Final Design

The Universal Hamud Rack houses a modular surfboard attachment and can accommodate to various other types of equipment racks designed onto a square shaft The entire system withstands normal driving conditions, which occur at a natural frequency range of 0.5 - 2 Hz, without experiencing resonance and can support a max weight of 341 lbs without experiencing deformations. The sliding lock mechanism remains secure throughout these normal driving conditions as well. All components mentioned previously are discussed in further details below.

The locking mechanism for this rack is a user-friendly sliding lock composed of water-cut 1018 sheet metal with delrin clamps inside to constrain the lock in the x and z direction. The mechanism moves in the y-direction and can slide into the slits of the vertical attachment and lock it in place; it's movement in the y-direction is limited by the length of the slit on the rack to prevent the locking mechanism from sliding too far out and releasing the attachment. Holes cut onto the handles of the lock can overlap and be securely locked with a padlock to prevent theft of attachments. 1018 steel was used for its high yield strength to withstand the weight of the aluminum attachment and the weight of the equipment fixed onto it. Sheet metal was used because of its ease of manufacturability and accessibility compared to the initial idea of welding rod shaped parts in parallel.

The surfboard attachment is comprised of two primary parts: the vertical shaft and the tray. 

The vertical shaft was created from an aluminum alloy stock tubing because of its strength to weight ratio; with a yield strength of 270 MPa, the material was strong enough to support a surfboard but light enough to reduce the load it applied on the sliding lock mechanism. 

The tray part was manufactured with 1018 cold rolled steel and lined with neoprene to prevent damage on the surfboard. Its geometry is in the shape of a rectangular bin with a curved bottom, which is more rigid but provides more room and structural integrity to withstand surfboards varying from 10-20 lbs. In order to accommodate surfboards of various lengths and thicknesses, adjustable pill-box brackets were 3D printed and secured via screws along pre-drilled holes on the shaft. To hold the surfboards in place from swinging around during the drive, rotating steel rods were installed onto the brackets. Elastic bicycle straps would then be tied onto the arms to prevent the surfboard from falling out in the y direction.