My QS205 runs circles around a QS273!

kebekua

kebekua

100 mW
Joined
Jan 18, 2016
Messages
44
I read that in a group a few years ago and thought that was quite a laughable statement.

I have both motors. I cooked a 205 at 30KW while the 273 happily handles 42KW and hardly gets warm. The maximum torque of the 273 surpasses that of the 205 by far, there’s no question about it.

However I recently acquired a Votol EM150S and tested it on both my rides. Same voltage, same settings. The 205 actually does run circles around the 273 when paired to that particular controller. The 205 sucks 300A battery amps from a dead start while the 273 only draws 180A at low RPM. Both motors draw 300A battery at higher RPM. I suspect phase resistance detection during the auto-learn procedure could cause the controller to set a different power delivery curve.

Anyone here has a better guess? Or, even better, actual usable knowledge about the matter?

My contact at the Votol factory is completely useless even for the simplest questions.
 
That’s interesting 🤔

Some questions just to clear out some possible contributors to differences not related to the motors:
Do you really outrun the 273 or is it mainly that you see different battery currents?

How are the battery currents measured? Asking since it’s not so easy to get correct peak measurements, a measured peak over 100ms compared to 500ms can give different numbers with same actual current. if it’s stable during a second or two measured with same tool then it’s more likely to be correct.

Is it the same battery that was used? I guess not since two different rides, are they matched in performance?

Same internal resistance and current capacity for these batteries (otherwise battery sagging might introduce a difference)?

Is it the same measurement tool for the current?

What are the kV’s and phase to phase resistances of the motors you compare?

Is there really an autodetection for the Votols? (I never used or saw one)
 
The Votol can´t handle the low inductance from the QS273
 
I wouldn’t think any hub motor to have low inductance in a way that causes problems for the controller, so many coils and a lot of steel. I could be wrong, that’s why this thread is interesting. knowing the winding helps of course.
 
Yes, the 205 actually has a lot more kick from the get go. Pops big wheelies. No wheely with the 273, far from it.
At higher speed I can't tell the difference.

Peak battery amps are measured using an analog Ammeter and readings are consistent with the BMS readings. I'm sure the measurements are correct, there's a huge dfference in battery amp draw at low RPM.

https://www.youtube.com/watch?v=Ij7dNrBuqR8

Same battery, but voltage sag is bigger with the 205 because it draws more amps!

Votol has auto tune, yes.

Windings are 3,23T for the 273 and 3T for the 205
 
If they pull that much difference in power at the same speeds, it's a significant difference in motor kV.

Do you have a power supply and dmm to measure the phase resistance?
 
Yeah. I measured it a while back, the phase resistance is substancially higher on the 205 than it is on the 273. I have a milliohmmeter. I forgot the exact numbers.

KV's are the same or almost the same, 14 rpm per volt.

I don't see how that would make a difference at 0RPM. The controller limits the max amp draw, not the motor.

It's the first time I get vastly different readings with different motors, same controller same battery.

The torque and speed output is different of course, but the input should be the same. In this particular case, it isn't.
 
I’m still interested in answers to the questions i had - if you could answer them?

Electrical time constant decides the transient response when voltage is applied, this is = Armature inductance/Armature resistance so if root cause would be the controller struggling with current control, therefore limiting current then the inductance of the 273 must be a lot lower than the 205. If you have the tools to measure the phase resistance and inductance then that will be really interesting to see.
 
I don't have tools to measure inductance.
Phase resistance is around 7 milliohm for the 273, more than twice that for the 205. I can try and measure again but neither resistance or inductance is dependent on RPM as far as I know of. Even if they are, I can only get a reading when the motor is stopped with my current equipment.
 
kebekua said:
I don't have tools to measure inductance.
Click to expand...
I still think the same "Lighter motor = faster motor" all other things considered, in my simple mind... I do not understand the differences in torque output based on stator dia... Measurement of magnetic flux,.... or things of the like....

I think the inductance is measured in numbers such as pico Henry? Something to do with the ripple current in the ESC? ( Ripple = "NOISE"... ? )

https://en.wikipedia.org/wiki/Henry_(unit)

I do not know for certain though, but i think a 205 should be in the order of 140 picohenry ( good) or even 120 pico henry (better?)

I do not know much of such things, but this is an interesting debate. If anyone wishes to tell us the importance here, i will listen intently.

larsb said:
Electrical time constant decides the transient response when voltage is applied, this is = Armature inductance/Armature resistance
Click to expand...

Thankyou Larsb very informative post.

More reading.. for myself here. Perhaps someone will tell us the nature of how inductance ( "change?") affects a motors current distributions. ( textbook def: "the tendency of an electrical conductor to oppose a change in the electric current flowing through it")... and/or how that is enumerated in these " Henry" things in electronics.

https://www.thesnellgroup.com/featured-tips/the-importance-of-measuring-inductance

https://www.celeramotion.com/applimotion/support/technical-papers/achieving-optimal-motion-system-performance-with-low-inductance-motors/
 
kebekua said:
I don't have tools to measure inductance.
Phase resistance is around 7 milliohm for the 273, more than twice that for the 205. I can try and measure again but neither resistance or inductance is dependent on RPM as far as I know of. Even if they are, I can only get a reading when the motor is stopped with my current equipment.
Click to expand...

OK then, one can only dream sometimes :wink:
Inductance is constant with rpm but it varies some with rotor position. I normally take an average over all three phase pairs (that works well as input on my sensorless controller so i think it’s a good way)
 
As I said in the original post, there isn't a single doubt a QS273 outruns a QS205 all day everyday.

Only when matched with a controller such as the EM150 can the 205 outrun a 273.

The controller output isn't the same for both motors, that's why.

If it was the same, with similar KV, the 273 would perform as well or better than the 205.
 
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