#25 Chain

[Joe Johnson]

Originally Posted by cbale2000

Can you give any examples of failures you get with a Live Axle system that you would not get by just using Chain on Dead Axles? In the 10 years I've been doing FRC I don't think I've ever seen a failure on a Live Axle, I have seen plenty of broken chains though.

What specifically do you see is the downside of a Live Axle system?

Bent axles are one failure I've had from past years. But I suppose that is more of a problem with cantilevered live axles than live axles alone.

The gear train to get the torque from one axle to the next is another point of failure. Many multidrive live axle systems need a bunch of gears betwixt & between the live axles. More gears, more axles, more gear to gear interfaces, more center distances to get wrong (or have to manage at a minimum).

Typically gears have smaller working radii where the force is transferred from axle to axle than chain (not always but often). This in turn means higher forces for a given torque, which isn't unmanageable (obvs) but can be tricky.

Back to failure live axle failures, the most memorable one for me was when in the Soccer Game where we had to go over the bumps (well you didn't HAVE to but we did). The team I was with then had an 8 wheel beast with an AndyMark shifter direct driving one of the axles on each side and chain in between as some have suggested.

We were in a good place with a win in our first match of the Quarter Finals at the Long Island Regional. During that match we went over the bump a little more energetically than we had up to that point in the tournament (think Dukes of Breakaway). We won the match and thought everything was fine - in fact we were thinking we had some great footage for our highlight reel at the end of the season.

As it turned out, match 2 didn't go so well because we just couldn't get going in high gear. Between matches we checked everything out, couldn't find a problem. We put the robot back out there for our 3rd match only to get the same result: High Gear was useless. It wasn't until we got back to the school that we realized that we had it so hard we had skewed our frame a bit which skewed the gearbox a bit which was enough to make the current go up in high gear to the point that our breakers kept tripping on that side. Loosening some screws, giving the robot a kick or two, and tightening those screws again had us running like a champ again (of course if we were going to compete again we would have had to solve that problem but it was our last tourney that season).

So, was that a live axle problem? I kinda think so but others may disagree.

Dr. Joe J.