Vertical Adjustment Mechanism

Overview

The vertical adjustment mechanism works in tandem with the one inch hole spacing that is present on the frame's uprights. Precise barbell height adjustments enable athletes of all statures to put themselves in the optimal position for maximum force output.

Enhanced Comfort and Performance with 1-inch Adjustability

The standard hole spacing for squat stands is two inches, which can be too drastic of an adjustment. This can place athletes too far above or below the optimal positions for their proportions, resulting in diminished performance during isometric training. To combat this, a squat stand was purchased and modified to have 1-inch hole spacing (Westside Hole Spacing) throughout the entire height of the stand's uprights. A total of 82 holes were added to each upright, resulting in a total adjustability range of about 7 feet.

Athlete Safety

To ensure that the vertical adjustment mechanism would be able to withstand forces applied by the collegiate athletes at UC San Diego, the design is completely manufactured from steel. The squat stand, a modified SML-2C squat stand from Rogue Fitness, is made of 11-guage A500 steel tubing. The twin components responsible for securely holding the barbell at each upright of the squat stand comprise welded assemblies crafted from a combination of A36, A514, and 1018 cold-rolled steel. These steels were carefully selected for their respective mechanical properties and weldability. The barbell is constrained in all directions through the use of steel rings and knurled set-screws. To prevent the mechanism from sliding out of the frame if the athlete were to lean backwards, the mechanism is securely fastened to the uprights using quick-release ball lock pins.

Design

Vertical Adjustment Component

The vertical adjustment mechanism utilizes two twin components consisting of a mounting plate, two bar-holding rings, two load-bearing pegs, and a quick-release ball lock pin. All of the components are welded together besides the ball lock pin. The bar-holding rings fully constrain the barbell in all directions while still allowing easy removal of the barbell through the use of knurled set screws.

Quick-Release Ball Lock Pin

With a press of the pin's button (shown in blue), the pin's locking balls retract allowing the pin to easily slide through the mounting plate and frame. Once the button is released, the balls protrude outward and lock, preventing the component from being pulled out of the uprights.

Simulations

Forces and Fixtures

A SolidWorks static study was used to gauge the safety of the design.

A purely-vertical force was applied to the barbell with a magnitude of 4000 Newtons (approx. 900 lbs.).

To reduce the amount of meshing required and simplify simulation calculations, only portions of the frame and its uprights were modeled.

Fixtures were applied to the bottom faces of the uprights to mimic the uprights being bolted to the frame's base.

The setup for the SolidWorks simulation is shown above. The red arrows represent the 4000 Newton vertical load while the green arrows represent the fixtures.

For the entire mechanism, the maximum stress is located on the top edge of the inner bar-holding ring with a magnitude of 211 MPa.

The load-bearing pegs experience an estimated stress of 37.10 MPa at the interface with the mounting plate.

The powerlifting barbell from Bells of Steel experiences a maximum load of 109.9 MPa. To simplify the simulations, the set screws were suppressed and a contact interaction was assumed between the bar-holding rings and the barbell.

For the frame's uprights, it was calculated that the maximum stresses were not located within the holes but instead on the front face. This can most likely be attributed to the 1.25" moment arm between the center of the barbell and the front face of the uprights.

Maximum Stresses and Factors of Safety

Mounting Plates: 96.56 MPa

A36 Yield Strength = 250 MPa

FOS = 2.58

Bar Holders: 211 MPa

A514 Yield Strength = 690 MPa

FOS = 3.27

Frame Uprights: 72.68 MPa

A500 Yield Strength = 300 MPa

FOS = 4.128

Load Bearing Pegs: 37.1 MPa

1018 CR Yield Strength = 370 MPa

FOS = 9.973

Barbell: 109.9 MPa

Mild Carbon Steel = 965.26 MPa

FOS = 8.783

Stress plot of the mounting plate with an applied load of 4,000 Newtons.

Maximum Load Before Failure

In order to estimate the failure load of the mechanism, a detailed analysis was conducted on the component exhibiting the lowest factor of safety: the 3/8" thick A36 steel mounting plate. Taking its yield strength of 250 MPa under consideration, the mounting plate displayed a factor of safety of 2.58 with an applied load of 4000 Newtons. Utilizing incrementally applied loads within the simulations, it was approximated that the mounting plate, and consequently the entire mechanism, would yield at approximately 10,750 Newtons (equivalent to approximately 2,417 lbs).

3D-Printed Prototype

3D Printing the Mounting Plate using an Original Prusa MINI+

Testing the 3D Printed Prototype in the frame's uprights to see if the Quick-Release Ball Lock Pin would be a viable option. Earlier iterations of the bar-holding rings are shown.