Question regarding transmissions on an electric kart

Zubber

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So I'm mainly a car guy and have experience putting together just about everything on the everyday car.

But I've got time on my hands and I've been thinking about starting an electric drift kart project for a while.


I want to go electric for the instant torque that's perfect for drifting I guess I'm just confused on how to control the power. I'd like to have a gearbox on there so that I can switch to a lower gear quickly in order to break traction. Not to mention I'd get a reverse gear. Just like I would in my car. However most DIY builds have the motor linked via chain directly to the rear axle. Also I am aware that an electric motor needs to be paired with a controller that with likely have multiple speeds etc, but to me that sounds like it's limiting the total output of the motor. Whereas a gearbox would keep the same power just give me more torque.

I should also mention I'm looking for quite a big build. My other idea is to buy a miata and strip it down and turn it into a beefy two person drift cart. But, I like the smaller one person ecart idea more as it won't take up as much space in the garage and I really want to drive something electric with a ton of torque!
 
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itsid

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Hi..
but to me that sounds like it's limiting the total output of the motor. Whereas a gearbox would keep the same power just give me more torque.
that's a quite common misconception.
any transmission takes up power, the simpler it is the less it takes (simple chain wins everytime except for direct driven hub motors)
And that holds true for all motors and engines alike.
"All" the power you only get with direct drive.. (ommitting power loss between rubber and road here)
~97-98% you get with a chain or toothed belt drive,
~87-93% with a six speed mechanical gearbox
~80% with a multispeed automatic transmission
~75 but well below 80% with any CVT that's belt driven
all the rest will be lost to friction (heat and material wear).

Anyways.. yes you need a controller for the motor, but it's not only a speed regulator (albeit that being it's main purpose)
it's also a safety device keeping you from burning the motor by accident by applying the brakes at the same time as the throttle..
(if you step on the brakes, the motor automatically get's depowered in order to prevent it from overheating)
And in case of a BLDC for example it's also the much needed electronic commutator for the coil phasing.

So no.. you cannot get around a controller at all.

Up to the net misconception (even more common)
An electric motor has it's peak torque at exactly ZERO rpm!
means the lower the motor turns, the higher it's possible torque will be
very unlike an engine where the peak torque sits usually a few hundred rpms above idle speed.
So you wouldn't need any "first or second gear" at all if the simple chain is set up as the third gear
you'd be golden.
thus a gearbox for an electric motor would need to be very differently geared than one for a combustion engine
to act about the same.. the torque range is quite a bit wider and gears could therefore be longer etc.

And worst: you will not find one that's suitable for a go kart anyways.. finding one that's taylored to take an electric motor is
(since it's usually a rather pointless device there) even less likely.
for combustion engines one would need to make a case for motorcycle gears
(and usually people just use motorbike engines then.. more power anyways)
And for electric motors... no such thing exists to my knowledge..

That's where your scale comes in.. carparts are surely a thing and surely some can be used..
I even know a company that converts classic cars to electric drive, flanging an electric motor to the original gearbox.
(still it needs the same motor controller as it'd need without the gearbox mind you)

Anyways.. no you cannot ommit the controller,
and if you want to break traction on a hefty kart close to a car's weight you're in for quite a ton of batteries
since you'll need quite a powerfull motor and ..
that then adds weight and needs more power which needs more batteries..... it's getting difficult quick ;)

Not mentioning that this is also getting very expensive very quickly.

'sid
 

Zubber

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Hi..

that's a quite common misconception.
any transmission takes up power, the simpler it is the less it takes (simple chain wins everytime except for direct driven hub motors)
And that holds true for all motors and engines alike.
"All" the power you only get with direct drive.. (ommitting power loss between rubber and road here)
~97-98% you get with a chain or toothed belt drive,
~87-93% with a six speed mechanical gearbox
~80% with a multispeed automatic transmission
~75 but well below 80% with any CVT that's belt driven
all the rest will be lost to friction (heat and material wear).

