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HomeAircraftHelicopterMain Discussion › v-curve vs flat... efficiency...?
06-07-2009 03:23 AM  9 years agoPost 21
flipteg

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Lilburn GA

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that's fine if you want to run 100% flat and i understand the performance advantage of running 100% flat, it's just that for the type of flying that i do, running 100% flat just uses up more power for performance that i'm not really using... i didn't really start the thread to start people arguing...

your comment is like "i have a race car and i drive it at full acceleration, full top speed, full braking capability every time i drive it, because anything less than 100% and it drives like junk..."

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06-07-2009 04:12 AM  9 years agoPost 22
dodgemcopter

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Oztraliya

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I used to run my 600 on 6s @ 100%, 5mins max and putting back 4000 in a 5000 pack. Everything was hot, packs, esc and motor.

I changed to Scorpion 890, Turnigy 100HV and 2 x 4s 3700mah Outrage. At 100% and 4mins I recharge 2880ish mah, a curve of 100,83,78,83,100 Im recharging 2100ish mah after 5mins. On top of that everything comes down cool or warm (packs and motor warm, esc cool). Don't realy understand why, don't know if what Im doing is right......all I know is thats just how it is and I'll keep going until it "isn't". I just put it down to the ESC can handle low % throttle and Scorpion 890 is better at using torque rather than reliying on high headspeed to keep blade momentum up like high kv motors.

Sports type flying only, FFF with loops and rolls etc.....no pitch jambing 3D

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06-07-2009 09:00 AM  9 years agoPost 23
f penfold

rrKey Veteran

uk

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most people who fly 3d use a flat line throttle curve. V CURVE IS SET UP FOR INVIRTED FLIGHT. you need the throttle to work when up side down. if you just flying round right way up you dont need a v curve you could set up you idle up curve as a non linear line ie start it off at say 65 and work it up . a friend of mine does this he is a non 3d pilot and gets about 7 mins on a 6s 5000 pack that used to belong to me and i could only get about 3 mins out of with a 100%
flat line flying 3d

I know I used lock tight why did my head explode

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06-07-2009 10:54 AM  9 years agoPost 24
nivlek

rrProfessor

Norfolk England

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You will get better performance efficiency from a flat 100% curve because this puts the motor closest to it's peak efficiency rpm along with providing more enertia and less blade deflection etc for a particular control rate
The improved efficiency at 100% comes from the fact that the esc is just switching between each of the three phases , not switching the FETs on and off to modulate the rpm . When FETS are on , there is virtually no dissipation , when they are off there is no dissipation .
It's the transient stages between states when power is dissipated as heat .

At the end of the day , it gets dark .

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06-07-2009 04:38 PM  9 years agoPost 25
AirWolfRC

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42½ N, 83½ W

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Running at 100% and letting the ESC do the speed control is really the way to go. What gives problems (low efficiency) is the way the controller controls. If the ESC controls speed by timing only then you have great ineficiency. To run at partial power (but still target speed) the controler needs to do some pulse width modulation.

Assuming all ESC's work the same way is wrong.

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06-07-2009 05:02 PM  9 years agoPost 26
flipteg

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Lilburn GA

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so is it safe to assume that with 100% flat curve that head bog is still there but since the head speed at 100% is already very fast, it is much less noticeable...? because the way i see it, if you are getting a certain head speed at 5 degrees of pitch at 100% throttle, if you increase that load to 11 degrees of pitch, you are still at 100% throttle... something has to give and the head speed should drop a little bit...

at 100% flat throttle curve, if the head speed is supposed to remain constant across the pitch range, where does the extra power comes from to hold that head speed when the rotors are loaded up...?

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06-07-2009 05:21 PM  9 years agoPost 27
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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It will get some of it's HS retention by pulling more amps as per the volt constant (kv) of the motor - The motor will try to hold an rpm per volt and when more load is applied to the motor it will just pull more amps to compensate - There is some HS loss but not much with having inertia etc on it's side

Electric motor's torque curve is opposite of IC engine's torque curve - IC engine's have more torque at higher rpm so more throttle better translates into higher torque to grunt against HS loss - Electric motor's have less torque at higher rpm so throttle doesn't translate into torque as well - So it's better to run the higher HS and let it bog down little with the higher initial HS and inertia etc on it's side than to maintain a lower HS with throttling

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06-07-2009 05:35 PM  9 years agoPost 28
flipteg

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Lilburn GA

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so if we compare similar scenarios 100% flat compared to 100-90-100 curve, for both, at either ends of the collective stick, each setup will spin the rotor at the same speed since they're both at 100%...

the discrepancy comes from the fact that a 100% flat will use up more power at 0 pitch trying to spin the head faster than the 100-90-100 setup would...

