Motor comparison spreadsheet

Electric Motors and Controllers
Punx0r
10 GW
10 GW
Posts: 4246
Joined: May 03, 2012 8:16 am
Location: England

Re: Motor comparison spreadsheet

Post by Punx0r » Jan 15, 2016 2:13 pm

Crossbreak, that's interesting info regarding tooth root strength utilisation in standard car gearboxes, but I think extrapolating this to "three times manufacturer's torque rating will be OK" is over simplifying it. Drag strips are littered with broken gearboxes from cars running nowhere near 3X standard power ;) Either the teeth fracture or the gearbox casing breaks from the radial bearing load resulting from the repulsive forces of the gear pair.

Shock loads from taking up drivetrain backlash are apparently a big problem for manual transmission cars. Electric drive could offer a simple solution by building in a torque ramp. I have a gut feeling that only 50ms or less from zero to full torque would be sufficient :)

User avatar
Arlo1
100 GW
100 GW
Posts: 8485
Joined: Apr 26, 2009 10:36 pm
Location: Nanaimo BC Canada
Contact:

Re: Motor comparison spreadsheet

Post by Arlo1 » Jan 15, 2016 2:21 pm

Punx0r wrote:Crossbreak, that's interesting info regarding tooth root strength utilisation in standard car gearboxes, but I think extrapolating this to "three times manufacturer's torque rating will be OK" is over simplifying it. Drag strips are littered with broken gearboxes from cars running nowhere near 3X standard power ;) Either the teeth fracture or the gearbox casing breaks from the radial bearing load resulting from the repulsive forces of the gear pair.

Shock loads from taking up drivetrain backlash are apparently a big problem for manual transmission cars. Electric drive could offer a simple solution by building in a torque ramp. I have a gut feeling that only 50ms or less from zero to full torque would be sufficient :)
I have personally seen trannys take more then 3x the HP But where I come from you up the power till something fails then you fix that and up the power more.

I was with luke at speed factory HQ about 6 years ago and we saw a oem honda 5 speed with a custom billet end housing that was there to take the stress of the gears trying to push it apart, and at the time they were flashing 1400hp on the dyno and running mid 8s
My Leaf motor controller build. https://endless-sphere.com/forums/viewto ... 27#p963227
My YSR build http://www.youtube.com/watch?v=BRo8r5g4NBg
RC and most types of Lithium batteries you MUST know your individual cell voltages charging and discharging.
Don't keep them were you cant afford smoke or fire!
Never above 4.2v never below 2.7v EVER!!!
HI power controller design. Game Changer

User avatar
speedmd
100 MW
100 MW
Posts: 2748
Joined: Nov 14, 2012 12:16 pm
Location: new england

Re: Motor comparison spreadsheet

Post by speedmd » Jan 15, 2016 2:26 pm

crossbreak wrote:
speedmd wrote:Better stator iron (higher T) is key limiting factor to max current?
yep, using Vacoflux50 or Hyperco50 Permendur alloys, you can reach 2.3 Tesla http://www.vacuumschmelze.com/fileadmin ... -004_e.pdf
That alloy is almost a third more flux capability than the standard motor steel. Huge upgrade. Wonder what is in the stock leaf motor.


User avatar
speedmd
100 MW
100 MW
Posts: 2748
Joined: Nov 14, 2012 12:16 pm
Location: new england

Re: Motor comparison spreadsheet

Post by speedmd » Jan 15, 2016 2:56 pm

If so, Arlo could go from 1800 amps max to better than 2400 amps with the better core steel! :shock: Nitrous for EV's


John in CR
100 GW
100 GW
Posts: 13760
Joined: May 20, 2008 12:58 am
Location: Paradise

Re: Motor comparison spreadsheet

Post by John in CR » Jan 16, 2016 1:33 am

crossbreak wrote:the 1800A figure is pulled out of thin air, but yes
PFTA is the acronym for that, Pulled From Thin Air.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 18, 2016 2:25 pm

Finally a break-through: Wikipedia now has the same Km definition as we call it Km². I propose we all agree on that definition and forget about the Nm/√W story. Sadly big companies like alliedmotion still use that faulty definition :oops:

What do you think? I think there should be just one Motor Size Constant. The old definition of Km was faulty. The "corrected" Km² figure i came up with got rid of that fault. I think it's time to stick to this common and correct definition
Edit: All wrong too :lol: :lol:
https://en.wikipedia.org/wiki/Motor_constants
Attachments
2016-01-18 20_14_43-Motor constants - Wikipedia, the free encyclopedia - Iron.png
2016-01-18 20_14_43-Motor constants - Wikipedia, the free encyclopedia - Iron.png (22.81 KiB) Viewed 918 times
Last edited by crossbreak on Jan 18, 2016 7:06 pm, edited 1 time in total.

