pic: Team 188 Teaser 2

[Matt Adams]

Originally Posted by Bob92

A little info on shear ratings

Shear Capacity Calculation

To roughly calculate the ultimate single shear capacity of a bolt, multiply bolt area at full shank diameter times ultimate shear strength rating, e.g. 8-32 18-8 stainless steel bolt, 0.164" diameter. (A standard 8-32)

Area = πr2; 3.1416 x 0.082" x 0.082" = 0.0211 square inches

Single shear = 90,000 psi x 0.021 = 1890 lbs. at full diameter

This calculation is for shearing a 8-32 on the thread. I am pretty confident it will hold your robot.

Consider that bolt not flush against the load.. such as a tiny "negligible" bending moment of only .25 inches....

Stress = M * y / I

Stress = M * y / I

130 lbs * .125 * .082 in / (3.141 * .164^4/64) = 75,500 PSI

Compound that with some shear stress... you're in a danger zone. Consider and extra load of an extra robot hanging with you... eek! In my opinion.. using a #8 bolt is definitely pushing a reasonable factor of safety.

However, the van door motor, being 11mm or so, should work out to be just fine.. but I'd definitely try to avoiding doing anything cantilevered... that freaks me out. Keep in mind that those bearing are bought from the cheapest bidder...

Nevertheless, good luck!

Matt