E-Motorcycle build advise

Hey team, I'm about to start on a project to convert an motorcycle into electric.
In the past I've made an 52V E-Bike, but that was very much plug and play, so I'm looking for some advise and critique on my plans.

For context I live in New Zealand and currently drive a 650cc motorcycle
The goal/purpose of this build is: to build a fun/fast street legal city commuter that can handle cruising at ~100km/h for short periods but mostly stop start riding at 50km/h

Donor bike
I'm looking at using a KTM Duke 2016 200cc
The specific one I'm looking at is currently street legal, however after the conversion I'd need to take it through compliance, which i've been reading this document: https://www.lvvta.org.nz/documents/standards/LVVTA_STD_Electric_and_Hybrid_Vehicles.pdf
Which appears simple enough for the most part, I'm just not confidant in this area, any advise on ensuring it's able to be made street legal would be appciated

The other concern with this bike, is if the frame is strong enough for the motor. I'm not looking at using it's full power all the time, but I don't want it to fall apart when I do give it some juice.
From the googling I've done, it looks like the frame on this bike is the same frame as the same bike in a 390cc variant, which would indicate it's able to handle a bit of load, so could be alright?

Battery Pack
I'm looking at making a 26S 20P 18650 pack, fused at 300A (or maybe 200A - see below)
To make this I've found someone selling recycled P26A cells that are all >2500mah capacity at a good price
I plan on using the 0.1mm copper + 0.1mm nickel plated steel sandwich method mentioned on this forum
A few small things im not sure about here:
What connector to use for the batter pack? I've seen Anderson 175A mentioned, is that enough? there's also 350A but it required 1g AWG, which feels like overkill?
What AWG wire to use? I've seen some people say 6 or 4, but still unsure

Then the big one I'm not sure about here is the BMS.
I have found a 26S 200A BMS: https://www.aliexpress.com/item/4000206471196.html which would be easy to work with, but means the motor cant deliver it's full power, which required 250A.
So to hit 250A I found https://www.aliexpress.com/item/32997552090.html which has a 7-16S 300A variant, which would allow the motor to run to it's peak if I ran two of these (13S) in series
However, I'm finding conflicting information for wiring to battery modules with BMS in series, I've read on here about needing diodes in between the packs, but then I cant find any diodes that appear to be able to handle 300A and other people say they're not needed
Also how do you charge a 2x13S pack? can you use a 26s charger (109.2V) charger and then just charge them in series?

Motor
I'm looking at a QS 273 8kW 96 hub motor paired with SIAYQ96260 (96V 260A) motor controller
I've sent off an inquiry to QS Motors about this and a few other items and they've quoted this motor as having a top speed to 130 kph, max power at 23602W, max current at 254A, which I wont be able to hit with the single BMS approach, but dual battery modules would allow the motor to pull it's full current here.

Other parts that I plan on putting in:
- Main contactor
- Inertia switch
- Throttle with lighting control switches
- Rear disk break

That thing would be an absolute blast with a mid motor, the geared QS 138 70 would be ideal! You'll get much higher performance with the hub motor but handling will suffer some, that mid will definitely manage your criteria, 60-70mph should be no problem and lots of punch below that. All cycle parts will be plenty strong enough but that frame definitely uses the engine as a stressed member, bridging all the mounting points with a rigid enough structure could be difficult.

stan.distortion said:

You'll get much higher performance with the hub motor but handling will suffer some

Click to expand...

Thanks! I didn't think about how the handling would be affected, do you know in what way it would change? The main reason I'm leaning on hub was the ease of installation, I'm not much of a metal worker and don't have welding tools so doing mid drive would make it quite a bit more difficult.
I think considering it's mostly a commuter, i'd be ok with a hit to the handling for how much easier it would be.

Also it's nice to hear that the cycle should be strong enough, I've found it difficult to find cheap donor bikes, there's a few insurance write offs, but I'm a little scared at how bad condition they might actually be in.

Toxicable said:

The main reason I'm leaning on hub was the ease of installation, I'm not much of a metal worker and don't have welding tools so doing mid drive would make it quite a bit more difficult.

Click to expand...

Some metal work will be required for both.

I have switched from the idea of using a hub motor to a mid motor because:
- didn't find a hub motor with an axle long enough for my rear swing arm
- didn't want to alter the rear swing arms (inevitable for a hub motor)
- didnt want to use a China-made rear wheel, and putting a hub motor into my original rim was beyond my abilities

In my opinion, changes to the basic structure of the bike are bigger with a hub motor.
And don't forget-the hub motor needs a rim to sit in...

