Final Design

Background

     Teradata desires a powered server cabinet mover to provide the transportation in a safe and timely manner.  The current method of transportation requires the use of up to 4 workers, taking up to 30 minutes to load and transport, at high cost.  The cabinets weigh up to 2200 lbs. when fully loaded and reach up to 7 ft. high. An off-the-market electric pallet truck was suggested by Teradata engineers as a suitable starting point for our design.   A mixture of both ready-made and custom-made components was request to be incorporated in the final design.

Figure 1: Teradata Server Cabinet

Summary of Design Solution

             The design solution consists of a purchased pallet truck that was redesigned to support our cabinet cargo.  This modified pallet truck includes a steel platform to hold the cabinet, and larger diameter wheels to suppose the load of the cabinet. The pallet truck legs were modified to be wider and straddle the cabinet, as was the pallet truck linkage as well.  Furthermore, new legs were required to accept larger diameter wheels and bolt locations for the platform, which runs across the width of the truck.

            This design allowed for very simple operation.  An operator rolls the cabinet onto the platform. After the cabinet was secured to the back hoop using tie downs, the platform rises up to allow for ground clearance, and the pallet truck is driven away.

            The pallet truck was sandblasted and  powder coated in yellow and gray colors, as requested by the sponsors. The chassis plates of the truck are yellow, and all the steel tubes and platform are gray.

Figure 2.  Redesigned Pallet Truck

A. Electric Pallet Truck

This project required moving a 2200 pound server cabinet from one location to another, including elevator access and inclined ramp.  By considering the sponsors input as well as researching the products available for moving heavy loads, pallet trucks were the most viable option. Several distributors were visited, and the Big Joe PTE-30 was found to be the best possible truck for purchasing.

The Big Joe PTE-30 is a motorized pallet jack with a load capacity of 3000 lbs a powered travel and lift, up to 7.8 inches in height.   The truck dimensions are 27 by 48 by 64 inches, with the truck legs resting at a lowest height of three inches. Larger pallet trucks could not be purchased because of the 38 inch width and 69 inch length size constraints. The PTE-30  comes with rechargeable battery pack and a 24 volt fully programmable transistor control, rather than an on/off switch.  The controlled acceleration allows safer transport of the loaded cabinets. Overall, the PTE-30 was chosen due to its cost, its compactness for the office environment and its availability of detailed information about the design assembly online.  This detailed information was crucial, since a drawing was needed for any design alterations.  Additionally, this pallet truck required the least amount of modifications compared to other pallet trucks.

Figure 3. Big Joe PTE30 pallet truck

B. Steel Components

• Legs

            The leg material chosen was ASTM A500 hot rolled steel rectangular tubing.  This material has rated yield strength of 250*106 N/m and was more than adequately strong for the large 2200lb load.  The profile selected was 5” x 7” rectangular tubing with a 3/16” wall thickness.  This profile allows for ample room inside the leg to house the lifting linkage components as well as the hardware for mounting the platform to the legs.

Figure 4: Hot Rolled Steel Rectangular Tubing

• Platform

ASTM A36 steel was selected as an appropriate material for our platform under the design criteria.  Since the platform spans the gap between the legs, it must be able to withstand the worst case scenario: the whole load spread across four point loads.  With a minimum yield strength of 250 MPa this steel performs above the necessary requirements.  Our stress analysis performed using SolidWorks echoes our initial calculations, far under the minimum yield stress.  The piece we purchased, 48’’x 60’’ was cut into four pieces, the platform, and three separate pieces to be welded to the platform in order to secure the platform to the rest of the machine.

• Back Brace

A back brace was added to the design solution to provide greater support for the cabinet, as seen in Figure 2. The diagonal pieces of the back brace also serve as mounting points for the securing straps.The back brace consists of A500 steel tubing of various sizes. Two  linkages are  2 x 1.5 x 56'', in the vertical, upright position. Two  more linkages are 1.5 x 1.5 x 64'', providing the diagonal support of the back brace assembly. Finally, a tube of size 2 x 1.5 x 31'' lies horizontally in the back brace assembly. All tubes are welded together to create a frame that is approximately 31 x 56 x 35''.   

• Wheel Linkage

Figure 5: Wheel Linkage Assembly

            The wheel linkage is an exact replica of the original wheel linkage of the purchased pallet truck, but with larger dimensions in two components of the linkage assembly so that the legs could be extended outwards (recall that this extension of the legs was necessary to accommodate the size of the cabinet).  The link connecting the pallet truck chassis to the wheels is from the original truck, and lies within the tubular legs. The wheel link and the chassis link were custom made to be a larger version of the original parts, discussed further in "Fabrication".

Figure 6: Chassis link (left) and wheel link (right)

C. Wheels

            For the modified pallet truck, new wheels were purchased because the original truck wheels were only 3 inches in diameter. A larger wheel diameter was desired to allow the cabinet mover to more easily travel over cracks and thresholds. A diameter of 6 inches was chosen for the final design solution.    

