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HomeAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › U-shape or 100% Flat on Stunt Throttle Curve?
01-21-2010 08:03 PM  8 years agoPost 1
helicanfly

rrNovice

Fairfield, ca

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As a fairly new heli pilot (I went inverted for real on purpose and didn't crash for the very first time the other day), I've done some research and asked some questions, but one subject has me stumped and I need the help from some pros (that's you guys!). I have an Align 450 Pro (stock everything except the canopy)that was my first heli build and it flies great! Thanks to Hoss at my LHS in Sacramento, he helped me fine tune my throttle and pitch curves. For the idle up mode, he set the throttle curve at 100% all the way across, and the ESC using soft start, governor off. I asked about overspeeding and that I had heard about using a U or V shape (depending on how many settings the Tx has). His explanation was, I'm certain, very good, but slightly over my head at the time. In any case, his doing tic tocs, inverted flight, and some other stuff I still don't know the names of, with my brand new helicopter made me a believer. I was wondering if you folks could chime in on the pros and cons of the two, because I don't know them. I know some like governor on, some hate the governor, some use v-shape others use 80% flatline, etc. My brother, who learned and flew on gas engines (he had a joker and two beautiful Bell 230's (see v-eastonline website for pics , those are the ones my bro built!)) He insists a V-shape curve is better so you keep the head speed the same and predictable throughout, but looking at the forums, most 3d guys are using a flat curve (constantly changing headspeed with changing pitch and bogging the motor). I'd like this to be an objective, fact based, not too technical discussion, so a new guy like me can come to one spot and get the answers. I've read a lot about setup, but no one explaining why one way is better than the other. I realize this is mostly a matter of preference, but I'm looking for hard data. If this has already been discussed, please direct me to that post. Any help from you folks out there? Apologies in advance for any and all ignorance on my part... Thanks. Steve

I'm like Alan Szabo, just without the control

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01-21-2010 08:13 PM  8 years agoPost 2
Big Fil

rrKey Veteran

Santa Rosa, CA

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V curves are much more common on IC helicopters. Electrics by the nature of how they work will do better on a flat curve.

No need to worry about changing to a V curve. Hoss did you right.

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01-21-2010 08:16 PM  8 years agoPost 3
Gyronut

rrProfessor

Martinsville In.

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I'm running flat lines on all my sparky birds.

I also us U shaped curves as BU's on my Nitro helis should the gov's crap out.

Rick

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01-21-2010 08:17 PM  8 years agoPost 4
cdrking

rrElite Veteran

Seattle

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What about the difference between using the governor mode on an ESC or non-gov mode? Also what about the brand/quality of the governor mode in the particular ESC?

Jeff

To hover is divine, the alternative is rather PLANE.

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01-21-2010 08:17 PM  8 years agoPost 5
helicanfly

rrNovice

Fairfield, ca

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IC helicopters... not sure what that is? I'm guessing Internal Combustion. Thanks for the reply. Can you eloborate on this at all?

Steve

I'm like Alan Szabo, just without the control

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01-21-2010 10:08 PM  8 years agoPost 6
cbflys

rrVeteran

Nesconset, NY - USA

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Performance wise, a flat throttle curve on an electric bird works fine. Efficiency wise however, it pays to take a little time to adjust the curve.

The KV of the motor will only allow it to spin so fast, so at any given pitch, you can reduce the throttle value until you notice the motor starting to slow down. You'll want to settle just above that point. Any value higher than that will just be keeping the motor coils energized longer than they need to be, essentially waisting energy.

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01-21-2010 10:25 PM  8 years agoPost 7
helicanfly

rrNovice

Fairfield, ca

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So, should I set a target headspeed at 0 pitch (which, in my case would be the third or middle point on my curve because I only have five) and then adjust my throttle curve at point three that achieves that headspeed?

In other words, say I want 2500 RPM at 0 pitch (mid-stick), and 85% throttle gives me that, then I should set, say 86% and then linear to point 1 and point 5?

The wasted (potential) energy comment was good. I didn't think about that.

Thanks

I'm like Alan Szabo, just without the control

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01-22-2010 12:43 AM  8 years agoPost 8
Swoop

rrElite Veteran

Newark, DE USA

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V curves are much more common on IC helicopters. Electrics by the nature of how they work will do better on a flat curve.
My sentiments exactly.

Chris
X50, B320, Radix, Spartan
Titan,Kasama,MP5,Radix,JR770
Trex450SE,MavrikkG5,Phoenix35

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01-22-2010 02:30 AM  8 years agoPost 9
cbflys

rrVeteran

Nesconset, NY - USA

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There has been much written and discussed about this topic. You'll have the camp that says "Use flat throttle curve and fly". That will work and you'll have maximum performance, but as I said above - "at the expense of waisted energy."

If you set zero pitch and run 100% throttle, you can tach your headspeed and determine your true maximum RPM. Motor efficiency, gear train drag, etc. are all ready taken into account when doing it this way. If its too fast or too slow, correct with a pinion change (within reason). If it's way out of wack, you probably have the wrong KV motor.

