Time to read: 12 min

To gain actionable insights on how real hardware products are developed and manufactured, we interviewed top engineers and designers in the San Francisco Bay Area in our Hardware Sessions series.

In this edition of Hardware Sessions, we sit down with Hind Hobeika, a mechanical engineer and founder of Instabeat, a connected accessory for swimming goggles that captures real-time heart rate, stroke type, and laps. Hind is an expert in waterproofing and reliability testing, and in this Hardware Sessions interview, gives us her candid thoughts & insights on:

  • How to avoid bias in design and user testing (00:00:57)
  • How to conduct waterproof testing (00:02:32)
  • How to make prototypes last longer in user testing (00:05:12)
  • Using o-rings and gaskets for sealing (00:07:56)
  • Creative ways to do reliability testing without a lab (00:10:00)
  • How to organize testing data (00:11:50)
  • Recommended waterproofing resources (00:14:08)
  • What she wishes she knew around waterproofing 5 years ago (00:15:12)

Check out the video below, as well as the full written transcript.

Dave Evans: Hey everyone, I’m Dave Evans, and this is Hardware Sessions. On today’s episode, we’re going to be covering reliability testing and waterproofing. To help us out, we’re walking over to meet with Hind Hobeika, founder of Instabeat. Instabeat is an attachment for your goggles to get real-time heart rate and lap times as you’re swimming in the pool. Let’s go dive in.

How Do You Avoid Bias in Design and User Testing?

Dave Evans: Well let’s jump into your product a little bit. We talked a little bit about that you’re a competitive swimmer, and how we generally build a product for ourselves. So how do you not have a bias toward the design?

Hind Hobeika: It’s really hard.. I don’t have clear cut answer to that. I think having a team makes it a little bit easier for you not to impose your ideas because you need to be respectful and mindful of their decisions. Also, I made it a point that most of the team members are swimmers, and so they also have valid opinions that don’t agree with mine. So I try to be as open as possible, but it doesn’t always work. If something is not the way I want it, it bugs me so much! But i don’t voice it because I feel like I can’t.

We also try to do lots of pool tests and pool surveys, so I spend a lot of time at the pool actually talking to other swimmers. And I am from the school that observing is better than asking questions, so I actually go and just watch people using the product and it gives me a lot of insights on what the majority wants. But it’s hard. It’s not easy and you don’t realize that you’re subjective.

How Did You Conduct Your First Waterproof Testing?

Dave Evans: So maybe diving into some more of the technical stuff now — You’ve been working on a vast variety of all these products and you must have an immense amount of knowledge. So maybe talk to me a little bit about how you guys conducted your first waterproof testing. How did you think about tackling that really hard challenge?

Hind Hobeika: You know, waterproofing is really, really difficult, especially when you are trying to build a product that is small and flexible. You can’t just have a plastic box with gaskets and screws. This, it was kind of waterproof, but it was so big swimmers didn’t want to wear it and didn’t want to test it. And so we moved actually from this, the very first design, to this: this is the form factor we established. To be very honest with you, it took us almost a year before we were able to get in the water, just because … I tried nail polish. It just wouldn’t work. I tried epoxy, then it would fail after an hour or it would crack because it needs to be flexible and mounted. We’ve even tried hand pouring silicone. It works for an hour, then it fails.

The first real waterproofing test we were able to do was only when we actually did it with a professional. They actually did the over molding for us and this is when we were really, really able to test in the water and understand the limitations of the product in the water.

Dave Evans: Do you have an understanding of what they did differently, in terms of tooling or fixturing versus your handmade one?

Hind Hobeika: Yeah, so they have a better process, first of all, to cover the electronics and an epoxy that is actually waterproof and that would bond to the PCB, that would dry and cure at the right temperature with the right amount of time. And then actually being able to work with the silicone that bonds to the epoxy so that there’s actually a chemical bond that wouldn’t let water in. That was the key in actually making the product waterproof.

You can’t find the silicone just off the shelf and melt it in your oven. It’s not a thing. We just tried to hack a solution. We used Sugru a lot. We used some cases that have the plastic dip on top of it. There are so many chemicals, your eyes fume after you swim with it. But you have to be creative knowing that your prototypes are gonna fail, just so that you’re able to at least prove some of your subassemblies before moving into tooling.

Since Athletes are So Hard on Their Products, How Do You Keep the Prototype From Destruction?

Dave Evans: So, wear-testing. This looks like it broke, maybe not this specific one, but something that I know about athletes is that they’re super hard on their products.

