Comparing motor specifications

Turnigy RotoMax 150cc Size Brushless Outrunner Motor
4.8 Nm/kg
Kv 150 rpm/V
Kt 0.064 Nm/A
Rm 0.011 Ohms
Wt 2.530 kg
Km 0.61 Nm/✓W
Specific Km 0.24 (Nm/✓W)/kg

Turnigy RotoMax 100cc Size Brushless Outrunner Motor
4.7 Nm/kg
Kv 167 rpm/V
Kt 0.057 Nm/A
Rm 0.021 ohms
Wt 2.074 kg
Km 0.39 Nm/✓W
Specific Km 0.19 (Nm/✓W)/kg

Turnigy RotoMax 80cc Size Brushless Outrunner Motor
3.8 Nm/kg
Kv 195 rpm/V
Kt 0.049 Nm/A
Rm 0.013 ohm
Wt 1.916 kg
Km 0.43 Nm/✓W
Specific Km 0.22 (Nm/✓W)/kg

Turnigy RotoMax 50cc Size Brushless Outrunner Motor
6 Nm/kg
Kv 172 rpm/V
Kt 0.056 Nm/A
Rm 0.021 ohm
Wt 1.080 kg
Km 0.38 Nm/✓W
Specific Km 0.35 (Nm/✓W)/kg

http://www.hobbyking.com/hobbyking/store/__18184__Turnigy_Aerodrive_SK3_6374_149kv_Brushless_Outrunner_Motor.html
5.3 Nm/kg

http://www.hobbyking.com/hobbyking/store/__17364__Scorpion_S_5030_220kv_F3A_Special_Brushless_Outrunner_Motor.html
5.0 Nm/kg

http://www.hobbyking.com/hobbyking/store/__17985__Turnigy_RotoMax_1_40_Brushless_Outrunner_Motor.html
4.4 Nm/kg

http://www.hobbyking.com/hobbyking/store/__17986__Turnigy_RotoMax_1_60_Brushless_Outrunner_Motor.html
3.9 Nm/kg

http://www.hobbyking.com/hobbyking/store/__17401__Scorpion_HK_5035_500_Brushless_Outrunner_Motor.html
3.4 Nm/kg

http://www.hobbyking.com/hobbyking/store/__19040__Turnigy_G160_Brushless_Outrunner_290kv_160_Glow_.html
4.0 Nm/kg
Km 0.22 Nm/✓W
Specific Km 0.35 (Nm/✓W)/kg


C80 100 - 180
Kv 180 rpm/V
Kt 0.053 Nm / A
Rm 0.017 ohms
Wt 1.81 kg
Km 0.407 Nm/✓W
Specific Km 0.22 (Nm/✓W)/kg

Scorpion S-5545
Kv 150 rpm/V
Kt 0.0637 Nm/A
Rm 0.03 ohms
Wt 1.026 Kg
Km 0.37 Nm/✓W
Specific Km 0.36 (Nm/✓W)/kg

Astro 3210 8t Wye
2.7 Nm/kg
Kv 169 rpm/V
Kt 0.0565 Nm/A
Rm 0.08 ohms
Wt 1.0 kg
Km 0.2 Nm/✓W

[NB Specific torque based on claimed max amps figures]

The reason for using specific torque values and the specific motor constant to compare motors is that it levels the field. You can see how a motor compares with others on the basis of its effectiveness in turning electrical power into mechanical power. The motor constant doesn't account for parasitic losses, though...

Kt torque constant: Nm/A
Rm motor resistance (phase to phase): ohms
Km motor constant: Nm/√W
Km = Kt / √(Rm)

Specific torque: Nm/kg
= Kt * max. cont. amp rating / weight

NB: http://www.control.com/thread/1026217558


Looks like the RotoMax 50cc is in the lead, so far....

OK, now...explain this to me..I am being a lazy bastard and not doing any research, having only ridden and built hub motor bikes.

