Re: VEXPro 2014: After The Season
 

I looked at it briefly at the competition. It was broken at the e-clip groove.

Re: VEXPro 2014: After The Season
 

That is what I was afraid of. We went ahead and ordered the 3CIM ball shifter without the 54:30 option (hoping to add it at a later time). Well, at least the team will still be able to work it into our skateboard frame.

Thanks for the head up.

Re: VEXPro 2014: After The Season
 

Revisiting this: I have a little nitpick about the WCP cams.

AFAIK, the original design of these cams in traditional west coast drives was with a single smooth contour at a constant slope of 10 degrees (logarithmic spiral, nautilus cam, whatever you want to call it) with the slope selected so that it's tangent was less than the coefficient of static friction between the bearing block and the cam, and force applied by the bearing block (via chain tension) could not rotate the cam and chain center distance. Please correct me if I'm wrong about this.

The WCP/Vex cam added grooves along the contour. This idea seems to make sense: the rounded tip of the bearing block falls into the groove and can't hop out. Retreating the block still allows you to rotate the cam to adjust tension. However, the change in geometry means that the friction condition no longer holds (there is no longer a uniform slope along the entire contour), so the the block will always slide along the cam into the nearest valley. The problem is that this forces the chain center distance to be at the one these points, which are about .010 apart near the base of the cam and up to .025 apart at the tip. We'd really like to get our chain tension to within .005, and have noticed that despite proper tensioning before a match, tightened bolts, etc., certain chains would invariably become a little looser than others based on slight differences in where the cams are mounted near each wheel slot. I don't believe this ever caused any catastrophic failures, but it made us nervous, and I'm sure it also affected efficiency and wear.

Is this something other people have seen with these cams? Are we using them incorrectly?

Re: VEXPro 2014: After The Season
 

I'm surprised you need to keep your chain tension within .005; this seems excessively precise. We ran a WCD using these cams, and kept the chain (McMaster) slightly slack. We almost never had to tension them. Perhaps you're tightening the chain too much?

Re: VEXPro 2014: After The Season
 

I don't feel that having your center to center for a chain off by ten thousandths of an inch vs. five thousandths of an inch really does much. Chain doesn't have to be ridiculously tight. In fact, tight chain is bad for bearings and such, and has lots of friction filled rubbing. Running them on the loose side gets more efficiency.

If you did want superior adjustment, you could likely grind down the existing cam and edge of the bearing block into a smooth surface. The cam doesn't have to be a fancy shape, just something with a non constant radius.

Re: VEXPro 2014: After The Season
 

The design that 254 ran for years, and that we (and others) later copied has the clicks you describe.

Re: VEXPro 2014: After The Season
 

Perhaps it is excessive... Somehow my earlier measurements were bad, looks like the jump is uniformly about .010 all the way around (as one might expect due to the geometry). So one should always be within 0.005 anyway.

The chain should not be tight, but it should also not be hanging loose, rather it should be at length. But there is probably more variation due to sprocket rotation that causes transient chain sag. So I seem to be way off the mark.

This is sort of what I was wondering. Good to know.

I'm just paranoid.