked like a day after we tapped the wheels for the 10-32 screws and applied LocTite.

Bummer!

17-01-2009 21:01

gallo26

Re: pic: Wheel problem.

Well we did not locktite the wheels. It was hard enough to get those screws in there after we tapped the holes. But i do know that there is not a lot of friction on the wood. Its a gym floor. basketball court. whatever you want to call it. Theres no hub, just a sprocket spaced by the spacers provided with the wheels. Theres a ton of clearance using #35 chain. So... i hope it was a bad batch or something... because this competition requires drifting and sliding. Who knows what went wrong...

17-01-2009 21:02

Nathan Streeter

Re: pic: Wheel problem.

Yeah, a pic of how you mount your wheels to the sprocket would be helpful for advice; however, I'm guessing its how you screwed the sprocket onto the wheel... What I would suggest doing (what has worked for our team this year, and with the past KOP AM wheels) is using a 2" long 8-32 going on the sprocket through the entire wheel, with a nylock on the other end. Tapping may seem like a weight savings, but its a little more work, harder to repair/replace, puts the weight in a smaller area, and may loosen if you don't use LocTite, which can weaken the plastic!
So, I don't know what your team was doing, but I think if you reconsider the wheel mount and buy replacement wheels you should be fine!

17-01-2009 21:09

gallo26

Re: pic: Wheel problem.

Yup! i thought about that... I was a little tired after the first 2 wheels we did. So we might end up doing that for competition. Thanks!

17-01-2009 21:15

Chris Fultz

Re: pic: Wheel problem.

If you tapped the wheels to install screas to hold the hubs, you probably waekended the plastic enough to cause this after running.

As suggested above, #8 screws and nylon insert lock nuts work very well and would save you a lot of time.

17-01-2009 22:03

seraphim33

Re: pic: Wheel problem.

we were puttin our wheels together on a test bot and one fell off the table to the floor(a 3ft fall) and cracked the white part of the wheel

17-01-2009 22:14

Alan Anderson

Re: pic: Wheel problem.

It shouldn't be that hard to insert screws after tapping. Maybe you didn't tap it correctly?

17-01-2009 22:28

s_forbes

Re: pic: Wheel problem.

Our wheels are tapped and we haven't had this problem (although, we haven't had a lot of drive time either). How far did your screws go into the wheel? Using longer screws might eliminate this problem.

17-01-2009 22:47

KRUNCH DUDE

Re: pic: Wheel problem.

I doubt that tapping the holes could do that much damage also next pictures will be taken with a camera sorry

17-01-2009 22:56

blhenze

Re: pic: Wheel problem.

When I saw that they suggested to tap the holes in the wheel, I did a quick comparison to last year's wheel rim. I strongly recommend using 8-32 1.25" UNC screws with washer, lock washer, and nut. The 8-32s fit perfectly through the holes and provide a much stronger connection to the gear/wheel then a tapped hole with short screws.

18-01-2009 04:29

artdutra04

Re: pic: Wheel problem.

Why are people tapping the wheels for #10 hardware?

The specs on the wheels say the six holes should be 3/16", or just barely smaller (.0025") than #10 close fit tolerance. In real life however, it seems that everything on the KoP wheels is about .05" larger than the posted specs. Checking the wheels on calipers reveals the six holes to have a diameter of about .17", which is #8 clearance but is too large for #10 tapping!

#10/32 should be tapped with a .159" (#21 drill) hole, and #10/24 should be tapped with a .1495" (#25 drill) hole. And without reaming the hole larger to #7 drill (.201"), you cannot tap for 1/4-20. I'm halfway amazed you were even able to get threads to stay in after tapping these holes.

18-01-2009 08:26

Jacob Paikoff

Re: pic: Wheel problem.

Because if you look at the directions for the C-Base Chassis on AndyMark it says to tap the wheels for #10.

18-01-2009 09:44

Teched3

Re: pic: Wheel problem.

