QS Motor Torque Wattage curve

[ebikeFan1234]

I have a Stealth Bomber bike with QS273 motor, 4KW, 2.5T nominal and 8 KW peak. Detailed specs here.
This is paired with 72v 40 ah battery, Savoton 150A controller, 21" moto wheels

I am looking at upgrades for a very fast acceleration from standstill, esp 0-30 mph. And top speed with solid power delivery till 55 mph
For reference I have ridden a Talaria MX4 Sting R and it's startup torque is mind blowing. Its so high that one has to be careful with throttle otherwise it would wheelie. See detailed specs here. It indicates a max torque on the wheels at startup of 45 nm x 8.35 (gear ratio) = 375 nm

On the other hand, the QS273 4KW motor specs indicate a torque of 30-200 nm. The peak of 200 is still almost half of Talaria
Stepping upto QS273 8 KW motor has max torque of 266 nm.

I have few questions

How can I improve my current bike's acceleration and make it similar to Talaria?
Currently is bike is very anemic from 0-15 mph range. Then the power delivery is pretty solid until 50 mph or so. How can I improve 0-15 mph performance?
The QS Motors have different turns like 2.5T, 3.5T, 4T, 5T etc. How do the turns affect the torque, is there a graph that someone can share?
When is the max torque produced?
I assume its when the current is max. My current controller can feed 150 A. Can I tweak the controller to feed that much amps at startup?
If I go to a smaller wheel like 19" from the current 21", will it increase torque by 21/19 = 10% approx?

 

[dominik h]

More phase current equals more tourque.
SVMC72150 does 350A phase current. Change to a Fardriver ND72680 with up to 680A phase current and you will nearly double your starting tourque.

My 180kg scooter with QS260 60V5000W and SVMC72150 350A phase current and 165A line current.


The same with a Fardriver ND72680 680A phase current and 280A line current.



The Sabvoton reaches his max line current at 40kph, from there on the phase current gets reduced.

The difference from 0-30kph is only from the higher phase current. I would definitiv go for more phase current, it is also the cheapest way.

The same scooter with QS273 10kw and Fardriver 721800 with 1400A phase current and 400A Battery current , picture Shows 0-100kph.

 

[DogDipstick]

I do not trust the specification of the fake clone QS website, you should use the SIA website to quote spec, not the reseller who only wants to make money.

The math for the wheel tork is very easy if you learn it. There is a kT ( tork per amp) for every motor and dia is easy to calculate for in imperial numbers from my experiences.

 

[DogDipstick]

When is the max torque produced? At 1RPm forward to rated RPm under a loading .

 

[DogDipstick]

QUESTION :

If I go to a smaller wheel like 19" from the current 21", will it increase torque by 21/19 = 10% approx?

REPLY:

YES.

 

[ebikeFan1234]

Thanks for the insights! What would be your recommendation for my goal - fastest acceleration in 0-55 mph zone.

Can I get more low-end torque out of the current QS 273 4KW 2.5T motor by tweaking the controller. The motor with the current settings feels anemic in 0-15 mph zone.

OR buy a new motor like QS273 4KW with 4T/5T

Here's a Youtuber who moved from 3.5 to 5T and says 5T is great for 0-25 mph acceleration and then it tapers off. After watching the video, perhaps 4T is a better fit for my needs

 

[E-HP]

The main things that limit acceleration off the line are insufficient phase current, voltage sag, and any ramping applied to the throttle. Unfortunately removing throttle ramping can make the bike unpleasant for daily riding.

Here's an example of how phase current is limited in system A (flat portion of the torque curve), vs. the motor getting sufficient phase current in system B (42% more acceleration off the line). The "anemic" range is between 0 to 15 mph in this example. Voltage sag and slow throttle ramping make it worse.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[ebikeFan1234]

Do suggest what should be my options. Eg, the 5T motor does have immense off the line acceleration, but loses steam above 25 mph

My current 2.5T is weak in 0-15 mph or so, and then it really picks up steam till 45 mph
Looking for best of both world experience

 

[DogDipstick]

OR buy a new motor like QS273 4KW with 4T/5T

Here's a Youtuber who moved from 3.5 to 5T and says 5T is great for 0-25 mph acceleration and then it tapers off. After watching the video, perhaps 4T is a better fit for my needs

Josh is a good friend of mine, his opinion is good. He broke his leg about two years ago on an ebike.

