Motor comparison spreadsheet

Electric Motors and Controllers
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Miles
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Motor comparison spreadsheet

Post by Miles » Thu Jan 01, 2015 12:10 pm

Developed from the ideas discussed in this thread:
https://endless-sphere.com/forums/vi ... 23#p980223

All columns are in protected mode, apart from the columns with white background ("speed" and "torque output" columns), but no password is needed to remove the protection.

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Miles
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Re: Motor comparison spreadsheet

Post by Miles » Thu Jan 01, 2015 12:10 pm

Source - Reference for the source of the data inputted, be it personal testing or publicly available data.

Motor - Reference for the specific motor, including the number of winding turns, if known.

Slot - Number of slots or teeth. For most brushless motors this number will be divisible by three.

Pole - Number of magnet poles. This is usually the same as the number of magnets but sometimes a magnet pole will be segmented and contain two or more magnets of the same polarity. The segmentation can be circumferentially or axially, or both. In all cases the number of magnet poles will be divisible by two.

Gap - Diameter of the airgap between the stator and the rotor, measured at the middle of the gap. If you know the dimensions of the stator it's usually accurate enough to add 1mm to the outer diameter for outrunners or subtract 1mm from the the inner diameter for inrunners.

Stck - Stack height or length of the laminated core.

Gap A - The area of the airgap in square centimeters, calculated from the figures in the previous two columns.

Mass - Mass or weight of the motor in kilograms.

T.B.C.

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Re: Motor comparison spreadsheet

Post by Miles » Thu Jan 01, 2015 12:10 pm

Res.

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Re: Motor comparison spreadsheet

Post by teslanv » Thu Jan 01, 2015 12:47 pm

subscribed.
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Re: Motor comparison spreadsheet

Post by Miles » Sat Jan 03, 2015 6:14 am

Do you think it would be useful to have a column for peak efficiency at the chosen speed?

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Re: Motor comparison spreadsheet

Post by John in CR » Sat Jan 03, 2015 1:14 pm

Miles wrote:Do you think it would be useful to have a column for peak efficiency at the chosen speed?
Sure, but include the power too so it has more meaning.

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Re: Motor comparison spreadsheet

Post by Miles » Sat Jan 03, 2015 1:57 pm

Will do that.

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Re: Motor comparison spreadsheet

Post by John in CR » Sun Jan 04, 2015 11:50 am

Miles, I was looking at your motor's phase resistance. Is that correct? If so, are you sure you're not skimping too much on the copper to obtain such low iron losses. It seems like the end result will be extremely high efficiency at cruise with very low cogging, so you'll barely feel the motor if pedaling unpowered and regen braking can be part of the equation, which are great criteria. The compromise is increased losses during acceleration or the sustained loads of hills or strong headwinds, when higher current is required.

What peak power input are you planning? Based the rpm numbers, it looks like a 74V pack, so does that mean single digit current limits?

An approach that intrigues me for a European or Australian street legal ebike is one capable of efficiently delivering full legal limit power even at very low rpm and the controller limiting it to legal power across its operating range.

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Re: Motor comparison spreadsheet

Post by Miles » Sun Jan 04, 2015 1:03 pm

John in CR wrote:Miles, I was looking at your motor's phase resistance. Is that correct? If so, are you sure you're not skimping too much on the copper to obtain such low iron losses. It seems like the end result will be extremely high efficiency at cruise with very low cogging, so you'll barely feel the motor if pedaling unpowered and regen braking can be part of the equation, which are great criteria. The compromise is increased losses during acceleration or the sustained loads of hills or strong headwinds, when higher current is required.
Hi John,

The phase resistance can only be interpreted in the context of the torque constant..... Of course it's only a simulation but note that my design has the highest specific Km of all the motors on the chart, so far. Which is precisely what I was aiming for :)

I did quite a lot of experimentation varying the loading of the electrical circuit against that of the magnetic circuit and I think I'm pretty much where I want to be with that.

Running it at 2400 rpm, which is the intended speed for this iteration, the efficiency is 94% for 1355 Watts output and the peak efficiency is 95.4% for 680 Watts output.

If I wanted to run it at 6000 rpm, the iron losses would still be manageable.

NB Just to be absolutely clear, the figure in the sheet should be the phase to phase resistance not the phase resistance.