John in CR
100 GW
100 GW
Posts: 13760
Joined: May 20, 2008 12:58 am
Location: Paradise

Re: Motor comparison spreadsheet

Post by John in CR » Jan 18, 2016 5:01 pm

Nm per Watt of copper loss is a useful number, but that's not what Km2 in the spreadsheet boils down to, is it?

Hillhater
100 GW
100 GW
Posts: 8329
Joined: Aug 03, 2010 10:33 pm
Location: Sydney ..(Hilly part !) .. Australia/ Down under !

Re: Motor comparison spreadsheet

Post by Hillhater » Jan 18, 2016 6:07 pm

crossbreak wrote:Finally a break-through: Wikipedia now has the same Km definition as we call it Km². I propose we all agree on that definition and forget about the Nm/√W story.

I am curious as to who has recently changed the Wiki definition ?
This forum owes its existence to Justin of ebikes.ca

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 18, 2016 7:34 pm

it wasn't me, as i saw it i just made it a look a bit nicer (more links and references). Think it was NOrbeck https://en.wikipedia.org/wiki/User:NOrbeck Still this article is a bit messy. Checked on some of the references, they appear to not so very good.
John in CR wrote:Nm per Watt of copper loss is a useful number, but that's not what Km2 in the spreadsheet boils down to, is it?
Sure, as i pointed out so many times, it is Torque² per Watt of copper loss.

Edit: I just saw it's defined faulty too. It must be (Nm)²/W, not Nm/W :oops: too early happy... look like i still have to do a lot persuasion
crossbreak wrote:This motor constant shall be expressed by the SI Units N²m²/W, since resistive power loss "P" is not dependent on current (or torque) linearly, but quadratically.
P = I²R (resistive loss)
Torque "T" and armature current "I" are proportional to each other. This is expressed by the Torque constant Kt. Back EMF Force (or Voltage) constant "Ke" in [Vs/rad] or Torque constant "Kt" in [Nm/A], as it is both the same.
T= Kt * I
Some manufactures specify the motor torque constant as Nm/√W
But this is wrong, too as i can show you by a little example.
Imagine a machine that has a Ke = Kt of 1 Nm/A and a terminal resistance "R" of 1 Ω.
At 1Nm it pulls an armature current of 1A. It’s resistave power loss is I²R=(1A)² x 1 Ω = 1W
At 10Nm it is 100W as it pulls 100A armature current respectively

A motor that is double the stack oft the above one, would hat a Kt of 2, as Back EMF would be doubled, too. Resistance would be doubled, too, as conductor length was doubled. So the resistance of this machine is 2 Ω.
Everything is double the motor oft he first one. So we should expect a Km figure that is double the Km figure of he first machine.
By definition Km =T²/P=Kt²/R = 2²/2= 2 this is the case. With the other definitions if have seen, this is not the case.
For example Kt/R = 2/2 which equals one. Makes absolutely no sense.
Or Kt/√R = 2/√2 which equals 1.41. Better, but still not near a figure of 2.
Last edited by crossbreak on Jan 18, 2016 8:15 pm, edited 1 time in total.

John in CR
100 GW
100 GW
Posts: 13760
Joined: May 20, 2008 12:58 am
Location: Paradise

Re: Motor comparison spreadsheet

Post by John in CR » Jan 18, 2016 8:06 pm

crossbreak wrote:Edit: I just saw it's defined faulty too. It must be (Nm)²/W, not Nm/W
Why does the definition have to be faulty? Let's come up with a route to that number instead of the Km squared thing, or to me similarly flawed Km. I've been pondering a simple torque/resistance constant, which would be similarly useful as torque/watt of loss. Another would be to normalize the torque constant in terms of Kv, and then all I need is resistance no-load losses, and physical dimensions to get all I need to know about a motor.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 18, 2016 8:14 pm

John in CR wrote:Why does the definition have to be faulty?
it may not be faulty. It must be scientifically precise. Which those both definitions:

Km= T/P and T/√P are not.

