The Power Cleaner

Overview

My device is called the “Power Cleaner” and it sprays disinfectant on dumbbells at the gym by letting ultrasonic sensors and servo motors do the mechanical work so that gym-goers can focus on their workout, especially during COVID. It was created for my Mechatronics class in the fall of 2021 where we were tasked with designing and building a device that combined both mechanical structure with electronics for an individual project.

Design

The Power Cleaner is broken down into two main components. The first component consists of two 3D printed stands to represent the dumbbell rack at the gym and a set of ultrasonic distance sensors that will detect when the dumbbell is placed back on the rack. This works as the input. The second component consists of the two servos (one positional and one continuous) attached to the spray bottle. This works as the output. Furthermore, the two Parallax ping ultrasonic distance sensors detect when the dumbbell is back on the rack by measuring the distance in front of them. They are placed on either side of the dumbbell so when it reads a distance of less than 8 cm, it then sends a signal to the output to begin its task. The spray bottle has two servo motors attached to its sides that are connected over the handle of the spray bottle by a small piece of rope. As the input detects the dumbbell being placed back on the stand, the two servos rotate backwards causing the rope to tense up and pull back the handle of the spray bottle leading to disinfectant being sprayed on the dumbbell handle.

Manufacturing

For this project, we were provided with a kit of starting materials which included a breadboard, an Arduino Uno R3, various wires, and several other electrical components. We were also provided with a $20 budget which we could spend on ordering additional materials for our projects. Below is the bill of materials for my project.

Once all of the necessary components are collected, the assembly can be broken down into the following steps:

1. Construct the circuit based on the circuit diagram below in Figure 1

2. Download the stand in the attached .stl file at the bottom of the page under “Files” and open it in a CAD software program such as Fusion360 to the dimensions given in the image and 3D print two of these using the stronger ABS filament

3. Once the two stands are 3D printed, attach the ultrasonic distance sensors to the sidewall of the stand, as shown in Figure 3, using tape or a zip tie

4. Use the dumbbell to set the two stands and sensors at the necessary distance for the head of the dumbbell to be the only thing on the stand as shown in Figure 4

5. Attach the two servo motors to the sides of the spray bottle at a slight angle like in Figure 5 using duct tape

6. Place the spray bottle next to the dumbbell and the stands as seen in Figure 6, a distance of 15 cm works best usually but you should test it beforehand

7. Then using a small piece of rope or a wire, connect the servo horns over the handle of the spray bottle under tension, so that the rotation of the servos can pull back the handle with enough force to have spray come out; the best results involve using knots tied using the holes in the horns and duct tape at the handle

8. Your final product should look similar to the main figure at the top of the page

Operation Instructions

Once the “Power Cleaner” is fully assembled, take off the dumbbell to prevent any unwanted activations by your circuit. The first thing you have to do is download the code under “Files” at the bottom of the page to the Arduino board using the Arduino IDE. To do this, you will download the code and then copy and paste the code into the open Arduino IDE and save the file. Once the code is successfully saved, you can upload it to the Arduino board and power the circuit using a 4-AA battery pack or an equivalent voltage battery hooked up to the Arduino Vin and ground connections as seen in the circuit diagram in Figure 1. You can then place the dumbbell on top of the two 3D printed stands and the ultrasonic distance sensors will automatically detect the dumbbell and wait 3 seconds before rotating backward, giving time to the user to remove their hand. It will then release the spray and wait 10 seconds before returning to its original position. In these 10 seconds, you will need to remove the dumbbell or remove the battery from the Arduino connections, so that the circuit does not run in an infinite loop and drain the battery.

Conclusion

The advice I would give to someone attempting to replicate the “Power Cleaner” would be to focus less on how the dumbbell would be placed on top of the ultrasonic distance sensors without breaking them and focus more on how you would securely attach the servos to the spray bottle and the rope to the servo horns. I believe that I spent too much time trying to create a stand for the dumbbell to lay upon when in the real-life application the dumbbell would just lay on a rack and what would really matter is how the circuit and spray bottle would be integrated into the rack.

If I could do the entire project over with the same constraints, I would still purchase two ultrasonic distance sensors but I would try to purchase a second positional servo and design a 3D printed ring jig for the spray bottle. The jig would allow both servos to be held firmly and allow for a stronger force when pulling back the handle compared to being held with duct tape. I think that these adjustments would allow for a better demonstration of how the final product would work as the positional servos are much easier to control. I would also spend more time thinking about how you could attach the rope to the two servos better so that it does not come apart every time you test it. If I could do the entire project over with more time and money, I would spend time testing having the spray bottle in different positions and at different angles to see which one results in the greatest amount of surface area being disinfected. Then I would incorporate all of the features I mentioned in my answer above regarding the spray bottle jig and using a second position servo. Lastly, I would try to think of a way to cover the handle of the dumbbell as it is being sprayed so that a person won’t try to reach for it right away and get sprayed. All of these improvements would create a more marketable prototype that can be seamlessly integrated into gyms.