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Re: Motor comparison spreadsheet

Post by Miles » Sun Jan 04, 2015 1:23 pm

John in CR wrote:An approach that intrigues me for a European or Australian street legal ebike is one capable of efficiently delivering full legal limit power even at very low rpm and the controller limiting it to legal power across its operating range.
It's a reasonable idea but I'm not sure it would pass the testing criteria..... The European power limit is for continuous power capability. So, what limit would you set?

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Re: Motor comparison spreadsheet

Post by John in CR » Sun Jan 04, 2015 1:41 pm

Miles wrote:
John in CR wrote:An approach that intrigues me for a European or Australian street legal ebike is one capable of efficiently delivering full legal limit power even at very low rpm and the controller limiting it to legal power across its operating range.
It's a reasonable idea but I'm not sure it would pass the testing criteria..... The European power limit is for continuous power capability. So, what limit would you set?
Whatever the law said, and hopefully it's continuous power out, not power in. It would require something different in the way of controller, but the legal power limit at something like 10-20rpm would be tremendous hill climbing torque.

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Re: Motor comparison spreadsheet

Post by John in CR » Sun Jan 04, 2015 2:29 pm

Miles wrote:
John in CR wrote:Miles, I was looking at your motor's phase resistance. Is that correct? If so, are you sure you're not skimping too much on the copper to obtain such low iron losses. It seems like the end result will be extremely high efficiency at cruise with very low cogging, so you'll barely feel the motor if pedaling unpowered and regen braking can be part of the equation, which are great criteria. The compromise is increased losses during acceleration or the sustained loads of hills or strong headwinds, when higher current is required.
Hi John,

The phase resistance can only be interpreted in the context of the torque constant..... Of course it's only a simulation but note that my design has the highest specific Km of all the motors on the chart, so far. Which is precisely what I was aiming for :)

I did quite a lot of experimentation varying the loading of the electrical circuit against that of the magnetic circuit and I think I'm pretty much where I want to be with that.

Running it at 2400 rpm, which is the intended speed for this iteration, the efficiency is 94% for 1355 Watts output and the peak efficiency is 95.4% for 680 Watts output.

If I wanted to run it at 6000 rpm, the iron losses would still be manageable.
Ah ok, at 20A it still looks great. The .166 ohms just took me by surprise, but you could always wind it for a Kv of 70rpm/v if you wanted to run higher power. Then the copper resistance is much more comparable to the Joby.

It will be interesting as we get a big population for your spreadsheet. We'll see different ways to skin the cat. To me efficiency is the "great equalizer" much more than Km, because it makes motors of all types and sizes comparable. I do love those super low iron losses that resulted from you targeting Km though. I want ridiculous power, but don't want to give up silence, so that means a bigger motor to keep the rpm down and very low resistance.
Miles wrote:NB Just to be absolutely clear, the figure in the sheet should be the phase to phase resistance not the phase resistance.
Yes, of course phase-to-phase.

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Re: Motor comparison spreadsheet

Post by amberwolf » Sun Jan 04, 2015 11:02 pm

Even though they are discussed in the linked threads in the OP, it might be useful to have a post in this thread with the specific step-by-step instructions to measure what's needed for each column of data about a new motor to be added to the spreadsheet (for anything that isn't calculated by the spreadsheet from other columns).

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Re: Motor comparison spreadsheet

Post by Miles » Mon Jan 05, 2015 1:05 am

Sure, I was planning to do this amber - that was the reason for reserving the subsequent posts. I'll try to make a start this evening.

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Re: Motor comparison spreadsheet

Post by amberwolf » Mon Jan 05, 2015 1:47 am

Ah, ok. :) It'd certainly help people like me that get lost in long threads :oops: cuz I'd like to try to help by measuring any functional motors I happen to have around here.

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Re: Motor comparison spreadsheet

Post by cycborg » Mon Jan 05, 2015 8:46 am

amberwolf wrote:Even though they are discussed in the linked threads in the OP, it might be useful to have a post in this thread with the specific step-by-step instructions to measure what's needed for each column of data about a new motor to be added to the spreadsheet (for anything that isn't calculated by the spreadsheet from other columns).
Looking forward to Miles' writeup, but in the meantime Justin describes the basic measurements and calculations here:
1) Put a known current through a pair of phase wires and measure the voltage with a multimeter.
2) Measure RPM and no load amperage at full throttle at one voltage V1
3) Measure RPM and no load amperage at full throttle at another voltage V2
Kudos to Miles for putting this all in one place; this will be a great resource.

