Shafts in Drivetrains

[sanddrag]

We've bent 6061 and 2024 1/2" round shafts. Never a problem with 7075 1/2" round for wheel axles. Just don't cantilever it out too far. In 2012, we had 6" pneumatic tires and 7075 axles, and we jumped the robot over the center field bump (and speed bumps at school) to where the whole thing was a clear 8" in the air, and it was never a problem. Also, I would sometimes ride the robot, and I weigh twice as much as it does.

[Tottanka]

im planning on a 3/8'' dead shaft, for a 6x6 or 8x8 DT.
is that a problem in your opinion?

[Qbot2640]

Originally Posted by Tottanka

im planning on a 3/8'' dead shaft, for a 6x6 or 8x8 DT.
is that a problem in your opinion?

There are many variables to consider: total load, length of shaft from support to load, Modulus of Elasticity of the chosen material, etc. But the comparison of section modulus in 3/8" round to 1/2" round (and to 1/2" hex) is rather surprising.

3/8" Round has a section modulus of 85mm^3
1/2" Round has a section modulus of 202mm^3
and 1/2" Hex has a section modulus of 213mm^3

We have bent 1/2" steel round in a non-drivetrain robotics application, and we have bent 1/2" bolts used as dead axles supported on both sides of the wheel (estimate 5" spacing)...this comparison would make me very hesitant to use 3/8"

Sources:

http://67.237.145.72/PDFs/SECTIONPROPERTIES.pdf
http://www.engineersedge.com/calcula...re_case_15.htm