3D'ers like the extra stability at the lower pitches afforded by the faster head speed and the advantage of storing that extra energy in the way of rotor inertia...

please keep in mind that 100-90-100 is an arbitrary number... when i say 100-90-100, i'm trying to achieve as perfectly stable an RPM as possible throughout the entire pitch range...

i know a constant RPM and a flat curve has different feel in flying... so can we then say it basically comes down to preference...?

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06-07-2009 05:42 PM  9 years agoPost 29
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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It comes down to flying style - If you're just flying circuits etc then none of this is going to mean anything but a little difference in flight time via the different average HS since there's not much loading happening - But if you're an aggressive flyer doing tic tocs and such then you will definitely appreciate the performance of a flat 100% curve vs a V-curve - Performance aside then yes constant HS is merely a personal preference

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06-07-2009 05:46 PM  9 years agoPost 30
flipteg

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Lilburn GA

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i re-read your post... you say that it is better to let it bog a little bit letting the inertia take care of it... of course this is assuming that the pilot is flying in such a way that he's transitioning between low and high collective very often... because if he's not, then the advantage of the rotor's inertia becomes irrelevant... for basic aerobatics, the stability of the extra head speed is nice, but for such flying, a lot of power is being used up just spinning the motor faster than necessary...

EDIT: never mind... i posted at the same time as your last post...

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06-07-2009 05:49 PM  9 years agoPost 31
AirWolfRC

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42½ N, 83½ W

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so if we compare similar scenarios 100% flat compared to 100-90-100 curve, for both, at either ends of the collective stick, each setup will spin the rotor at the same speed since they're both at 100%...

the discrepancy comes from the fact that a 100% flat will use up more power at 0 pitch trying to spin the head faster than the 100-90-100 setup would...
You're comparing apples and oranges.
The whole idea is to maintain a constant head speed.
If you load up the rotor head beyone the motor's ability to deliver power, you will bog.

By setting the ESC in the heli or constant speed mode, you let the ESC modulate the current to the motor so as to control the speed of the motor.

If you use something other other than 100% throttle curve, you are just getting in the way of the ESC trying to do it's job.

If you want to do a throttle curve other than 100%, you should not be in constant speed (gov) mode on the ESC.

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06-07-2009 05:50 PM  9 years agoPost 32
Ronald Thomas

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Gainesville, Fl, USA

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Why not just turn on the Gov mode? Best of both worlds then......Ron

Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!

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06-07-2009 05:51 PM  9 years agoPost 33
AirWolfRC

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42½ N, 83½ W

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The Gov. mode IS the constant speed mode.

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06-07-2009 05:54 PM  9 years agoPost 34
Ronald Thomas

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Gainesville, Fl, USA

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Airwolf
You posted before I got done. I was referring to the OP

Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!

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06-07-2009 05:56 PM  9 years agoPost 35
flipteg

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Lilburn GA

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i understand that about the governor... but i have an Align ESC and many people will say that Align ESC governors are not really good... this is the same experience that i had when i tried governor mode on the Trex 250...

yes, i understand what you're saying about constant RPM with a GOOD governor but i raised the question because i see a lot of people say that they are at 100% flat with governor off...

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06-07-2009 06:00 PM  9 years agoPost 36
Ronald Thomas

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Gainesville, Fl, USA

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If you have to choose one until you upgrade, go for the setup that keeps the temps low. That will save your electronics until you have the funds to upgrade........Ron

Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!

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06-07-2009 06:00 PM  9 years agoPost 37
AirWolfRC

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42½ N, 83½ W

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If you are running 100% flat with govenor off then I would expect major speed variations.

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06-07-2009 06:02 PM  9 years agoPost 38
Heli_KV

rrKey Veteran

Ottawa, Canada

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So that what I am wondering. Why not to use governor mode?

If ESC is on flat curve without governor, why speed will be constant then? It maybe constant (or nearly constant) on 100%, if having powerful enough motor, which does not feel load that much.

As far as I know - Jazz operates in governor mode all the time. In CC ESCs, there is a choice - governor/not governor. You want constant HS - turn on governor.

I understand, that some ESCs does not have good governor, so people use flat curve. I can understand flat curve at 100%, but hardly flat curve lower than this. I guess v-curve should be used them.

Am I mistaken?

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06-07-2009 06:13 PM  9 years agoPost 39
Ronald Thomas

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Gainesville, Fl, USA

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i understand that about the governor... but i have an Align ESC and many people will say that Align ESC governors are not really good... this is the same experience that i had when i tried governor mode on the Trex 250...

Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!

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HomeAircraftHelicopterMain Discussion › v-curve vs flat... efficiency...?
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