Quote:
Originally Posted by nuclearnerd
Yeah, I'm still *really* surprised at the things FRC people use 7075 for. It's aluminum trying to be steel - same strength as (mild) steel, but way less stiffness, way less toughness and way less hardness. (The latter can sorta be overcome with hard anodizing, as long as you don't actually stress the coating too much.)
7075 could maybe find use in highly stressed structural plates, where you want to save weight on a big piece. But for small shafts & gears, don't be silly - just use steel!
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This is terrible advice and I hope people don't blindly take it. You cannot possibly make a blanket statement like that without way more justification. The one use case that you feel 7075 is justified in is the one case I can't possibly imagine using it in, on a FRC robot.
7075 is perfectly good enough for almost any shafting or gear use in FRC, provided something stupid like putting snap ring grooves in the loaded portion of the shaft, or otherwise adding stress risers isn't done. These robots don't see the kind of duty cycle required to make steel a justifiable usage in all but the most highly loaded, atypical scenarios.
Frankly, the steel gears that are available for FRC use in COTS form (ie: hex broached, 8mm bore 2mm keyway, dog gears, etc) are all inferior in quality to VEXPro aluminum gears.
254 has been using 7075 shafting possibly longer than anyone in FIRST (11+ years now) and not once have we ever sheared a shaft, that I can recall.
So yes...if you want to be absolutely sure that you can mask most possible bad design decisions with material choice, feel free to use steel...just don't wonder why your robot doesn't make weight.