FSAE Bell Cranks

Our goals for suspension during the 2026 FSAE season wer to keep suspension "Low, Light, and Tight". In order to acheive these goals, we designed a pullrod system that moved the shocks down, below the center of gravity. With the geometry we selected, clearancing rod ends with bell cranks proved to mea difficult problem to solve. The bell crank geometry was predetermined to maximize the performance of our suspension dampers, but manufacturing proved to be the downfal of the design. 

Solution

Typically in the UC FSAE teams, belcranks are machined out of a solid peice of metal, whether that be titanium or aluminum. We do this because it is very mass efficient, so for these bell cranks, I specified machined 6061-t6 aluminum. I then checked clearance in cad and defined pockets for the pullrods to fit inside. From there, I cut away as much material in the model as I felt like we could viable machine away. From there, the cad I ran consisted of a pin joint at the pivot point, a bearing force at the damper  mount, and a fixed constraint at the pullrod mount. 

Results:

Front:

Mass: 0 .1648kg 

FOS: 11

Rear:

Mass: 0 .1427kg 

FOS: 4.9

What I did Wrong

1. I did not consider other designs that would be easier to manufacture, such as water jet plates to sandwich the bearings and the rod ends. 

2. I did not account for off axis loads from the pullrod system coming out of plane.

3. I did not consider bump loads that could occur on an uneven surface