I’ll Be Your Personal Test Chimp

Picture of Adam Bahret
Adam Bahret

I have a customer that has developed an impressive wrist worn biometric sensor for athletes. The system is worn on the athletes wrist, like many other personal devices. But this product is for serious athletes that aren’t just looking for non-descript data like step count and heart rate. What are you even supposed to do with that information?

 The system collects multiple complex data points about your body’s performance. But not just when you are active, it also tracks and uses complex biometrics when you are at rest, ‘recovery.”  This is an often overlooked, but very important part of training. For example, the system doesn’t just measure your sleep, it measures your REM sleep. Their software then analyses your entire performance profile and recommends changes to improve all aspects of your game.  

 I was excited when this team wanted to include Apex Ridge in their next generation product development program, Why? Talk about a cool challenge. This device could not fail, missing data sets means a total loss of next phase training strategy.  This product was going to be seriously challenged by it’s customers, extreme athletes.  

 As many of you who have worked with me know I take “Use Case” definition very seriously in reliability programs. Errors in estimation of use cases can have devastating effects in product development, and surprisingly so many product teams don’t spend much time ensuring they are accurate.

 Why are use cases so important? Because they are the foundation that all reliability measurements and statements stand on. These reliability measurements that are made from testing programs are what drive the development program. It’s not just about making the most reliable product you can. It’s about making the product with the correct reliability, not too much, not too little. A product that is under reliable and the customer is going to be disappointed. Over reliable and there will be compromises to cost point, weight, and time to market. These can hurt market share just as much as poor reliability.

 The use case initiative involved developing seven types of athletes. Everything from the Surfer to the Golfer. We had the mountain climber, the Mixed Martial Arts fighter, and the Ultra Marathoner. But best of all we had a composite case that included all the worst factors of the other cases. I wanted to see if I could personally contribute in some way to bringing this use case to life. I am very abusive to my personal items, and also the creator of the concept of Use Case 7. Use Case 7 (as many of you know) is my own specialized method for improving products through marginal destruction and creative use.

My athletic lifestyle is a bit odd as well. It’s not really “serious athlete.” It’s more akin to a five year old who has had three Red Bulls but also has money and looks like an adult, so totally unsupervised. The team knew this and gave me a system right away to see what would happen. 

Step 1:
I practice and compete in Brazilian Jiu Jitsu (BJJ). This is a grappling (wrestling) sport where bending joints backwards and choking people out is permitted (actually, it’s the point). It’s a submission sport, which means the two opponents beat the crap out of each other until one submits by tapping out. It’s 50% of what MMA is based on.  The other half of MMA being Muay Thai punching and kicking to the head. I’m 47 and can’t take anymore of that striking stuff if people want me to show up to their product development programs and actually speak in an articulate manner.  

Ok we need to know how the product works with Grapplers. Roger! I’m on it. Well obviously it can’t be on the wrist. It will be ripped off in 10 seconds when some gorilla grabs your arm and uses it to try and throw you. So I thought about it. The best place was going to be on the inside of my bicep. Why?, Well on my legs won’t be any good.  We act like primates in BJJ and use our legs to fight. We wrap them around torsos and squeeze. They also get grabbed and used to flip and drag.

On the outside of my arm it’s going to get slammed on the ground. The product may be fine but I’m pretty sure it is going to leave a hell of a mark on my arm or shoulder. It also can’t really go there because grapplers love to grab the tricep of an opponent to manipulate them. It would be right under their hand and get ripped off.

