RC-Monster Forums - Efficiency of Lehner motors

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- - Efficiency of Lehner motors (https://www.rc-monster.com/forum/showthread.php?t=5589)

Quote:

Originally Posted by Serum

I have got no idea what you mean.

To create motor profile you need motor constants. Motor constants can be measured or calculated, last one requires a lot of input parameters. But most motor manufactures specify motor constants, which they obtain from testing, while during design phase they use calculation to figure out how to create one with parameters they type into model.

To create graphs you need motor Kv, I no load, I max, Resistance. To create more sophisticated graphs you need to add inductance, inertia and core parameters. But for RC applications the first 4 constants will do the job of defining efficiency, power, torque and current draw.

As reference you can check any motor manufacture datasheets for motors or even Lehner excel spreadsheet where you can click on cell and check for math behind. I was trying to bring all motor data under one roof :)

But here is the question; you say lehner date is calculated? because this is not the case, it's real measured data.

Quote:

Originally Posted by Serum

But here is the question; you say lehner date is calculated? because this is not the case, it's real measured data.

I was reffering to this document

I don't know artur.

They claim it's measured. I thought dafni told it was done with a prop. why is the current changing, as well as the voltage? It would be easier of it was used as a set parameter.

And can you explain the large dip in efficiency with this one;

http://www.lehner-motoren.com/diagra....s26_liste.txt

Quote:

Originally Posted by Serum

Because with RPM BackEMF comes to play and in addition to active resistance come reactive from inductance (capacity plays as well). Then you can add core hysteresis and eddy currents. Not even touching ESC efficiency which you use to dyno test motor.

When you add timing to equation it becomes tricky, in general with timing set at zero (my program default, adjustable in future) efficiency of the motor has linear relation factor (in calculation) with motor RPM, when you change timing you pushing this relation to be less linear across entire RPM but to be higher in the mostly used range. That is why you see a big dip in efficiency when you get out of tuned efficiency envelope.

Nice theory, but since they also included the Delta and the Wye windings, it would make the calculations far more complicated than you are describing. PLUS they DO use timing in their numbers. This STILL doesn't explain why they don't use a set number of voltage. (this is variable as well) I know one reason why this number would be variable, but it simple makes no sense to 'assume' a resistance of a battery, since this is variable as well..

And now we are getting deeper into it; why are brushless motorcans not made from plastic? aluminum is magnetic active when there is a magnetic rotor is turning in it. (even a U, or an unclosed piece of aluminum has this 'problem') I think plastic motorcans would help making a brushless motor even more efficient.

but here is the big q;

What makes you think/presume they use calculated data instead of measured? agai'n; Daf mentioned they use a propellor to measure the power; the other numbers that you call measured is static data.

Quote:

Originally Posted by Serum

Delta or Wye is covered by the same constants. Same motor with Delta wiring will have different constants if you wire it as Wye.

Can material will make big difference if it would be close to magnetic field, for current configurations we talking about fractions of %, which still loss but so small.

I am not following you about constant V, You can dyno motor at constant power, but then it would be not easy to read data. And actually there are cases when you would like to test motor under constant power, but you talking about voltage.

As for Q, click on any cell in calculated area and then check in entry field, you will see formula on how particular cell data was obtained.

Heck, now i see.

Okay, that's calculated for sure.

I never paid close attention to the excel sheets..

Rene, I said they use props to get a loaded KV value, nothing else.

Okay, thanks for clarifying Daf.