Banebot 56mm gearbox - double D related

[Joe Johnson]

Originally Posted by cbpetrovic

Dr. Joe.

We are using 1 CIM w/ 12:1 ratio.

An ME here would like to know how you calculated the stress. Below is his observation from the photos as well as conversations with me.

"The initial interface is 2 lines of contact (essentially zero area) between the shaft and the D hole. It is only after material begins to deform (ever so slightly) that area contact is made. I am curious what he uses for stress area and how he determines it."


C. B. Petrovic

I assumed a linear stress distribution normal to the joint surface starting at the center line and increasing to a peak at the corner of the D. I then integrated the torque to get the sum (on both sided of the D) which had to resist the torque on the joint. I found an engineering rule of thumb that allowed me to estimate failure of the joint by saying the material will start moving at 1.5X the tensile yeild stress. Once the material begins to move, the stress distribution changes but the joint is losing the battle. So I used the torque that made my linear stress distribution have a stress in the corner greater than 1.5X Stess_Tensile_Yeild

I hope that helps.

Joe J.