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Old 09-17-2015, 11:04 AM   #1 (permalink)
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Default Could someone please explain throttle curves?

Hello - I just bought Phoenix 5 and the DX6i. I'm trying to understand why throttle and pitch are on the same stick. I've read about setting curves but I don't really understand that concept.

To me, having my left stick centered and having throttle at 50 and pitch at 0 is a bad thing, because if I invert and need to move the stick down for negative pitch, I also get less throttle. So, I'm feeling like this is a situation where the answer is right in front of me, I'm just not seeing it.

I read the DX6i setup guide thread on this forum, but frankly, I got very lost in it. It seems like my experience level(just got the sim a couple of days ago and have never flown any other heli besides a blade MSR RTF) is keeping me from properly digesting the concept of curves. Can anyone explain this to me like I'm in kindergarten?

Thanks!
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Old 09-17-2015, 01:41 PM   #2 (permalink)
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Quote:
Originally Posted by burgertime78 View Post
To me, having my left stick centered and having throttle at 50 and pitch at 0 is a bad thing, because if I invert and need to move the stick down for negative pitch, I also get less throttle. So, I'm feeling like this is a situation where the answer is right in front of me, I'm just not seeing it.
Spot on, you are 100% correct. that's why most larger helis dont use throttle as such but instead have a governor that simply maintains the rotor spinning at your desired RPM.

Without a governor you would just make the throttle 'curve' almost flat or slightly 'V' shape (for instance 80% at the mid stick and 100% at zero and full stick travel).. That way the rotor does not slow when you apply negative pitch.

To start and stop you have motor on/off switch which we call throttle hold... that basically applies a flat zero % throttle curve to kill the motor.
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Old 09-17-2015, 02:05 PM   #3 (permalink)
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Ahhhhh... Throttle hold. Ok, now that's a term I've heard as well. So then what is a normal flat throttle percentage? I would think you would want to fly your heli(holy smokes, here's where I might be looking really stupid) at 100% all the time.
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Old 09-17-2015, 05:38 PM   #4 (permalink)
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If your heli is really twitchy, you can lower your throttle curve to make it more docile. Also, more speed requires more power, so you drain your batteries faster. By lowering your headspeed, you get to fly for longer.

Flat percentages are usually between 80% and 100%. A lot of ESCs don't like values less than 80. If you find that you need something lower, then you should look at changing out your motor pinion for something with fewer teeth.
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Old 09-18-2015, 01:27 AM   #5 (permalink)
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Here ya go. A good explanation on how to set up a Heli in a mode that beginners are more likely to learn with and a link to a Phoenix Flight school. I highly recommend that you read both threads and then contact Jack for lessons on the Phoenix Sim.

http://www.rcgroups.com/forums/showthread.php?t=1901484

http://www.rcgroups.com/forums/showthread.php?t=1234396

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Old 09-18-2015, 02:54 AM   #6 (permalink)
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Quote:
Originally Posted by burgertime78 View Post
Ahhhhh... Throttle hold. Ok, now that's a term I've heard as well. So then what is a normal flat throttle percentage? I would think you would want to fly your heli(holy smokes, here's where I might be looking really stupid) at 100% all the time.
As others have said, you can simply program a 'flat' % value. the problem there is that the rotor will slow down when you apply load such as when you increase collective pitch. If you use 100% throttle all the time you will run your battery down quicker and might also over speed the rotor when the blades are at low pitch.

Think of this like cruise control on a car. A heli governor is like cruise control on a car, it automatically adjusts throttle to maintain a constant speed. A flat % throttle is just like wedging the car throttle down with a brick. It maintains constant throttle but when the car comes to an uphill it will still slow down, and on downhills it will speed up. So constant throttle doesn't maintain constant RPM.

A V shape curve is an attempt to match throttle opening to collective pitch blade angle so that the throttle % increases along with collective pitch and so RPM is constant. It's only ever a compromise and it doesn't work as well as governor but it can work a lot better than a simple flat %.
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Old 10-22-2015, 02:03 AM   #7 (permalink)
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It sounds like you're asking about fundamentals, so I'll add a little more basic explanation than those above without getting into governors and RPMs and overheating ESCs.

