Innovative Spring-Powered Lifting Device: Engineering Design

Introduction

This group project involved designing a lifting device that satisfied several design criteria, including dimensional limitations, minimum lifting ability, speed of operation, and duration of life. In view of the power source limitations — electrical and chemical energy sources were not permitted — identifying the source of power required and determining how to use it to satisfy the design requirements was a major focus of the project.

The approach used to achieve the design goals is presented below, including the design considerations taken into account, as well as the specifications and objectives that guided the project. The group's process for selecting the most appropriate concept is followed by a description of how the device was manufactured. A description of the completed device, including CAD drawings and photographs, is followed by a listing of the materials used to build the device and how they were sourced and purchased. Finally, a description of the testing methods employed and the risk assessment steps taken is followed by a summary of the project's outcomes and the individual experiences of each group member.

Design Specifications and Objectives

The project specifications for the device are shown in Table 1 below.

Table 1: Project Specifications for Lifting Device

Specification — Wish / Demand

At start, the device must be contained within a 400 × 400 mm cube. (Demand)

The canister must remain on the platform for the duration of the lift, including a rest period of at least 20 seconds at the elevated position. (Demand)

After release, the device must not be in contact with anything apart from the canister and the operating surface. (Demand)

Elevation must not take longer than two minutes. (Wish)

Elevation must not take longer than one minute. (Demand)

Total weight limit of device: 4 kg (8.8 lb). (Demand)

The device must win. (Wish)

The objective for the device was to successfully complete a lift of winning height for the required duration using an innovative approach to design and manufacture, as discussed further below.

Initial Concepts and Discussion

Some of the first ideas developed by the team through brainstorming involved the use of compressed gas to power a piston-driven mechanism that would lift the decontamination canister. Other ideas involved the use of levers and springs, and how these power sources could be used alone or in combination with each other to achieve the design goals. The compressed-gas concept received additional attention at first, since it was considered a potentially viable alternative capable of delivering the amount of energy needed to lift the canister and keep it aloft for the 20-second duration required by the design specifications. The best concept in this category was a vertical piston-driven apparatus, similar in appearance and operation to an ordinary bicycle pump, powered by compressed nitrogen; this concept was designated Concept A.

The second option was the result of discussions about using a lever-driven mechanism to achieve the desired lift. Several lever-driven concepts were discussed, with the best one designated Concept B. Finally, a scissor mechanism powered by a spring was discussed by the team. Following a series of refinements, this design was designated Concept C. All three alternatives were then compared for advantages, disadvantages, strengths, and weaknesses as described below.

Concept Selection

The comparison of the three alternatives resulted in Concept A being eliminated because of weight concerns for the total apparatus, including the compressed nitrogen gas canister and the heavy regulating valve required to keep pressure within acceptable limits. Concept B was eliminated because of limitations on the height achievable with a single lift action and the estimated aggregate weight of all components needed to make the device operate reliably.

This process of elimination resulted in Concept C being selected as the optimum approach to satisfying the design requirements. The respective advantages and disadvantages of each concept are summarised in Table 2 below.

Table 2: Three Concepts' Respective Advantages and Disadvantages

Concept A — Compressed Nitrogen Gas Powered Lift Device
Advantages: (1) Reliable source of energy; (2) satisfies most design specifications; (3) possibility of using an off-the-shelf bicycle pump to simplify manufacture.
Disadvantage: Complete device too heavy.

Concept B — Lever-Driven Mechanism for Lift Device
Advantages: (1) Reliable source of energy; (2) satisfies most design specifications.
Disadvantage: Inadequate lifting ability in a single action.

Concept C — Spring-Powered Scissor Lift Device
Advantages: (1) Reliable source of energy; (2) satisfies all design specifications; (3) device is stable both at rest and in operation.
Disadvantages: (1) Complicated manufacture process; (2) numerous moving parts introduce additional opportunities for device failure during operation.

Conclusion

One of the main findings that resulted from this project was that there are significant trade-offs involved when selecting one material over another in terms of weight, performance, and cost. The strict specifications for the device design also resulted in some ideas that were clearly unworkable, but which led the team to develop other approaches with greater potential. Although the team's device did not achieve the lifting height originally targeted, it satisfied all of the mandatory design specifications and had the added benefit of being an aesthetically pleasing design.