The only valid definition is

Km= T²/P

A constant you want, torque/watt of loss, T/P does not exist. It can not exist, as P_loss = I²R but not IR. It's the ohmic law. Accept it or not

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 18, 2016 8:22 pm

this valid constant definition Km = T²/P still is as useful as you want it: resistive loss can directly be derived:

For example, Km= 10 N²m²/W and torque demand is T= 100 Nm

P = T²/Km = (100Nm)²/(10 N²m²/W)= 1000W

both miles and me are happy with that definition. see absolutely no reason to change anything.
John in CR wrote: Another would be to normalize the torque constant in terms of Kv
This does not work either, since Kt = 60 / (2π*Kv). It's basically the same

It would be nice to relate eddy and hyst. torque to Km. A motor that has double Km may have double eddy and hyst. torque, thus it would have the same efficiency as the smaller one. Still we wont come around these 3 figures to compare motors, as there are 3 basic characteristics that describe them in terms of efficiency. If we look at windage loss, too, then it will be even 4

John in CR
100 GW
100 GW
Posts: 13760
Joined: May 20, 2008 12:58 am
Location: Paradise

Re: Motor comparison spreadsheet

Post by John in CR » Jan 18, 2016 10:35 pm

crossbreak wrote:both miles and me are happy with that definition. see absolutely no reason to change anything.
The only reason would be if we came up with something better for comparing motors. Isn't it obvious by the results that Km and Km2 aren't all that useful? I guess when push comes to shove the real number is efficiency, so maybe we could add some value by expanding it somehow beyond just peak efficiency at a given voltage.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 19, 2016 1:39 am

Isn't it obvious by the results that Km and Km2 aren't all that useful?
i dont see the point. lifeforphysics and you ride about this Km figure. It is not valid to compare motors just by this figure for sure. There is no "one figure" that you can compare every motor to every other one, and this can never exist, as there is no way to pack all 5 valuable aspects into one single figure.

the only way to get it down to two basic figures is: ignoring the rest + only talk about specific figures to merge them with weight. I proposed a way to merge hyst. and eddy torque: Treat them 1:1, which gives you an efficiency number at some "random" (in my eyes a reasonable) rpm. Have you ever looked at the rpm that come out of this 1:1 thing? Most times it is a perfect match with "nominal" rpm. It's the best way i see. This way you get a power figure and an efficiency figure to compare. As you can see, the more expensive designs gain significantly higher figures than the cheap motors, no matter if it is inrunner or outrunner. What more can we ask for?

the only other way i see to get it down to two is: completely ignore eddy current torque. just compare Km and hyst torque. Still not as reasonable as this 1:1 thing IMO. A significant value is left out: The ability to spin fast and get a high power out with reasonable power loss (heat-out). Seems like we have to live with comparing 3 figures or stick to this 1:1 hyst./eddy torque story. Or even compare all 5, as there is weight and heat sinking ability, too. There is no easy way to compare apples and oranges. Both fruit, but the apple never becomes as juicy.

My proposal on a "rank": Make it specific power at 1:1 eddy/hyst. torque. Efficiency is very high for the top members anyway, otherwise they would not gain such a great specific power figure

Rank1: Nissan Leaf @ 1904W/kg @ 97% @ 7325 rpm @ 178Nm
Rank2: HubMonster @ 1612 W/kg @ 95% @ 1459rpm @ 61.4Nm
Rank3: MidMonster @ 962 W/kg @ 94% 1080 rpm @ 33Nm
Rank4: Joby JM1S @ 624 W/kg @ 92% @ 1621 rpm @ 5Nm
Rank5: Astro 3220 @ 495 W/kg @ 92% @ 9000rpm @ 3Nm

just to give an example, i played around a bit with figures, so they may be off at some point. Still it gives you an example i think

this is very unfair for the old joby though. it is designed so it has quite some eddy current torque, so the 1:1 calced rpm is very low. They lowered eddy current torque significantly for the newer revision ( i heard the use .12mm lams now), so i think these values are not correct. The joby should be rank 2 actually.

sadly we have WAY too many holes to plug! We need many many more motors to compare, more precisely measured no load figures. This only the community can achieve as a whole

Punx0r
10 GW
10 GW
Posts: 4246
Joined: May 03, 2012 8:16 am
Location: England

Re: Motor comparison spreadsheet

Post by Punx0r » Jan 19, 2016 4:29 am

I think Crossbreak is right: Km is a useful comparison, but only for comparable motors (e.g. very useful for comparing industrial induction motors of a certain frame size). The motors we wish to compare are much more varied in size and construction, hence the other variables mentioned. It's good to gather data for motors and compare them, though. There may be a good constant or just rule-of-thumb that reveals itself as a decent guide to compare motors based on basic characteristics.

