[Al Skierkiewicz]

OK,
Let me try to restate this. Teams regularly come up with unusual bumper designs, some are legal and some are not. It is legal to add aluminum plate to the back of a bumper system to aid in easy mounting of the bumper to the frame. These are most often used in one piece bumper designs. The backing plate is also used to strengthen the bumper in addition to mounting. Backing plate is limited of course by the gap rule. 1/2" plate would obviously violate the bumper rules.
If the team adds something to the bumper to satisfy the supporting structure part of R29, then that weight is required to be part of the robot weight and not the bumper weight. The LRI at each event is trained to make that determination.
The illegal addition of weight which I stated earlier violates several parts of the bumper rules including the hard parts distance limit and unmodified pool noodles.
As to variations in weight. Depending on the materials in use on the robot, humidity plays a significant role from event to event. Also while it wouldn't seem possible, concrete floors do have some flexibility and therefore standing near to the scale can affect it's accuracy. That is why teams should be asked to step back from the scale during weighing. Scales are also somewhat temperature sensitive and so significant cold drafts at floor level can also affect readings. Inspectors should be aware of these variables and know how to accurately measure the weights of all robots. Calibration is checked at minimum every day with known 25 lb. standard weights.
BMartin, I hope this answers your question.
Everyone, a committee was formed last summer to investigate the bumper rules and try to make them easier to understand, more open to design and construction, better for rookies and in general to make it easy for all teams. The result was a recommendation to the GDC which accepted the report and incorporated that into the 2013 rules. Inspectors, veteran mentors and rookie mentors all had input.
On a personal note...I do not like ugly bumpers. I don't like to see flaps hanging down, bumpers that are crooked on the frame or have a sloppy mounting. Teams spend so much time making beautiful machines that look good in print and on TV. Why would you want that image spoiled by an ugly bumper system?