GEEN 2400: Belay Buddy

BACKGROUND 

Client Interviews

The first part of our process was to determine a problem we wanted to solve. To do this, we picked a very broad topic: the outdoors. After deciding that we wanted to solve some problem in the outdoors we picked several groups to interview: the Boulder Rock Club, the park rangers at Chautauqua Park, the local Boulder County Firefighters, and the climbers at the CU Rec Center. We asked them about their daily lives at work, what they like about the outdoors, and other questions specific to each group such as how government funding affects what the Chautauqua Rangers spend money on  or how often the climbers at the Boulder Rock Club go climbing outdoors vs indoor. As we interviewed the various groups we began noticing that they seemed to have issues with finding affordable and effective communication.

We decided to pick the Rock Climbers as our "client" for this project because of something one of the people we interviewed said in passing. She made a joke about making a light up rope, which gave us the idea to make a communication device for rock climbing that uses some sort of light to communicate.

Research

After we decided on the problem we wanted to solve with our project we began to think about how to actually solve it. We sent out a poll to various outdoor and climbing communities to ask what they would want in a communication device and got good results. They wanted something that was versatile and could be used for several outdoor activities, something with multiple cues of a message being sent/received, and something that wouldn't cause new issues.  We also did research on our own to discover what existing devices were on the market. We found that the primary item that people used was a Rocky Talkie, but many people didn't use them because they cost $100 to $120 per individual device, and relied on auditory communication. This meant they were inaccessible to people who were just starting climbing, couldn't afford to spend $200 on a pair of devices, and people with any sort of hearing impairment. They also were not useful if you were climbing somewhere noisy and couldn't hear what people were saying through the device.

DESIGN REQUIREMENTS

Design Constraints:

• $375 budget (Bill of Materials at bottom of page)

• Buildable in 14 weeks

Qualitative Requirements:

• Fits comfortably/doesn’t slide

• Doesn’t impede climber movement

• Compact

  1. Minimize excess space in electronics case

• Durable Materials

  1. Withstand accidental drops

  2. Withstand bumps into rocks

Quantitative Requirements:

• 200 meter communication range

• Minimum 4 hours of use

• Weather proofing at least IP52

  1. IP 52: dustproof and resistant to splashing water from all directions

PROTOTYPES

Initial Prototypes

With this new info we were able to begin prototyping. Our initial prototypes (Fig.4) had four buttons (falling, slack, take, and pause) and four LED colors. After we sent out another poll, we discovered that having a fall button would not be helpful to climbers and that it would be better to have an accelerometer in the climber device with a red light that automatically lit up when the climber fell. We also decided to add a haptic motor in both the climber and belayer devices so that they would be able to feel when the other person was trying to communicate with them, since they won't be looking at the device all the time.

More Prototyping

Once we had some initial cardboard prototypes (Fig.4) we began experimenting with what materials we wanted to make it out of. We talked with Natasha and she recommended that we do a hard inner case to protect the electronics and surround it with a squishy outer shell to disperse any forces the device may receive from falls or hitting rocks. To keep costs low we wanted to use materials from the ITLL, and we were primarily interseted in acrylic or PLA for the electronics box. We tested an acrylic box, but the corners were too sharp so we opted for cadding and printing a PLA case for the electronics. For the outer squishy shell we tossed around several ideas. We considered silicone molding a soft shell, using memory foam, and using TPU. We needed the outer shell to be pliable but also stiff enough to keep the PLA case from slipping out of the shell. After heavy consideration we decided to try TPU because we were worried the silicone would make a mess and had too much room for errors like uneven setting, and we weren't sure if memory foam would be stiff enough.  We created miniature TPU shells to make sure that it was the material we wanted. We also made a CAD model of the PLA box that would fit the electronics.

To prototype the electronics we created a circuit on an arduino to get an idea pressing a button and having the corresponding LED light up. We then tested several iterations of buttons, first really large ones and then we eventually ended up using micro buttons and creating button covers for them. We also tried to use LED lights but quickly realized they would not be bright enough to see through the box. We opted to use a strip of neo-pixel lights, and after much research decided to use the AdaFruit Feather M0 with LORA Radio to transmit signals between the devices.

FINAL PRODUCT

The final version of the Belay Buddy featured three buttons that each triggered a different light and haptic vibration pattern. We placed a large hole in the side of the TPU shell so that the light from the neo-pixels would shine through the side, since a climber or belayer would not necessarily be able to see the light from the top of the box all the time. We added a curved base to the TPU shell for the belayer device so that they could wear it on their arm and a flat base to the climber device so that the velcro could go around and lie flush with a harness. The TPU shell had a lip on two sides and a tight tolerance to the PLA case, so it would not slip out of the shell while it was being used.  The CAD files for the TPU shell and PLA case can be found at the bottom of this page.

The final electronics (Fig.3) were all from Adafruit: a motor and driver, Feather M0, accelerometer (for climber device), and neo-pixel strip. These fit snugly inside the PLA case with no room to move around inside. The electronics were programmed to light up a certain color and produce a certain vibration pattern when the corresponding button was pressed. This code can be found in the appendix at the bottom of this page.

