pic: New gear failure on 2471

This was a new one for us. I bet someone can guess what the loading situation was.

And that kids is why keys suck and we should be very grateful for the advent of hex shaft solutions in the last couple of years.

Because hex doesn’t produce stress concentrations…

And splines aren’t used in torque transmission applications…


By any chance, was that a recently purchased vex pro pinion? I just bought a couple new ones and had to throw one away because it had a hair-line crack in it. I didn’t noticed it until I started running it in the gearbox (very low load) and it was going “clackclackclack”.

Of course hex shafts produce stress concentrations. It’s just that the induced stress is far lower. They are also far more convenient in a number of ways.

Although I don’t know how new this pinion was, I can say that it was making a minor “clackclack” sound before the failure. However, this pinion didn’t need any more reason to break, given that it was a 12 tooth made 7075 aluminum and was taking the load of two CIMs.

After replacing it with a steel equivalent, the gearbox has been working great so far. (Fingers crossed)


Hey its the open source hardware logo!

Did you get your wires crossed and let two CIMs fight it out to see which way the bull gear would spin? :rolleyes: