Part 2: Designing Lift Arm Assembly

Question

In Part 2 of this OEMP project you will be designing two aspects of the Lift Arm Assembly while

ensuring functionality of your design. You will be selecting the length of parallel members CD

and EB, as well as the height of chair assembly DEF. Throughout this project, all team's will be

using US Customary units (pounds, slugs, feet, inches).

E

LOF

do

H

d

hu

hg

hc

Figure 1: Side View (x-y plane) of Pool Lift with variable dimensions

The lift arm assembly consists of a four-bar linkage, BCDE, where members CD and BE are the

same length and remain parallel to one another at all times. The four-bar linkage ensures that the

seat mount/chair DEF will maintain a vertical orientation throughout its motion. The goal of this

OMEP is to develop your team's most competent Pool Lift Model allowing for a variety of users

to comfortably enter and exit the pool safely. To limit the scope of this project, all teams will use

the following dimensions: hc=56 inches and do = d = 2 inches, where he represents the

height of pin C above the pool deck, hg represents the height of pin B above the pool deck, and

de and d represent the length of hinges G and H, respectively, from the pin to the centerline of

the member to which each hinge is attached. The lift arm assembly must be designed to

successfully achieve your chair's selected vertical range of motion while limiting the necessary

operating range of a angles (suggested less than 60°). Consider how the length of the parallel

members and the height of the chair assembly affect the chair's vertical position.

• Design the length of parallel members CD and BE (lcp in figure 1).

Design the height of chair assembly DEF (DF in figure 1).

Select the height of pin B above the pool deck (hg in figure 1).

Based on your design, use geometry to find the a angles corresponding to your maximum and

minimum chair positions. If your range of operating a angles is greater than 60° you need to

consider redesigning lcD and lor as large ranges of angles may cause the hydraulic cylinder to

overextend.