And so how do you think about keeping an athlete from destroying the product?

Hind Hobeika: So going back to the observing bit, if you observe swimmers, they actually get out of the pool, take their goggles, and throw them on the deck. I have to design a product that people are gonna throw on the deck. And you can’t come and tell a swimmer who just swam for two hours and is starving, “Don’t throw your goggles on the deck.” They’re not gonna respond very well. For us having a rubbery, flexible product makes it a little bit easier because it deals with shock much better.

But this definitely something that we’ve tested for … We’ve thrown the product on walls in order to make sure that it works. And then I’ve also seen swimmers shred their goggles during their swim super aggressively, so we do all kinds of stretch testing in order to make sure that … I mean, it’s eventually gonna break, but at least not in the first few years.

Dave Evans: Do you think about having to make a certain number for the yield of prototypes? For example, we want to do 10 users that are gonna use this, so I have to make 15, knowing that five will break?

Hind Hobeika: Yes.

Dave Evans: Would that change in different stages?

Hind Hobeika: Yes, and it depends on what you’re testing. So when we weren’t doing water testing, we were doing 10 boards, 10 prototypes at a time and were able to get 10 people to test them. When we actually went into water, we got 50 boards for 10 people because we knew that things are gonna fail because of water, because of yield, because it’s not the right material. So yeah, you definitely have to account for that; otherwise, your whole prototyping cycle becomes much slower.

Dave Evans: So you actually budgeted for five prototypes per user there?

Hind Hobeika: Yeah.

Dave Evans: And has that been a good metric for you?

Hind Hobeika: I don’t think it’s a rule of thumb, but we’ve computed the hours of how much time we want the swimmer to spend in the water and how much time we think the device is gonna survive, and then that was the rule for us. But I think, depending on your application, that might change.

Dave Evans: So cool — I think of reliability test, and the very scientific one of the “chuck against the wall”, so I think that’s a good one.

Hind Hobeika: There’s a lot of very scientific things we do to pass this here.

Dave Evans: We call it the “flex and the throw”.

Hind Hobeika: Yeah, exactly! And we even have big buckets of water here and then you just put your head in it and we stretch it. I mean, you have to get creative. We don’t have the ability to go to very expensive test labs to do these kinds of tests. We need something that’s representative enough. So we get creative.

Do you Use O-rings or Gaskets for Sealing?

Dave Evans: So let’s talk a little bit around sealing. So when you talk about any type of electronics with waterproofing, sealing is always the hardest thing. Do you guys use O-rings or gaskets?

Hind Hobeika: In our prototypes, yes. In the final product, no. So the way we make our final product waterproof is that we have a productive layer on top of the PCB that is some kind of resin that protects it from water, but also from pressure and temperature of the over molding. And then we over mold the entire product with a kind of TPU rubber. So this is actually what makes sure that the product is waterproof. Our limitation is that it needs to be flexible.

So you see this arm needs to bend, depending on the goggle size. If the goggles are big, it needs to bend more. If they’re small, it needs to bend less. And so we can’t afford to have something that’s super rigid and we didn’t want to have any room for the water to go in by having a rigid plastic here, and then going to a flexible plastic here. So we just decided to over mold the whole thing.

Dave Evans: That’s really interesting.. so when you were doing the initial prototypes, were any of your gaskets or O-rings custom made or did you try to stick just to off the shelf?

Hind Hobeika: We tried to stick to off the shelf because it would’ve taken so much more time to actually do custom made, but then we ended up with much bigger prototypes. So they weren’t representative. Again, it’s subassembly testing, so for example, we were testing heart rate with a device that was, like, two times bigger than this. So if someone told us, “It’s annoying”, “I don’t want to wear it”, or “It’s making my goggles leak, I don’t want to wear it,” then you can’t do anything, even though you’re not testing for fit, you’re testing for heart rate. You just can’t make the test because of this limitation. So it definitely limits you a lot. But time versus cost versus …

Dave Evans: …Quality, all the way around.

Hind Hobeika: Exactly.

What are Some Creative Ways to Do Reliability Testing Without a Lab?

Dave Evans: Something I thought that was really interesting you talked about was the bucket of water from the testing. Could you share with us maybe some of the other unique reliability testing that you’ve done, where you’ve said, “Hey, a lab does it this way. We can simulate 90% of it this way.” Expose a little bit of how creative, I think, engineers are.