How would you use these on an e-bike...mid drive or friction drive I guess...but what type of controller. I believe RC ones are no use for e-bikes, so what controller? they do not have hall sensors, and i believe I read they cant be used with normal sensor less controllers..so how would you drive one of these?

If you're looking for a plug and play solution, you should come back in a years time.

Miles said:

Looks like the RotoMax 50cc is in the lead, so far....

Click to expand...

By which metric anyway; weight to power ratio?

5300 watts is pretty respectable; however this is probably an exaggerated figure, no?

120A ( max current ) x 42v ( 10S pack fully charged ) = 5040w.

Maybe continuous current is half ( 60A? ), thus 2520 would be the continuous wattage? still damn good for an eBike, if that can get you up to 40mph / 64kph or beyond.

It'd be spinning at 7224RPM, 80% loaded figure would be 5779.2RPM..

A dual reduction drive system w/a 1:3 + 1:4 reduction would get you a nice 37mph / 60km-hr on a 26" wheel, or go with two 1:3 reduction stages and ya got 49mph / 79km-hr on a 26" wheel.


As far as a controller goes .... yeeeaaahh, about that :lol:

http://endless-sphere.com/forums/viewtopic.php?f=31&t=31961

Burtie made these optical hall sensor boards for the turnigy 80 and astro motors.

I think the RC motor craze has died down lately though, i remember when everyone and their grandma had an RC powered bike. Then we got big hub motors, and suddenly it seemed like things died down.

Miles said:

If you're looking for a plug and play solution, you should come back in a years time.

Click to expand...

Ummm no not at all. If you have seen any of my posts regarding .....well anything.. you will see I don't do plug and Play. Just want to know a bit about this sort of motor and how they can be used for e-vehicles..actually thinking a small kick scooter, that I keep trashing the Brushed DC motors on...they don't like 1500 W at 50 volts


Like I said waht controller how do you run them at a controlled rate on a bike or scooter?

neptronix said:

http://endless-sphere.com/forums/viewtopic.php?f=31&t=31961

Burtie made these optical hall sensor boards for the turnigy 80 and astro motors.

I think the RC motor craze has died down lately though, i remember when everyone and their grandma had an RC powered bike. Then we got big hub motors, and suddenly it seemed like things died down.

Click to expand...

Ah...I see, cheers

I had not come across this before,.. So add a hall sensor system to one and then run with normal controller.. Neat

The reason for using specific torque values and the specific motor constant to compare motors is that it levels the field. You can see how a motor compares with others on the basis of its effectiveness in turning electrical power into mechanical power. The motor constant doesn't account for parasitic losses, though...

Kt torque constant: Nm/A
Rm motor resistance (phase to phase): ohms
Km motor constant: Nm/√W
Km = Kt / √(Rm)

Specific torque: Nm/kg
= Kt * max. cont. amp rating / weight

N.B. http://www.control.com/thread/1026217558

A Practical Use Of The Motor Constant KM
An Aid In The Selection Of
DC Motors Or Generators
In Power Limited Or Efficiency Sensitive Applications.
George A. Beauchemin
MicroMo Electronics, Inc.

Good stuff Miles. Is there any way to predict where saturation starts from these parameters? To me it's one of the most useful bits of info, and more useful than peak current and torque. Other than the data posted by Justin about saturation for a 7 turn 9C, I've never seen it and I've only been able to guess at it thru experimentation.

John in CR said:

Is there any way to predict where saturation starts from these parameters?

Click to expand...

I'm afraid not.

