Oliver Wendell Holmes once wrote a poem entitled “The wonderful One Hoss Shay”, about a shay (buggy) belonging to a minister, that when it finally failed, completely fell apart — all parts broke at once. It is here. It was given quite a bit of notice when I was in engineering school, because one goal of designing a good product is to ensure that it does not contain weak components that cause early failures. The last stanza of the poem is the punch line.
The challenge to minimize weak components in a product is a worthy one, and my experience is that it is not receiving enough attention these days. As an example, I have had problems the past few years with actuators (the components that convert electrical signals to mechanical outputs) in my cars. Due to emphasis on reliability in the 1980’s and 1990’s, manufacturers have done a good job on the drive train (engines, transmissions, etc.) and body. But cars have acquired more and more remote and automatic features. The integrated circuits and wiring harnesses are quite reliable (until rats, mice, or squirrels chew on the wiring insulation— a common occurrence). But many of the features (electrically operated door locks, windows, trunk lids, climate control systems, etc.) must at some point turn the electrical signals into a movement, and here the problem seems to lie.
A common way to perform this function is through a solenoid, a device that uses an electro-magnet to do the needed work. But the last Ford pickup I owned had so many solenoid failures, typically in actuators that were difficult to replace, that I bought a Toyota because I could get one with old fashioned mechanical window cranks, door handles, and other features. So far, so good, but as I write this I am feeling pressure because the front door lock actuator on my wife’s beloved Acura TSX has failed. Viewing the internet and talking to a mechanic friend, I find that is not unique. Looking at a photo of one, I am not surprised, because the exterior is a very complex plastic injection molding, and I would bet that inside there is a plastic gear or two that has simply worn out. But to replace this, I will either have to order a replacement from the internet and spend several hours cursing and dropping fasteners inside the door where they are difficult to retrieve, or take the car to a mechanic and give them several hundred dollars for doing so.
I was perhaps overly trained when I worked at JPL, since there are no mechanics in interplanetary space, so failures of components before the mission is complete are very bad news to everyone except the media. So attention is paid to all components to ensure that they will not fail and compromise the mission.
I know from briefly working in the automobile business that the major components of automobiles are thoroughly life-tested for reliability, and much attention is paid to the design and manufacturing quality of them. But how about things like door lock actuators? Or if for some reason (cost or whatever) they are of shorter average life, how about making them easier to replace? Instructions on how to do almost anything are on the internet, but how about ensuring their quality in the case of diagnosing and replacing components of complicated products that are likely to fail? And how about having nuts and screw heads visible like in the old days with some attention to allowing the use of traditional tools, rather than special plastic body panel removers, Torx-head drivers, and custom clips? Arms with extra joints and tiny hands would help also, if maintenance is not better considered in design.