full-throttle
1 MW
Are you going to experiment with delta and star termination as well?
Hmmm I have read about that somewhere. I though you would just see it in the controller...adrian_sm said:@Arlo1, But I am definitely seeing more heat in the motor at higher PWM frequency.
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 said:@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.
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 said: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.
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.
As long as Km is the same and they are the same size, there shouldn't be any difference.... in theory.....adrian_sm said: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.
Miles said: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)
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
Sure. I wrote that because there may well be variations in Km for different Kv versions of the same motor model/size.adrian_sm said:Really? This whole debate is about parasitic losses, which the motor constant doesn't take in to account.
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.
Best to use the reciprocal of Kv (in radians/sec) to calculate Km, or it gets inverted.adrian_sm said:Here is the data (if you believe the spec sheet) for the range of SK3 motor in the similar size.
Code: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
Unless you have the same Km, you'll need to deal with the resistive losses separately.adrian_sm said: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.
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 said: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.
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.Miles said:Best to use the reciprocal of Kv (in radians/sec) to calculate Km, or it gets inverted.
Miles said:Kt torque constant: Nm/A
Rm motor resistance (phase to phase): ohms
Km motor constant: Nm/√W
Km = Kt / √(Rm)
Miles said: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.
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 for spotting that!adrian_sm said: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.Miles said:Best to use the reciprocal of Kv (in radians/sec) to calculate Km, or it gets inverted.
It says:
Miles said:Kt torque constant: Nm/A
Rm motor resistance (phase to phase): ohms
Km motor constant: Nm/√W
Km = Kt / √(Rm)
Thanks Adrian.adrian_sm said:Here is the corrected data table for the motors:
Code: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
Not quite...Miles said:Interesting that Km consistently increases with Kt for each of the SK3 sizes.....
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
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.adrian_sm said: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.
Or lamentations over the losses....Arlo1 said:you always get some losses in the lamentations......
It only has an efficiency advantage at very high frequencies, though....Arlo1 said:I played with iron powder for a stator and can tell you its amazing!
Much more in the magnets themselves, though.Arlo1 said: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.