Toxicable said:

stan.distortion said:

You'll get much higher performance with the hub motor but handling will suffer some

Click to expand...

Thanks! I didn't think about how the handling would be affected, do you know in what way it would change? The main reason I'm leaning on hub was the ease of installation, I'm not much of a metal worker and don't have welding tools so doing mid drive would make it quite a bit more difficult.
I think considering it's mostly a commuter, i'd be ok with a hit to the handling for how much easier it would be.

Also it's nice to hear that the cycle should be strong enough, I've found it difficult to find cheap donor bikes, there's a few insurance write offs, but I'm a little scared at how bad condition they might actually be in.

Click to expand...

I've never ridden a hub motor bike so can only comment on the physics behind it, others experience will have a lot more value. You're increasing the wheels unsprung mass in a big way, many times more than stock and that will have a huge effect on the suspension, if damping is increased to match the extra mass it would feel almost like there's no rear suspension, especially on a lightweight bike.

Then there's rotational inertia, mostly "flickability". The spinning wheels act like a gyroscope, even changing tyres from something thin and light to thick and heavy has a considerable effect on responsiveness, it can make a bike feel lumbering and unwilling to turn at one extreme and twitchy to the point of unstable at the other so adding that much spinning weight will have a big effect, shouldn't be much at inner city speeds but will have a much bigger effect as speed rises. That's not nessasarily a bad thing, it will be far less willing to be thrown into fast corners but the flipside of that is a bike that feels far more stable.

Rotational inertia also has an effect on braking and wheelspin but that shouldn't be a big issue, modern brakes have plenty to spare for the extra load and if controlling wheelspin was ever a problem then traction control is an easy addition (hypothetically, who knows how big hub motors will get someday).

For the frame, how sure are you everything is the same as the 390? It would be worth double checking that, a few things I read yesterday suggested otherwise (I only scanned though, nothing in-depth) and if the swinging arm is different then the 8kw hub motor will possibly be more than it can safely handle, it's already overkill for such a light bike imho and could be dangerously so if the major cycle parts are different to the 390.

For the frame structure to replace the engines support, if you think mounting a mid motor might be more than you can take on then I'd suggest getting a metal fabrication company to do that part. Chances are it will be part of the battery box and you'll likely be mounting several other parts to the same structure so there could be quite a lot of mocking up to do before you can get something made up but it shouldn't be overly expensive. Try and get a quote from several companies beforehand though and if they're not interested, walk away as they vary a lot, some may be doing high end work and charge through the nose while others might only be interested in making gates and build you something from welded up girders an half inch plate! Fwiw, a lot of bikers tend to work in metal fabrication so if you see a well worn bike parked outside you might have struck gold

It looks like the engine plays a big part in the twisting stiffness of the frame as well as tying the swinging arm pivot area to the front upper engine mount area and I'm guessing there's also an upper rear engine mount, try to keep a straight line clear between all the mounting points and it should be simple enough to build a structure with enough stiffness and carry everything you need.

Sorry I can't offer any help on your other points, they're not things I've got much experience with so can't really comment on them, looks ok to me but others will be able to offer far more insight.

EDIT: Just re-read your original post. Maybe have a read through some build threads with the 8kw hub as I'm fairly sure it will handle a lot more current than the figure QS provided, the 3kw 138 can easily handle the same sort of currents and the em150 controller can provide them (possibly overstressing it for road use though).

Believe it or not, 8awg silicone insulated wire is enough for those currents. I'd been advised on it (in the ES Telegram group) when the standard wire current tables and what I was actually seeing on builds (from amateur to manufacturer) didn't line up. 8awg looks like two bits of string hanging out the back of a 175a anderson plug but half a meter of it doesn't even get warm with consistent 150a loads and longish peaks over 200a.

That's on a temporary lipo pack for testing and I'll be stepping it up to double or more the cross sectional area for the finished pack but there's definitely no need to try threading inch thick cables everywhere. Not 100% sure on the andersons, the 175s certainly aren't struggling with the loads above but I'd be wary of over rating them too much, I'm sure someone here knows just what they'll take but there's not much contact area and they're not overly expensive, if you plan on pushing that 8kw hub then my guess is you'll need the 350s.

