P16006: Tub Lift 2

Subsystem Design

Table of Contents

Team Vision for Subsystem-Level Design Phase

During this phase we wanted to complete our design analyses as well as compile a bill of materials for the device. Although this has been completed in part, iteration is still needed to arrive at a final design. The project plan will need to be updated in order to reflect the necessity of this iteration. These updates will be accomplished during the next phase. Additional feasibility analysis has also been accounted for as depicted below.

Feasibility: Prototyping, Analysis, Simulation

Requirement Tweaks

As a team, we have agreed to some alterations to some of the requirements that were identified during the problem definition phase of the project. The main feature that we will be choosing to omit regards the reclining of the tub lift seat. Both the customer requirement that calls for an adjustable recline and the associated engineering requirement that specifies a reclining range of motion will not be implemented in our final design. We are opting to utilize an ergonomically crafted chair that the "Revision 1" group had purchased. utilizing this seat will enable us to salvage some of the value from the previous group;s efforts. Additionally, this will mitigate our purchasing cost when moving onto the prototyping phase of the project; we will not need to worry about purchasing or crafting a new seat. The seat that will be used, in addition to being ergonomic, has built-in handle bars on its sides and a fixed recline position to promote comfort. The result of these features is that we already have a predefined solution to two of the features identified in the systems phase. These systems include both the recline and assistance into and out of the tub.

Human Subjects Analysis

The question of whether the Tub Lift 2 constitutes human research, or just a research project is a lingering questions that needs to be addressed. Human research consists of two main aspects: is I research and is it research with humans? The Tub Lift 2 is a second iteration product seeking to cater to the needs of the customer, Theresa Loce, whose paralyzed from the waist down and suffers from polio. Theresa Loce, a wheelchair user relies on a hydraulic power bath lift to assist her with entering and exiting her bath tub. The water-powered lift that she currently utilizes has been requiring frequent repairs due to its age (parts are becoming scarce, expensive and possibly unreliable). We seek to develop a new, affordable and easy-to-use lift. The final mechanism will lower, lift and rotate Theresa into and out of her tub.

Now it is true the final product will be utilized by a human on a regular basis, the Tub lift 2 is a product designed specifically and ONLY for Theresa; the final product will not be commercialized and utilized by a large population of people. Therefore, because the commercialization aspect is not a factor, the project in it’s entirety is considered only a research project and the completion of the 30 day IRB process is not necessary.

Water Pressure Constraints

According to Monroe County Water Authority, the average water pressure at the customer's location is approximately 48 psi. Since this pressure is on the lower end of what we had expected, we will have to design the final product to accommodate for more of a "worst-case" scenario. The lift will still need to sustain a given maximum weight, despite this new-found constraint. Please find relevant images below:




The below image shows the calculations we utilized when determining the needed piston dimensions for the lift. These were kept in mind when developing the concepts seen below in additional sections. These calculations can also be found within the Systems Phase directory. Based on the information regarding the customer's water pressure, the hydraulic approach will still be feasible.


Click the following link to download:

Tap Card
Hydraulic Grade Calculation
Feasibility Analysis

Drawings, Schematics, Flow Charts, etc.

Front View


Isometric View


Extended Isometric View


Side View


The views above show the initial depiction of our final design. Both the retracted and extended view of the lift can be seen. More tweaks will be needed through iteration to finalize the concepts. Technical concerns addressed in the risk management section are present and need to be mitigated.

Bill of Materials (BOM)


The above image displays the tentative bill of materials. The bill of materials be a work in progress; it will be updated as more is developed.

To download the file, please click the folowing:

Tentative BOM

Risk Assessment


Please click the following link to download:

Risk management Assessment

Plans for next phase


The above image shows where we expected to be during this phase. Although we have some aspects of the bill of materials and designs made, iteration is still needed to mitigate additional risks. The project planning file will be updated in the following phase to account for this noteworthy change.

Please refer to the following attachments to view individual plans for the next phase of the project:

Branch - Preliminary Detailed Design Plan
Hall - Preliminary Detailed Design Plan
Krall - Preliminary Detailed Design Plan
Swearingen - Preliminary Detailed Design Plan

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