-----Original Message-----
From: MichaelNot
Subject: [EVDL] Electric Drive for Formula Student Vehicle
if i have an electric motor of equal or greater torque will I
still get the same performance as the petrol engine?
It really varies depending on other variables, most notably the battery
weight. Acceleration from a stop will likely improve, especially the lowest
speeds. Top speed will probably decrease, although this can be corrected by
sacrificing acceleration just as with an other engine. Cornering will likely
suffer badly, the added weight of the battery will impact it substantially
in the turn. How much will this affect it on your chosen track? That depends
on the track. In a 1/4 mile drag race 150HP electric will compete admirably
with 400HP petrol. Around Nordschliefe (forgive the spelling if I messed it
up) electric sacrifices a lot against petrol, IIRC the record for electric
is about 9 minutes, comparable petrol is a bit under 7 minutes.
It all comes down to power delivery and weight. A petrol engine will save a
significant amount of weight, but power delivery follows the bellcurve shape
we all know and hate. An electric motor adds weight because of the batteries
but torque delivery is instant and peaks at 0 RPM, HP/KW delivery is flat
until you reach a certain RPM(depends on the motor itself) at which point it
rolls off. If you look at the integral of the curves then for any given peak
measurement electric has a significant advantage.
Also, do I need a gearbox for electric motor or can it run on a single
gear?
For a relatively low power motor like the 66Nm you mention you will probably
see better performance with a single gear. The only reason for a gearbox in
low power systems would be to address the roll-on of the engine, but an
electric motor has effectively 0 roll-on (technically there is a small
amount but it can be ignored). The only consideration would be if you have
extremely high speed requirements where you are pushing that 66Nm to the
absolute fastest it can go, there a gearbox will have value to increase
acceleration.
If you are preparing the same vehicle for multiple tracks without
modifications, a gearbox is ideal, simply tune each gear to a specific track
and use it as a track selector. If you are preparing for only one track, or
can swap the single gear between tracks, a single gear is almost certainly
better. This extends to the point that as I recall the aforementioned
Nordschliefe record was a single gear.
Joe
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