2009 KOP sprocket issues

[wilsonmw04]

After some searching, I have not been able to find the problem my team has had this year: our KOP sprockets seem to be incorrectly spaced. I can hear some of the CD members saying, "what the heck does that mean?" Here's what I mean: If you try and wrap a chain around the sprocket, the tooth will hit the roller of the chain every 5-6 teeth. The alignment is correct and the tension is fine. We replaced the sprockets with the sprockets we used last year (AndyMark 26's) and it has worked fine. Is anyone else having the same issues, or are we doing something wrong?

[JamesByrne]

I would find it hard to believe that you are doing something wrong because all you are doing is wrapping chain around a sprocket. I would think that your best bet would be to contact first and get a new one sent to you. The one you have seems to have not been made correctly in manufacturing.

[wilsonmw04]

what's weird is that it isn't just one, it's all four. I can't believe that Andymark would be that sloppy in their quality control.

[Madison]

We've found the same thing to be true of some of the #25 aluminum sprockets we got from AndyMark. It seems as if the pitch is just a little off.

[MrForbes]

We noticed the 1-1/8" hole in the center needs to be reamed to 1-1/8" to fit a bearing into it..but we didn't notice the pitch issue....they seem to work. I guess if we looked we might see a problem!

[R.C.]

AndyMark is usually pretty good with there stuff, the only problem we ever had was a wobbly toughbox gear. And he sent me a brand new one a few days later.

[Ben Piecuch]

To echo Madison, we had an issue with (I believe) 35 pitch sprockets from Andymark in the past as well. I informed Andy of the problem, and he send replacement parts that day, free of charge.

We had the same "chain wrap" issue, the chain would seat in a few teeth just fine, but it would eventually fail to mate with the gear. Seems like the Pitch Diameter is off by the slightest amount.

Again, Andy should be able to take care of your problems. He has always stood behind his product, and has always been prompt with my experiences with him.

Bengineer

[wilsonmw04]

Originally Posted by Ben Piecuch

To echo Madison, we had an issue with (I believe) 35 pitch sprockets from Andymark in the past as well. I informed Andy of the problem, and he send replacement parts that day, free of charge.

We had the same "chain wrap" issue, the chain would seat in a few teeth just fine, but it would eventually fail to mate with the gear. Seems like the Pitch Diameter is off by the slightest amount.

Again, Andy should be able to take care of your problems. He has always stood behind his product, and has always been prompt with my experiences with him.

Bengineer

Thanks for the replies, folks. I'll be sending AM an email soon. I just wish we noticed the problem before we put the defective parts on the final robot.

[V block]

We had this same problem with some small sprockets. We found that the set screws that we used were a bit too long. This allowed the chain to ride on top of the set screws and would not allow the chain to seat properly in the sprocket when it was touching the set screw. It was a tough one to find since the chain and sprockets were inside a tube and hard to see. if you have a digital vernier you can measure between every 4 to 6 teeth and compare the measurements all the way around the sprockets. keep looking I'm sure you will find the problem.

[dlavery]

I would like to echo the comment from V Block. Check VERY carefully to see if there are ANY obstructions that are preventing the chain from seating fully on the sprocket. The symptom being described fits the case where the pins of the chain are not fully seated, thus causing the effective pitch diameter of the sprocket to increase. This will cause the chain to "skip a tooth" periodically. Two frequent scenarios where this can happen include the protruding set screw mentioned above, and the case where the hub of the sprocket is pressed inside another object (such as a piece of tubing). Sometimes the outer tube is thick enough to cause the side plates of the chain to rest on the tube rather than letter the chain pins seat in the sprocket teeth. The pitch diameter is increased, the pins on the chain are only partially engaged with the sprocket teeth, and the chain will skip. We have been caught by this before - it is an easy thing to overlook.

-dave


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[IndySam]

Yes any little thing can throw off the pitch. We epoxied some AM sprockets to AM hubs and were having the same problem. One of the parents (non-engineer) pointed out that a little epoxy had oozed out and might be causing the problem. Me, the ever knowing engineer, said that little bit of epoxy wouldn't cause a problem. I was wrong.