Inside the bicep was perfect because it would be an unusual place for an opponent to grab.  In addition when I fall on that side it is going to be pressed between my arm and rib, which shouldn’t hurt, relatively.So I used a grapplers favorite sports accessory to put it on, tape. We tape everything, we buy tape by the box. We tape fingers, toes, elbows, knees, and ears. Ok the big question, “How did the product do?” Great! It worked perfectly and collected great data. What did we learn. Something extremely valuable.  Something that would have taken years of field use to discover. It was in the category of chemicals and debris.We had thought about chemicals and debris when we created our use cases. We included exposure to chemicals like sunscreen, bug spray, perfume, and skin lotion. We expected dirt, mud, and grass as well. For chemicals we had a specific recipe for test called “Cocktail X.”  It is used in our long term high temperature accelerated life test. But we didn’t consider tape glue. Tape glue actually has a primary stress and (more importantly) a secondary stress. The first is a mechanical issue of glue build up. The second is a chemical one, “What are they using to clean it?”
First the mechanical issue. The glue is soft because athletes don’t’ want it to rip skin off when applied and removed each day.  But soft means it stays behind, which isn’t a big deal if you are headed to the shower next. So I found white tape glue on the product after I removed it from my arm. I could see the possibility of multiple sessions of this being an issue because the charging contact could get glue on them. In addition there was the possibility of the channels in the housing getting enough glue to have issues.  Both serious issues to performance.They do make a compression band that the product can be placed in instead of the wrist band.  But here is the thing, grapplers are always going to go for tape first. We don’t’ like things on our body because they get pulled off, or twisted around, and then the match has to stop.  There is also the issue of tournament regulations. Competitors are not allowed to have anything on their body for both their and the opponents safety, no jock cups, no wedding rings and no knee or elbow braces, not even a t-shirt under the GI jacket.  The shirt could get grabbed twisted and ripped. A compression strap on the arm might be a debate before a match with the ref. Tape on the arm won’t even be questioned.So what is the second issue?  How do athletes clean the glue off?  Athletes may use any number of chemicals from soap to acetone to try and remove glue.They manufacturer could be getting product returned with cracked casings and deteriorated plastic. That could be a hell of a time figuring out what is happening in the root cause process.
We now have the opportunity to figure out an advised method of cleaning tape glue. We are also testing other cleaning methods that may cause serious degradation and create a catalogue of symptoms to aid in root cause analysis.  It will be great to be able to immediately diagnose returned product with damaged plastic. “Yup that is what it looks like when gasoline is used to clean it.” So we are now planning an accelerated life test program with a new “Cocktail X” to study cleaning chemicals. Step 2:
Ok what next? I took it dog sledding in Northern Quebec. How’s that for extreme. I mean why not. The question that I was going after here were going to be primarily temperature based.  This is my mission: “What are the most extreme use case temperatures that can be experienced and what are the fastest temp transition rates that can be experienced.” I was ready to find out.

When we were defining the temperature ranges in our use cases at the lab we were having a hard time with one thing. What was the extreme low temperature the Product could be in? Seems like an easy question to answer at first. The product is always on a person’s wrist, right? Turned out to be more difficult than that. 

We had done HALT testing to find out what the current product could do. The ranges for operation were -20C to 90C. Ok that doesn’t mean anything to us unless we can tie it to actual use cases. What temperatures do people go out in?  Athletes will go out in temperatures colder than the limit -35C for some sports. But what temperature would the product see? That was the hard question. It wasn’t a camera that was going to be on top of a helmet, totally exposed. It is placed directly on the skin and is very thin.  So in theory it’s exposure when in operation is going to be similar to what an athlete’s skin experiences.

But wait even that may not be true. It’s possible the glove and sleeve could be pushed back for an extended period of time.  We decided our worst case scenario may be this. The bottom of the product has the athlete’s wrist as a heater, the sides of the product are insulated with the glove and jacket, the top is open to exposed air. So now the hard question.  What temperature do the internals of the product equalize at under these conditions?

We made a simple device that we thought might tell us. It was an arm heat simulator that could be put in a cold chamber. It created the heat skin would generate to the bottom of the product, had insulation for the sides and left the top exposed.  We are scheduled to try it out next month, but guess what, I beat them to it and did my own test. I’m a test chimp that doesn’t’ wait for the guy in the lab coat.

Dog Sled trip in Northern Quebec in February. I drove up from Boston, 11 hours.  The first morning it was -28C outside. A personal record as far as I knew and I had the product on my wrist. The cold chamber was the great outdoors, and instead of an arm simulator I had hot blood powered by Crepe’s and maple syrup running right under the product, no arm simulator needed. Ok let’s find out what the answer is to our perplexing max cold temp question. 

Do you want to know? IT’S A NON-ISSUE. There is no way anyone is walking around outside when it is that cold with their wrist exposed for any period of time. Do you know what gloves used in -28C look like? They are gauntlet gloves that cover the first part of your forearm. The product was snuggly against my warm skin under and especially thick jacket which was under an especially thick glove.  The only exposed piece of skin I had was a thin section of my upper cheek below the goggles and above my face mask, and it hurt.