When you look at ant bms you could just go with this one instead:
https://www.aliexpress.com/item/32826469363.html?spm=a2g0o.store_pc_groupList.8148356.1.44611d15WNwni1

Elektrosherpa said:

- didn't find a hub motor with an axle long enough for my rear swing arm
- didn't want to alter the rear swing arms (inevitable for a hub motor)
- didnt want to use a China-made rear wheel, and putting a hub motor into my original rim was beyond my abilities

Click to expand...

Interesting, that's some good points in favour of mid drive.
This is the specific motor I'm looking at: http://www.cnqsmotor.com/en/article_read/QS%20Motor%2017inch%208000W%20273%2050H%20V3%20E-Scooter%20Hub%20Motor/248.html
My understanding is that it would fit in my swingarm and comes attached to the wheel.
However I wasn't aware of what would be required to be altered on the arms, do you know what's required here? I had thought there would be a strut that would connect to the swing arm from the hub to stop it from turning, but I haddn't thought about specifics on that.

j bjork said:

When you look at ant bms you could just go with this one instead:
https://www.aliexpress.com/item/32826469363.html?spm=a2g0o.store_pc_groupList.8148356.1.44611d15WNwni1

Click to expand...

Oh thanks! that looks perfect! I somehow never found that one in my searches, thanks for pointing it out.

Toxicable said:

However I wasn't aware of what would be required to be altered on the arms, do you know what's required here?

Click to expand...

First of all, your rear swing arms must be open at the ends, to allow the hub motor axle to enter.
Second, their openings must have EXACTLY the diameter of the hub motor axle, and really firmly hold it.

If you look through the hub motor build threads here, you will find a lot of examples showing which efforts people had to make for realizing a reliable connection between hub motor axle and swing arms (and it must REALLY be reliable, since all the torque of the motor goes at this connection).

stan.distortion said:

I've never ridden a hub motor bike so can only comment on the physics behind it, others experience will have a lot more value. You're increasing the wheels unsprung mass in a big way, many times more than stock and that will have a huge effect on the suspension, if damping is increased to match the extra mass it would feel almost like there's no rear suspension, especially on a lightweight bike.

Then there's rotational inertia, mostly "flickability". The spinning wheels act like a gyroscope, even changing tyres from something thin and light to thick and heavy has a considerable effect on responsiveness, it can make a bike feel lumbering and unwilling to turn at one extreme and twitchy to the point of unstable at the other so adding that much spinning weight will have a big effect, shouldn't be much at inner city speeds but will have a much bigger effect as speed rises. That's not nessasarily a bad thing, it will be far less willing to be thrown into fast corners but the flipside of that is a bike that feels far more stable.

Rotational inertia also has an effect on braking and wheelspin but that shouldn't be a big issue, modern brakes have plenty to spare for the extra load and if controlling wheelspin was ever a problem then traction control is an easy addition (hypothetically, who knows how big hub motors will get someday).

Click to expand...

Thanks for the detailed explaination! I really appciate it!

This along with the other comments about hub motors is making me reconsider this choice
Thinking about it a bit more, the engine mounts wouldn't be that hard of a job for myself, or if I got someone experienced to do it.
And it would allow me to keep the original wheel, which i'd take as an advantage.
Looking at options for motors, QS motors only appears to have a 4kw mid drive.
I might need to look through some other mid drive posts to see what other people are using.

They do several mid drive motors, 1, 2, 3, 4 and 8kw as far as I know. They released a version of the 3kw with a built in reduction gear this year, there are at least a couple of build threads using them on here. You'll probably find top speed a little limited with the 3kw, some members have hit 80mph with that and the em150 controller but that's pushing the controller far too hard for a dependable road bike imo. 60mph would be no problem at all, 70 with mildly favourable conditions and no lower than 50 on any but the steepest hills, they pull like a train at lower revs but run out of steam a little early.
https://endless-sphere.com/forums/viewtopic.php?f=10&t=110723

If you contact QS, maybe ask if they doing the same drive cover on the 4kw yet. It's basically the same motor as the 3kw but about an inch longer, should have enough extra power for motorway speeds and the geared drive would make installation a hell of a lot easier, without that you'd need to either build a primary reduction stage or fit a huge rear sprocket.

