Dual CIMs and #25 Chain

[GRT808]

We ran into a frustrating problem similar to the one you are describing in San Diego that probably cost us the regional. We also use #25 chain from AndyMark but have switched to #25 from Mcmaster-Carr after getting some advice from The Holy Cows at SDR.

During the regional at least one chain would break and end up on the field, usually the one from our transmission to drive wheel. This happened at least 7 times at that regional.

Upon closer inspection it almost always broke at the masterlink. It took quite a bit of time to figure out what the problem was. There was a number of things that went wrong.

1: Shaft collar on the transmission output shaft was too close to the chain. If you run the wheels manually it may look fine. But flying at several hundred rpm looks quite different. The shaft collar was basically flicking the master link lock off the masterlink and then the tension on the chain bent the master link pins making the chain looked like it broke under load.

2: Make sure you install the masterlink locks on properly. Another reason why the locks flew off so easily is that we weren't installing them till they "clicked". This was a bit tricky for us to tell, the locks can go on and then stay on for a manually inspection (turning the wheels with your hands) but may fly off under faster speeds and higher loads. For both Mcmaster-carr and AndyMark links you have to make sure the lock is installed well, otherwise it will fly off during a match and then destroy your chain.

3: This was probably not the reason our chains failed during the regional, but we made sure it would not be a problem. Our bearing block bolts were not countersunk, we had a 1/4-20 button head sticking out and with the smallest amount of space from the chain. We added another spacer so that it was a good 0.125" away from the chain so it wouldn't nick the master link.

Not too sure how you broke your sprockets, we abused our AndyMark ones to the max when we ran our robot with slack chain during early testing, we never broke any gears or sprockets and I've seen many teams with 7075 sprockets that never failed them.

Hope this helps, it really sounds as though installing the locks on the masterlinks or having something too close that was contacting it may have been your problem. It was quite a puzzler for us to solve.

[Thad House]

We didnt have a shaft collar on until st louis, so I do not know if that is an issue, but we will look for sure.

For anyone that is wondering, we use a 6wd and live cantilevered axles with 3 chains coming off of the center axle. 1 going to the front, 1 going to the back, and the one closest to the bearing going straight up to the transmission. We have a 1:1 gear ratio coming off of the standard toughbox mini ratio. All sprockets are 16 tooth steel mcmaster sprockets. We also use the KOP wheels, so it is geared for about 9.5 feet per second.