21kw+ QS273 won't outrun a 250cc?

Some of you guys might know that I'm collecting parts for a Ninja conversion. The build is based on a 150Kg Ninja 250R frame, which should drop to about 130kg once I strip all the petrol burning gear, and add back the weight of batteries and controller, etc. To be honest, I did very little modelling before buying parts. A bit unlike me, but I realised there was a ceiling for consumer parts you could easily get, and I figured that would be "fast enough".

The build is:

Battery 144v @ 280A capable
Kelly 144v 400A Phase
QS 273 50H 8kw (21kw to 30 seconds) edition

I threw out the comment on a Ninja forum that if I could get towards the low 3s 0-100 (0-62mph), I'd be happy. A mechanical engineer, a big fan of the Kawasaki 250Rs, told me I was dreaming, and that I would have gotten the bike faster by $500 of mods on the stock bike.

That didn't sound right, so I was at first wondering if he was just a bit zealous for his "babies" being converted to electric, but we nutted out the figures from publicly available sources. The hardest one was the QS 273 performance figures at 144v. I found a performance graph for 72v @ 200A, which he did some modelling on to convert to 144v @ 400A and generated some predicted torque graphs, and came up with this:



Electric motor in red, petrol motor in blue.

He suggested that I'd be faster off the line to 30km/h, then only have an advantage, as I won't need gear changes at roughly 63 and 88km/h.

The maths all seems to check out, but if this is the case, I'd be pretty disappointed. Is this all an electric conversion is going to get me? Maybe a second off the stock time - achievable with a new intake and exhaust? Obviously other benefits of going electronic, but I recall when I first came here, people were saying 5kw electric bikes could blow off 600cc petrol bikes, and I was skeptical. Now I'm building a 21kw+ bike, and being shown evidence that it will barely outrun a 250.

Anyone have any thoughts on this one?

I'd hazard a guess that he wouldn't catch up to and pass you until about 110kmh. After all, it is the area under the curve you should be comparing, not the curve itself.

M

The advantage of building on a bicycle frame is weight, and that is making all the difference. If you build on a motorcycle, you’d better forget the hub motor as a competitive solution.

Ah right, so it could be that he is right.

Damn.

Maybe its time to start losing some weight.

... or to build with a big mid drive motor.
1st you need to size the available space in your frame to fit a motor.
Then just weight the gasser motor that you took off.
That is the begining. If I would build it, I guess I’d try fitting a good 165 HP in that frame.

I like building bikes that my fellow riders are scared to ride.

It should be noted that QS now offers 12kW V4 hubs in 17x6".
I believe these require 230mm dropouts, not 200mm.

See: https://www.qsmotor.com/product/17-inch-12kw-hub-motor/



M

They do... but according to their website, 8/10/12kw all have the same torque, which doesn't sound right to me.

I suspect they all have the same internals, and hence the same stall current - but the bigger motors have more metal mass to sink heat, hence a bigger rating.

Yeah, not going mid-drive. One of the main reasons for going electric is simplicity. I don't want to have to worry about chains or belts, etc.

Sunder said:

...
Yeah, not going mid-drive. One of the main reasons for going electric is simplicity. I don't want to have to worry about chains or belts, etc.

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Then choose a lighter frame. Some dirt bike frames are much lighter than your Ninja. You can mod a lightweight frame and give it the geometry that you need. Choose light weight. components too. Only weight advantage can make your DD hub build competitive with the gears of the gasser motorcycles.

Then, you can feed this hub more power, once you can test its saturation point. My guess is that it would survive 500A, but the only way to know is risking. Optimal performance of a system, sometimes can only be found with destructive tests. I have fried many motors and controllers to find the limits of mine.

Why are you so worried about what can you outrun and what not? Is it a track race bike or a drag strip exclusive bike?
Build your dream bike to ride it, not to enter internet penis measurement competitions, to impress people that you don't know and don't care about.
I'd rather have a 1kw bike than a 100kw gasser. It costs $500 because that's what it worth, for good reason.

Because I find my current 250cc lacks the acceleration needed to move with agility in traffic. I had expected with the higher ungeared torque and instant power of electric to provide a responsiveness of a much larger bike while retaining a midsized frame.

Sunder said:

Because I find my current 250cc lacks the acceleration needed to move with agility in traffic. I had expected with the higher ungeared torque and instant power of electric to provide a responsiveness of a much larger bike while retaining a midsized frame.

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You should get exactly what you hoped for, in stop and go traffic. It's only when the traffic is going 65+MPH and not stopping that you'll find the setup you intended to use to be lacking. It's the classic EV power curve: fantastic off the line and to 30-40MPH, with no shifts at all, then the motor starts to fade as it revs higher and higher. Imagine a V-8 roadster...with one speed. I briefly owned a Zero SR, and the mid-drive setup on that made it a screamer all the way to 80+MPH - I had to dial back the power on the Custom setting so it wouldn't dislocate my shoulders. If you want simple, go with a big hubmotor. If you want fast at higher speeds as well as low, then you pretty much have to use a mid-drive. It doesn't have to be all that complicated.

Isn't the Zero gearless mid drive? As in fixed ratio?

I have no real interest in speeds above 110, really. So maybe I won't be disappointed. I do know when selecting the controller I was disappointed with the lack of choices for 144v. Nothing over 400A phase current when the motor can handle up to 600.

Also for donor bike weight, I know there are some dirt bikes and street fighters that are lighter, but I prefer fully faired bikes. Both for looks and efficiency at higher speeds.