The 8kw should be a real daemon, frighteningly quick at anything under 80mph is my guess but they're bigger than the 3 and 4kw motors, not much on paper but it's a big difference when it comes to installing and without the built in reduction gear they'll be complicated to install.
https://endless-sphere.com/forums/viewtopic.php?f=12&t=109878

Maybe work out what battery space you have before planning what motor to use as it looks a bit limited. That's a very short engine and long swinging arm, could be you'll need all of it just to have enough battery capacity and a hub motor is your only option. Hopefully not, it looks like the 3 or 4kw should leave a fair amount of space but range probably won't be great. You'll need a kwh/km figure to work that out, Zero motorcycles claim an average of around 75 watt/hour per km. Not sure how realistic that is but it should be ok as a ballpark figure.

stan.distortion said:

If you contact QS, maybe ask if they doing the same drive cover on the 4kw yet.

Click to expand...

From what I seen on their facebook page it is planned, but not more than that yet.
But ask, if nothing else maybe it at least leads to them understanding that there is a demand for it

Toxicable said:

j bjork said:

When you look at ant bms you could just go with this one instead:
https://www.aliexpress.com/item/32826469363.html?spm=a2g0o.store_pc_groupList.8148356.1.44611d15WNwni1

Click to expand...

Oh thanks! that looks perfect! I somehow never found that one in my searches, thanks for pointing it out.

Click to expand...

Running motorway speeds and the associated continuous power needed then i’d go with the sealed LEV200 contactor controlled with a smart bms. Much more robust and can handle a lot more than this power level if you outgrow your system

If you’re doing a street commuter i’d go with a hub. So much easier to build a high performance and high range battery with the freed space but i agree mid drives are more fun :wink:

j bjork said:

stan.distortion said:

If you contact QS, maybe ask if they doing the same drive cover on the 4kw yet.

Click to expand...

From what I seen on their facebook page it is planned, but not more than that yet.
But ask, if nothing else maybe it at least leads to them understanding that there is a demand for it

Click to expand...

+1, it would be great if they could offer it on all their mid-motors! I was originally planning to try out the 3kw in a 125 trials frame but it's got far more low down torque than would be needed, the 2kw or maybe even 1kw would be better suited as it wouldn't need to be geared for anything much over 30mph and the peak outputs would be extremely brief and infrequent.

j bjork said:

stan.distortion said:

If you contact QS, maybe ask if they doing the same drive cover on the 4kw yet.

Click to expand...

From what I seen on their facebook page it is planned, but not more than that yet.
But ask, if nothing else maybe it at least leads to them understanding that there is a demand for it

Click to expand...

I just got an email reply from them on their 8kw mid drive:
>Our 180 8kW mid drive motor is still in developing. It may hit ur performance goals.
>Maybe it can be get into normal sell at the end of this July.

However, thinking over it a bit more, I think the whole thing might be too big of a project for me.

So I've been looking around at other options that might be a bit easier.
I looked at importing a second hand Zero from CA - but that nears on about $11K USD - depending on model
I've looked at local Electric motorcycles, but the only one in my country (NZ) is the Super Soco TC Max - which is 3.9kw, 95km/h max speed and $5600 USD new

Then I found Alibaba electric bikes and the video series from "The Inja" about his experience
So i've been looking at this one https://kingche.en.alibaba.com/product/60840091037-806549463/High_power_motor_the_electric_motorcycle_5000w_8000w_10000w_motorcycle_electric.html
I messaged them about it and they have a model that comes with an EEC certificate, 5kw, 60Ah 72V, inclduing shipping to my country (CIF) 2.5k USD which is the same price I was looking to pay for just the motor + controller from QS.
The EEC cert would be it quite easy to get on the road (in comparison), and i'd probably need to replace the batteries kind of soon, but it would be something I can tinker with, my only hang up is the Import process and the 5kw motor, they say it does 100km/h max, but what would the torque look like at 90km/h, I guess it would would really feel like it's out of juice at the high end, so not too sure at this stage.

Toxicable said:

So i've been looking at this one https://kingche.en.alibaba.com/product/60840091037-806549463/High_power_motor_the_electric_motorcycle_5000w_8000w_10000w_motorcycle_electric.html
I messaged them about it and they have a model that comes with an EEC certificate

Click to expand...

If I look at this offer, it looks to me "typically chinese" (i.e. inaccurate - e.g. they say they remove front wheel and handle bar for shipping, but they show a picture of a boxed bike with both items still on), and from my experience I would not believe them a single word.
Especially the thing about the European certificate (which strangely enough is NOT mentioned on their offer page) is hard to believe -the costs of getting such a document would require them to sell dozens (if not hundreds) of bikes for their low price, until they start to make profit.