Photograph of flange, prohibiting lateral movement of
differential
Summary This project has been completed in conjunction with Hope
Colleges FSAE team. FSAE is an international competition where
students design, fabricate, and test one-fourth scale formula one
type cars. The goal for this project was to provide a mount for the
differential onto the frame of the car. The concept of a
differential mount is not new, but every cars frame is unique and
this is where the challenge lies in designing the differential
mount. The differential that the team has purchased includes
bearings. These bearings are the only components of the
differential that can be captured. This mount was designed for a
performance car and thus several performance-related requirements
were identified. Because the frame of the car is steel, there
should be steel components to ease the degree of difficulty of the
welding process. The remaining fabricated components should be made
from aluminum in order to reduce the weight of the mount. Related
to the weight of the mount is the amount of space the mount
occupies. The available area where the mount will be located has
approximate dimensions of twelve by fifteen by six inches. The
mount should be large enough that there are no concerns about its
durability yet overcompensating will result in unnecessary weight.
The design should also be simple enough to fabricate in the time
allowed. All concepts considered included two aluminum plates
(0.375 inch-thickness) with mirrored dimensions whose purpose is to
capture the differentials bearings. These concepts also shared
three female threaded rods to be fastened in between the aluminum
plates. The purpose of these rods is to keep the aluminum plates
parallel and spaced correctly. Another component shared amongst the
concepts is the steel tab (1.50 by 1.25 by 0.375 inches). These
tabs will be welded to the frame on one end and either fastened to
the aluminum plate with 0.5 inch diameter bolt or fastened to a
turnbuckle with a 0.5 inch diameter bolt. Concepts utilizing a
turnbuckle will incorporate one turnbuckle for each aluminum plate.
The turnbuckles will allow for the position of the differential to
be altered towards the front of the car and in turn will allow for
the tension in the drivetrain to be adjusted. Because the
differential will ideally be mounted six inches from the rear of
the car, the deciding factor in choosing whether or not to employ
the use of turnbuckles was finding a turnbuckle short enough in
length while having a high enough load limit. The final design
consists of two aluminum plates (6.25 by 6.00 by 0.375 inches), two
turnbuckles (6 3/8 inch closed length, 130 pound limit), three
female threaded rods (6 inch length, -28 thread), and eight steel
tabs (1.625 by 1.50 by 0.375 inches). The aluminum plates have two
-inch clearance holes; one centered on the width of the plate and
the other 0.50 inches from the bottom and 0.5 inches from the edge
closest to the front of the car. They also have three -inch
clearance holes spaced around a 3.936-inch diameter (0.312-inch
deep) bore, concentric with a 3.930-inch through-bore. The smaller
through-bore provides a stop for the bearings so they do not push
all of the way through the plates. The plates will be press-fit
onto the bearings so that the stops face outside of the car. The
steel tabs include a 1.00-inch diameter half circle cut at one end
centered on the 1.50-inch edge in order to fit on the cars
1.00-inch diameter steel tube frame for welding. Finite element
analysis of the fabricated components revealed a low factor of
safety of twenty-five. This factor of safety occurred in the
aluminum plate when the two -inch clearance holes were restrained
and a one-hundred twenty pound force was located on the inside of
the 3.936-inch bore, directed towards the front of the car.
