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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Vincent Corwell on July 16, 2011, 04:04:45 AM
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I have my FM 9 timer setup for throttle compensation mode , which works fine
with my ESC, Stuka, 2300mah 4 cell battery, 4:50 flight time, 65% power
and compensation of 15 but is drawing 81-82% of battery, I want to keep the
time and power settings , would the compensation factor of 15 , if reduced to
??? ???
say 10 or 12 make a difference to battery usage ?
not sure if that represents 15 steps of compensation or what ?
need to find that 2% somewhere without losing power or flight time ???
Vincent
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I think you will need a slightly larger battery.
If you are using 82%, is that in wind or calm?
You use quite a bit more battery in dead calm weather.
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Vincent,
I'm not sure that the 2% over the 80% battery usage is all that significant. If you want to reduce battery usage, I'd look at reducing the prop diameter a little or going up in pitch a little while reducing RPM a little to keep the same lap times.
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thanks Russel & Chris
points taken, but still curious about the compensation factor,
what effect would reducing that be ?
Vincent
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It would slightly (to moderately) reduce the amount that the RPM is ramped up to compensate for battery sag - so turning it down would very slightly reduce the current draw over the latter part of the flight and the plane would (very slightly) lose some RPM over the same parts of the flight. If you turn compensation to 0, then the battery sag MIGHT become an issue, but since your power setting is only 65%, it MIGHT not also. It very much depends on all the external factors - prop, plane, battery size (and quality), weather, etc. - that make up your 'normal' results. Since it doesn't look as though this constitutes actual Stunt Pattern flying (at least at a runtime of only 4:50), you could just turn the time down 10 seconds also, that would represent roughly 3% of your flight time and, presumably, 3% of your total draw.
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Hi Vincent,
I'm not sure what ESC you are using but if it's available I would consider setting the "Initial Spool Up Rate" (Castle Creations Terminology) to a very low value, The current used to accelerate the prop to flying speed from a standing start is a significant "spike" and although probably not going to give you your 2% it will certainly help.
TTFN
John.
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Here's how the "Compensated Throttle" mode in the FM-9 adds throttle during the flight, based on the chosen compensation factor of 0 to 15.
(It originated with the earlier FM-1a timer, before the governed/constant-RPM mode was available, and was made available for those still using ESCs without that mode. It could be used by those who use a governed mode by switching over to the throttle mode after achieving the desired starting RPM, which will allow them to see what throttle setting gives them that starting RPM, and then choosing the compensation factor to get a real increase -- not just compensation -- later in the flight. But I don't know if anyone has tried this...)
Compensated throttle mode: Value vs. time
Factor 30s 1m 2m 3m 4m 5m total
0 0 0 0 0 0 0 0
1 0 0 0 0 0 1 ½%
2 1 0 0 0 0 0 ½%
3 1 0 0 0 0 1 1%
4 0 0 0 0 1 1 1%
5 0 0 0 1 1 1 1 ½%
6 0 0 1 1 1 1 2%
7 0 1 1 1 1 1 2 ½%
8 1 1 1 1 1 1 3%
9 1 1 1 1 1 2 3 ½%
10 1 1 1 1 2 2 4%
11 1 1 1 2 2 2 4 ½%
12 1 1 2 2 2 2 5%
13 1 2 2 2 2 2 5 ½%
14 1 2 2 2 2 3 6%
15 2 2 2 2 2 3 6 ½%