Technical Challenges

We ran into several technical challenges in this project. The largest challenge was finding the right buttons to use. The initial buttons we picked for the box had the clicking sound we wanted, but they were incredibly deep, so we needed a large PLA case to fit them and the other electronics. To remedy this we decided to use micro buttons on the circuit and make larger button covers out of TPU. We printed dozens of button covers to get the correct feel and size for them. We wanted the user to feel the click and be able to feel the difference between the buttons without looking. To do this we used thinner button walls (thinner walls = more buckling = more click) and added symbols that stuck up from the top of the button cover.

Another challenge was getting the devices to be transceivers. The devices needed to be able to send and receive signals at the same time. This was difficult to do because many radios only allow sending or receiving at separate times. After consulting various engineers in the ITLL, doing research on the internet, and extensive coding we were able to achieve this.

My Role on the Team

For this project our team opted to not put one person in charge, rather we split into two teams: manufacturing and electronics, and then divvied up the work from there. Two members, Kyle and Curtis, worked on the electronics together. Three of us, Gaby, Jess, and I, worked on the manufacturing aspect of the project. Gaby designed the PLA case, Jess designed the TPU button covers, and I designed the TPU shell.

There were several requirements I had to keep in mind while designing the TPU shell:

•  The belayer shell had to have an attachment that was comfortable to wear on the arm

• The climber had to be able to see the lights while the device was on their harness

• Both shells had to 

  • Be thick enough to cushion 

  • Be thin enough to keep the device small

  • Have holes for straps or velcro to go through

  • Have no sharp corners

  • Have a tight tolerance to the PLA case

Once I knew what requirements I needed to fulfill I began to CAD. I first created a shell for the belayer with 15% infill that had 2mm thick walls, with a 1mm tolerance to the PLA case, and a curved bottom with slots for velcro to go around an arm. After printing this shell I learned several things: the infill needed to be higher, the walls needed to be a bit thicker, the tolerance to the PLA case needed to be tightened, and the bottom needed to be curved more. I also learned that the shell for the belayer had to be printed on its side as opposed to the bottom, otherwise the curve for the arm would be rough from the support material. 

Once I learned this I decided to print a shell that was much smaller than our actual case so that I could quickly iterate to find the ideal wall thickness and infill density. I increased the wall thickness was bumped to 3mm and the infill to 20%. After the small test box printed I decided that this was a good infill density, squishy but supportive, and the walls were not so thick that it would greatly increase the size of the device. The next step was to print a scale size of the belayer shell with an increased attachment curve and the new wall thickness and infill density. In this print I also added a plug for a charging port and tightened the tolerance to the PLA box to 0.35mm. We originally wanted to be able to charge the case from inside the shell, but after we printed this version I learned that adding a hole in the TPU and creating a plug for it that would be properly water and air tight through both the TPU and PLA case was not feasible with the time we had. I also learned that a tolerance of 0.35mm was perfect for being able to put the PLA case in the shell and take it out. The final thing I learned from this iteration was that a curve with a radius of 45mm was perfect for the arm attachment of the belayer device.

Now that I knew this, I wanted to add extra security to make sure the case would not fall out of the TPU shell. To do this I made a 3cm by 4cm cube of LEGOs and created a TPU shell for them, with 20% infill, 3mm walls, and 0.35mm tolerances, and added a lip that stuck out 1mm over the inner edge of the shell -- like how phone case lips stick over the edge of your phone to keep the screen safe. After printing the shell at a LEGO scale I learned that it was not possible to get the intended LEGO cube into the case. To remedy this I trimmed the lip off of the two long sides and tried to put the LEGO in. This worked wonderfully! The cube went into the case, and did not fall out no matter how hard I shook it.

I printed a new belayer shell with a lip on two sides, infill of 20%, wall thickness of 3mm, and a curve of radius 45mm, and a climber shell for testing. The only difference between the shell for the climber device and the shell for the belayer device is that the climber shell has a flat bottom under the velcro straps as opposed to a curve.

 Once I had a good enough design for the climber and belayer TPU shells (Fig.10 and Fig.11), the rest of the team had completed most of their work as well. The devices were functional except for a few small kinks in the electronic programming. Since we were at a good point as far as usibility my team decided to go to the climbing gym in the CU Rec Center. Gaby rock climbs so we gave her the climber device and had her climb the wall. We learned a lot about the functionality of the buttons and case from this. The most important part that I learned what that the climber device needed to have a hole in on of the long sides of the TPU shell so that the climber could see the light from the device. Because the climber device is designed to sit flush with a harness, and we needed the climber to not press the buttons when they curved their body, the buttons and lights face away from the body. To remedy this problem, I added a design of the flatirons across a hole in the side of both shells so that the lights could be seen from the side. Thus, the final design of the case was born. 

TESTING AND ANALYSIS

To ensure our design met the requirements we conducted extensive testing and analysis. We tested the durability of the PLA case with and without the TPU shell, as well as the IP rating of the PLA case, and the battery life of the electronics. 

Electronics

• Runtime: 28 hours of use

• Range: 230 m

• Charge time: 45 minutes

• Power draw at rest: 0.18 W

• Power draw (during transmission and alert): 0.775 W

Case

• Expected waterproofing performance - IP52

• Case withstands falls of up to 65 feet without damage

The full details of our testing and analysis can be found in the paper directly below.