Basics:
Throttle is available power.
Pitch is the amount of power taken from turning the rotor and used to push the heli up or down.
Generally, a constant speed is best, but trying to take the rotor from stationary to full speed instantly is inefficient and puts stress on the system (lots of noise/fuel for diminishing return.)
You want to be able to bring the rotor from stationary to usable speed smoothly, but you also want a way to keep the speed roughly constant while you do other things with the throttle stick. This is where your mode switch comes in.

Switches and curves:
Your F. MODE switch lets you change between curves (2 on the Dx6i, 3 or more on more advanced TXs.) The NORM setting is used for spooling up the head and is plenty wide enough to get into a hover and move about once it's up to speed. The STUNT setting is for setting the throttle for aerobatics or whatever flight mode you prefer. When you're just practicing basics, you don't need to worry about going inverted (can stay in NORM), and the low-end pitch can start only slightly negative; just enough to hold the heli on the ground in case a gust of wind comes along. Since you won't be using this setting for aerobatics, you don't need a lot of positive pitch either.

So, for the NORM throttle curve you want to start at zero and move up to 70-80% (somewhere close to what it will be in STUNT mode.) On my Dx6i right now, it's (0.0, 56.5, 72.5,72.5, 72.5). The pitch curve is (30.0, 30.0, 68.0, 78.0, 80.0) which works out to (-4.3, -4.3, +3.9, +6.0, +6.4) with +/-12 pitch travel. This is enough to make the sim's T-Rex 700 nitro light on the skids at center stick. (YMMV, I've modified my model slightly.) It also makes it so the thing doesn't go rocketing off into the blue if you give it full throttle. Really this is all you need to get hovering and into slow circuits and figure eights and such.

The STUNT setting is where you get into worrying about keeping the throttle steady over the full range of the pitch. There are mechanical reasons why you would set a throttle curve to something other than 100% all the time (something like (100.0, 90.0, 80.0, 90.0, 100.0)), but for the sim you can just set your STUNT curve to (100.0, 100.0, 100.0, 100.0, 100.0). This makes (basically) full power available at all times. In real life if you were doing non-aerobatic flying you might leave the throttle at 75-85% to save fuel/charge and extend your flight time. (Depending on the power plant, model helis are crazy overpowered for just getting off the ground and buzzing around, though there can be hardware complications for running this low.) The pitch curve stays linear (0.0, 25.0, 50.0, 75.0, 100.0). This gives you the full range to do all your aerobatics. (Again, you might set this to something only moderately more aggressive than NORM if you won't be taking it upside-down.)

The TH HOLD switch provides a third set of throttle and pitch curves and is universally used as an idle-switch. DO NOT USE THIS TO SET YOUR THROTTLE FOR POWERED FLIGHT! On the Dx6i, the throttle curve is actually just a horizontal line. In an emergency, throw the TH HOLD and the power is cut no matter the position of the stick. The pitch curve, however, is still a full 5-point curve, and you generally leave it linear 0-100 like the STUNT setting. This lets you have full control (while the head is turning) in a power-off situation to do an autorotation.

Note: For reasons known only to the Horizon firmware programmers, the 0-throttle point on the TH HOLD "curve" is 10. This is unique to the Dx6i, and doesn't matter much in the sim, but might give you trouble in RL on a non-electric. 0 in TH HOLD equals a negative throttle setting at the servos and will pull your engine below idle, where it dies. Not the end of the world, but inconvenient if you wanted to auto in the middle of a routine and then pop back into the air. (Incidentally, this is how the THROTTLE CUT button stops the engine on a nitro/gas model.)

You can tweak the curves from there to find a point where you can get the heli in a hover and flip the F. MODE switch without it jumping up or down. (I haven't done this yet, but it's pretty close and I want to practice, not tweak )

Hope that helps. I'm sure the experts will tell me where my curves need adjustment (I'm long on study and short on experience, 72.5 throttle is probably a bit low and +6 pitch is probably a little aggressive for NORM) but this has been working for me.
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