[RahulNagaraj]

Kawasaki showcased two electric motorcycles at last year's EICMA show in Milan. Now, according to reports, both electric bikes are ready for launch.

The reports state that the pair of electric motorcycles from the Japanese brand has begun their homologation process in Australia, indicating it could be one of the first international markets to receive the Kawasaki e-bikes. The homologation filings have designated the two bikes as Ninja e-1 and Z e-1.



The two electric motorcycles are also said to have bodywork similar to the brand's 400cc counterparts, the Ninja 400 and Z400. While the prototypes showcased last year had a power output of around 15 BHP, the homologation filing in Australia lists a power output of 9 kW (12 BHP). It also reveals that the Z e-1 could weigh around 135 kg, while the Ninja e-1 tips the scale at 140 kg.

Kawasaki is yet to reveal whether or not the two e-motorcycles would come with removable batteries. However, earlier reports suggested the bikes could be offered with two removable battery packs, each weighing 12 kg and having a combined output of 3 kWh. If this holds true, both electric motorcycles could come with limited range and top speed, making them the brand's first mass-market electric street bikes.

Source: Motorcycle.com

Link to Team-BHP news

[audioholic]

To justify the performance aspect of these bikes I hope they can integrate two motors and a well designed battery pack distributed along the frame. Why two motors? So that we have one motor with a high starting torque and relatively shorter gearing and another motor with a lesser torque but designed for speed. This will give the same linear pull that the twin cylinder and inline fours offer all the way till red line and insane speeds. Using a single motor will give good initial acceleration but that will ramp down as speeds pick up. This will also aid in good regenerative braking helping in dropping speeds well.

[Samarth 619]

You know I always had this idea of dual batteries in e vehicles. In fact, I imagined a basic Ather 450 with a small battery initially, but with 1-2 more slots for battery expansion. Few brands already sell such a setup, like Okinawa, but with 2 slots.

My daily commute is just 16 kms, and I'm from a small city. For me, an e bike with a smaller battery and further expansion slots for batteries, makes perfect sense.
30-40 kms/charge is enough for me. The bike will be lightweight and cheaper. For big cities, they can still sell with both batteries in place. It makes perfect economic sense.


SIDENOTE: At one point, I imagined an e bike, a Hayabusa killer, but with quite a small battery, just for drag races and nothing else. A kind of bike which will do around 4-8 drag races per charge, but will weigh around 155 kgs, something giving a motoGP bike like experience.

Originally Posted by audioholic

To justify the performance aspect of these bikes I hope they can integrate two motors and a well designed battery pack distributed along the frame. Why two motors? So that we have one motor with a high starting torque and relatively shorter gearing and another motor with a lesser torque but designed for speed. This will give the same linear pull that the twin cylinder and inline fours offer all the way till red line and insane speeds. Using a single motor will give good initial acceleration but that will ramp down as speeds pick up. This will also aid in good regenerative braking helping in dropping speeds well.

But what's the need for two motors? A single motor can easily give max torque right from 0 rpm.

Also, there's one confusion: when one motor is lashing out top end, what will the other motor do, clearly at higher than normal revs?
You can't even use it for regenrative braking because one motor powering and other being powered is an unnecessary conversion, a waste of energy overall.
At best, the non-driving motor can retain a neutral of some kind, where its not rotated all the time?

Yes, a gearbox will help with acceleration and top speed, but won't it also result in extra mass? Also, gearshifts are zero power zones, which cause some delay in acceleration. Will the tradeoff be worth it?
Gasoline powered engines don't have a choice, but electrics can choose, due to their power delivery nature.

[audioholic]

Originally Posted by Samarth 619

But what's the need for two motors? A single motor can easily give max torque right from 0 rpm.

Also, there's one confusion: when one motor is lashing out top end, what will the other motor do, clearly at higher than normal revs?
You can't even use it for regenrative braking because one motor powering and other being powered is an unnecessary conversion, a waste of energy overall.
At best, the non-driving motor can retain a neutral of some kind, where its not rotated all the time?

Yes, a gearbox will help with acceleration and top speed, but won't it also result in extra mass? Also, gearshifts are zero power zones, which cause some delay in acceleration. Will the tradeoff be worth it.

You didn't seem to get the concept. I did mention that a single motor can give max torque from 0rpm but that starts going down midway to its max speed. What I preferred is that the second motor will have a taller reduction gear which will help it perform well at higher speed of the bike and the combination of motors will ensure a very good torque spread even at higher speeds.

When the second motor kicks in, the first one needn't operate and only can operate under high power demand conditions for limited time.