Breathing hurt. When you inhale for the first time it feels like someone stuffed two metal tubes up your nose. The skin inside your nose freezes as the air rushes in. For reference I can tell when it is -15C out because you feel the hairs inside your nose become spikes as soon as you take your first inhale. We went right past that step to the “inside nostril skin freezing” stage.

 Ok this is a fantastic thing to have found out, Use Cases don’t need to consider extreme below freezing temps.  So we now know we don’t have to do redesign if we found the product can’t work below the temp from the exposed condition. So how low should we go for the use-case then?  Good question. I believe the lowest temp we should use in our use case is freezing, 0C. I’ll tell you why. 

I think that a person jumping into freezing water is the lowest it will see where the unit can fully saturate to equilibrium. Even when I took the product at -8C and tried to leave it exposed (orange jacket picture) it still stayed above freezing. Even the short ski gloves pulled back would revert to covering it when I started moving around. Like I said, extreme air temps are a non issue.

How about high temp and thermal transition?  What could I do to help with those stress definitions? Back in Boston we had decided that high temp would most likely be in a sauna. We read that Joe Rogan, MMA fighter and hysterical social media character, said that he does a quick jump in a sauna at 100C (212F). We found this unbelievable but I imagine possible if you did it very quick. If that was water you would be instantly cooked, but air is possible because thermal transfer in convection of dry air is not as fast. Ok should I try this? I guess??? 

Well while in those ridiculously cold temps in Northern Quebec I also found a nice sauna and hot tub. They are a necessity up there or in any Nordic culture. I was able to reserve the sauna alone so I could do whatever I wanted. The hottest I did in the sauna was 85C (185F). That was all I could stand for any practical period of time. By practical I mean a few minutes. We know most plastics melts at 90C. To give you an idea of how hot this is, it is almost impossible to keep your hand on a piece of material that is above 50C (120F) The air was 35C hotter. I have a small metal chain around my neck.  The links that were touching my skin were using my body as a heat sink. The links that weren’t touching my body (every other one) were free to equalize with the air. When I moved and the chain rolled. So the links that were not touching my skin were in fact now touching my skin and I was very aware of it. They burned as they rolled into contact. So when I sat up I had a chain too hot to touch all the way around my neck.

Now we already knew the high temp performance of the product from our HALT work, it can handle it. I was ready to endure the greatest thermal shock an athlete could deliver to the unit.

So this was my use case profile. I knew what I had to do.

  • I first went into the hot tub at 40C (104F) to get a good baseline saturation temp.
  • Then endured the 85C (185F) in the sauna until I was dizzy.
  • Next? Run out into the snow and throw myself in it.

If you are curious what that feels like, it pretty much feels like jumping on a group of porcupines followed by a burning sensation. Then strangely refreshing. The product did great. No issues.

We now have accurate temperature extreme and transition characterizations for our use-cases. Very valuable when we are using our test results to make design decisions and reliability predictions. 

The product showed it’s grit. I would say that the most important fact we found out was that we in fact did not have to make the low end temp limit as extreme as we thought. This meant we weren’t going to send ourselves on a path of unnecessary redesign.  Redesign isn’t free, it’s program cost, product cost, weight, and time to market. 

That is what good reliability work does.  Its’ Goldilocks, Not too high, not too low, reliability that’s just right.   But we can’t underestimate the importance of finding a totally new mechanical and chemical stress, the glue.  The value of discovering this so early in a program is beyond measure. Finding issues in the field are exponentially more expensive, not just in direct cost, but in brand value.

I’m excited for the work to continue with the team.  I’m sure they are also looking forward to see what I do with it next.  Use Case 7 or die.


P.S. I have discovered that my passion for extreme wasn’t’ learned.  It’s clearly genetic. My 12 year old daughter, Natalie, always loves to go on these trips with me. She mushed her own dog sled for the first time on this trip. She did great! If you remember last year we went sledding in Fairbanks Alaska and then climbed a mountain in a WWII era tracked beast, The Bandvagen 206, to see the Northern Lights.  You can read about that adventure here.

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