RunRyder - More thoughts, and data, on the Lepton tail...

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e-Hirobo SRB Quark - Lepton - XRB Coaxial > More thoughts, and data, on the Lepton tail...

2atlo8
Senior Heliman
Location: Cedar Park, TX -- USA

I have had my Lepton since April and have crashed it twice. Both crashes occurred when it went into uncommanded piro's and I lost control before I could recover it. Upon thinking about these crashes I realized both occurred when I did something which badly bogged the head and caused loss of headspeed. This week I decided to try and determine what really happens when you badly bog the headspeed down.

I used my strongest and weakest lipos to do a series of full power climbouts while recording the data, including headspeed, on an EagleTree data recorder. My setup is:
Hyperion 3025-10 with 26T pinion
CC 60 governing at 2700 rpm
401/9254 on the tail
extended tail boom
4S lipos
+10/-10 collective
425 frp blades and 68mm CF blades on tail

Results were interesting. With my strongest lipo I could not bog the head enough to lose the tail, even though headspeed during climbout dropped into the 2000-2100 rpm range.

With my weakest lipo, the tail went into full uncommanded piro's about a second into each climbout. Data logging showed the head had bogged down into the 1900 rpm range each time.

As an aside, the peak current draws during climbout were in the 75-78 amp range, which is ok for a few seconds on the CC60.

My conclusions from this are several:

1. The 26T gearing is definitely too tall for this 4S setup and motor. I plan to repeat the tests using 24T, which will drop my governed headspeed into the 2500 rpm range staying on 4S. This may lessen the loss of headspeed in a bog by giving the motor more mechanical advantage (a lower gear). It should also drop the peak current draw.
2. The Lepton would certainly benefit from higher tail gearing because it will keep the tail running faster than it does now during a bog. A drop-in 13T tail pulley will be very welcome. My data showed that the difference between losing the tail and not losing it was less than a couple of hundred rpm on the head.

2atlo8
3D is my age....in hexadecimal.

12-22-2007 11:41 PM

Qooo
Senior Heliman
Location: Hong Kong

I use the following setup, max current is 48A.
Tail is very solid.
However, if I use MAH425, the tail will wag but if I use Funkey430, the tail will be solid. MAH425 definitely gives more power.

1. Hitec 81MG x3 pcs for CCPM
2. Align 75A ESC
3. SportBEC
4. Futaba GY401 + S9254
5. 2000mah 6S1P 30C (total ~320g)
6. Spektrum DX7 + AR6100
7. Main blade : Funkey 430mm
8. Tail blade : HDX500 plastic in black 64mm
9. Motor : Hacker A30-12XL - 14 Poles
10. 18T

Pitch : -12, 0, +12
Idle1 : 100, 85, 100
Idle2 : 100, 100, 100
Motor : Hacker A30-12XL - 14 Poles
ESC : Align 75A (TREX600CF)
BEC : SportBEC
Main gear : 94T
Pinion gear : 18T
Gear ratio : 5.22

Qooo - MARZ

12-23-2007 02:46 PM

HOMEPAGE

2atlo8
Senior Heliman
Location: Cedar Park, TX -- USA

Qooo,

Thanks for your setup info. No question in my mind that the 5S and 6S setups have an advantage in tail strength. You are spinning the motor a lot faster, which requires a smaller pinion and correspondingly lower gear ratio. That gearing helps to makes it more difficult to heavily bog down the headspeed, which in turn keeps the tailspeed up.

I am planning to continue to experiment with my 4S setup and some different pinions and headspeeds. I am too heavily invested in 4S lipos to shift to 6S right now....

2atlo8
3D is my age....in hexadecimal.

12-23-2007 08:12 PM

Tday
Key Veteran
Location: Needham, MA

2atl,

You're right on as I see it. The 68's are a must. Even with a 5s, you will bog a little on occasion and if you're being aggresive, the tail can "slip" a 1/4 turn. Disconcerting and I just ease a little on the collective for a split and it's back in the groove. And that's with the amazing logictech 6100t...lightning fast and very good sensor/program box.

Better tail ratio would fix a lot.

Tom

2 + 2 = 5 for extremely large values of 2.

12-23-2007 08:53 PM

HOMEPAGE

Qooo
Senior Heliman
Location: Hong Kong

I read a Taiwanese RC Heli magazine last week.
It talks about conversion kit for Freya Evo 90 HPM to 120 degree CCPM.

They mention one thing saying Hirobo means to make a low tail gear ratio because they attempt to use low tail gear ratio with longer tail blade in order to use less power consumption. I don't know if this point will help to gain more power.

Qooo - MARZ

12-24-2007 08:51 AM

HOMEPAGE

Jafa
Elite Veteran
Location: Sydney, Australia

12-24-2007 11:37 AM

Tail_BoomStrike
Veteran
Location: Virginia Beach

Jafa,

Try AXi 2826/8 1130kv. This thing got lots of torque. Doesn't bog too easily on 4S and 19 and 20 teeth pinion......

12-24-2007 02:36 PM

Jafa
Elite Veteran
Location: Sydney, Australia

12-24-2007 10:19 PM

2atlo8
Senior Heliman
Location: Cedar Park, TX -- USA

More data....

I repeated the test described in my opening post, but with a 24T pinion instead of the 26T. Nothing else was changed. Results were disappointing. Using my strongest lipo, the tail broke loose into uncommanded piro's on every full power climbout. It was worse than with the 26T pinion, even though the bogging only dropped the headspeed to about 2100 rpm. On the positive side, average current was down into the 26-28 amp region. Peak currents on climbout were in the 72-78 amp range.

