Electric kart

[Hillhater]

It depends what level of racing you are aiming for.
At the “pro” level, 125cc two stroke direct drive , it a “no expense spared” , F1 , type of game, with teams turning up with 10 x $5,000 motors for each kart..running a fresh motor in each heat and race.
At Club level , weekend racers, as i said much of the competition classes are now based on 4 stroke B&S industrial based motors , or Chinese “Clones” that are dirt cheap. $30 c/f clutches, etc.
I dont see how you can put a suitable electric motor, controller and battery pack , together at a cost that could compare on a $/kW basis.
Electrics have other advantages, which should be exploited for their own class/competitions
Even 30 years ago there was an international electric kart competition in Europe, but it never became “mainstream” due to cost and weight. ( they were seriously hampered by battery tech)

 

[hallkbrdz]

I hope to change that equation so that electric karts don't need nearly as many batteries with a new motor design that is high kw/hp but low torque. Possibly the first electric kart that needs a clutch like a 2-stroke - the trade-off for high speed efficiency. So far no technical road-blocks, just electronic design hurdles to get past (such as exact timing pulses down to 1/100000 of a second). Power curves based on engineering math, so final results may be somewhat different.

 

[Ianhill]

Sorry to break your bubble but a clutch won't give you any free lunch.

The clutch will allow the motor to disconnect and use its rotor mass as an accelerated weight that still takes battery power then when the clutch is dumped with the motor at full rpm the bearings experience a shock load as the rotor slows the current rises if there enough torque and horsepower so the rotor never slows when the clutch is dropped theres little point of the clutch to begin with and we end up with direct drive systems.

So what can a clutch really do if designed well on an electric motor ? Allow powerful starting torque like what yamaha do on the trials bike but as for saving power no theres a little more mass and complication in the design meaning more wh per km and more serviceable parts to contend with.

Electric motors allow an overcurrent state so that can implement a 10 second power curve that emulate the clutch by pushing the motor harder for a measured time its why we have peak ratings and nominal.

So why do yamaha choose a clutch ? The bike needs to repeatable use that starting torque to much to emulate with a high power 10 second start a trails rider may need 5 or 6 hits of power in 30 seconds stressing a bldc to heat exhaustion

 

[Ianhill]

My honest opinion on making a kart is to go with a 4 stroke engine thats got a long throw rod setup and use a decompression plate, a efi unit that measures postitve preasure and get a oil catch can small intercooler and turbo it running e85 map that up and you will be ripping the tyres to pieces.

Way more complex than an electric kart but setup right it will chug along all day enjoy the jungle juice while its available someone's gonna burn it one way or another.

 

[hallkbrdz]

The clutch option is to smooth out the start, that's all. It has nothing to do with saving battery. It may not be necessary, but it will be an option based on testing and software development.

 

[Egor.dp.ua]

The clutch is extremely necessary as a limiter of the engine's moment of inertia when the brake is pressed, otherwise we have a large load on the transmission, the chains stretch and even break.

 

[nuxland]

Guys please keep off the topic talk somewhere else please!

I was thinking of buildin myself a new battery pack, because my first 4kwh pack is halfdead (few years ago i went to 0 volt).
Samsung 40T 21700 cells in 14p28s configuration. Using custom made 0,5mm copper interconnections (succeeded of welding 0,2mm nikkel to 0,5mm copper). Weight wise will be similar to my lipo pack but it has a lot more Ah so I could drive 20 laps

 

[Ianhill]

Sorry nuxland for diversions i felt a need to answer the clutch topic and its wasted time, best of luck with that battery the copper to nickel is a big improvement with 21700 cells good effort and best of luck.

 

[Hillhater]

I was thinking of buildin myself a new battery pack, because my first 4kwh pack is halfdead (few years ago i went to 0 volt).
Samsung 40T 21700 cells in 14p28s configuration. Using custom made 0,5mm copper interconnections (succeeded of welding 0,2mm nikkel to 0,5mm copper). Weight wise will be similar to my lipo pack but it has a lot more Ah so I could drive 20 laps

Nuxland, i am sure you are aware, but remember there will be much more voltage sag under load, and more voltage drop from discharge level with those 21700s than the Lipos.
You may expect a 20+ volt voltage range between fully charged and near empty.

 

[nuxland]

Nuxland, i am sure you are aware, but remember there will be much more voltage sag under load, and more voltage drop from discharge level with those 21700s than the Lipos.
You may expect a 20+ volt voltage range between fully charged and near empty.

Yes, there will be more sag under load, but with 21700 bruto will be 56Ah and with lipo I have 35Ah.
As you can see in the picture my lipo was 116v when started and 104v when finished, so 10V difference.
For the same 28Ah 21700 will be around 50% left and lipos were only 20% left. So I think there will be the same 10V difference.
But yeah, when I will drive 20 laps voltage will go around 90-95V or so.

 

[hallkbrdz]

Curious... how are you generating the "spark" RPM signal for the Mychron?