But once you determine your max RPM, you can fly with a flat 100% throttle curve and see if the machine performs to your liking. Then you can go back and start to decrease the throttle at each of your points as discussed above. Try it, you may be suprised to see that performance doesn't suffer, but run-time increases.

The key is don't run the points on the edge. Find the throttle value that just starts to decrease the RPM, then kick it up by 5 - 10%. Do one point at a time and fly, you shouldn't notice any difference between the flights. If you do, your last point lowered is too low.

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01-22-2010 04:47 AM  8 years agoPost 10
helicanfly

rrNovice

Fairfield, ca

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I'm really sorry, sir, but I'm not sure I understand. I am running all stock in my 450 Pro and I'm using 100% across with the governor off. I do need to tach my headspeed at 0 pitch, but what do I do then? I'm not sure if what I'm getting is the most, or best, performance wise. I love how it flies now, but if I can reduce the throttle input and still get the same performance, and increase my flight time, I'm all for it. You mentioned that once I determine my max RPM, I can fly 100%. I don't know what the max RPM should be (too fast, too slow, preference?), so I don't know if I need to change the pinion. From what I gather, you are saying start at 100%, then go to maybe 95% across to see if the performance is the same and so on. Is it possible to have a curve that goes 95-87-80-87-95 and still have the same performance? I thought you wanted to run a motor to its limit to keep it from overheating. If you don't, the ESC has to dissipate the incoming voltage as heat. Geez, I could be way off here and might need to go back to some college courses I took.

Thanks for your time to help me understand this thing.

Steve

I'm like Alan Szabo, just without the control

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01-22-2010 05:31 AM  8 years agoPost 11
rotormonkey

rrKey Veteran

Ottawa, ON - Canada

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I think what CBflys is trying to say is you can lower your mid point on the throttle curve a bit to keep the same performance, and save a little energy. imho the energy you'll save will be negligible.

You are correct. Things will run more efficiently if you have the curve at or close to 100%. That doesn't mean you have to though. There's nothing wrong with dialing down your curve if you don't want max performance. At least that's what I'm given to understand, I'm no electronics guy.

Anyway, long story short, generally the aim with helis and throttle curves when flying 3d is to keep your headspeed the same or at least as close to it throughout the flight. So at full pitch you want 2500rpm. At mid stick when the head is unloaded, you still want 2500rpm.

Most people will run a flat curve on an electric motor just because of the way they work. They just draw more current all my themselves to keep the rotor RPM up when the head is loaded. So having a V curve isn't as important.

They're used more commonly on internal combustion (IC) motors because a 100% flat curve will guarantee that the head will explode from overspeeding when you descend. Why? Because the throttle curve on an IC engine determines how open the carb is, and therefore how big the explosion is. You don't want big powerful explosions when there's no resistance. Regardless, the idea on an IC engine is the same. Keep the head speed the same no matter what stick position you're at.

Hope that helps.

If it can't hover, it ain't worth flying.

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01-22-2010 08:33 AM  8 years agoPost 12
bcm

rrApprentice

Tuolumne,CA

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our normal electric setup consists of:
Normal mode: 0 at low stick, 65-75 at half stick,and that same value striaght across to the high stick position.

idle/stunt 1: flat at 75 to 85
idle/stunt 2: flat at 100

I added this because I havent seen any reference to gyros. I have found that the gyros seem to work much better when using straight curves. I have tracked quite a few gyro issues down and solved them by simply using "flat" curves. They just seem considerably more "solid" while using the flat curve.

I've never attempted to scientifically determine any difference in efficiency or run time, simply because flat curves solved the other problems.
As for gov mode, my opinion is that they are redundant with electric motors. The esc sets a duty cycle(frequency) that controls the motor RPM. The motor will then draw as many or as few amps as it requires while attemping to stay at that speed. I've found them to be self governing, as some other have stated above.

Hopefully I added a few more reasons for you to continue to be happy with Hoss' set-up. I agree with him and your set-up, for what that matters! Tell him I said hello next time you see him!

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01-22-2010 12:50 PM  8 years agoPost 13
Justin Stuart (RIP)

rrMaster

Plano, Texas

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Here is how I see it: If you use a really high quality ESC like a Kontronik, then you can run it in governor mode with flat throttle curves. If you are running a cheap ESC, then you do not want to use the governor because it will cause more problems that good. In this case, you will want to use a 100-95-100 or maybe even 100-90-100 curve. This will ensure that you maintain a constant head speed.

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

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01-22-2010 12:58 PM  8 years agoPost 14
Smok

rrApprentice

Antwerp, Belgium

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Also the governor on Castle Creations seems to work well,
especially with recent firmware. And the slow spool-up
looks and sound cool too... With the USB programming cable
I am setting three fixed RPMs that are only getting switched
by the throttle curve - so all RPM programming is via USB
and this way I am saving on a RPM tacho (anyone wants to buy
a Skytach which I do not need anymore ?