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Re: Motor comparison spreadsheet

Post by teslanv » Tue Mar 17, 2015 11:58 am

I have confirmed via inspection and testing on the MXUS 3000W Motors as follows:

21X3T Winding:
12.02 Kv
0.796 Kt (Nm/A)
0.072 Ohms resistance (Measured from end of base phase wire, (~1 meter Lead to Motor axle)
Weight (Bare Hub Motor): 9.0 Kg
Km (per Miles' Database Formula): 2.965

16X4T Winding:
8.9 Kv
1.073 Kt (Nm/A)
0.112 Ohms resistance (Measured from end of base phase wire, (~1 meter Lead to Motor axle)
No-Load Current at 50.2V: 0.6A, 447 RPM
Weight (Bare Hub Motor): 9.0 Kg
Km (per Miles' Database Formula): 3.206

12X5T Winding:
7.2 Kv
1.335 Kt (Nm/A)
0.170 Ohms resistance (Measured from end of base phase wire, (~1 meter Lead to Motor axle)
Weight (Bare Hub Motor): 9.0 Kg
Km (per Miles' Database Formula): 3.239

On the 3T Winding which I upgraded the Phase Wires, I have the following:

21X3T Winding:
12.02 Kv
0.796 Kt (Nm/A)
0.060 Ohms resistance (Measured from end of base phase wire, (~0.5 meter Lead to Motor axle)
Weight (Bare Hub Motor): 9.0 Kg
Km (per Miles' Database Formula): 3.248
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Re: Motor comparison spreadsheet

Post by crossbreak » Wed Jun 03, 2015 9:55 pm

Km constant is an interesting thing to compare torque production capability. A reduction drive does not reduce Rm but it increases Kt (as it reduces Kv). So Km get a lot larger (if a 10:1 reduction is used for example). sKm is Km/mass (specific Km). this value may stay the same (or could even be reduced), as a reduction gearbox increases over all weight

we could easily expand this spreadsheet with sKm values from existing drives! pure benchmark?!
Last edited by crossbreak on Thu Jun 04, 2015 8:31 am, edited 1 time in total.

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Re: Motor comparison spreadsheet

Post by Miles » Thu Jun 04, 2015 4:49 am

Sure. In practice, we are doing this already when geared hubs are used for comparison.

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Re: Motor comparison spreadsheet

Post by Lebowski » Thu Jun 04, 2015 7:34 am

Miles wrote:Sure. In practice, we are doing this already when geared hubs are used for comparison.
long time no Miles ?

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Re: Motor comparison spreadsheet

Post by Miles » Thu Jun 04, 2015 7:57 am

It's true. I haven't been very active on the forum this year.... Hope to start the first motor build soon, though :)


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Re: Motor comparison spreadsheet

Post by John in CR » Thu Jun 04, 2015 8:58 am

crossbreak wrote:we need a value for parasitic loss. like [Watts/rpm²]
We already have that...no-load current X voltage. The current is so low that copper losses are negligible, leaving just the parasitic losses. Measure the bare motor, and then again with wheel or gearing to get those parasitic losses at a given rpm.

Mile's spreadsheet goes further and computes the torque side of core losses.
Last edited by John in CR on Thu Jun 04, 2015 2:47 pm, edited 1 time in total.

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Re: Motor comparison spreadsheet

Post by marcexec » Thu Jun 04, 2015 10:08 am

Awesome idea. Just added a few minor details on the 80-100 and attached it.

I'd actually like to extend this to the physical dimensions and manufacturer specs similar to http://www.diyelectriccar.com/forums/sh ... #post61212 and put it into the wiki.

The table should maybe be an overview only, including the link to a detailed "motor fact sheet".
I don't want to derail this thread from the very detailed info here on the technology, so I started a new thread:
https://endless-sphere.com/forums/viewto ... 30&t=69970

your input would be very welcome
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Re: Motor comparison spreadsheet

Post by crossbreak » Thu Jun 04, 2015 6:01 pm

strange data. no load current should rise linearly, shouldn't it? It's all parasitic loss. which should rise with the square of rpm. So both no load voltage and current shall rise with rpm, doesn't they?

In the data given, no load current rises less than linearly
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