QS 3000w midmotor

[minde28383]

This is what I had as reference:
https://www.maedler.de/product/1643/1615/362/1656/2123/kettenradscheiben-krl-ohne-nabe-08-b-1
your example: 114 teeth, 9kg, 88 € (excl VAT)

quite some figures, admittedly - but a feasible solution.
Aluminum would be nice, sure, but I doubt that it will be cheaper.

You have to trade off the effort, cost and weight of a two stage drive with an additional shaft, bearings, sprockets, support.

What is your intended ratio?
With 10T front, you're over 1:11 . oops

If shaft size is 20mm than 10teeth front sprocket is an option.
I used to be against small sprockets ie 10 and 11 teeth, because I thought they make more noise than bigger ones 13teeth or 14teeth. To lower chain noise chain has to travel in lower speed. As an example low rpm motor, very silent compared with high rpm motors even though chain geared.
Speaking about rear sprocket. Maximum teeth rear sprocket I would be willing to install is 65teeth, in worst scenario 72teeth. So it's it either 6.5 or 7.2 gear ratio (keep in mind that motor max rpm is 6000) in ~600mm wheel diameter is still too fast.

You was talking about 100teeth. Either 95teet or 115teeth industrial standards available. 115 teeth of 420 standard would be ~46cm diameter. Can you imagine such sprocket on the 60cm diameter wheel...
65 tooth sprocket is ~26cm diameter.

Very big sprockets on rear wheel looks not too good. At the end of the day such big sprocket would be simply impractical, especially offroad because it would go in dirt being too near to ground. If it's diy than whateverer but people don't dig such look too much.

Your motor was wounded in a way that it can achieve up to 100kmh having front ~20teeth and 110teeth pulley with Votol 150 and 72v batt in 130/70x12'' tire.
So if you want to have the same speed (more speed is just impractical) but in a bigger wheel than gear ration needs to be higher. You can make the same ~5.5 ratio but will loose torque and will have unnecessary top speed. So having big rear wheel there are two options:

- smallest front sprocket 10T and big rear sprocket 65T or better 75T, but bigger sprockets just not practical. This option is noisy option. And ugly because of big sprocket if with 75T.

- or doing first reduction like you suggested with your parts list from maedler. And then going normal common sprocket sizes on second reduction. In this option there will be less chain noise but will make it: heavier, expensier, more parts, more complex will take up more space in your frame, will lose few percent of efficiency due additional reduction.

Knowing people anyway gear it with sprockets they have (you gotta do what you can..) and get lowered initial torque, too big top speed, and what a heck still nice ride... Motor is ok, no overheat issues reported so far.

 

[eee291]

Sorry to butt in but what top speed are you aiming for?

I also thought that on my derbi a 1:5 gear ratio would be too low but after experiencing it I don't even want to put a bigger sprocket on the rear anymore. The torque is already terrifying.
I'm using a 420 13T on the front and a 65T on the rear, I'm thinking of going back to 53T on the rear (1:4) to see how fast I can go.

Useful Calculator:
https://www.bmikarts.com/Go-Kart-Gear-Ratio-Speed-Calculator

 

[minde28383]

eee291,
Can find out whom you are asking about speed.
Anyways.
If you are terrified by your bike than goal reached
Lowering gearing you will lose thrust, instead just reduce amps till you get to safe zone. What's your top speed with current 5:1 gearing and what speed you aim for?

If you terrified with 5:1 gearing on senda rear 590mm wheel diameter than imagine what would you experience with 470mm diameter (12'' rim); this motor was originally put in (in scooters) with 6:1 gearing.

Did you made adapter for 65T or was original spare part for Senda?

 

[eee291]

you can get them online for pretty cheap.
https://www.racing-planet.de/xanario_search.php?language=de&sessID=6f7f55fb0702740b3ddeb9fdf90270b5&hea_sea_pd=0&query=kettenrad&x=0&y=0

I'm guessing about 80-90Kph with 24S and 53T Sprocket.
I have to install the bigger battery this week and give it a test ride.