Turnigy RotoMax 150cc
4.8 Nm/kg----Sp. Km 0.24

Turnigy RotoMax 100cc
4.7 Nm/kg----Sp. Km 0.19

Turnigy RotoMax 80cc
3.8 Nm/kg----Sp. Km 0.22

Turnigy RotoMax 50cc
6.0 Nm/kg----Sp. Km 0.35

Turnigy G160
4.0 Nm/kg----Sp. Km 0.35

Turnigy C80 100
Specific Km 0.22

Astro 3210
2.6 Nm/kg----Sp. Km 0.20

Scorpion S-5030
3.0 Nm/kg----Sp. Km 0.43

Since some of the hubbies I have are closer to RC outrunners than typical hubmotors I want to try to compare them to the data you gathered. I don't understand what "✓W" means. Also, how should I handle a 24 slot motor wound as 6 phase and terminated as two 3 phase motors on alternating teeth? It's essentially 2 separate motors in one, so how do I handle the phase to phase resistance?

John

John in CR said:

I don't understand what "✓W" means. John

Click to expand...

It's normally the square root of the rotational speed, W, in rads/S, where 1 rad/S = 57.2958 degs/S or about 377 rpm.

Jeremy Harris said:

It's normally the square root of the rotational speed, W, in rads/S, where 1 rad/S = 57.2958 degs/S or about 377 rpm.

Click to expand...

Which shows what a minefield motor terminology is. In this case, as it's upper case, it was meant to stand for Watts. It would have been better if I hadn't made the abbreviation.....

John,

All you need to know is that Km is a measure of the relationship between torque and the heat generated to achieve it.

Take your torque constant (Nm/A) and divide that by the square root of the phase to phase resistance (Rm).

Km = (Nm/A) / ✓(Rm)

If you want to compare motors relatively, divide Km by the motor weight in kilograms to get "specific Km".

Miles said:

Jeremy Harris said:

It's normally the square root of the rotational speed, W, in rads/S, where 1 rad/S = 57.2958 degs/S or about 377 rpm.

Click to expand...

Which shows what a minefield motor terminology is. In this case, as it's upper case, it was meant to stand for Watts. It would have been better if I hadn't made the abbreviation.....

Click to expand...

The problem, I suppose, is that it's not always that easy to enter Greek characters like ω into ES posts, and we're not always consistent about using normal characters as substitutes. Mind you, it would have helped if I'd have realised John was referring to a post earlier in the thread, rather than asking a general question!

Jeremy,

I've started a new thread on motor terminology: http://endless-sphere.com/forums/viewtopic.php?f=30&t=45840

Please comment if you think anything there is adding to the confusion!

For comparison:

GNG Gen1
Wt 2.63kg
Km 0.53 Nm/√W
Specific Km 0.20 (Nm/√W)/kg

Astro 3210
Wt 1.0 kg
Km 0.20 Nm/√W
Specific Km 0.20 (Nm/√W)/kg

Turnigy C80 100 - 180
Wt 1.81 kg
Km 0.41 Nm/√W
Specific Km 0.22 (Nm/√W)/kg

Turnigy RotoMax 150
Wt 2.53 kg
Km 0.61 Nm/√W
Specific Km 0.24 (Nm/√W)/kg

Joby JM1S
Wt 1.8kg
Km 0.83 Nm/√W
Specific Km 0.46 (Nm/√W)/kg

Miles said:

Jeremy Harris said:

It's normally the square root of the rotational speed, W, in rads/S, where 1 rad/S = 57.2958 degs/S or about 377 rpm.

Click to expand...

Which shows what a minefield motor terminology is. In this case, as it's upper case, it was meant to stand for Watts. It would have been better if I hadn't made the abbreviation.....

Click to expand...

what would be a possible usefully agreement is to use [] around the letter when it is a unit of measure like this: [W]

John in CR said:

Good stuff Miles. Is there any way to predict where saturation starts from these parameters? To me it's one of the most useful bits of info, and more useful than peak current and torque. Other than the data posted by Justin about saturation for a 7 turn 9C, I've never seen it and I've only been able to guess at it thru experimentation.