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01-22-2010 01:44 PM  8 years agoPost 15
Rotowerkz

rrApprentice

Windham, NH

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You are correct. Things will run more efficiently if you have the curve at or close to 100%. That doesn't mean you have to though. There's nothing wrong with dialing down your curve if you don't want max performance. At least that's what I'm given to understand, I'm no electronics guy.
Brushless ESCs are most efficient at wide open throttle. When you reduce throttle, there is a slight amount of resistive loss that creeps in as the pulses traverse the linear region of the output transistors.
It's not much, but it does explain why it's not optimal to run an ESC at 70% for long periods. If you must reduce output speed, it's a good idea to regear rather than depress the output power using the throttle curve.

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01-22-2010 01:53 PM  8 years agoPost 16
helicanfly

rrNovice

Fairfield, ca

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Great feedback you guys. Thanks a lot.
OK, Rotormonkey, this was great info. You said "Anyway, long story short, generally the aim with helis and throttle curves when flying 3d is to keep your headspeed the same or at least as close to it throughout the flight. So at full pitch you want 2500rpm. At mid stick when the head is unloaded, you still want 2500rpm." I absolutley agree, and I thought that's what the governor did, but mine is off. My brother insists that with the governor off, the HS is alway changing with pitch, but that is with Engines, for sure. I think what you are saying is that the governor is redundant because the motor draws more current off the battery to keep running the same RPM equivalent to the percentage you have set in the throttle curve. I guess then the limit would be the amount of current available. To include what CBFLYS is saying then, is that I may not need 100% for two reasons: I'm not flying to the capacity of the helicopter, or, the motor has greater caability than the imposed drag on the blades.

I like the comment about the gyro from bcm. Come to think of it, I have noticed less deviation with 100%. What's funny is I'm still seeing about a 50/50 split on V shape versus Flat. All the input is great though, and very appropriate. Looks like I'll be running some battery packs through some workouts!

Excellent stuff, thank you!

I'm like Alan Szabo, just without the control

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01-22-2010 03:35 PM  8 years agoPost 17
rotormonkey

rrKey Veteran

Ottawa, ON - Canada

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helicanfly.

That IS what the governer is SUPPOSED to do. Generally they're more useful on an IC heli though. On electrics, like the other guys have said, it's sort of self governing. The ESCs often do have governers built in, but some of them sort of pulse the motor to keep HS the same. That's where you'll come into problems with the gyro. The motor is constantly revving up, and slowing down, loading and unloading the head. Because of the constant sudden changes in torque, the tail ends up seeming to wag a little, almost like gain is too high, but it isn't. This issue has caused many a folks big headaches.

Mind you not all ESCs are created equal. The Align ESCs seem to be notorious for this, at least my 35a esc on my 450 did it. So I run a flat curve on that one, and it works just fine. On the other hand I also have a Castle Creations ESC with governer mode, and gov mode works fine on that one. The only advantage I can see is that you don't have to bother putting a tach on it to get a specific head speed. That and the HS will be the same no matter what size battery you put on there, so if you have different batteries, it might be worth using. Not if it's the align one though imo.

If it can't hover, it ain't worth flying.

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01-22-2010 04:05 PM  8 years agoPost 18
Smok

rrApprentice

Antwerp, Belgium

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On the Castle ESCs you also have an adjustable Governor gain,
that helps to eliminate rpm oscillations, plus on the new ICE ESCs
you can also record lots of runtime parameters and then view
the graphs on a PC - that helps to spot control loop instability
or oscillations. Lots of fun to play with it...

Also the PC setup program for Castle shows if the governed speed
is optimal for the given motor and gear ratio - easy to play
with gearing ratios to find a good one...

..not to say that it's the best thing since sliced bread,
but I am really happy with CC ESCs...

If no Governor - then I would stay with a flat (or almost flat)
throttle curve as most seem to agree here...

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01-22-2010 07:22 PM  8 years agoPost 19
MrMel

rrProfessor

Gotland

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For a smaller heli I say it doesn't matter much if you run flat 100 or a V-curve, since the mass in the rotor head is so little it don't overspeed anyway.

On a bigger machine it will overspeed quite alot, so then its better to tweak a good V-Curve.

That is if you don't run governor.

When you run a governor, you should run a FLAT curve, which is "relative", meaning, running a curve of 75% isn't necessary 75% of max RPM, its 75% of the GOVERNORS given range.
Why we aim at 75% is for the governor to have headroom to keep the RPM regardless of Load and drop of the pack in the end.
(with ICE controllers you can actually see what the "real throttle is", if you hit too much at 100% you could get better performance)

Now, all this comes at a cost, running Partial throttle WILL be less efficient.
Actually when you run governor on a bigger heli your pack will see something called microbursts, ranging up to 300amps, even if you push max 100 on a datalogger.

But the thing is, when running a governor, even 100% isnt really 100%, so the partial throttle rule is always there, it totally depend on the governor (again, it has it's own range)

The microbursts is because the ESC is, when running at 70% actually switching between 100%/0% several thousands times per second (PWM Rate), it dont know "70%", it only know on and off, at 100% its always ON.

When you go from 0->100% in that single instance out of several thousands, AND you have max load at the motor, voila, Microburst.

So everything is a trade-off, good performance WILL cost flighttime and stress on electronics.

Gone fishing..or hunting..or something
My site: http://heli.dacsa.net - VBar videos and more

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