Muscle Strength Testing Device Capstone Project

Muscle Strength Testing Device Capstone Project

Project Description:

For my Senior Capstone Engineering Project, my engineering team and I collaborated with a client who was a Doctor of Physical Therapy. Since we were the first engineering team to take on this project, our goal was to create a first-iteration muscle strength testing device for various isometric strength tests. 

Our Design goals were to: 

  • Construct device capable of accurately measuring isometric shoulder flexion muscle strength muscle force output
  • Construct device capable of measuring force to a magnitude of at least 100 lbf with a margin of error within 1 lbf 
  • Device height adjustable

Work Completed:

The mechanical design of the device was first modeled and simulated with SolidWorks. Static stress analysis in Solidworks was also applied to test if the material is capable of sustaining patient forces, from this analysis we were able to decide on cheaper material with adequate yield stress. 

Afterward, we ordered 80/20 metal parts for our frame assembly which we then mounted onto a plywood base. We chose to use 80/20 metal parts since it allows for rapid prototyping, easy customization, and is strong enough to withstand the forces of our application.

As shown above you can see the device being used for strength testing the shoulder flexion movement. You will also notice we designed the testing pad in Solidworks which we then 3D printed to hold the load cell inside. The testing pad is integrated into the frame which is the point of contact for where the force is being applied.

We constructed our device to be vertically adjustable, we used linear bearings with locks to traverse along the two 80/20 beams. This allows for patients to apply forces in a variety of movements and also accounts for different patient heights.

For the electrical portion of our design, we used a load cell sensor hooked up to an amplifier and an Arduino. Our load cell circuit is set up in a Wheatstone bridge configuration, which is used to measure an unknown resistance. When a mechanical force is applied to the sensor, the sensor undergoes elastic deformation, which changes the resistance of the loadcell, this altered value of resistance causes voltage fluctuation, this electrical signal is then amplified and received by the computer which it then converts it into a force measurement.

At first, we used a breadboard to hook up our electrical circuit but we found that it took up too much space and also did not support strong wire connections. To solve this, we implemented an IO Shield and soldered all the connections there. This resulted in a more compact and robust electrical design. In addition, we modeled housing for both the load cell and the whole circuit in Solidworks and then 3D-printed them. 


Lessons Learned:

This project gave me valuable experience in building up my own engineering skills while working in a team and collaborating with a client all while taking on a real engineering project from the ground up. I got to build up my experience with using SolidWorks, 3D printing, programming, and electronics. I learned more about how load cell sensors work and how to make them work. I learned how to implement an automatic tare function as well as new conditional statements for ease of gathering accurate and consistent data 


ADV Support Frame Project

ADV Support Frame Project

Project Description:

We have a 2-axis motorized Velmex bislide. Each axis of the bislide is 0.5 m in length (Fig 1). Figure 2 shows a photo of 1 Velmex Bislide. These Bislides are used to traverse an ADV (Acoustic Doppler Velocimeter) which is then used to gather 3D water velocity data inside of a water channel. 

 The first iteration of this whole apparatus (shown in Fig. 3 and 4) used 1″ 80/20 framing to attach the ADV to the bislide and for overall support for the apparatus. However, it was found that it performed poorly because it was not sturdy enough. The wind and water currents in the channel caused significant shaking of the instrument.

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To design and build the mount, we took inspiration from Pete Bachant’s design. His mount was made to support a larger bislide, but we were able to adapt some parts of his design into ours, as shown below:

Figure 5

Design Requirements:

  • Resist vibration from water currents and wind in the water channel
  • Overall length of mount must be 1.2 m from end to end
  • Must be able to adjust mounting point to reduce length down to 1 m to accommodate different water levels (this means that at least the part of the mount within 0.2 m of the top should be made of 80/20)
  • Horizontal distance from the vertical strut to the ADV transducer: (0.91/2 – 0.25) = 0.205 m
  • In our case, unlike in Pete Bachant’s design, the ADV transducer needs to point up. To avoid interference from the strut while measuring velocity, it also needs to be mounted some distance to the side of the strut. 
Figure 6

Figure 6 above shows a sketch of the overall frame shape and structure. Compared to Benchant’s design, our apparatus was smaller and did not consist of all the same parts Benchant’s design had. The three cross beams shown in the design sketch were inspired by Benchant’s design. Although the final apparatus did not look exactly like the design sketch it was followed closely. 


The design includes a top beam placed higher on the bislide supported with diagonal beams attached to the lower part of the frame. This was to provide extra overall support due to the existing large moment caused by the fluid drag on the ADV mount (because moment = force of the fluid drag x length of the vertical strut).


The frame was completely built using 80/20 parts ordered from Mcmaster. A small batch of 80/20 parts were ordered to begin building the skeleton of the frame and to evaluate what specific 80/20 parts were best suited for this project. 

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The frame was being built quite closely to our original design sketch. Of course, a few revisions were made given time and resources constraints but still met the specified requirements. A few challenges that arose included attaching the frame to the bislide, namely:  


  • Attaching the frame to the bislide
  • Missing a part that allows the vertical bislide to traverse along the top beam

At first, it was uncertain as to how the frame would attach to the bislide as the brackets and screws we had were not completely compatible with each other. This required some experimenting and out of the box thinking. Various ideas and methods were attempted to do this. It was found that the only way to make this work was to use a particular type of black brackets and screws that could successfully attach the bislide piece to the frame. 

