Editor's Choice

The dangers of gut-feel engineering

23 June 2021 Editor's Choice News

No responsible engineer would make a guess about the current flowing through a lamp without knowing the resistance of the wire or the voltage rating of the power source. The variables involved make it impossible.

The human brain is very good at understanding the world around us. An everyday example can be found when driving a car. An experienced driver will be able to judge how large their car is and how close they can approach an obstacle. The driver does not need to think about or analyse the situation. Instead, they simply respond instinctively.

Other examples can be found in sports. Baseball players regularly hit a ball that is less than 80 mm across, traveling towards them at nearly 160 kilometres per hour, despite having just a fraction of a second to react. That the best players can not only connect with the ball but actually control where it goes is a testament to the power of the brain to learn from experience and respond instinctively.

Instinct versus accuracy

There are many other areas of life in which we can respond instinctively but, as engineers, how much can we trust our gut? Sometimes we can allow our experience to guide us. We can often use our instincts when it comes to physical units, such as those used to define weight and distance. These measurements form such a familiar part of everyday life that many of us are able to estimate a length or weight with some accuracy.

But there are measurements that we cannot estimate. No responsible engineer would make a guess about the current flowing through a lamp without knowing the resistance of the wire or the voltage rating of the power source. The variables involved make it impossible.

There are other values that are similarly impossible to guess without measuring them. The performance of the latest high-speed connectors is described in gigahertz, a measurement of one billion cycles per second. There is no way that even the most experienced engineers could estimate any aspect of their performance without the use of complex measuring equipment.

However, even the most responsible engineers can fall victim to trusting their gut in certain situations, especially when mechanical forces are involved. In engineering, we measure torque in Newton-metres (Nm). How easy is it for us to estimate torque? For example, how much torque is required to undo the lid of a pickle jar? Google tells me that the force might be anywhere between 2,7 and 6,1 Nm, depending on the diameter of the lid and how much force was applied when the lid was closed.

Read the manual

I use this as an example because torque is important when it comes to components. To assemble many electronic connectors, or to fix them to a printed circuit board (PCB), requires the installer to apply the correct torque. There is a temptation to imagine that it does not matter. Some engineers assume that ‘finger tight’ is enough, while others will keep turning the wrench until it doesn’t move any more. The problem is that too much torque, or too little, can hide a problem that might not be apparent on visual inspection. Regardless of how expensive and well-made the components are, cables can be crushed, PCBs can be cracked and seals can be compromised.

A few years ago, I explored the testing required to certify switches. I won’t bore you with the whole story, but the summary is that I broke two switches because I didn’t follow the instructions and apply the right torque.

The sensible course of action would have been to use the right tool. Torque wrenches are not expensive and they are not hard to use. However, I assumed that fixing a nut somewhere between ‘finger tight’ and ‘turn it until it squeaks’ was good enough. The truth is that, even if you have spent a lot of money on a high-performance component, you are putting your design at risk if you do not read the instructions and apply the correct force.

The geek’s golden rules

I would like to leave you with two golden rules. Okay, maybe not golden, but they could make you richer. Well, maybe not quite so poor…

The first lesson is that it can be risky to trust your gut. Modern technology is moving so quickly that we are frequently faced with measurements in the range of millions or billions. As responsible engineers, we should never design a product without employing the correct calculations and yet there is a temptation to trust one’s gut and adopt a strategy of ‘that’s good enough.’ If a design is important enough to install an expensive component, it is important enough to do the maths first.

Secondly, read the manual and make sure you follow the instructions faithfully. It may take a little longer and you might have to do a little thinking, but it will be worth it in the end.

Trust your gut when deciding where you’re going for lunch. Once you get back, let your head make the engineering decisions.


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