It doesn't have a Tacho installed yet, I'll have to rely on my phone.

 

[wjr]

To lower chain noise chain has to travel in lower speed.

Well, yes, but not only.
I came across some calculation tool
http://www.renoldchainselector.com/ChainSelector?setLanguage=en
which cried if I ran above 14 m/s chain speed.

(btw: just finished a nice afternoon on my BMW F650 GS Dakar.
I'm quite sure, that in the 5th gear, the chain speed is far beyond 14 m/s there.
But I won't tell the renoldchainselector 8) )

But the online tool does not make a difference if I run this high speed in a one stage on the whole chain or in a two stage on the first stage.
In practice, I think there IS a difference:
First stage chain is shorter, and it has constant tension, as opposed to the rear wheel chain that changes lenth as suspension works.

What makes smaller sprockets louder is the unequal speed - in the end, a sprocket is a polygon, not a circle.
The lower the tooth number, the larger the deviation of the polygon from the circle.
So in, terms of noise, chain speed is somehow offset by uniformity if you go towards smaller sprockets.
Which effect prevails - I don't know, had to be tested.

Anyway, going for a smaller chain (428 in favour of 520) will ease noise problem in any case, I think.
Would it be an option to go to even smaller chains?
Maybe we hit the static force limit.
Ther are duplex chains (and even triplex ones) at offer for industrial use, but things geht heavy and expensive then, I'm afraid.
And I don't know where to get sprockets that fit the QS motor.
But maybe, a smaller chain could be an option for the first stage in a dual stage drive?

You was talking about 100teeth.

Just because this was the largest one on the maedler site.
I'm not seriously planning to mount such an flying saucer on my bike :lol:

115 teeth of 420 standard would be ~46cm diameter.
Can you imagine such sprocket on the 60cm diameter wheel...

then I had to lift my bike around corners as if it were a Harley

- smallest front sprocket 10T and big rear sprocket 65T or better 75T, but bigger sprockets just not practical.

I 'll try with 10 - 53 (already ordered, fitting the Kawa hub) and agree that not far beyond 70T, there will be the limit.

Knowing people anyway gear it with sprockets they have (you gotta do what you can..) and get lowered initial torque, too big top speed, and what a heck still nice ride... Motor is ok, no overheat issues reported so far.

Well yes, but It's an enduro, and I haven't even seriousy checked the street legality issue in civil-agent-state-Germany.
Maybe it never will see paved roads.
So torque IS important for me.

But it's a hobby trial anyway :wink:

Sorry to butt in but what top speed are you aiming for?

roughly 100 km/h
calculated it here in a german forum.
https://www.pedelecforum.de/forum/index.php?threads/elektro-kawasaki-enduro-auf-basis-einer-250er-kla.70411/post-1324435
Essence:
ratio 1:6,3 would be perfect - 6200 U/min at 103 km/h
ratio 5,3 (that's what I'm going to try now) is 16% longer.
6200 U/min at 119 km/h, Peak Power at 73 km/h, max torque at 25 km/h

The torque is already terrifying.

 

[larsb]

You won’t get 6000 rpm out of it if your planning 72V. Field weakening will only give you a bit more than normal rpm with this motor in my experience.

 

[wjr]

You won’t get 6000 rpm out of it if your planning 72V. Field weakening will only give you a bit more than normal rpm with this motor in my experience.

well, that's what they say - here:
https://ae01.alicdn.com/kf/HTB1X0xHXVT7gK0jSZFpq6yTkpXag.jpg

So you think they tell us lies?
Hm... would be sad.
I liked the idea to plan for top power at 60 kmH and get the rest for free :wink:
In terms of gear ratio, lower max rpm would call for lower ratio - and make life easier.
At the cost of low speed aka off road performance, of course

Or could it be that your gear ratio ist too low to utilize flux weakening?