Anyways.. yes you need a controller for the motor, but it's not only a speed regulator (albeit that being it's main purpose)
it's also a safety device keeping you from burning the motor by accident by applying the brakes at the same time as the throttle..
(if you step on the brakes, the motor automatically get's depowered in order to prevent it from overheating)
And in case of a BLDC for example it's also the much needed electronic commutator for the coil phasing.

So no.. you cannot get around a controller at all.

Up to the net misconception (even more common)
An electric motor has it's peak torque at exactly ZERO rpm!
means the lower the motor turns, the higher it's possible torque will be
very unlike an engine where the peak torque sits usually a few hundred rpms above idle speed.
So you wouldn't need any "first or second gear" at all if the simple chain is set up as the third gear
you'd be golden.
thus a gearbox for an electric motor would need to be very differently geared than one for a combustion engine
to act about the same.. the torque range is quite a bit wider and gears could therefore be longer etc.

And worst: you will not find one that's suitable for a go kart anyways.. finding one that's taylored to take an electric motor is
(since it's usually a rather pointless device there) even less likely.
for combustion engines one would need to make a case for motorcycle gears
(and usually people just use motorbike engines then.. more power anyways)
And for electric motors... no such thing exists to my knowledge..

That's where your scale comes in.. carparts are surely a thing and surely some can be used..
I even know a company that converts classic cars to electric drive, flanging an electric motor to the original gearbox.
(still it needs the same motor controller as it'd need without the gearbox mind you)

Anyways.. no you cannot ommit the controller,
and if you want to break traction on a hefty kart close to a car's weight you're in for quite a ton of batteries
since you'll need quite a powerfull motor and ..
that then adds weight and needs more power which needs more batteries..... it's getting difficult quick ;)

Not mentioning that this is also getting very expensive very quickly.

'sid
Well... Darn is it worth going electric at this point if I'm looking for a drift rocket??

So let me ask you if I'm at speed what would be required to break traction? Would I hit breaks then slam the accelerator after the engine has whined down? To get the most torque? I imagine I would need a differential that unlocks the axle when no torque is applied and then as soon as the accelerator is pushed it could lock the engine to the axle. That would make it easier for the engine to whine down.

ALSO.

What if I have two engines then... A high gear engine and low gear engine. When I want to lose traction I'd tap the low gear engine. Maybe have it set up to where my shifter just switches power between the two engines.

EDIT: I think I've got it!! So I'd link a second engine to the same rear axle or maybe I'd have the first engine linked to the front and the second high torque engine to the rear. They would need to be brushless as they will be working on top of each other. The high torque engines controller would me wired to a lever throttle the shape of a hand break. The harder I pull the more throttle while the other engine could be keeping the car going at a constant speed or slowing down or getting me out of a drift if it's powering the front wheels.
 
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itsid

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drift rocket... breaking traction at speed.... more gearboxes...differentials.... multipe engines (I thought you were toying with an electric approach) ....uhmm
I think what you have in mind is WAAAY out of scope of this forum tbh..

an electric motor does NOT behave like a combustion engine, and those movie-maneuvers
(crash into second in a high speed corner, forcing the engine to howl, then drifting round a corner to escape the cops yadda yadda...)
is a bit of a wetdream especially with electric motors.. they simply don't work well in such situations.

So no.. My advice would be to stick to combustion engines.. wayyyy cheaper for that sort of toy
strip the weight of the miata down to the bare minimum, then a bit further.. crank up the engines HP a notch
no need to lock the diff, but if you're not good at breaking traction at speed a locked diff can help you with that
(at the cost of a set of new tyres every now and again)


As with all motorisation (no matter if electric motors or combustion engines)
you have but ONE option to break traction and that is.. accelerate the wheel quickly enough that it looses grip.
that can usually be done in one of three ways.
a) the common: abrupt change of direction.. let inertia break traction for you
any sensorless car can do that easily.. whip the steering wheel and thus the tail and off you go... narrow wheels preferred
on wider tyres usually combined with ...​

b) the anchor: abrupt slow down of the rear wheels only (usually done by whacking the hand brake)
if done right, you can then use that to initiate a drift... famous by the BluesBrothers Parking scene​

and what pubertarian boys think of when they see drifting cars..
c) the Tim Taylor: Way more grunt in the engine than the car would ever need..
at speed.. gear down, hit the pedal hard.. and let the raw engine power ripple the road.
(very few cars can do that stock... I know three that are not considered supercars that might... )​

On a std race kart you can burn out with as little as 6kW electric
if you want to have enough power to do that at 50mph you need around 50kW for the same kart
(KART!! not car! not mid or large size buggy!! .. single seater kart!)