However, I think a larger controller and a stronger battery ( NOT round, 21700, or 18650 they will not work for powerful bike unless you have some 400+ cells in your pack) like a EV lipo cell battery from an OEm auto maker.

the definitive in my opinion is whether you reach the loaded RPM at the rated voltage under the riders weight... I reach 820RPm on my 72v system with a 4500w controller with a very powerful battery.. 19" wheel... the bike will flip you right over. From 2mph to 50mph you can pull the front up, 62mph max. hit full throttle up a hill at 50mph.. the bike is lifting the front wheel and tossing you off.

Do not bog, have tork. Do not lope the motor, get hot, never reach full RPm.... slow up hills, make bad heat in motor... .Do not " bog " the motor, if you do, your battery and controller is under powered. get better battery and try again.

I have a max of 200 phase amps with my controller ( 180A actually) ... It is 4500W kelly.

It is a buck boost converter, the controller, and takes voltage and makes lower voltage to sync with the speed o commutation... applied phase voltage is less, applied phase amps are more, in the trade.

Where ever there is loading the current will apply. the stronger the loading, the more current, until stall. Stall from locked rotor loading or loading stop the wheel ( wheel under braking when current applied is bad) . .

A 3T can be made very fast, ie 3-6sec to 60mph easy. Buy 1000$ controller and EV lipo battery so voltage never sags and the 3T will wake up. I have been told the 3T begins to be fun at 500 phase amps. Anything under that you might be disappoint.

 

[dominik h]

Cheapest way is ND72680.
Fastest will be QS273 8kw 3T or 4T and a ND721000 and a battery that can handle 400A

 

[ebikeFan1234]

To make this more objective, it would be great to have published numbers for 1/8 mile run, with metrics being 0-30 mph time, total time and top speed of the run. I have seen some Youtubers do that, esp for Talaria and Surron.

Back to the Bomber, changing the battery would be very intrusive option. I will be more inclined to change controller or motor, and approach it in a step by step manner.

I assume my bike has a Savoton 150A controller. How would Fardriver ND72680 controller make it better? I understand battery may be a limiting factor but I don't have detailed specs other than 72v, 40 ah

Would changing the motor to 4T (from 2.5T currently, 4 KW nominal, 8 KW peak) achieve a big portion of my goals? Everything else remaining unchanged

 

[E-HP]

I assume my bike has a Savoton 150A controller. How would Fardriver ND72680 controller make it better? I understand battery may be a limiting factor but I don't have detailed specs other than 72v, 40 ah

My guess is that the controller is the limiting factor right now, but if you upgrade to the Fardriver with higher phase amps, the battery will be the limiting factor.
Don’t discount the throttle ramping though. I did some 0-40mph testing last month, and forgot to remove the ramping, which made a 36% difference in elapsed time.

 

[ebikeFan1234]

That’s an interesting tip. On the MQCom app which setting(s) affect throttle ramping?

Also as a side note, I want to replace my half twist throttle with a full throttle. Can you point to such a product that will work with Savoton controller

 

[ebikeFan1234]

I have heard that smaller wheels lead to greater torque output in non-geared hub motors (like in Bomber). So people suggest going to 19 or 16 inch rims and gain 10-20% torque. is it as simple as that? from science/physics standpoint, it's the outer diameter (including tyre height) that matters right, vs inner diameter (=rim diameter). Can someone clarify pls?

 

[Gruesome]

Torque divided by lever arm length (from center of axle to the road) equals tractive force. E.g. 360 Nm / 0.36m = 1000 N.
Or 250 ft.lbs / 1 ft = 250 lbs forward force.
Force / mass (rider + bike) = acceleration. E.g. 1000 N / 200 kg = 5 m/s^2 = 0.5g (1 Newton is 1 kg m / s^2 ).

 

[ebikeFan1234]

So you are basically agreeing that it’s the outer diameter that matters. Smaller rim + thicker tyre can offset the torque benefits

 

[ebikeFan1234]

I did some 0-30 mph runs. The least I could get was 4.3 secs and Avg was around 5.5 secs. Does that sound about right for 2.5T motor?

For reference this YouTuber achieved 3s, his motor is 3.5T and similar battery as mine at 72v, 40 ah -

Also with talaria sting R I can consistently hit 3.5 secs

 

[E-HP]

I did some 0-30 mph runs. The least I could get was 4.3 secs and Avg was around 5.5 secs. Does that sound about right for 2.5T motor?

A bit sad. You have the wrong winding for what you’re trying to achieve.

 

[ebikeFan1234]

I am simply trying to understand whether those times are expected for 2.5T motor

And if I simply swap the motor to 3.5 or 4T, would 0-30 mph become 3.5 secs ballpark..

