Al's Annual Inspection Thread 2015

[IKE]

Originally Posted by Thad House

I get the zip tie thing, but at the same time I don't. The field is held together with zip ties and Velcro, and it seems to work just fine. As long as you buy good quality zipties, they could easily hold a robot together.

Emphasis was mine. Often when writing a rules for any sort of sanctioning, the ruless have to written in such a way that if to prevent something dangerous from happening, it is inspectable. For example, in amatuer racing, roll cages are often specified at Steel, of a particular diameter and wall thickness with an inspection hole. While not all steel is created equal, the lowest common denominator is used and specified to ensure that at a minimum the cage should be safe.

As most of us know, Zip-ties vary in quality and strength by a very large range. Do I think you can find Zip-ties that could handle impact loading... Yes. Do I think I can tell the difference between those and "junk ones"... NO (or at least not easily).
A simple McMaster Carr search shows 15 varieties of cable ties with a wide range of ratings. It is also worth noting that with plastics, just because it was originally rated at 100 lbs strength does not mean it will always be that strong. Some plastics degrade with humidity. Other plastic degrade with UV light exposure.
At the end of the day, there is just too high of variation which is why you get the pushback.

Does this mean you will never see a robot with a dumbell ziptied to the back? Doubtfull. It does mean though that once it gets noticed, it will likely be asked to be correctly anchored.

I would still be very impressed if a team showed me the calculations for the resultant G loading of a 10 feet per second robot hitting the wall, the documents that show the cable tie rating, and the calculations and safety factors that make them believe it is OK.*

*for a 10 FPS robot with bumpers that compress 2" ideally it is around 10G. If you assume about 0.25" of deflection it is nearly 100G. Thus a 10 lb dumbell might exert 100 to 1,000 lbs. of force on those restraints.