Sunder said:

They do... but according to their website, 8/10/12kw all have the same torque, which doesn't sound right to me.

Click to expand...

Can you say: "cut and paste"?

Also found this regarding V4 vs other versions:

High quality of silicon steel raw materials, customized and enlarged groove make more copper wire into motor, produce more powerful magnetic force.

Click to expand...

So in theory, with more copper there should be more torque.

And then there is this page which supposedly demonstrates V3 vs V4 comparison (very unscientific):
http://www.cnqsmotor.com/en/article_read_848.html

If this is to be believed, they somehow exchanged low-end torque for high-end torque.

Isn't the Zero gearless mid drive? As in fixed ratio?

Click to expand...

Yes it is, but with a mid drive you aren't forced into a setup where the "gearing" is too high at very low rpm. You can use a motor that will rev much higher than a hubmotor and thus give both low speed power (from the reduction pulley or chain drive) and high top speed (relatively speaking) from the motor revving higher.

Excuse me, but why are you bothering with a hub motor?
Why not just go with a large motor mid-mounted with a chain on it for massive power?

Bicycle comments of those speeds makes scared for the rider. However I bet the motor bike with all gas torn out, still will be light enough for your needs. 250cc is about 215lbs, 250cc motor 125lbs, trans say another 25lbs. Yeah 120-140lbs with gas ripped out sounds right, and thats what you want I would assume for the road right? Then add your lets say now 40kw+ mid motor and battery, probably puts it over stock 250cc weight.

MJSfoto1956 said:

Also found this regarding V4 vs other versions:

High quality of silicon steel raw materials, customized and enlarged groove make more copper wire into motor, produce more powerful magnetic force.

Click to expand...

So in theory, with more copper there should be more torque.

Click to expand...

Thanks, but I've already bought the motor, and besides its not the limiting factor.

I wonder if anyone has modded a Kelly controller for more power - like solder on the shunt...

Sunder said:

MJSfoto1956 said:

Also found this regarding V4 vs other versions:

High quality of silicon steel raw materials, customized and enlarged groove make more copper wire into motor, produce more powerful magnetic force.

Click to expand...

So in theory, with more copper there should be more torque.

Click to expand...

Thanks, but I've already bought the motor, and besides its not the limiting factor.

I wonder if anyone has modded a Kelly controller for more power - like solder on the shunt...

Click to expand...

If you wanted a Kelly to not shoot fire, derating its shunts would get you further than turning up a device thats already ran way beyond it's ability to survive long.

Also, 273*50mm is bicycle size (i run one on my mt bike). You want 273*70 or 273*80mm minimum for a motorcycle.

liveforphysics said:

If you wanted a Kelly to not shoot fire, derating its shunts would get you further than turning up a device thats already ran way beyond it's ability to survive long.

Also, 273*50mm is bicycle size (i run one on my mt bike). You want 273*70 or 273*80mm minimum for a motorcycle.

Click to expand...

This is starting to get a bit depressing.

I guess there's no need to de-rate its shunts since it can be software limited. Will putting some fans on the heat sink help? Or mounting it so that the snorkel that used to feed the air-box, now blows over the controller instead? Which part is under-rated?

The 70H and 80H motors only came in 4.5" and 6.0" widths. I wanted the frame to be as small and light as possible, given still full fairing, so I was looking at a 250s as the donor. The most common of them (Honda, Suzuki, Kawasaki, etc) had 3.5" or 4.0" wheels by default, and most people who wanted wider wheels on them, were talking of modifying the swingarm which I was pretty hesitant to do.

I'm committed though, and I guess this will be part of the learning curve.

any thoughts on 2wd ?

markz said:

any thoughts on 2wd ?

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Yeah. Not worth it. It only adds a small amount of power but will really unbalance handling.

In my experience so far, the main thing that 2WD does is significantly increase my acceleration on my heavy ebike and etrike (say, taking a 0-20MPH time of 7-8 seconds down to 4-5 seconds or less).

Sunder said:

Yeah, not going mid-drive. One of the main reasons for going electric is simplicity. I don't want to have to worry about chains or belts, etc.

Click to expand...

Simple is only simple until you spin an axle by stuffing kNm through a couple cm^2 worth of axle cross-section.

amberwolf said:

In my experience so far, the main thing that 2WD does is significantly increase my acceleration on my heavy ebike and etrike (say, taking a 0-20MPH time of 7-8 seconds down to 4-5 seconds or less).

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If there is enough weight, sure. But for lighter, fast bikes, accelerating hard would take even more weight off the front and it would just spin.

Chalo said:

Sunder said:

Yeah, not going mid-drive. One of the main reasons for going electric is simplicity. I don't want to have to worry about chains or belts, etc.

Click to expand...

Simple is only simple until you spin an axle by stuffing kNm through a couple cm^2 worth of axle cross-section.

Click to expand...

Torque is torque regardless of what the source. Unsprung weight and centrifugal forces will make it worse, but I guess thats the point of this. It looks like max torque isn't much higher than stock. So the risk of spinning the axle isnt that much greater.

Sunder said:

Chalo said:

Simple is only simple until you spin an axle by stuffing kNm through a couple cm^2 worth of axle cross-section.

Click to expand...

Torque is torque regardless of what the source.

Click to expand...

You can anchor the torque of a shafted motor at the outside of its casing. The torque of a hub motor has to resolve at the axle, which is a much, much smaller radius.