Basically checking if such performance data is available for these motors

On the mid drive bikes like Surron and talaria, such data is readily available

 

[E-HP]

Who knows. I haven't seen the specs on your battery, nor whether or not you've maxxed out your phase amps to 350W on your controller.

For choosing a motor, just determine what top speed you'd like, without field weakening, and use that to determine the winding with the most turns that still gets you to that top speed. For acceleration, besides phase amps, the weight of bike and rider is important info.

Not your motor, but in this made up example, assuming you've maxxed out your phase amps to 350W, simulating a 2.5T vs 4T winding, to show the difference in the torque curves, and what potentially is happening due to battery/controller limitations by using such a fast wind. The darker blue torque curve represents the fast wind. You can see the flat spot in the 0-7mph range where even 350A of phase current isn't sufficient for this motor, so it butts up against the current limit. If in this example you had sufficient phase current, the curve would be smooth, up to something like 230nm, just eyeballing it. That might get you the launch to get closer to your goal, but I wouldn't count on it, based on the numbers you mentioned. You don't have the controller, and might not have the battery, to get to your goal with that winding.

It's pretty obvious why the 4T would accelerate much faster, given the area between the 2.5T and 4T torque curves up to around 23 mph. After that the 2.5T starts to quickly catch up. Still, a 35% advantage off the line makes a big difference, so you don't bog down when launching. If you have that flat spot in the torque curve, you need to get rid of it so you can launch with some authority. In this example, the 2.5T hits the 350A phase current limit at launch, but the 4T is only hits 293pA.

If you play around with the Grin simulator, you can get a feel for how wheel size, voltage, battery and phase currents, windings, weight, etc. interact and impact power/torque/speed, etc.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

I thought I saw a post recently with the Kv ratings of various QS motors. Plugging in the actual Kv's should help you make more informed decisions, or maybe detect whether you have a battery or controller limitation.

 

[ebikeFan1234]

Thanks @E-HP, such an insightful analysis and the type of stuff I was looking for. The torque and power curves say a lot. 2.5T has such a wide power band and area under the curve is high. 4T has narrower band and great for strong launches.

It will likely take me couple of days to have a shop inspect the bike and examine the battery&controller specs. It's so rare to find a local person who can service these bikes. Btw, if any of you in Seattle area, let me know

 

[ebikeFan1234]

Don’t discount the throttle ramping though. I did some 0-40mph testing last month, and forgot to remove the ramping, which made a 36% difference in elapsed time.

Please share how throttling ramping can be tweaked using MQCon app for Sabvoton 72150

 

[Elios.pk]

Please share how throttling ramping can be tweaked using MQCon app for Sabvoton 72150

If you have space (and money of course), I strongly recommand a fardriver controller. MQCON fells slow and the app isn't very advanced for any deep tuning to maximise performance. My only experience is with a SVMC7245 but I don't think such a parameter exist if not the throttle delay in ms (put it in the lowest value possible at 10ms)

 

[DingusMcGee]

Good luck with all the ebike simulators in the world.

If you want the QS 2000 & QS 3000 & QS 4000 varieties of mid-drive motors to perform MAXX you will have to have a controller that lets you change some PID settings. On a Fardriver 9 …. SERIES controllers(not the racing series) the default PID setting group is Heavy Duty Motor. These motors will run some what better by upping the default Heavy Duty Motor setting to the Super Duty Motogroup. Within the Super Duty Motor category are 4 PID’s you can change but you will have to experiment to see if any of these changes help performance better than what are true default settings of the group as there are no suggestions.

The QS1000 mid drive motor will not run on the setting groups Super Duty Motor nor Heavy Duty Motor but runs quite well on the next lower default group. It is no sleaze — i have put 138 amps to it and no burn outs.

The Lightening Rods standard mid drive motor(maybe comparable to the QS1000) will need lower PID setting than the QS 1000 just to run. On this setting it does start quite well. But it will never be a Super Duty Motor at least with Fardrivers Controller Settings.

another point: adjusting for optimal performance is very much motor/ controller specific & further tuning will help for bike & rider plus task.


I do have QS3000 mid drive motor mounted on a Specialized Big Hit home made edirtbike at 90 lbs with some groups of LiPO 20 AmpH batteries giving a max discharge of 480 amp with the group options of 18 cells, 24 cells or 27 cells. The motor can gobble the current if you are able stay with it.

When edirtbike riding the QS3000 on rocky steep single track I switch the PID Setting to the Heavy Duty Motor group.

But if say 130 lbs Taluria powered Sur Ron bike with the rider wanting to race came along I would switch to Super Duty Performance and likely wave BYE-BYE..,…

For you boneheads—these simulators do not simulate what PID settings you use.