View Single Post
  #23   Spotlight this post!  
Unread 24-10-2015, 08:29
Chris is me's Avatar
Chris is me Chris is me is offline
no bag, vex only, final destination
AKA: Pinecone
FRC #0228 (GUS Robotics); FRC #2170 (Titanium Tomahawks)
Team Role: Mentor
 
Join Date: Dec 2008
Rookie Year: 2006
Location: Glastonbury, CT
Posts: 7,769
Chris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond reputeChris is me has a reputation beyond repute
Send a message via AIM to Chris is me
Re: Which kind of Aluminum is a good choice

Quote:
Originally Posted by GeeTwo View Post
Yesterday evening, I verified that the mangled shaft is steel; a magnet sticks to it. I can't see using aluminum of any grade in this capacity. The shaft in question was not used in the drive system; it was used to swing a "hammer" that "kicked" the yoga ball. Despite always supporting the other side of the hammer, somewhere along the way, the shaft deformed, most particularly near the key slot. Curiously, checking the hammer, there is less deformation of the aluminum hub than of the steel shaft.
This isn't a reasonable argument against using aluminum shafts at all. There are tons of different ways that a motor driven "hammer" could load a shaft improperly such that any material would bend. For example, shock loading a long, 1/2" keyed shaft could potentially bend any material. You're putting a ton of force on that tiny area of the keyway. I also suspect the shaft was loaded improperly in some other way, but without details on your setup I can't really comment. But this isn't necessarily a part of your robot with less stress on it than the drivetrain.

This just further reinforces Cory's point - you shouldn't use material to compensate for a bad design decision, because the difference in strength is somewhat marginal anyway and you can still screw it up. 7000 series aluminium shafting isn't really that difficult to use, and instead of steering away from a common sense way to save at least 5 pounds per robot (once you add up all the gears, shafts, etc), you should steer away from bad design decisions that load shafts poorly. I guess if you're still convinced, I'll enjoy having 5 more pounds of mechanism than you do, or 5 pounds less mass to accelerate.
__________________
Mentor / Drive Coach: 228 (2016-?)
--2016 Waterbury SFs (with 3314, 3719), RIDE #2 Seed / Winners (with 1058, 6153), Carver QFs (with 503, 359, 4607)
Mentor / Consultant Person: 2170 (2017-?)
.
College Mentor: 2791 (2010-2015)
-- 2015 TVR Motorola Quality, FLR GM Industrial Design -- 2014 FLR Motorola Quality / SFs (with 341, 4930)
-- 2013 BAE Motorola Quality, WPI Regional #1 Seed / Delphi Excellence in Engineering / Finalists (with 20, 3182)
-- 2012 BAE Imagery / Finalists (with 1519, 885), CT Xerox Creativity / SFs (with 2168, 118)
Student: 1714 (2009) - 2009 MN 10K Lakes Regional Winners (with 2826, 2470)
2791 Build Season Photo Gallery - Look here for mechanism photos My Robotics Blog (Updated April 11 2014)