Conflicting advice - headspeed

[hioct8ne]

Maidened my 500 3D on Saturday - my first big heli and it was a real joy to see it hover as steady as a rock in a breeze almost "straight of the box" sounding great. And this is where I need some advice about headspeed.

I'm also only a few months into flying so set it up to hover at at 50% throttle as this forum seems to suggest 500/600s like a low headspeed. This made sense as it meant it wouldn't be as twitchy - wouldn't it? Turned out it was as twitchy as my Trex 250 and that's twitchy.

After a quick landing I took advice from a fellow club member who recommended a much higher headspeed as the gyroscopic effect would be much greater making it more stable. It worked !

Now I'm not sure that I understand why that should be. Surely a small stick movement at low headspeed would have less effect than the same movement at high headspeed. or is the gyroscopic effect more dominant?

All advice is good advice - I'd like to understand why the difference.

Have a couple of other contradictions which I'll post separately around midstick = 0 pitch and using low stick as throttle off ...

[Jdarc1]

What head speed are you running one.

[marcosp]

What motor, Kv and pinion? Or even better do you know what your head speed was at 50% and later? What FBL unit and what settings regarding agility or cyclic rates (depending on the unit).
By principle any heli with FBL will fly almost the same regarding stability on the upper 30% or more of the rpm range for that size. When you start getting too low you loose collective response first, you have to manage your collective better and take care that your blades don't stall. This is with really low head speed.
I bet the problem was more related to elevator and aileron rates rather than head speed or what you felt when raising the rpm is a more locked in feeling in collective so the heli feels stabler.
Low gains can make the heli feel loose and this be worsened by low rpm as well.
With more info we'll be able to help you come to conclusions that will enable your better comprehension of these variables.

[ElectricSheep]

In addition to marcosp's questions, what throttle percentages are you running at Normal, Idle 1, and Idle 2? Is your pitch curve linear -- so, negative X degrees at low collective stick, zero degrees at mid-stick, and positive X degrees at high collective stick?

From a couple of things you said, I'm just wondering if your throttle and pitch is set up as what used to be called "Normal" -- as in your throttle % and pitch rises as your collective stick position rises.

Here's what I mean:

Originally Posted by hioct8ne

I'm also only a few months into flying so set it up to hover at at 50% throttle as this forum seems to suggest 500/600s like a low headspeed. This made sense as it meant it wouldn't be as twitchy - wouldn't it? Turned out it was as twitchy as my Trex 250 and that's twitchy.

If your throttle % and pitch is changing as you move the collective stick up -- it's gonna be VERY twitchy.

Originally Posted by hioct8ne

Have a couple of other contradictions which I'll post separately around midstick = 0 pitch and using low stick as throttle off ...

This leads me to believe you're varying throttle as you move the collective stick. Sorry if this isn't the case, because if your throttle percentages are flat in all flight modes -- and it's still twitchy as a 250, then lots of other things need to be checked out.

[hioct8ne]

Thanks guys - that helps me understand better. The increase in headspeed made a big difference. I was being far too cautious - didn't want to crash first time up.

I was running 50% which according to Mr Mel v3 is 2,167 rpm. To compound the problem I was running dual rates at 60% on cyclic controls. Going to 80% and taking the dual rates off stiffened it up a lot and hovering was rock steady and I could confidently move around.
Tail was rock solid which was a relief.

ElectricSheep - you've guessed my follow-up question. Yes I was on a changing throttle curve and pitch curve as per the manual and advice. Would a throttle at say 0,85,85,85,85 and a pitch curve of -4,-2,0,+5,+10 work better?

Hope these questions aren't too basic. Your experience and knowledge are really helpful.

Apologies for leaving off the spec - it was meant to be in my profile - will update shortly.
Pretty standard - 1100kv, 14/153, 6S, MiniVbar set at 90.

[ElectricSheep]

Also, which motor and ESC?

[ElectricSheep]

Originally Posted by hioct8ne

ElectricSheep - you've guessed my follow-up question. Yes I was on a changing throttle curve and pitch curve as per the manual and advice. Would a throttle at say 0,85,85,85,85 and a pitch curve of -4,-2,0,+5,+10 work better?

