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Old Mar 26, 2012, 08:58 PM
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Arx
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Quote:
Originally Posted by photronix View Post
What I would really like to do is find a solid
repeatable test that allows us all to drive the ESC vendors.
Yes, this could help, but there's a certain amount of matching involved that
will probably prevent a single test from telling you everything. Someone
with a very lightweight copter that's going for high speed stunt flying is
probably going to be needing different things than someone who wants to lug
a heavy SLR. There are things that can certainly be improved which will
help across the board, but there's others that will probably help some
cases, and hurt others.

Quote:
I don't disagree that the video is interesting but I would like to figure
out a way to measure and document what is really happening.
Yes, It would be good to see a timing comparison of the output PWM vs the
input i2c/ppm. Unfortunately, not everyone has the equipment or knowledge
necessary, and misinterpretation of a single result can lead to a lot of
"This one is best" type things, which don't usually tell the whole story.
Quote:
I agree with your previous comments about TF by definition being applied
only to LTI systems. It almost never is actually, typcially assumptions
have to be made concerning the regimes where the measurement is linear. I
chose 25% based on many other tests. I have done the tests for other values
such as 5% and 10%. I'll post more results.
Yes, when you're testing the limits in that fashion, you will definitely run
into "attenuation". The problem is that depending on the type of slew
limiting that is being done, your results aren't necessarily going to say
anything that is useful. You'll get a good idea of the control bandwidth,
but you run into the point where it becomes non-linear, and that's where
things can easily get misinterpreted. It may be more important to know how
well an esc responds to hitting its limits, as opposed to just how high
those limits are. You may get one that seems to respond really well with
the prop, and conditions you're running it in, but which may behave
differently under different load, or different input conditions (non
sinusoidal)

Quote:
What I would really like to do is find a good test case, two ESCs to
compare. I'll measure it with my test stand and others can also measure the
same two. Then let's all decide.
Yeah. It would be cool, but I think there will need to be a suite of
standard tests for this to be useful.
Quote:
My intuition is that the momentum of the propeller limits realistic update
to about 50Hz with very very minor corrections up to 100Hz. Changes in RPM
greater than 10% can only occur lower than 30Hz.
That may well be true. I guess it depends on the dynamic range of the PWM.
There may actually be a high speed "dithering" occuring between a couple
steps of pwm which might turn into a slower vibration at lower speeds.

That's just hypothesis on my part though. I haven't tested it at all to see
if it's an issue or not.

Quote:
I don't disagree with comments like "well it just flies better with X brand
ESC" I disagree with "feel" being representative of fact which seems to be
the prevailing sentiment.
Yeah. A lot of people don't understand enough to know why it "feels
better", they just know that they have an easier time flying it, etc. In
some cases people exaggerate, but if many people are saying it works way
better for them, It would probably be a good idea to try and figure out why.
I doubt it's a shared delusion, and the few before/after videos I've seen
seem to show some definite improvement.
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