Tailboomstrike,
How does the axi handle climbout using your 19T pinion and 4S? Does the tail hold?

2atlo8
3D is my age....in hexadecimal.

12-24-2007 10:48 PM

Tail_BoomStrike
Veteran
Location: Virginia Beach

Jafa

Here's a couple of site that could ship internationaly. Don't forget to buy the fan (cool1)....

http://shop.singahobby.com/?q=node/12432
http://www3.towerhobbies.com/cgi-bi...?&I=LXPPX5&P=FR

This one is local to Assie, but out of stock:

http://www.euromodels.com.au/shop/i...products_id=322

Swift tuning test showed 700W max. While my testing using Watt Meter, max out 850W.

2atlo8

19T is untested speculation. My testings was actualy done with 20T. It produced so much torque, it literaly cleared the teeth on the main gear. Max amp draw registered 79A. But we all know this is just maximum spike.

About the result on your test with 24T. The motor may not be running at the maximum efficiency current, running 24T. Just like engines, there is a power band, anything below or higher rpm than the power band, the maximum power output drops. So if your motor manual provides the maximum efficiency current. Install a pinion that will result an amp draw very close to the max efficiency current range (but not on that range yet, You want it on that range of amp draw during heavy loading), at the target head speed. 2826/8 maximum efficiency current is 25-37A range.

So it maybe that 26T is already the optimum on your motor, or it maybe 25T, but we won't be able to figure it out until we put it into testings...... That's the reason why when I try a new motor, I always calculate the pinion size for the target HS, at .85% drag coefficient, then acquire size pinion called for, plus additional pinion one step bigger and one step smaller. Then run some tests......

12-25-2007 03:32 AM

2atlo8
Senior Heliman
Location: Cedar Park, TX -- USA

Tail_boomstrike,

Good thinking. I realize you have not tried 19T with the axi, but it appears that you have tried it with 20T. Have you tried any full pitch climbouts with that motor and 20T, and if so how was the tail in the climbout?

Don

2atlo8
3D is my age....in hexadecimal.

12-25-2007 04:07 AM

Tail_BoomStrike
Veteran
Location: Virginia Beach

It disappeared like a humming bird.......

The tail held, but that's due to I believed around 3K governed HS....

12-25-2007 04:17 AM

Jafa
Elite Veteran
Location: Sydney, Australia

12-25-2007 06:21 AM

Qooo
Senior Heliman
Location: Hong Kong

For me, i think as long as you have HS close to 2900-3000rpm with 64mm (plastic tail blade), the tail will hold solid. That is what I am flying my Lepton. I don't have 68mm CF TB on hand so I can't try it out. I tried JR Voyager blue TB 71mm long, it works very great too but I really don't like the color on my Lepton so I am glad 64mm plastic blades from HDX500 are working just fine to me.

If you want to try low HS, I think you should simply use longer tail blade to boost up the tail performance.

Qooo - MARZ

12-25-2007 03:07 PM

HOMEPAGE

Tail_BoomStrike
Veteran
Location: Virginia Beach

But the best HS for this bird IMHO, is in the range of 2650-2800RPM. Best balance of cyclic and collective response, and predictability.

And so the reason why I keep "harping" on power train redesign. The main gear diameter needs a little increase in diameter so we could better leverage the torque on the blades with higher kv motor. And also change in gear ratio for the tail so we don't need too high a HS to increase tail rotor RPM. This might require new frame, to accomodate the new gear train, but heck, it'll be a great improvement. No more crashing, caused by tail that won't hold.......

12-26-2007 11:36 AM

docjoe
Elite Veteran
Location: Stockton, CA United States

2atlo8,

You hit my problem with the Lepton from day 1 right on the head. The tail, if I was too aggressive, I found would blow due to significant bogging. I had the Hyperion 3025-10T on 4s just like you did and realized that if I made the setup more tame (10 or 9 degrees on the collective pitch), then it helped prevent bogging it. But I was never able to fly it like my other helis.

That is until I changed to 6s. I'm now running 6s (2x3s 2200mAH) as well as a Kora 15-14 with a 21T pinion and my throttle curve around 85%. It's giving me 3K head speed and I really like this setup. It does give the heli a little more pop.

The most recent thing I did with this heli was to use the highest hole on the main shaft which brought down the head slightly. After changing the link lengths to the appropriate size, I found today (which were my first flights) that the heli seems to be much more agile. It was very very windy but the heli felt much more responsive. I'd recommend this to anyone with a Lepton.

Oh, I found 68mm CF blades from Heli Direct for about 10 bucks or less.

Quote

nd so the reason why I keep "harping" on power train redesign. The main gear diameter needs a little increase in diameter so we could better leverage the torque on the blades with higher kv motor. And also change in gear ratio for the tail so we don't need too high a HS to increase tail rotor RPM. This might require new frame, to accomodate the new gear train, but heck, it'll be a great improvement. No more crashing, caused by tail that won't hold.......

We'll see how my TRex 500 compares with the Lepton. I think the craftsmanship on the Lepton is fabulous but the tail really has issues. I know of some people that are actually using 72mm blades from a Swift which seems to help the tail hold better.

Joe
We haven't seen Colonel Angus around these parts for years!

12-26-2007 10:03 PM

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e-Hirobo SRB Quark - Lepton - XRB Coaxial > More thoughts, and data, on the Lepton tail...

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