But if the above chart is true, i definetely wanna have my controller loaded with precisely this paramters.
Never wanna touch it then. Programming cable for sale :wink:

 

[larsb]

It’s not lies, only physics. You could get 6000rpm at no load but this is useless. You need a lot of torque to overcome the wind and friction losses at max speed. Normally you get 85% or so of noload speed as max speed.

Just look at the red/torque curve, you’ll see it dropping off quickly at high rpm.

 

[wjr]

Let me share with you how I see it.

...only physics. ...

no doubt, of course.

... red/torque curve

However, in the chart it's only after the last tick, where curves sharply bend down.
The ticks in the chart are 650 rpm.
So the last tick is 5850 rpm, the bend somewhere at 6000.

Just look at the red/torque curve, you’ll see it dropping off quickly at high rpm.

I agree with this just for the range above 6000 rpm.

Power = torque x rotation.
It's not the motor torque thats count for driving performance (marketing flyers put aside, of course), but thrust.
Thrust equals wheel torque times wheel radius, so if we're not changing wheels, wheel torque is what counts.

you can trade off torque and rotation by changing the gear ratio,
while power ist constant (gear loss put aside as close to neglible for the moment).

That's what people running internal combustors with switched gears keep doing all day long.

In case of constant power, torque is falling hyperbolically.
This is what you can only coarsely approximate with switched gears and get more exactly with cvr gears.
And this hyperbola is quite closely resembled by the red torque curve between 1300 and 6000 rpm:
power close to constant, torque falling hyperbolically as with a cvr gear.

You can write speed below the rmp values at the abscissa,
calculated by gear ratio and wheel circumference.
higher gear rate scales the speed up to the right, lower scales down to the left.

So changing gear ratio does not much affect the performance at speed values as long as they remain in the area of constant power when scaling the speed axis.
While the motor may run at different rpm, motor torque changes at the inverse of ratio change, so wheel torque and thrust force remain constant.

It's only at the beginning (roughly below 1300, more exactly below 2600) and at the end of the diagram (above 6000 rpm) where this relation does not hold.
Easily visible as constant power, not so easily seen at the toque curve, since our eyes are not so well trained to asses hyperbolae.
Might add a constant power hyperbola to support visualisation to the chart.

 

[larsb]

You can off course choose gearing :wink:

Please calculate what torque you need with a gearing to reach 119km/h

Match that with the torque available over 6000rpm

Do they match —> can you assume that you will reach this rpm?

 

[wjr]

Please calculate what torque you need with a gearing to reach 119km/h

Ah, now I see where I lost precision in laying out my thought.
I want to go as fast as I can with the motor and controller at hand.
Think the call it "optimization".

From other people's experience and the power at hand, I'd expetct it to be somewhere around 100 km/h
I think this experience is somewhere condensed in some values and formulae, maybe quoted even in this thread, but I think precise numbers don't change the fact that it will remain estimations, anyway.
Just think of my personal body constitution, far beyond any standard value.... :lol:

So 120 km/h is "just somewhat" beyond the top speed I'd expect.
And 6200 rpm is "just somewhat" beyond the rpm where the motor seriously drops off power.

So the not yet known max speed is not too far below this point.
Having a larger safety margin at the top speed range would hamper performance at the low end - out in the dirts.
Having a lower safetey margin at the top speed might hamper the chance to find really the optimum in terms of speed.
In this tradeoff, I'd prefer for low speed dirt performance, but .....

Knowing people anyway gear it with sprockets they have (you gotta do what you can..)

this would require ratio of 1:6 and more, more data I think I can gain from real life test only, anyway.
So by following my restrictions what I can do with some ease, I shift my priorities a little bit.
I can live with that, as long as I'm not too far off target - at least for the first test.

Comparing the costs of misfit:
Switching from a 53T-bike-shop rear sprocked to custom milled insdustrial source sprockets I think is easier than to rebuild the setup and switch from 1-stage to 2-stage gear.