Hind Hobeika: So we’ve done accelerated life testing by using fridges and ovens. We put it at really high temperatures because we think, what if you’re in Saudi Arabia and you leave your device in the car and then you go to a really cold pool? So we put it in the oven for X minutes, and then we put it in the fridge for X minutes, and then we have to test for functionality.

We’ve also done lots of stretch testing. That’s not very creative, but we actually had a person do this for a thousand times instead of using the machine.

What else? We used the bucket of water a lot for the light pipe testing and actually showing the real time display. We’ve had the bucket of water on the window outside and then have one of the team members sticking their head out to get the sunshine in order to test reliably in the water.

Dave Evans: And then beyond that, you’re actually doing real user testing as well?

Hind Hobeika: Yes. So we do real user testing. We try to recruit all kinds of swimmers, not just by performance, but also by head shape, and also by heart conditions, I would say, just because we try to find what are the corner cases where our device could potentially fail, and test for those just to make sure that we’re mitigating them either in the design or we need the communication, at least, if it’s not possible in the design.

How Do You Organize All of Your Testing Data?

Dave Evans: How do you organize a lot of the data and tests? And how do you know if that passes or fails?

Hind Hobeika: It’s a lot of trial and error. We have three test engineers that their full time job is just to test. And I’m obviously always testing also. It’s a lot of iterations, honestly.

I can talk about the ergonomic testing, for example. So the idea is that any person in the world picks any goggles that they like to wear, and they put them on it and it needs to work. And at first we thought it needs to work, they just swim free-style, and then it’s fine. If it doesn’t leak, it’s great. But then we realized that when people push off the wall, actually that’s when the leakage happens, but that only took us a few tests in the water to identify the source.

We also had some people leak when they breath, because their cheek is pushing up the device. So these are all things that you learn while running your initial set of experiments. Then you modify your protocol in order to account for these corner case scenarios.

It’s experience. It’s knowing the product really well. It’s using it yourself. I think it’s really important that every single person on the team uses the product and not just the test engineers because they get used to the product a lot so they stop seeing what newbies could see. So I have everyone on the team test all the time.

Dave Evans: Everyone — so hiring requirement for you is you must stick your head in a bucket of water in order …

Hind Hobeika: No, I’m not joking! If you look at our Angie’s list post, it’s actually “must swim at least one stroke.” I don’t think I can have, at least today, someone on my team someone that’s afraid of water. Everyone needs to get in the water at least once because we’re a product company and we’re only trying to push one product. It’s really important that everyone knows how to use it, at least tries it, has some connection to it, because that’s all you’re working towards.

What Resources Around Waterproofing Would You Give to an Engineer Today?

Dave Evans: I love it. So the last question … well, I have two. First one is what resources around waterproofing would you give to an engineer today that has to know more about it? Is there a textbook, a website, a video that you watched, anything?

Hind Hobeika: You know, the Fictiv blog actually. And I’m not just saying this because you’re here. But you guys had a great article on gaskets and O-rings and how to do the waterproofing, and we actually got inspired by that to do our big bucket cases for the heart rate testing. Otherwise, I think there are lots of hobbyists and articles online, especially instructables on how to waterproof things… I don’t think they work very well. I think we know the materials that work for us and they’re silicone, epoxy, and then Sugru is good sometimes, depending on the application. And we’ve always tried to use a combination of those in order to test in the water.

What Do You Wish You Knew Five Years Ago About Waterproofing?

Dave Evans: So the last question is, if you could tell yourself five years ago something just about waterproofing, what would you tell yourself that you wish you knew as you were first starting?

Hind Hobeika: I think there are two elements to it. I think, first of all, the psychological element of waterproofing is that, I used to get frustrated so much about units failing in the water and didn’t understand why nail polish wasn’t working. And I kept telling my team this: The last generation product, we weren’t able to test until we properly, all of the assembly, until we went to a professional model shop and that’s really important to know because, first of all, you don’t want to get frustrated along the way if units fail and second of all, you want to get creative with testing subassemblies first, but without trying to make it all in one go because it’s gonna fail. So you want to do small testing that prove out the main elements and then rely on the experts and the real materials in order to put everything together.

Dave Evans: So planning and budgeting, and don’t get frustrated when things don’t go right.

Hind Hobeika: Yeah, because it cues the way you want to test actually. So test subassemblies first and then the full assembly.

Dave Evans: Fabulous. Well thank you so much for taking the time. I’ve learned so much, personally. I feel like I’m a waterproofing expert now!