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Re: [EVDL] "Compression" slowing force with electric motors?

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Re: [EVDL] "Compression" slowing force with electric motors?

Martin Maitner wrote:

> Do you get any "compression" effect from the electric motor

Nope. When you're not providing power to the electric motor, it just
spins freely. There's nothing like the compression effect from an ICE.

In fact, this can be a problem! Electric motors have a maximum RPM
they can withstand, and it's sometimes possible to exceed this limit if
you leave the motor in gear going downhill. Since the motor doesn't
resist being spun like an ICE does, it just spins up really quickly and
can fly apart before you know it. So don't leave your EV in low gear
and go downhill unless you've calculated the maximum RPMs and are
watching the tach like a hawk. Put in the clutch and/or shift to
neutral. Brakes help, too :)

> or is gravity the only force slowing the speed?

Not gravity; friction. Gravity pulls in different directions depending
if you're going uphill or downhill, and you always get back the energy
you lose (what goes up must come down), but friction always slows you.
One of the ways people increase the range of their EVs is to reduce
friction wherever they can - low rolling resistance tires, reducing
toe-in, careful alignment, eliminating dragging brakes, putting extra
air in the tires, streamlining, low-viscosity oils in the gearbox, etc.

Doug Weathers
Las Cruces, NM, USA

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