Worlds Worst Dyno - Version 2

[full-throttle]

Are you going to experiment with delta and star termination as well?

 

[Arlo1]

@Arlo1, But I am definitely seeing more heat in the motor at higher PWM frequency.

Hmmm I have read about that somewhere. I though you would just see it in the controller...
I think this is where code and algorithms will really make a difference.

 

[adrian_sm]

@f-t. No. Not right now. I am restricting myself to using unmodified motors.

@Arlo1. Unfortunately I am also restriction myself to stock and available controllers.

 

[Arlo1]

@f-t. No. Not right now. I am restricting myself to using unmodified motors.

@Arlo1. Unfortunately I am also restriction myself to stock and available controllers.

No this is a good thing. What you have works. What im working on works but needs me to get it finished. I want to be able to compare data with you and see what you find. Its awesome you can do what you are this is great data!

 

[adrian_sm]

Anything in particular you are interested in?

I am not taking all the data I could, as everything is manually recorded at the moment, so I may miss something you are interested in.

 

[Arlo1]

Anything in particular you are interested in?

I am not taking all the data I could, as everything is manually recorded at the moment, so I may miss something you are interested in.

Ill take what ever you can show. Data is not easy to gather I have had little time gathering data but when things are not blowing up I love it. I test and test and test it takes a lot of time/patience to get good data! Keep up the great work.

 

[adrian_sm]

Cool. Will do.

Oh BTW Arlo have you stumbled across Sahne Colton's ESC work? Sounds like he is an undergrad at MIT or something. Some really interesting hardware and firmware development. Open source too, if you can dig through his blog.
http://scolton.blogspot.com.au/p/motor-controllers.html

If I was going to roll my own ESC, this would definitely be a starting point for me. Thought you might find it interesting.

 

[adrian_sm]

Speaking of Shane Colton. His 2008 thesis on 'Design and Prototyping Methods for Brushless Motors
and Motor Control' helped me understand Field Orientated Control, and why it is needed.

p.28.

Openloop phase advance is one possible way to accommodate for the affect of inductance: Simply placing voltage ahead of the q-axis by some angle (which could be a function of other motor
parameters, measured or known) could offset most, if not all, of the angle lost to inductance. However, any solution based on open-loop phase advance would be motor-specific. Fieldoriented control seeks a more flexible solution based on real-time current measurements.

So for my application where I am trying to optimise things for a single setup of motor/ESC/voltage I might be able to safely get away with just tweaking the timing advance.

 

[Miles]

The interesting question in my head is: does compensating with voltage for a different kV motor have any impact on waste heat across the full speed range.

As long as Km is the same and they are the same size, there shouldn't be any difference.... in theory.....

 

[adrian_sm]

Really? This whole debate is about parasitic losses, which the motor constant doesn't take in to account.

Ref: https://www.endless-sphere.com/forums/viewtopic.php?f=30&t=45489&p=663660#p663606

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)

Here is the data (if you believe the spec sheet) for the range of SK3 motor in the similar size.

	                Kv	 Rm	   Km
SK3 - 6374-149kv	149	0.021	1028
SK3 - 6364-190kv	190	0.028	1135
SK3 - 6354-215kv	215	0.032	1202
SK3 - 6374-168kv	168	0.019	1219
SK3 - 6364-213kv	213	0.023	1404
SK3 - 6354-245kv	245	0.028	1464
SK3 - 6374-192kv	192	0.016	1518
SK3 - 6354-260kv	260	0.023	1714
SK3 - 6364-245kv	245	0.018	1826

 

[Miles]

Really? This whole debate is about parasitic losses, which the motor constant doesn't take in to account.

Sure. I wrote that because there may well be variations in Km for different Kv versions of the same motor model/size.

With the same magnets and iron. How could the parasitic losses vary?

 

[adrian_sm]

Guess that is what we are trying to find out. But it appears that the parasitic losses are influenced by the PWM frequency from the tests I have conducted. So it stands to reason that different motors with different fill factors, inductance and resistance, will behave differently to the PWM induced current ripple.