I didn't mention that one motor would power the other. By regenerative braking, I meant that when the driver wishes to slow down, both motors act as generators and recharge the battery. This will give strong deceleration where needed and also end up recovering energy. Gearbox will result in extra mass but I only mentioned having a reduction gear which all vehicles will have at the final drive. Two motors can be connected with a single belt drive or a cascaded drive. The power delivery will be very linear and yet pack a punch. I don't think a single motor setup will be as much fun as a Ninja 400 or above ICE engine especially above 100+ kmph without some trade off with respect to motor life or even the availability of power for extended duration.
In comparison, even my Ninja 300 pulls upto it's top speed pretty briskly and doesn't struggle to reach that speed.

[Samarth 619]

Originally Posted by audioholic

When the second motor kicks in, the first one needn't operate and only can operate under high power demand conditions for limited time.
I didn't mention that one motor would power the other. By regenerative braking, I meant that when the driver wis...

I got your concept a little the last time, but I was concerned about the engineering implications, and I'm afraid the design might not be feasible, without some noteable compromises to vehicle working or the vehicle's weight. Let me explain.

You said the first, the undergeared motor wouldn't work beyond a point: but how? Its connected to transmission system, so it will rotate with the wheel, right? Unless you're planning a gearbox which moves itself to neutral.
But here's the key- if you're installing a gearbox, the second motor itself is not necessary as we can get the same gearbox to perform gearing duties. In fact, it is more of a lightweight solution, to have a motor and a gearbox, instead of 2 motors.
And by the way, some e-bikes sold abroad already have 6 speed gearboxes.

Supposing you avoid a gearbox entirely, and also wouldn't want to rotate the first motor constantly with the wheel, then you need a bicycle like setup, whereby you can stop pedalling, but the bicycle wheel keeps on rotating... that kind of transmission. (I don't know what's it called)
But again, regenerative braking will never work on this setup, because if the motor can only drive the wheel, but can't be driven by it, we can never have this motor make current.

Multiple equally capable motors can be connected, because they're constantly driven at same rpm. Supercars have done it before.
But, I'm not sure how to connect high & low rpm motors to the wheel's rotation, because while in high rpm, the low rpm motor would be very pressurised, and it would slow the entire vehicle (like a stuck brake would).


Now coming to your concern about losing power: Yes, you're absolutely right that beyond 70~% of the peak rpm, an electric motor starts to lose torque, but what if we avoid going to top rpm altogether?
We can always choose a bigger, more powerful motor, can't we?For example, Lightning LS218, an e-motorcycle launched in USA can:-
1. touch 10,000 rpm using a liquid cooled electric motor, I don't think we need more rpms.
2. touch upto 350 kmph right from 0 kmph, all without changing a gear.
3. lash out 200 bhp at the wheel, and 228NM torque.
Needless to say, neither power, nor torque, nor usable revs are any challenge in a purpose built e-motorcycle, it might be expensive though.

Multicylinders were great in petrol based ICE's, just because a cylinder makes power in one stroke, out of the 4 stroke cycle. Electrics don't have such strokes.
Overall, my opinion is that its better to go for a bigger motor, than to have 2 smaller motors with a complicated transmission system.

However, if you have prepared a design/ schematic, kindly share if you're ok with it.
I'm a professor of management, a hobbyist who doesn't have an engineering degree, so I might be missing a point somewhere, plus I'm myself intrigued by your idea, and its quite possible we might end up with an idea or a good discussion..

[audioholic]

Originally Posted by Samarth 619

I got your concept a little the last time, but I was concerned about the engineering implications, and I'm afraid the design might not be feasible, without some noteable compromises to vehicle working or the vehicle's weight. Let me explain.

You said the first, the undergeared motor wouldn't work beyond a point: but how?
I'm a professor of management, a hobbyist who doesn't have an engineering degree, so I might be missing a point somewhere, plus I'm myself intrigued by your idea, and its quite possible we might end up with an idea or a good discussio..

It is of course a good discussion because both of us have different ideas. But I dont have any schematics to detail it. I am only using basic ECE Knowledge and some experience from the automotive tech industry over the last few years. Based on your detailed explanation, I have some answers for the questions you have raised.
1. The undergeared motor needn't be decoupled mechanically. As long as it's no longer electrified and is free of regen load, the motor will have negligible resistance in the drivetrain. It can continue to rotate with the rest of the system without causing any noticeable loss of power..
2. A gearbox is overkill especially when we speak of more than 2-3 speeds because it has lot of components and weight that's practically useless. My suggestion was the intermediate between a single big motor and a small motor with gearbox. With two motor combination, just the size of the motor and wheel pulley can be varied to achieve the gearing. Simple and absolutely no complexity involved in the drivetrain. Only the power electronics part must be designed to integrate both motors. Thats anyway a topic that's aggressively developed in today's industry.
3. Why I prefer two motors to a single big motor is packaging. Two motors can be packaged better to fit the frame of a motorcycle either as a flat arrangement in place of the gearbox and crank or upright to resemble the engine block and head. Having one huge motor will make it tougher to package since it being circular will take up most of the space in the lower frame and will leave unusable gaps around the motor. We still need to package the motor controller and a battery pack both of which are heavy and shifting them upwards will kill handling. Things have to sit low and well packaged to provide the same handling like a ICE bike.
4. For a company like Kawasaki, it makes better sense to have a modular setup where they can delete the second motor for a lower grade of bike with simple changes only. Instead if they have to develop a whole new motor for a smaller bike, it will again increase R&D costs. If they need to launch a Ninja 400 and Bina 650 equivalent the former might be able to manage with a single motor or any such mix and match combination.

