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Today’s drivers take it for granted that they can simply twist a switch to turn on windscreen wipers, and vary the speed, and vary the intervals between wipes. I know this is normal, but it is also magical! How is it done? CM
It is indeed magical, and nowadays this wide and precise set of actions can even be achieved without a driver doing anything! That’s thanks to computerised sensors that “read” the weather and driving conditions, and instruct the electric motor accordingly, to vary the amount of power and engage appropriate “formats” of mechanical movement, using relays, resistors, timers and modulators etc.
The mechanical elements have been around for a lot longer, but they are no less ingenious. When cars first acquired windscreens, the wipers were operated by…hand!
On the top frame of the screen there were butterfly nuts which the driver and passenger manually turned this way and that, with whatever speed and frequency and direction their brains chose, and their wrists could manage.
When the power of an electric motor was added, it had a simple on-off switch to make it spin…and little mechanical triggers which – at the end of each sweep – made it reverse direction after less than half a turn, over and over again.
Through spindles and gears and wiper arms, clockwise and anti-clockwise, sweep right and sweep left.
The ability of electric motors to work equally well in either direction (depending on positive and negative polarisation) is something we will all become more familiar as EVs become more common.
Fossil fuel engines are designed to turn only one way, so to make the wheels turn in the opposite direction requires a gearbox. That box usually gives us five forward gears and one very low-geared reverse option that severely reduces the maximum reversing speed.
It is interesting to consider that, technically, a vehicle with an electric motor can go forwards or backwards with equal…enthusiasm.
The next advance was variable speeds of wipe, which uses relays to switch to different “resistance” formats – as do the switches on your food blender and your hair drier or your electric drill. They partially obstruct or enhance the strength of electric current.
Then came intermittent wipers (how did we ever manage without them?), by simply (hah) adding a set of intermittent timer circuit formats.
In sum, then, all the different things your wipers can do are separately built-in to the system; you and your switch lever (or a computer) decide which one you want, by turning off the relay to one format and turning on the format of another.
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