Are the eddy current losses only in the magnets, back iron and stator iron? Could they be in the copper as well? I saw reference to that in Shane Coltons thesis. p.56.

In many cases, it is beneficial to use multiple strands of smaller wire in parallel. This makes the wire easier to wind and reduces eddy current losses.

But as you can see from my table above the Km for the different winds are wildly different. So what does that tell us about the parasitic losses for the motors as they will be running at different voltages/currents to achieve the same output torque at the same speed.

 

[Miles]

Here is the data (if you believe the spec sheet) for the range of SK3 motor in the similar size.

	                Kv	 Rm	   Km
SK3 - 6374-149kv	149	0.021	1028
SK3 - 6364-190kv	190	0.028	1135
SK3 - 6354-215kv	215	0.032	1202
SK3 - 6374-168kv	168	0.019	1219
SK3 - 6364-213kv	213	0.023	1404
SK3 - 6354-245kv	245	0.028	1464
SK3 - 6374-192kv	192	0.016	1518
SK3 - 6354-260kv	260	0.023	1714
SK3 - 6364-245kv	245	0.018	1826

Best to use the reciprocal of Kv (in radians/sec) to calculate Km, or it gets inverted.

 

[Miles]

But as you can see from my table above the Km for the different winds are wildly different. So what does that tell us about the parasitic losses for the motors as they will be running at different voltages/currents to achieve the same output torque at the same speed.

Unless you have the same Km, you'll need to deal with the resistive losses separately.

 

[Miles]

Are the eddy current losses only in the magnets, back iron and stator iron? Could they be in the copper as well? I saw reference to that in Shane Coltons thesis. p.56.

In many cases, it is beneficial to use multiple strands of smaller wire in parallel. This makes the wire easier to wind and reduces eddy current losses.

Yes, there'll be some eddy currents in the copper from the stray field and also skin-effect variations with different gauges of wire.

 

[adrian_sm]

Best to use the reciprocal of Kv (in radians/sec) to calculate Km, or it gets inverted.

Ah. Thanks for the correction. You might want to correct the error I followed in the equation defining Km in this post I previsoul referenced.
It says:

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

Where it should be (as correctly stated here):

Motor Terminology
The Sphere is international, we use SI units.
Kv - velocity (speed) constant, expressed in (rad/s)/V or RPM/V [not to be confused with kV, kilovolt].
Kt - torque constant, expressed in Nm/A
Km - motor constant, (Nm/A)/√watts or (Nm/A)/√(Rm) [also, confusingly, used with the same meaning as Kt]
Ke - voltage constant, V/(rad/s) or V/kRPM.
Rm - motor resistance, in ohms, measured phase to phase.

Here is the corrected data table for the motors:

	             	Kv	 Kv	   Kt	   Rm	   Km
	                RPM/V (rad/s)/V Nm/A  Ohms	
SK3 - 6354-245kv	245	25.66	0.039	0.028	0.2329
SK3 - 6354-260kv	260	27.23	0.037	0.023	0.2422
SK3 - 6354-215kv	215	22.51	0.044	0.032	0.2483
SK3 - 6364-245kv	245	25.66	0.039	0.018	0.2905
SK3 - 6364-213kv	213	22.31	0.045	0.023	0.2956
SK3 - 6364-190kv	190	19.90	0.050	0.028	0.3004
SK3 - 6374-192kv	192	20.11	0.050	0.016	0.3932
SK3 - 6374-168kv	168	17.59	0.057	0.019	0.4124
SK3 - 6374-149kv	149	15.60	0.064	0.021	0.4423
C80 100 - 180	   180	18.85	0.053	0.017	0.4069

 

[Miles]

Best to use the reciprocal of Kv (in radians/sec) to calculate Km, or it gets inverted.

Ah. Thanks for the correction. You might want to correct the error I followed in the equation defining Km in this post I previsoul referenced.
It says:

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

Thanks for spotting that!