Click to expand...

yes, id like to know where saturation starts with these motors, so how should i test for it?

so far i thought up a wild plan to drive one (by the lathe) with all 3 phases shorted starting at low rpm, measuring NM and working my way up
in rpm, and torque, and even measure phase currents, and eventually get to a point (saturation) where the revs go up but the measured torque and phase current level off. -well it didnt work, i only got to about 4NM )with a ca120 that i know is ok to 20NM+) and it then starts to DROP with extra revs, till you can double the revs and the torque drops to 2NM and the motor begins to turn more and more freely..
-dunno about you guys, but with all 3 phases shorted, i would not expect a free spinning motor. :? -so im all ears on this..

otherwise ill have to put hundreds of amps into a static rotor, measure NM at lots of points like justin did, this needs quite a good 300a+ power supply for these motors.

toolman2 said:

otherwise ill have to put hundreds of amps into a static rotor, measure NM at lots of points like justin did, this needs quite a good 300a+ power supply for these motors.

Click to expand...

Or there might be a tendency to spot, even if saturation level currents are not available. I wish someone with a dyno would have a go at the C80-100.

toolman:
Calculation -- if you happen to know your turn count + wire guage + stack heighth, you may be able to suss out a field strength per amp [Tesla] through modelling/geometry? Your silicon steel will saturate around 1.4 Tesla.

measuring saturation -- "officially" a straight ahead motor dyno curve would show this (if run to high enough power -- which is rare), as the power out flattens out, and amps begin to skyrocket (i.e. efficiency plumets, heat runs away). It's a "knee", and not a hard wall, so it's somewhat subjective, when to say "it's saturating".

That said -- if you have a wound stator available, and some form of field measurement (Gaussmeter -- the missing ingredient), you are golden. Run DC through 2 phases, stator only (rotor absent), and measure field coming out of the center of one active pole. True/Actual magnitude is not important -- as much as seeing value grow with increasing amps . . until it doesn't. Once amps are climbing, and field intensity is not -- you're beginning saturation. For a low resistance/inductance motor -- this may be huge amps indeed; watch coil temp.

Miles ~
(from the text) "This method may not get you to exactly the
correct “house” but it will put you on the correct “street”."

I've seen two approaches to Km in this thread/paper, "defined as" :

Km =: Kt / (R)^.5

but also:

Km = T / (Pin-Pout)^.5 where T may be written Kt * A . . and (Pin-Pout) may as well be called "loss"


Taking real data from my motor offering: http://endless-sphere.com/forums/viewtopic.php?f=31&t=44058
these two approaches give results differing by a factor of almost 2!

Kt = 9.5 Nm / 60 A = 0.158 (taken at actual max continuous operating point)
kg = 4.91
Rm = .03 ohm (phase-phase) (Bigmoose measured .04, my simulation shows 0.0285 . . . 10 mOhm can be tough to distinguish)

Km = Kt/(R)^.5 = .158/.173 = .9 --> (Spec Km = 0.9 / 4.91 = .183)

or

Km = 9.5 Nm / (3060-2686)^.5 = 9.5 / 19.34 = 0.491 --> (Spec Km = 0.491 / 4.91 = 0.1)

FWIW, the second approach (sqrt of loss) is based on a "required/specified" efficiency, and this equation is meant to define a minimum acceptable Km . .
Problems -- there's lots of room for magnitude of error in R . . .also -- Kt is never perfect, but changing by as much as 20% with load conditions.

I think ANY approach based solely on manufacturers (let alone distributors) stated specs will be lacking, as there is often a 'game' of "specsmanship" and plain old BS (or ignorance) with most motors on the market. It's sad to me that the RC community has accepted this specsmanship in their field, and act like a 2-4kg motor can be called 8-10 kW. It's nonsense, physics won't support it . . .

I would love for a simple 'normalizing' approach like this to work, and compare across motor platforms, but it will always be unfortunately limited by the BS advertised specs.

Solution -- only a real curve (+thermal conditions/duty cycle) can demonstrate real performance. That's why RC manufacturers/distributors don't provide them. (happy to be proven wrong, please post/point me to same)