Another challenge was to attach the top beam with the vertical bislide but also allow the vertical bislide to traverse along the top beam from side to side. In order for this to happen, a plate with custom drilled holes was required to be machined. With the custom plate, the bislide is now able to be mounted with the screws and brackets to the plate and the traversing 80/20 part (Figure 15). 

Figure 15

The final touch to the design was attaching the long beam (which the ADV will be mounted on) to the bislide and adding an airfoil strut to the portion of the beam to be submerged in water, in order to reduce drag (Figure 16).

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We also used a submersible vibration sensor to measure the level of vibration of the apparatus. The completed support frame proved to be successful as there were minimal to no vibrations compared to the first iteration when submerged and subjected to water current and wind force. 

Figure 18

Lastly, after looking into the Velmex bislide documentation. We were able to use MATLAB to control the Velmex Motors. This allowed us to traverse the ADV along the YZ axis. 

Figure 19

SDV – Propeller Design Project

SDV - Propeller Design Project


This report entails the design of a propeller for a notional Seal Delivery Vehicle (SDV). The objective is to use OpenProp to best design a propeller capable of a relatively high speed (4 m/s) for the SDV. Figure 1 on the right shows a few examples of propeller and nominal hull designs for an SDV, while they are unrelated to this project, they are provided for conceptual reference. This report includes a parametric study which includes sizing, powering, and efficiency calculations. In addition, blade designand cavitation analysis are also considered in this report.


  • Design speed: 4 m/s
  • Hull length: 9.4 m
  • Hull diameter: 1.5 m
  • Design depth: 3 m to hull centerline
  • Propeller Speed: TBD
  • Hull drag coefficient Cd: 0.15 based on frontal area


To conduct a parametric study to begin a propeller design. Some additional design specifications and assumptions are required to be found. In the design specifications above, a Hull drag coefficient value of Cd = 0.15 is given based on frontal area. This drag coefficient is used to find drag and then thrust of this SDV using the following formula.

In this design we set the Thrust equal to calculated Drag.

Figure 2

Now that Thrust and Drag has been calculated. We are able to conduct a Parametric study for potential propeller designs. Figure 2 above shows the OpenProp Parametric Study User interface that is displayed when running the OpenProp software through MATLAB. On the left hand side we input our propeller design specifications (thrust, speed, diameter, etc). On the bottom section called “Range” we input our minimum and maximum number of blades, rotations speed as well as rotor (propeller) diameter. In the center of the User Interface we see a table of Geometric Blade Design Values. We assume the Cd for the propeller remains 0.008. We also keep r/R values the same. The c/D values inputted in this design report are from NACA66 (DTRC modified) data [1, page 15].

Figure 3

After inputting all the blade design values and propeller specifications, we run OpenProp. Figure 3 above shows the output of the OpenProp software. We are given a parametric study that charts an assortment of a wide variety of propeller designs depending on the number of propeller blades, their rotational speed as well as their diameter. The program then calculates each design’s efficiency. For this project, we select the propeller design with the highest efficiency.

This yielded in a propeller design of 3 blades, 60 rpm, and a rotor diameter of 1.9 m with an efficiency of 0.78 (78%).

Figure 4

Now that a specific propeller type is decided we move forward with a single design study. As shown in Figure 4 above, the detailed propeller design specifications are once again input into the OpenProp user interface.

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Figure 5 and 6 showcase the 3D geometry of the propeller design, as well as the design performance after the single design study, is executed in OpenProp.

Figure 7

Figure 7 above shows the MATLAB code that is used to conduct cavitation analysis of the chosen propeller design. This code consist of an input script and a usage script. The input script is for the propeller specifications (c/D values, blade number, Kt, J, Vs, etc.). We inputted the propeller specifications into this script. The propeller usage script draws propeller specifications from the input script to conduct a variety of analyses. For this report we focus on the cavitation analysis of our propeller as shown in Figure 8 below.

Figure 8

As shown in Figure 8 above. OpenProp analysis shows that the propeller design is not prone to cavitation based on propeller specifications. This is ideal as it is known that cavitation is problematic for propeller blades. Known detrimental effects to propellers caused by cavitation include increased noise (especially for military equipment that is not ideal for stealth), as well as overall damage to the propeller thereby reducing its life and effectiveness.

Cavitation is known as the rapid formation and collapse of vapor bubbles within a liquid. Cavitation bubbles mainly occur when static pressure decreases below a liquid’s vapor pressure. In the case of a ship propeller, as it moves through the water, there is high pressure on the side of the propeller facing the flow and lower pressure on the opposite side. The area of lower pressure essentially causes boiling of the liquid (due to decreased pressure not related to temperature) and thus creates bubbles of steam trailing behind the propeller. It is also important to note that increasing a propeller’s RPM will increase the risk of cavitation.

When conducting propeller design, it is critical to consider the balance between a propeller’s rotational speed, thrust, and cavitation risk. Increasing rotational speed may increase thrust but also increases the risk for cavitation.


In conclusion, OpenProp analysis shows that a 3-bladed propeller with a rotor diameter of 1.9 meters serves to meet propeller design requirements as stated in the beginning. This propeller has an efficiency of 78% and is also not prone to cavitation.