[Samarth 619]

Originally Posted by audioholic

It is of course a good discussion because both of us have different ideas. But I dont have any schematics to detail it. I am only using basic ECE Knowledge and some experience from the automotive tech industry over the last few years. Based on your detailed explanation, I have some answers for the questions you have raised.
1. The undergeared motor needn't be decoupled mechanically. As long as it's no longer electrified and is free of regen load, the motor will have negligible resistance in the drivetrain. It can continue to rotate with the rest of the system without causing any noticeable loss of power..
2. A gearbox is overkill especially when we speak of more than 2-3 speeds because it has lot of components and weight that's practically useless. My suggestion was the intermediate between a single big motor and a small motor with gearbox. With two motor combination, just the size of the motor and wheel pulley can be varied to achieve the gearing. Simple and absolutely no complexity involved in the drivetrain. Only the power electronics part must be designed to integrate both motors. Thats anyway a topic that's aggressively developed in today's industry.
3. Why I prefer two motors to a single big motor is packaging. Two motors can be packaged better to fit the frame of a motorcycle either as a flat arrangement in place of the gearbox and crank or upright to resemble the engine block and head. Having one huge motor will make it tougher to package since it being circular will take up most of the space in the lower frame and will leave unusable gaps around the motor. We still need to package the motor controller and a battery pack both of which are heavy and shifting them upwards will kill handling. Things have to sit low and well packaged to provide the same handling like a ICE bike.
4. For a company like Kawasaki, it makes better sense to have a modular setup where they can delete the second motor for a lower grade of bike with simple changes only. Instead if they have to develop a whole new motor for a smaller bike, it will again increase R&D costs. If they need to launch a Ninja 400 and Bina 650 equivalent the former might be able to manage with a single motor or any such mix and match combination.

Thanks for the detailed explanation.
In reference to point no. 1, according to my limited knowledge, a motor can't be freely rotated like you said. It generates resistance and electricity is produced, which is exactly how regenerative braking works.
The only way to reduce this resistance is to supply electricity to the motor in little volumes, I think this is how multiple levels of regen braking are applied commercially.
But, I might be wrong here.

But there's one more issue you didn't touch:- At near the top speed, the highgeared motor might be doing say, 4-5000 rpm, but the undergeared motor will be doing 7-8000 rpm, won't such highrevving be bad for its health in general? (Assuming there're no resistance and regen effects)

In reference to your point 2, yes a 6 speed gearbox as such makes very less sense for an e bike. But the companies who did it, actually did it for marketing reasons:- They wanted to imitate petrol ICE bikes, so that the rider feels at home. Plus, a 6 speed gearbox was readily available in spares, while a 2 speed wasn't.

I would like other TBhpians too, to chime in their thoughts on this topic.

[audioholic]

Originally Posted by Samarth 619

Thanks for the detailed explanation.
In reference to point no. 1, according to my limited knowledge, a motor can't be freely rotated like you said. It generates resistance and electricity is produced, which is exactly how regenerative braking works.

It generates electricity and offers resistance only when connected across a load. Not when left open circuit. When the motor spins in an open circuit condition, the only resistance if anything will be from the shaft bearing. Rest of it is pretty free. If you have driven an electric car with regen set to zero then you will realise how freely it can coast when off throttle. Thats not the case when you start increasing regen and will come to a point where it will retard heavily the moment you let go of the throttle.

Regarding the other point about the motor running at higher speed, yes this is a problem, but mostly the wear will be on the shaft and bearing, which can be addressed. Motor being live at 9000RPM and producing power is different compared to a free motor rotating on its shaft at the same speed.

[Samarth 619]

Originally Posted by audioholic

It generates electricity and offers resistance only when connected across a load. Not when left open circuit. When the motor spins in an open circuit condition, the only resistance if anything will be from the shaft bearing. Rest of it is pretty free. If you have...

Thank you for the knowledge, regarding the motor's electricity generation.
I'm now beginning to understand the concept, and I think we might have a future concept here..
Although, I still have reservations on the efficiency and performance part..
Let's hope we have such a design to work some time.. Good luck to you.