A generator of hurricanes, at first sight it only looks like a generator of a really tiresome household chore. At least it moves forward on its on, thanks to energy of the motor. As soon as we yank the cord, it begins turning. But, it turns far too quickly to transmit the same movement directly to the wheels. If it did, the mower would instantly start racing across the lawn at 75 miles per hour.
The challenge? Taming the motor’s incredible power. (0’34’’)
(0’45’’)
To start, the movement of the motor is transmitted to a pulley which turns at the same speed. Then we slow it in four ways:
(0’55’’)
First the pulley transmits its movement to a much larger pulley. It takes several turns of the smaller pulley to turn the larger second one. The machine’s already a little calmer.
(1’06’’)
Second the transmission belt linking the two pulleys isn’t doing a perfect job. It actually slips and slides on the pulleys intentionally. It’s yet another way to calm the beast.
(1’18’’)
Third the second pulley transmits its movement to a gear of an even larger diameter.
The rod at the end turns even more slowly than the pulleys.
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Fourth, the wheel makes one turn for every four turns of the rod.
Thanks to this ingenious set up, lawn mowing has managed to avoid becoming in extreme sport. Together the pulleys, transmission belt and gears managed to restrain the power of the motor enough to make the wheels turn 20 times slower.
(1’48’’)
But wouldn’t have been simpler to make a slower motor in the first place? No way. To mow the lawn, we need hurricanes. Creating hurricanes requires a motor capable of turning the blade extremely fast. To see the rotation of the blade moves air is a serious understatement. And all that air isn’t just moving randomly.
(2’09’’)
The blade is curved at its extremities and near the centre. When the blade turns, these curves generate whirlwinds of air, whirlwinds that spin at more than 70 mph:
hurricane wind speed.
(2’22’’)
The mini hurricanes straighten the grass blades, which is key to a perfect cut. A fraction of a second later, the blade whips around and chops them at 225 mph.
Record speed, in F1. Cleverly calculated. Oh but, there is more.
(2’40’’)
To get the cut grass blades to their final destination, the lawn mower relies on laws of fluid dynamics.
(2’46’’)
If the door is open, a low pressure zone is created. The air pours into the area where pressure is lower; the cut grass is pulled along and then pushed outside.