I hope my estimations are safe enough that I can correct misfit (to be expected) with sprockets, without major rebuilding.

 

[wjr]

One question left:
Looks like nobody yet reported experience with small 10T motor sprockets.
Reducing sprocket diameter increases chain force and so as well lateral load to motor bearing and motor shaft.

14T is shipped with the motor, so going down to 10 increases lateral force by 1.4
Can we assume this still to be safe?
Usually at this point, I'd look into the data sheet of the motor, but I haven't yet found such a thing

Any experience?
Any feedback from QS, if they follow this thread?

 

[eee291]

You lost me there, If you want a higher top speed you need to lower the gear ratio like 1:3 or 15T and 45T at the rear.
Of course this will decrease starting torque, but 25% less torque for this motor isn't that bad IMO.
Or do you need the best possible acceleration and speed?

 

[wjr]

to be honest, I do not NEED anything with regard to this project.
It's just a hobby fun project where I want to get aquainted with EV technology and look what comes out.

I know fork lifts with lead acid technology and closed source controllers, where the travel expenses of the serviceman are not much lower than the cost of the whole QS motor kit.
Talking to them revelals that they may know less about nuts'n bolts of motors and controllers than me, but they have access to this f'...reakin manufacturer's software, repair manual and service gadget.
Scrapped 3 of those the last couple of years for this reason.
Maybe could have saved them just by equipping them with curtis controllers.

I have a photovoltaic storage project in parallel with 22S10P LTO, so learning about planning and building a battery pack is one of the short time goals, too.

In the long run, I'd like the idea of small sized light weight farming machines.
I don't know whether I'll really spent time, effort and money to build such one.
But if I will ever do, I'll have to start somewhere. That's why I am here.

Back to topic:
Since the KL250 base is an Enduro and I want to postpone the issue of street legality, the primary focus is on torque and accel at lower speed - say 20 ...60kmh,
If I should gain street legality one time, then I might use it as a farm bike to check my fields.
Smooth behavior at 6... 20 km/h would gain importance then.
7 km commuting distance, most in town (or crossroad), does not impose special requirements.

For day long ride outs of 300...500 km I think EV is not really mature yet.

just take a look at the KTM freeride E-XC. That's the benchmark 8)

 

[wjr]

If you want a higher top speed you need to lower the gear ratio like 1:3

But imho this should not be necessary if the flux reduction charts are correct.
If flux reduction works as shown in the charts, you can safely increase the gear ratio in favour of low speed performance without sacrifying significant top speed performance.
I think that is what flux reduction is all about, isn't it?

Anyway, I think changing towards lower ratio's is not a big deal.
I've ordered 10T 11T 12T 13T in addition to the genuine 14T front sprockets.
The ali shop offers them up to 19T for 1,15€ each - just a question of delivery time.
The challenge I have to plan for ist at the slow end of high ratio.

 

[larsb]

Ah, now I see where I lost precision in laying out my thought.
I want to go as fast as I can with the motor and controller at hand.
Think the call it "optimization".

you’d still not get 6000rpm and that is what i pointed out. you need a lower gearing to still have some torque to drive with. Next time you can skip the theoretical lecture, that was not connected to reality.

 

[wjr]

.... skip the theoretical lecture, that was not connected to reality.

Agree.
I'll stop mulling over and over now and come back when I have somthing to report from reality.
Let's see then whether physics is where reality and theory come together, as it's supposed to be :wink:

 

[eee291]

Well qs does sell a 48V version
If you run it at 72V with Flux weakening you might get close to 6000 rpm under load

 

[larsb]

Do they? Where did you see it? That would give 50% higher theoretic top speed. Wouldn’t be too shabby mated with a 600A controller

 

[eee291]

https://www.alibaba.com/product-detail/QS-high-turque-V2-3000W-138_62087613940.html?spm=a2700.icbuShop.41413.12.49fb72bc9oOG6i

48V 60V and 72V versions are available 8)

 

[wjr]

That would give 50% higher theoretic top speed.