John in CR
100 GW
100 GW
Posts: 13760
Joined: May 20, 2008 12:58 am
Location: Paradise

Re: Motor comparison spreadsheet

Post by John in CR » Jan 19, 2016 9:26 am

Useful in certain circumstances makes sense.

I misspoke before about the Kv/Kt combination. What I should have said was to put resistance on a level playing field in terms of Kv to make it directly comparable between motors.

The spreadsheet is great and we really need to get it populated with all the motors used, and especially including the often missing no-load measurements to get core loss info and efficiency.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 19, 2016 12:46 pm

What I should have said was to put resistance on a level playing field in terms of Kv to make it directly comparable between motors.
that's easy, just try it. you will see, that the figures derived are anti proportional to Km :D Just the same thing in green. If you level all resistance figures to 1Kt, values should be exact reciprocal of Km i think.

Edit: I just tried it. It's works. The thing you aim for is 1/Km, we could call it "normalized terminal resistance", normalized to Kt=1 (or Kv=9.55)

User avatar
speedmd
100 MW
100 MW
Posts: 2748
Joined: Nov 14, 2012 12:16 pm
Location: new england

Re: Motor comparison spreadsheet

Post by speedmd » Jan 20, 2016 12:00 am

Both copper losses and iron losses will most likely vary in their respective loss curve slope when pushed either direction from the nominal rpm based on some design configurations will they not. Some may show lower iron losses / behave better with field weakening and be better choices to run high rpm (thinner lamination's comes to mind). Others motor designs may be better (more efficient) electrically at driving high torque to near stall conditions (more copper, stronger magnets, more poles..etc?). Interested if / what may be some of the other factors effecting the slope of the loss curves if any and how these slopes can best be quantified in the motors for comparison.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 20, 2016 4:32 pm

this should show in an individual core loss diagram. The 1:1 point is at much lower rpm for a hub motor then it is for an RC motor
Attachments
core loss - hub motor.png
core loss - hub motor.png (26.24 KiB) Viewed 798 times

User avatar
speedmd
100 MW
100 MW
Posts: 2748
Joined: Nov 14, 2012 12:16 pm
Location: new england

Re: Motor comparison spreadsheet

Post by speedmd » Jan 20, 2016 9:22 pm

Thanks crossbreak for posting the explanation. Was not expecting a straight line hysteresis loss curve. Found another chart that was more what I was expecting. Straight lines would be easy to compare slopes. http://www.infolytica.com/en/applications/ex0146/ Image
Last edited by speedmd on Jan 20, 2016 9:28 pm, edited 1 time in total.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 20, 2016 9:28 pm

think that one is wrong. link?

field loss (=rotor loss for BLDC) is insignificant. what we talk about here is armature loss (=stator or core loss for BLDC) mostly. maybe this chart is meant for a brushed-DC machine, where stator=field and rotor=armature (exact opposite of a BLDC)

even if your chart is about rotor loss in a BLDC alone (which is almost insignificant, as said before), i'd expect the hysteresis loss to rise linearly with rpm

the only online reference i found quickly was this: http://www.electricaltechnology.org/201 ... ormer.html
here it is stated that hyst loss is related to frequency (hence rpm) and eddy current is relate to frequency² (hence rpm²)

but i can dig out some books for sure that state the same, just too lazy to get up from my desk :)

User avatar
speedmd
100 MW
100 MW
Posts: 2748
Joined: Nov 14, 2012 12:16 pm
Location: new england

Re: Motor comparison spreadsheet

Post by speedmd » Jan 21, 2016 11:59 am

Just so I am understanding the two losses correctly, the hysteresis losses are from the irons magnetic pole direction switching in both the stator and rotor core steel and the eddy current losses are those currents induced from magnets passing by the stator's copper coiled steel teeth. Would not these eddy's in turn induce further hysteresis losses on their own and cause somewhat a small curve in the hysteresis loss plot. Thinking this may be small in the normal RPM range, but significant when pushed to high RPM's.

User avatar
crossbreak
100 MW
100 MW
Posts: 2818
Joined: Aug 02, 2011 11:20 am
Location: Germany
Contact:

Re: Motor comparison spreadsheet

Post by crossbreak » Jan 21, 2016 5:13 pm

So you think that eddy currents create flux? Yep, that should be the case. Guess that the influence is very small and it thus it becomes a part of the calced eddy current loss or rpm² dependent loss.

Post Reply