I would keep the throttle percentage the same across the board (flat throttle "curve") and use the throttle hold switch to cut the power. Now that you're flying a collective pitch heli, get out of the habit of quickly pulling the collective stick down to cut the power.

The pitch curve is OK having -4 degrees at the low end is good if you're just at the hovering level, because you'll still be able to get the heli down quickly if you need to -- and not completely auger the heli into the ground. That's what would happen if you had a fully symmetrical pitch curve, or -10 degrees at the low end, and slammed the collective stick down. When you start hovering & flying inverted then go to the fully symmetrical pitch curve. On a Spektrum/JR radio, it looks like 0, 25, 50, 75, 100. (and 50 is zero pitch).

[int2str]

Originally Posted by hioct8ne

I was running 50% which according to Mr Mel v3 is 2,167 rpm

....

1100kv, 14/153, 6S, MiniVbar set at 90.

These two statements don't jive somehow... First of all, Mr Mel's calculator doesn't calculate down to 50% last I checked. Also, 1100kv x 6S x 14/153 x 50% will be no where near 2167rpm. At full throttle maybe, but not at 50%.

Is 14T a typo?

And yes, to answer your question, depending on your ESC, running a 85% flat throttle curve is probably a good idea.

[hioct8ne]

Motor is Scorpion 4025-1100 and ESC is Jive 100LV - all stock kit from Mikado. Their website confirms 14T pinion and 153T main gear.

Mr Mel's calculator shows the full throttle range if you click on extended results - looks like v3 is available now at:-

http://heli.dacsa.net/calcv3/

If I plug in my numbers you'll see the results I quoted.

ElectricSheep - this has been very helpful. Makes a load of sense to fix headspeed then just vary pitch. Being able to start up with stick at midpoint would freak some people out but I'm too new to worry about that.

Also answers my other burning questions about starting up using Throttle Hold.

Much clearer now - thanks to you all - appreciate the help.

[int2str]

Originally Posted by hioct8ne

Motor is Scorpion 4025-1100 and ESC is Jive 100LV - all stock kit from Mikado. Their website confirms 14T pinion and 153T main gear.
Mr Mel's calculator shows the full throttle range if you click on extended results - looks like v3 is available now at:-

http://heli.dacsa.net/calcv3/

If I plug in my numbers you'll see the results I quoted.

No, it doesn't (see attachments).

Not trying to beat on the details, just making sure your aware of your actual headspeed and wondering if you have the right pinion.

[hioct8ne]

Oh - that's weird as I see something different. Your chart makes more sense to me - that the 50% headspeed is really too low.

Yet I can't see what I'm doing wrong - here are screenshots from HS v3 and from the Mikado website showing pinion size. I've counted it and it is definitely14T.

Very strange ..... thanks for coming back on it though.

[surfgeorge1]

Originally Posted by hioct8ne

Motor is Scorpion 4025-1100 and ESC is Jive 100LV - all stock kit from Mikado. Their website confirms 14T pinion and 153T main gear.

Since you are using a JIVE, I ASSUME you are using the JIVE governor (Mode 4), which means you HAVE to use a completely flat throttle curve, i.e. 50-50-50-50-50 etc.
To spool up you just hit the TH switch - perfectly smooth spoolup.

I run exactly the same setup with a JR radio (unchanged throttle end points), and am getting:
1750 @ 44% throttle
1900 @ 54% throttle
2050 @ 65% throttle (can bog to <2000 at the end of the flight)

Measured with the JLog2 connected to the JIVE.

I almost only use 1750 and 1900, but I am no stick banger.

Cheers,

Surf

[Ah Clem]

I originally had mine over 2200, and it was completely unnecessary.

I think it is around 2050 now (tached) and it is nice and stable and smooth.

I am sure I could go lower.

[surfgeorge1]

Originally Posted by Ah Clem

I originally had mine over 2200, and it was completely unnecessary.

I think it is around 2050 now (tached) and it is nice and stable and smooth.

I am sure I could go lower.

I think you should give it a try. You will increase flight time and reduce battery load. A side effect that I like is that the LOGO becomes really quiet at lower head speeds, and starts sounding more like a real helicopter.
In terms of flight time, I am flying 8 minutes "big air" (loops, turns, funnels) at 1750 and 1900 and charging less than 3000mAh into my 6S4500 25C Nanotechs.

Cheers,

Surf