'sid
 

Zubber

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drift rocket... breaking traction at speed.... more gearboxes...differentials.... multipe engines (I thought you were toying with an electric approach) ....uhmm
I think what you have in mind is WAAAY out of scope of this forum tbh..

an electric motor does NOT behave like a combustion engine, and those movie-maneuvers
(crash into second in a high speed corner, forcing the engine to howl, then drifting round a corner to escape the cops yadda yadda...)
is a bit of a wetdream especially with electric motors.. they simply don't work well in such situations.

So no.. My advice would be to stick to combustion engines.. wayyyy cheaper for that sort of toy
strip the weight of the miata down to the bare minimum, then a bit further.. crank up the engines HP a notch
no need to lock the diff, but if you're not good at breaking traction at speed a locked diff can help you with that
(at the cost of a set of new tyres every now and again)


As with all motorisation (no matter if electric motors or combustion engines)
you have but ONE option to break traction and that is.. accelerate the wheel quickly enough that it looses grip.
that can usually be done in one of three ways.
a) the common: abrupt change of direction.. let inertia break traction for you​
any sensorless car can do that easily.. whip the steering wheel and thus the tail and off you go... narrow wheels preferred​
on wider tyres usually combined with ...​

b) the anchor: abrupt slow down of the rear wheels only (usually done by whacking the hand brake)​
if done right, you can then use that to initiate a drift... famous by the BluesBrothers Parking scene​

and what pubertarian boys think of when they see drifting cars..​
c) the Tim Taylor: Way more grunt in the engine than the car would ever need..​
at speed.. gear down, hit the pedal hard.. and let the raw engine power ripple the road.​
(very few cars can do that stock... I know three that are not considered supercars that might... )​


On a std race kart you can burn out with as little as 6kW electric
if you want to have enough power to do that at 50mph you need around 50kW for the same kart
(KART!! not car! not mid or large size buggy!! .. single seater kart!)

'sid
Yeah the more I look into it more the miata kart sounds like the best option... I've also found out there is a market for affordable exo frames that seem like a great option with a nice high reving honda engine or something.

Also I think my issue is I keep thinking in terms of building a car since I've got all my experience in that area... But currently I have a genesis coupe that I use on the track for drifting which I love!! But It's also my daily... Not very comfortable since It's built for the track and beat up. So I was thinking of fixing it up to be a daily and then buying a toy to mess with when I feel like going crazy. Something specifically for drifting and I can adjust on the fly. Was looking for a since I having to drive to the track is a chore and I could use this thing around the back roads. Anyways!! I'm going to keep doing research.
 

Functional Artist

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IMO for drifting & burn-outs the most important thing is your power to weight ratio ;)

You want the most power, that you can "pack" into the lightest package (with out "over doing" it )
...the "key" is to find the best "balance" for your specific situation :thumbsup:

Ex:
Remember back when guys used to put big V8 engines in them old Chevy Vega's (little, super light, 4 cyl engine car)
...a big 'ol heavy big block 454cu. in. would make 'er scoot right along
...but, if ya "ran" something a bit lighter like a small block 350cu. in. the vehicle would usually be quicker & more agile too

Check out my Excalibur kart
2020 - Excalibur Electric Racing kart | DIY Go Karts
SAM_6975.JPG

In this video, she is running a 60V 2,000W BLDC motor that's powered by (5) 12V 15AH SLA batteries :cool:

(324) Excalibur Electric Racing Go Kart prototype 15 Doin' Donuts - YouTube
 
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Also as a sidenote about gearboxes and electric stuff, the Teslas don't have a gearbox, but some of them will do 145mph. Electric motors can be designed to function well anywhere from 0-100krpms or more with the right speed controller. So there often is no need for a gearbox for well designed, purpose-built electric motors.
 
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