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#Post#: 1454--------------------------------------------------
Electric drivetrain options
By: M.Z.Nahajski Date: September 29, 2019, 5:47 am
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Hi all,
I'm here to add yet another layer of complexity ;D
With me making an electric cyclekart do people think I should
use a torque converter (if so what type), a direct chain drive
(no gearing) or a geared ratio chain drive?
marek
#Post#: 1457--------------------------------------------------
Re: Electric drivetrain options
By: RhysN Date: September 29, 2019, 6:58 am
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Direct chain drive.
#Post#: 1458--------------------------------------------------
Re: Electric drivetrain options
By: M.Z.Nahajski Date: September 29, 2019, 7:37 am
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what is the reason you say that? I'm intrigued because from what
I can find this is a discussion in the production car world as
well (how to drivetrain an electric car).
#Post#: 1459--------------------------------------------------
Re: Electric drivetrain options
By: RhysN Date: September 29, 2019, 8:46 am
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I say direct drive, because it's what all the electric, proven ,
cyclekarts use. Formula E has given up on multi speed gearboxes
too, they are now single speed. It has been experimented in
cyclekarts for at least 8 years in the US, and I am offering you
what has been learned.
#Post#: 1460--------------------------------------------------
Re: Electric drivetrain options
By: M.Z.Nahajski Date: September 29, 2019, 9:17 am
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Thats interesting :)
Tesla use a direct drive but with a ratio.
I've also seen a few electric cars with gearboxes built into the
motor housing.
Also, surely a torque converter would get the best
acceleration-to-top speed ratio although the clutch means
regenerative braking would not be possible.
Jaguar's I-pace uses a direct drive although it is unclear of
whether it is geared or not.
Thanks for the input
Marek
#Post#: 1461--------------------------------------------------
Re: Electric drivetrain options
By: RhysN Date: September 29, 2019, 9:50 am
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To be clear Marek, not having the axle at motor speed, but no
clutch or gearbox is what has been found to work. As per my
normal suggestion, go to www.gittrevillegp.com and look at car
builds. The most information on what you want is in "Cars C" and
the Austin Boulogne build. Since Doug did this blog he has told
me he is now using the Golden Motor 3 kw. Also there the blog
about the Morgan "Green build" in Cars B, also electric.
Gittreville is always the best source for direct info, not
gained by internet trolling, but real hands on, and they show
their mistakes too.
#Post#: 1462--------------------------------------------------
Re: Electric drivetrain options
By: M.Z.Nahajski Date: September 29, 2019, 12:02 pm
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Ill have a look.
#Post#: 1474--------------------------------------------------
Re: Electric drivetrain options
By: StefanN Date: October 2, 2019, 3:31 am
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Interesting comparison trying to match performance:
Standard 6.5HP petrol engine peak torque is about 12.8Nm.
Putting this through a 7:1 sprocket ratio and max ratio of 2.7:1
from torque converter (TC) gives 226Nm at the axle.
The Golden Motors 48V 3Kw motor peaks at 20.8 Nm - so to get an
equivalent torque at the axle requires a ratio of 11:1 (approx
45cm diameter main sprocket assuming 10T drive sprocket and no
intermediate shaft/ratio)
To compare max speed - the overdrive ratio of the TC is 0.9:1
giving a combined TC/sprocket ratio of 6.3:1. This would need
the electric motor to have a significantly (75%) faster peak RPM
than the petrol engine (6.3:1 compared to 11:1)
You could go for the higher voltage electric motor but that
increases battery weight (for the same capacity) and cost.
The comparison ignores losses in the TC.
#Post#: 1475--------------------------------------------------
Re: Electric drivetrain options
By: RhysN Date: October 2, 2019, 6:36 am
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It also ignores the knowledge gained by the folks who have now
completed 8 electric cyclekarts who have openly said there is
little if any comparison from raw numbers as the characteristics
are so different Stefan. Initially Doug/Johnny did exactly what
you ave and chose a 5 kw Golden motor, and has said it's
entirely a different thing. Hence the step back to 3 kw.
#Post#: 1476--------------------------------------------------
Re: Electric drivetrain options
By: StefanN Date: October 2, 2019, 7:08 am
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Not at all Rhys. I'm not ignoring it, I'm trying to get to an
engineering understanding of the factors. A simple headline
power number comparison of a 5/6HP ic engine takes you to a 5KW
BLDC motor - which is not what I'm looking at. Undoubtably the
torque/rpm curves of the two technologies are different and I'm
interested to understand how that plays out in the design of the
powertrain and ultimately the driving experience.
I've not yet found much data shared about the various electric
cyclekarts, nor have I got access yet to any electric cyclekarts
to drive. Any pointers to electric cyclekart performance data
would be great (Rhys - we've tried to contact the person you
recommended, so hopefully we'll get a reply)
Marek and I are meeting some of the engineers at an electric
race team in a couple of weeks. Hopefully there'll be enough in
common between the two design challenges to make it helpful. If
not, we'll learn lots of new stuff anyway.
Of course, this is just the approach that I'm interested in
taking to understand more about electric powertrains. Other
approaches are available and if someone else is building a
cyclekart then they'll go about it their way I'm sure.
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