Could it be that I have missed the basic concept of IPM?
I thought they were synchronous motors, so the speed were 100.000 % correlated to the frequency as delivered by the controller.

As opposed to "ordinary" commutated DC-motors, where indeed overvoltage produces roughly proportional overspeed, since no load speed is maintained as equilibrium between internal electromotoric force (dynamo voltage generated by rpm) and external voltage applied.
And different again to asynchronous motors, where you have some slack between frequency applied and rpm, which may be reduced by overvoltage, but will not produce the same overspeed as with DC motors.

Please correct me if I'm wrong.

 

[larsb]

Yes, you missed it.

Geez, tone it down a bit, if you don’t know this then we hardly need a lecture about commutated motors.

 

[eee291]

I think you mean basic concept of Brushless motors but whatever nice troll.

 

[wjr]

... but whatever nice troll.

Thanks for the compliment
But please let you be assured that I'm not bothering you out of evil intention.
I know that I like to jump into unknown areas without founded knowledge, but I also know that usually I can manage a steep learning curve. I also know that quite often this annoys the professionals already in, so I please beg pardon for that.

But this is a public forum, isn't it, and is the process of teaching a cumbersome idiot like me not something others may benefit from as well :wink:

I see that the controller does the work of the brushes by applying proper field acoording to the speed and position of the rotor, which it gets from the hall sensors (or maybe other means, in other cases - but the QS 138 has hall sensors).
It MAY resemble the work of an ordinary brush set, but is not restricted to do so, OK?

I see that in the range below max power, usually at constant torque, the controller roughly resembles the behaviur of a classical commuted machine. So with larger voltage, it can offset larger counter-emf, and thus gain higher rpm speed and still stay in the max torque regime where some important vector angles are perpendicular. Even if it is a synchronous machine mechanically, it behaves like a commutated one as the motor-controller-system.
1:0 for you.

As I understand flux weakening, this regime is applied above max torque.
The timining of the field is shifted, as you would turn the brushes of a classical DC-machine - and maybe even more complicated - right?
Said vectors are no longer perpendicular.
So counter-emf is reduced, the possible equilibirum is shifted towards higher rpm.
Power still is limited by max phase current (which still generates heat, regardless of phase angle) and voltage.
Same power,more rpm, less torque.
But higher voltage, same current, still more power, as long as current is limiting.
OK, you're right again, I was wrong.
2:0 for you. Shame on my head

But as far as I got till now, thermal load by excessive current is not the only danger to the motor.
I quote the controller manual (yes, there is a different thread, I know, but i'd talk about the motor-controller as a system here):
"3.4.4.5 ...flux value exceeds the motor and controller parameter values, causing the motor to demagnetize and the controller to burn MOS"
I think burning MOS is still the effect of excessive current, right?
But that does not bother us if we connect a larger controller to our motor under scrutiny.
But what about demagnitizing the motor? Is it only a function of current?
I think it's more complex, since different fields are superimposing in the motor, and timiming becomes an issue.
And as opposed to thermal damage, which builds up slowly and may be controlled by thermal supervision, demagentizen, I'm afraid, occurs instantanously.
I'd like to rely on the designer then. Maybe somebody knowledgeable can recapitulate this considerations.
I surely cannot - can you?

So I come back to my point:
Can we rely on the charts from QS I posted?
How is the controller to be parametrized to achieve this performance?
I doubt that if it comes to flux weakening at the edges of the performance limit, playing with parameters is still the valid approach.

I'll promise not to argue on simple mechanical calculations then any more, OK

 

[larsb]

You’re still lecturing. I normally try to answer peoples questions but I’m out, hopefully someone else finds the patience to answer you - i won’t.

A good attitude goes a long way on a public forum.