 

[xormic]

Installed forced air cooling to the motor and tested acceleration.
This should be not official word record with electric kart acceleration.
https://www.youtube.com/watch?v=2Xp41u1y9KI
2,640 seconds to 100km/h and 0-60mph is even faster in 2.577 seconds as 60mph=96,5km/h

This should be current official record I think to 60mph
https://www.youtube.com/watch?v=r0b6UoxqrPE

But in that track forced cooling is not enough for 10 laps. I can do sprint like 7 or 8 laps only.

How much BA and PA were you running to get 2.577 second from 0-60, and with what gear ratio?

 

[nuxland]

Installed forced air cooling to the motor and tested acceleration.
This should be not official word record with electric kart acceleration.
https://www.youtube.com/watch?v=2Xp41u1y9KI
2,640 seconds to 100km/h and 0-60mph is even faster in 2.577 seconds as 60mph=96,5km/h

This should be current official record I think to 60mph
https://www.youtube.com/watch?v=r0b6UoxqrPE

But in that track forced cooling is not enough for 10 laps. I can do sprint like 7 or 8 laps only.

How much BA and PA were you running to get 2.577 second from 0-60, and with what gear ratio?

Gear Ratio can't remember anymore, 15/40 I think it was. But you can get it from exel when you devide speed with rpm and take account kart tire size.
But what do you mean BA and PA? I found one old excel sheet for that time where I plotted some graphs, attaching it here

 

[nuxland]

Curious... how are you generating the "spark" RPM signal for the Mychron?

Not getting Mychron was used only to see lap times when racing (it had gps inside).

 

[xormic]

Installed forced air cooling to the motor and tested acceleration.
This should be not official word record with electric kart acceleration.
https://www.youtube.com/watch?v=2Xp41u1y9KI
2,640 seconds to 100km/h and 0-60mph is even faster in 2.577 seconds as 60mph=96,5km/h

This should be current official record I think to 60mph
https://www.youtube.com/watch?v=r0b6UoxqrPE

But in that track forced cooling is not enough for 10 laps. I can do sprint like 7 or 8 laps only.

How much BA and PA were you running to get 2.577 second from 0-60, and with what gear ratio?

Gear Ratio can't remember anymore, 15/40 I think it was. But you can get it from exel when you devide speed with rpm and take account kart tire size.
But what do you mean BA and PA? I found one old excel sheet for that time where I plotted some graphs, attaching it here

When you got from 0-60mph in 2.577 seconds. What did you set your battery amps amd phase amps to on the controller?

Also for some reason, It won't let me open the download you sent

 

[nuxland]

Attached screenshots where you can read your answers
x-axis is time, I zeroed it when kart starts to move aprox.
In youtube video I could do it more percise because I used there racerender where you can go frame per frame and adjust your data to video.

 

[Hillhater]

Hmm ? .. looks like there was 20v of sag under full power (109 v - 89v)…with the 21700 pack..
…compared to the 11v sag …or less ? …with the lipo (116v - 105v)
Was there any noticable effect on performance ( lap time etc )

 

[nuxland]

Hmm ? .. looks like there was 20v of sag under full power (109 v - 89v)…with the 21700 pack..
…compared to the 11v sag …or less ? …with the lipo (116v - 105v)
Was there any noticable effect on performance ( lap time etc )

This is from year 2017 as asked. Battery was there A123 round cells 10p34s configuration
I have not had the time to do acceleration test with lipo pack.
And that 21700 pack is still in the paper yet

 

[xormic]

Attached screenshots where you can read your answers
x-axis is time, I zeroed it when kart starts to move aprox.
In youtube video I could do it more percise because I used there racerender where you can go frame per frame and adjust your data to video.

I dont understand how to read these graphs man . I just wanted to know the phase amps and battery amps you set on your controller.

 

[nuxland]

Attached screenshots where you can read your answers
x-axis is time, I zeroed it when kart starts to move aprox.
In youtube video I could do it more percise because I used there racerender where you can go frame per frame and adjust your data to video.

I dont understand how to read these graphs man . I just wanted to know the phase amps and battery amps you set on your controller.

In first graph “Battery current” is battery amps, i did not limit it, controller draws what is needed.

Yellow (Iq) is phase current (it is set to 660A and that is sevcon maximum)
Grey (Id) is field weakening current (it is negative and it helps motor to spin faster) this is set to 440A if I remember correctly.

When grey starts to kick in then torque is declining and motor current also but battery current is still the same because rmp-s are faster and field weakening.
Actually allmoust all of the grey is going to heat inside the motor

 

[xormic]

Ok okay! I get it now. Thanks for your reply

 

[xormic]

For my project im planning on using a qs 180 90h with a ND721200 controller. I'm planning on using a 1:2 gear ratio. I hope it will be fast

 

[j bjork]

Yellow (Iq) is phase current (it is set to 660A and that is sevcon maximum)
Grey (Id) is field weakening current (it is negative and it helps motor to spin faster) this is set to 440A if I remember correctly.

Worth to mention is that th phase amps it is actually Arms, not peak like most controllers are rated.
I think 660Arms is about 900A peak.