Just to add my 2 cents to the wheel problem, based on my experience with the A/M wheels. Although your picture is not clear, it appears the bearing broke through the hub mount. Last year's wheel had a modification in this area by increasing the length of the webs at this bearing/hub mount, but they still did not fully come up to the outer edge of the bearing race. We felt this was still a weak area, and reinforced this by design. Initially, the first year, we filled the cavity at the hub/webs with a fiberglass resin mix, but still felt it was a weak area. Last year, we did not mount the bearings in the wheel at all. Instead, we bored our sprockets to accept a flanged bearing and made a washer of aluminum on the opposite side of the wheel and did the same. We only used three 10-32 screws though the A/M wheels for lightness, drilling clearance holes through the washer and wheel hub for the 10-32 bolts, and tapped the sprockets and jamb-nutted the bolts (to the sprocket) so they wouldn't loosen. We had zero problems with the A/M wheels last year, and the lateral load on the wheels in Overdrive would appear to be significantly higher than we would expect to see this year. A clearer photo would be helpful showing both sides of the wheel, and I hope this gives you some additional insight as to what may have caused this failure. By the way, we used flanged 7/8" OD x 5/16" or 3/8" ID shielded bearings instead of the 1.125" OD bearings as well. Finally, be cautious on how much you tighten the sprocket bolts, as overtightening is possible and can cause stress cracks to form that are very difficult to see.

18-01-2009 09:50

MrForbes

Re: pic: Wheel problem.

One problem with using #8 hardware is that the sprockets have holes that are sized to clear #10 screws, so things are a bit loose.

It would be very helpful to know how long the screws are that you used to hold the sprocket onto the wheel.

18-01-2009 10:14

Jacob Paikoff

Re: pic: Wheel problem.

Not to discredit anything you said, but I remember we were with you guys during elimination in Atlanta and I seem to remember you guys having a major problem with your wheels where you broke the two middle ones on one side of the drivetrain.

And to answer Squirrel's question we where using 3/4" #10 screws.

Just to let everyone know the side of the wheel in the picture is the side opposite the sprocket, the sprocket side of the wheel wasnt as bad but it was still cracked.

18-01-2009 10:18

MrForbes

Re: pic: Wheel problem.

I think 3/4" long screws are way too short for this application, the area that the screw goes into is pretty thin. 1-1/4" screws would probably be better.

The damage to the wheel was probably due partly to driving off a bump?

18-01-2009 12:17

Teched3

Re: pic: Wheel problem.

Just to clarify what happened last year in elims in Atlanta last year had nothing to do with hub disintegration. As a matter of fact, the hubs withstood the defensive attack from a robot that got under our frame with a side hit placing tremendous lateral load on the wheels, breaking the spokes as well as one of our drive chains. If the mods weren't done as outlined, these lateral loads would have disintegrated the hubs. The loads just got transferred to the next weakest link. In any event, the information was presented to help others solve a potential problem with the wheels as shown in the photo. Use or discard the information as you see fit.

18-01-2009 14:04

Wayne Doenges

Re: pic: Wheel problem.

We routinely fill the voids with epoxy. 30 minute will do. Let cure over night. Works great.
BTW, clean out the voids to remove any mold release that might still be present.

18-01-2009 16:39

amariealbrecht

Re: pic: Wheel problem.

we havent had this problem yet but i have heard of some other teams with the same problem...they said it was from the carpet to the playing surface but i am not entirly sure!
Good luck,
Alicia Albrecht
Electrical Subteam
The Robettes 2177

18-01-2009 22:41

Chris Fultz

Re: pic: Wheel problem.

The wheel hubs are sized for #8 screws. Did you drill them out before you tapped them for the #10's? If not, you could have stressed the plastic when you used the tapping tool to create your threads.

19-01-2009 13:07

Teched3

Re: pic: Wheel problem.

This is the link to the AndyMark Cad file, which clearly shows the sprocket mounting holes to be 3/16" (.1895).

http://lib.store.yahoo.net/lib/yhst-...lick-Wheel.pdf

The tap size for a 10-32 is about 5/32" (75% thread clearance), clearly smaller than the existing hole in the wheel. It would seen to be far better to open the hole slightly for the #10 bolts to go through, and jamb nut the bolt/sprocket /wheel assembly together. #8 bolts would be too sloppy in the existing holes (maj. diam. of .164").

21-01-2009 07:03

Teched3

Re: pic: Wheel problem.

Checked the wheel mounting hole size last night on a wheel, and they are definitely NOT sized with a 10-32 or 10-24 tap hole. An 8-32 clearance hole is about right, but a little more sloppy than I would normally like. If you keep your sprocket and spacers centered on the wheel hub, the 8-32 bolts should work fine, and you will eliminate sprocket runout. Sorry for my previous post, but I even checked with A/M and was assured the CAD drawing was correct a 3/16".

07-02-2009 09:54

MrForbes

Re: pic: Wheel problem.

Did you ask someone at AndyMark to try to push a 10-32 screw through the hole in a wheel?