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#16
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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!
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#17
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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. |
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#18
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Re: pic: Wheel problem.
Quote:
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#19
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Re: pic: Wheel problem.
It shouldn't be that hard to insert screws after tapping. Maybe you didn't tap it correctly?
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#20
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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.
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#21
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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
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#22
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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.
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#23
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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. |
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#24
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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.
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#25
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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.
![]() Last edited by Teched3 : 18-01-2009 at 09:46. Reason: correct typos |
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#26
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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. |
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#27
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Re: pic: Wheel problem.
Quote:
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. |
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#28
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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? Last edited by MrForbes : 18-01-2009 at 10:23. |
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#29
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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.
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#30
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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. |
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