[Joe Johnson]

Many folks imagine that FIRST has more resources that they really have. As a practical matter, there is nobody in Manchester with team experience. There are great people working for FIRST, but they just don't have the team experience.

The 56mm Banebot transmission was designed specifically for FIRST. Banebots asked me to help them with the requirements, which I gladly did. At this point, I wish I would have spent more time analizing the gearbox. It was not until after the kickoff (when I saw the picture of the 4:1 gearstage from Banebots' website that allows the 56mm gearbox to convert to 16:1) that the double D joint came to my attention. I should have noticed it sooner, but it just didn't come to my mind.

FIRST insisted on the 2 motor solution. I was not a big fan of it, but I did not oppose it either. After seeing the double D joint, I was very worried.

Seeing a picture of a FIRST test mule made me think that perhaps FIRST did not do enough testing. The picture has been removed. For those who did not see it, it had a long unsupported shaft that simply could not have stalled 2 CIM motors.

Initial calculations did not provide comforting answers. I have spent 3 weeks getting the data I need to make a reasonable recommendation. Yelling the sky is falling when it is only an acorn is just as damaging to FIRST as failing kit gearboxes.

What I still don't know is what is the dynamic load that a single motor CIM gearbox with 12:1 ratio. We really need someone to build up a 120lbs test mule and just cycle it Full forward, full reverse for about 500 cycles and then open the gearboxes up to see how much the double d had turned into a bow tie*. This is a big question. Is this just a problem for the 2 motor CIM adaptor or is it a problem that is more widespread. At this point, we don't know.

The fix is not that hard, but it is not free either.

As to whether we should have caught this earlier, yes, I believe we should have. But, mistakes are part of the human condition. Me, FIRST, Banebots, the subcontractor that builds the parts, there is plenty of blame to go around.

Right now, we need to understand the extent of the problem and come up with the best solution possible.

Joe J.

* see the attached photo for an idea of what happens to the joint. This was done with 100 cycles of +/-40in-lbs torque (approx. 2 CIMs). During the test, it was clear that each cycle is opening up the joint. I started with about 180 degrees of backlash at the input to the transmission. By the 100th cycle, the doulbe d had opened to the bowtie shown in the photo and the backlash was over 270 degrees.