Monday, July 18, 2011

On the Limits of Feedback in Product Design

My wife drives a Mini Cooper, made by BMW.  The Mini has power windows.  As with most modern cars, the cabin seals very well, sometimes preventing the doors from closing all the way against the air pressure without slamming them. 

The Mini engineers came to a clever solution.  They arranged for the electronic controls to lower the window about one centimeter whenever the door opened and to close the windows all the way after the door closed and the latch engaged.

Power windows have been around a long time.  The mechanism is well understood and reliable.  Unless you raise the window every time you use the door.  And stall the motor against the stop each time.

The window motors that were used were DC motors with brushes and a mechanical commutator.  Each time the motor stalled under power the brushes burned.  Eventually, the motor would not be able to get power while it was in the window-up position. 

I have had three sets of window motors installed (under warranty) in the last five years.  I have explained my analysis of the problem to the local service people.  There is virtually no way that this information will ever make it back to the engineers that need to know it.  There is also no way that I could improve my Mini by installing a set of proper, brushless DC motors to prevent the problem in the future.

* * *

Adrian Monk and I are probably the only two people in the world who are obsessive about ice cube trays.  I like to use ice cube trays as an example when I discuss quality in today’s society. 

I believe Rubbermaid makes the best ice cube trays.  They are shaped correctly so that the ice cubes do not stick and simply fall out when the tray is inverted.  They stack correctly so that, even if over-filled, they do not stick together.  They last a long time since they are not being forced to bend while cold.  I used the same set of Rubbermaid ice cube trays for fifteen years.

There is a lot of engineering that went into these trays.  There is no business case for a quality ice cube tray.  Nobody else makes a quality ice cube tray, and the customers all expect a no-good product.  You can’t tell good from bad until you use it.  Nobody advertises ice cube trays.

How can Rubbermaid afford to design and develop a quality product and sell me one set in fifteen years when the competition is selling a set every six months and spending nothing on engineering?

The answer that I usually use in such discussions is that Rubbermaid is protecting their brand.  No individual product can justify the cost, but, on the whole, Rubbermaid is more successful because it sells a variety of quality products.

* * *

One might well ask why I would be obsessing about ice cube trays.  It is the twenty-first century, after all.  Why not just get a modern automatic ice maker and be done with it?

I have.  And I don’t like them.  I can’t feed bottled water to them (my tap water tastes terrible and the refrigerator’s filter doesn’t help).  Automatic ice makers create a row of nice separate ice-cubes and then dump them into a jumbled bin which becomes a single lump when the frost-free cycle happens. This iceberg-in-the-ice-cube-tray problem also interferes with the rudimentary “need to make more ice” detector.  There is no easy way to dispose of the oldest ice.  Ice cubes can get hung in the dispenser, then fall out onto the floor when they begin to melt.  The dispenser flings ice into your drink with such force that you get splashed in the process.  The dispenser sometimes grinds on and on before unexpectedly releasing a deluge of cubes.  I cannot adjust the speed of the cycle if I need more ice for a party.  If I don’t use the dispenser for a few days the cubes in the ice maker itself sublimate into little slivers, which jam the mechanism when it tries to cycle.

I even have a Whirlpool Gold product which uses an optical sensor to detect the ice level in the bin.  If the weather is humid, the sensor frosts over.  Unexpected result: no ice if it is raining.   I wonder how many people have requested service because of no new ice, only to have the service person (who doesn’t work in the rain) find no problem. 

So, I can name ten separate areas that need improvement relating to automatic ice makers.  I even have some ideas about what I might do that could help.  But I have no practical way to modify or improve one once I buy it.

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