            When choosing wheels, load capacity, hardness, and floor conditions were also considered. The two wheels both needed to support the 2200 lb max load of the cabinet. In addition to high load capacity, a high hardness value was desired so that the transporter could easily travel over carpet, which is considered a rough surface. Table 3 in the appendix summarizes recommended wheel materials based on floor conditions.

            Polyurethane wheels over an aluminum core were purchased from McMaster Carr. Polyurethane was chosen because the original pallet truck wheels were polyurethane in exterior, and the material was also recommended by the sponsors. The aluminum core was chosen for strength. Other metals such as cast-iron were not chosen in order to prevent possible floor damage.

            Each wheel has a load capacity of 1900 lbs, and the cost was $69 dollars per wheel. The hardness level is 95A, which is the minimum hardness required to travel over carpet. These wheels are dual wheels, which mean the wheel has two portions, each of which travels independently of the other. This style of wheel allows greater maneuverability, which was important for the movement of the powered cabinet mover.

Figure 7: Polyurethane over aluminum core wheels

D. Straps

            Two cam-buckle tie-down straps were purchased to serve as securing straps on the unit, holding the cabinet in place on the powered cabinet mover. These straps are made of nylon and are 12 ft. long.  The latch hooks are 2 inches long and the work load limit of the 1000 pounds each strap.  The mounting location for the straps is located on the diagonal bars of the back brace. Eye bolts were bolted into the outside of the diagonal brace.

Figure 8: Cam-style latch hook nylon securing straps

E. Front Bumpers

            A bumper was placed at the front of each leg, extruding from the end. These bumpers serve to protect walls should the truck run into them. These bumpers are made of heavy duty rubber guard SBR. This material is a durable synthetic rubber and its dimensions are 3.5'' by 6''.

Figure 9: Heavy duty rubber guards as front leg bumpers

Fabrication

In any manufacturing process, detail planning is an essential stage of fabrication.  Therefore, the fabrication process of the powered cabinet mover began with creating clear drawings and simulations of the design in solid works.   Considering the heavy machinery design required in creating the power mover,  the design  was consulted with experienced machinists.   With their approval, raw steel was bought and the fabrication process began. 

            The design of the powered cabinet mover consists of the platform, tubular legs, and most importantly, the wheel linkage within the pallet truck.  The constraints of the project required the powered cabinet mover to be able to handle a high capacity load, so a strong material such as steel was necessary. However, the powered cabinet mover also required precise machining, and steel is not as easy to machine as other metals such as aluminum. Due to the ease and accuracy of water jet cutting, purchasing a water jet cut became a viable option.  Therefore, the group decided to contract out the individual pieces of the wheel linkage and platform for water jet cutting.

            The wheel linkage was one of the essential parts of the design and required the most precision in fabrication. The wheel linkage is an exact replica of the original wheel linkage of the purchased pallet truck, but with larger dimensions, so that the legs could be extended outwards.  Once the individual parts were cut with a water jet, the holes and the length of the linkage were machined with mill and lathe to an accuracy of 0.001 inches.  The wheel linkage assembly needed to mimic the original linkage with the modified dimensions. After the individual components were completed the wheel linkage was welded together by using a jig to keep the exact dimensions and the pieces aligned.  

            The fabrication of the tubular legs required cutting the sides for welding the lifting plate, as well as clearance slots for the raising and lowering of the wheels.  An accurate and clean cut was required to weld the pieces together.  Thus, a programming mill was set up to make the necessary cuts and slots.  The tubular legs were also cut to the proper dimensions using a portable band saw.

            Once each part was machined and was welded together, the powered cabinet mover was assembled.  In order to ensure the platform had correct, the platform pieces were welded while the entire powered cabinet mover was assembled.  

Figure 10: Finished, unpainted pallet truck

Conclusions

            The modified pallet truck design solution meets most of Teradata's desired qualities. The cabinet mover is aesthetically pleasing and professional looking, which was important to the sponsors. The cabinet mover  also raise to the height of Teradata's shipping pallet, which aids Teradata in another step of the cabinet transportation besides simply moving from building to building. The cabinet mover  adheres to the size and weight constraints, but not all of the floor constraints. While the cabinet mover can travel over concrete, carpet, asphalt, and the aluminum ramp with ease, the tile chips when the mover travels over it. The design solution also lacks a shock absorption system within the truck, which was desired by the sponsors to increase the safety of the cabinets and the flooring during transportation. Such a system might help with the tile chipping problem. We did, however, include external protection on the truck for the cabinet, such as strips of adhesive rubber and polyurethane on the steel tubing.  

            Though not all deliverables were reached with this design solution, the cabinet mover we created is a success for an initial design. Many of the requirements and deliverables were achieved, the sponsors are satisfied, and the team members are satisfied.