 

[Miles]

Here is the corrected data table for the motors:

	             	Kv	 Kv	   Kt	   Rm	   Km
	                RPM/V (rad/s)/V Nm/A  Ohms	
SK3 - 6354-245kv	245	25.66	0.039	0.028	0.2329
SK3 - 6354-260kv	260	27.23	0.037	0.023	0.2422
SK3 - 6354-215kv	215	22.51	0.044	0.032	0.2483
SK3 - 6364-245kv	245	25.66	0.039	0.018	0.2905
SK3 - 6364-213kv	213	22.31	0.045	0.023	0.2956
SK3 - 6364-190kv	190	19.90	0.050	0.028	0.3004
SK3 - 6374-192kv	192	20.11	0.050	0.016	0.3932
SK3 - 6374-168kv	168	17.59	0.057	0.019	0.4124
SK3 - 6374-149kv	149	15.60	0.064	0.021	0.4423
C80 100 - 180	   180	18.85	0.053	0.017	0.4069

Thanks Adrian.

Interesting that Km consistently increases with Kt for each of the SK3 sizes.....

 

[Miles]

Interesting that Km consistently increases with Kt for each of the SK3 sizes.....

Not quite...

 

[Miles]

I've added the values for weight and specific Km

                     Kv     Kv       Kt       Rm       Km     Wt   Sp.Km
                    RPM/V (rad/s)/V Nm/A     Ohms    
SK3 - 6354-245kv    245    25.66    0.039    0.028    0.2329  489  0.4763
SK3 - 6354-260kv    260    27.23    0.037    0.023    0.2422  489  0.4953
SK3 - 6354-215kv    215    22.51    0.044    0.032    0.2483  485  0.5120  
SK3 - 6364-245kv    245    25.66    0.039    0.018    0.2905  718  0.4046
SK3 - 6364-213kv    213    22.31    0.045    0.023    0.2956  706  0.4187
SK3 - 6364-190kv    190    19.90    0.050    0.028    0.3004  697  0.4310
SK3 - 6374-192kv    192    20.11    0.050    0.016    0.3932  858  0.4583
SK3 - 6374-168kv    168    17.59    0.057    0.019    0.4124  840  0.4910  
SK3 - 6374-149kv    149    15.60    0.064    0.021    0.4423  840  0.5266
C80 100 – 180       180    18.85    0.053    0.017    0.4069

 

[Arlo1]

Cool. Will do.

Oh BTW Arlo have you stumbled across Sahne Colton's ESC work? Sounds like he is an undergrad at MIT or something. Some really interesting hardware and firmware development. Open source too, if you can dig through his blog.
http://scolton.blogspot.com.au/p/motor-controllers.html

If I was going to roll my own ESC, this would definitely be a starting point for me. Thought you might find it interesting.

Yes I think he is one of the top people I learn from. Very cool stuff and I thank him very much for posting as much as he did online.

 

[Miles]

Don't forget this, too: http://endless-sphere.com/forums/viewtopic.php?p=236417#p236417

 

[Arlo1]

Eddy current losses can be in anything that is on the right axis. So if your magnet is spinning on a x axis then any piece of electrically conductive material on the same angle to the magnet will have eddy losses the thinner is is (lamination's) the lower the losses. The copper is on this axis but is thin and also lower down the stator tooth and off to the side so the losses are probably not in the copper. If you look at the axial flux motors like the one lebowski made and some of the wind generator guys you will see if the cooper is on the same path as the magnet and close enough it will add some losses so you will see most of the wind generator guys take precautions to keep the end turns away from the magnet path. So no matter what you always get some losses in the lamentations but the thinner they are the lower it is. I played with iron powder for a stator and can tell you its amazing! Now I don't know but I figure there might be a bit of losses from the magnetism the stator produces and the eddy current in the part of the can or rotor where the magnets are held.

 

[Miles]

you always get some losses in the lamentations......

Or lamentations over the losses....

 

[Miles]

I played with iron powder for a stator and can tell you its amazing!

It only has an efficiency advantage at very high frequencies, though....

Now I don't know but I figure there might be a bit of losses from the magnetism the stator produces and the eddy current in the part of the can or rotor where the magnets are held.

Much more in the magnets themselves, though.