Team Update 5

[writchie]

This appears to be a major change to the game. It changes the apparent design intent of the hitch from a rigid tight fit along the pitch axis to a wobling loose fit. The nominal pitch planes of the robot and trailer can now differ by more than 10 degrees instead of less than 1 degree, even more with the inevitable enlargement of the hitch pin holes in the aluminum c-channel that will now occur.

This pretty much invalidates the strategy of transferring the bulk of the trailer weight to the wheels of the robot (through CG), increasing the normal force on driven wheels by as much as 30 lbf.

This kind of rule change, half way through the build season, would seem to at least warrant an explanation as to why the change was necessary and what it is intended to accomplish rather than just slipping it in as a drawing change.

What is the lesson to be learned here? Our team happens to have submitted a Q&A (still unanswered) to confirm the alignment angles implied by the original drawings (and pointing out that the hitch pin is actually too tight of a fit under worse case tolerances). Instead we get what amount's to a new spec for the robot. The trailer is an integral part of the robot this year and the hitch and its attachment are the most critical part of this "system".

What is the engineering lesson to be conveyed to our students by this change? 1) Don't point out to the customer that her specs have a minor problem because instead of adding a bit of extra tolerance she might change the whole design intent and force you into re-design at your expense? 2) Don't assume that specs that are supposed to be frozen are actually frozen? 3) Be careful, a seeming innocuous drawing change can invalidate an entire design approach? 4) S#%*$t happens - get used to it?

I'm sure I've missed a few more.