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Apr 20, 2008, 04:19 AM
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EQMOD's Avatar
Discussion

The Brushless Direct Drive Tail Rotor with Servo Control Concept


Well, this is not meant to prove anything yet (perfomance, response, etc.). I made this mod to demonstrate the possibility of having a brushless tail rotor rotating at a constant speed (well based on the speed fed at Channel 3), and which the blade pitch is being varied by the usual gyro controlled tail servo. Others may have already tried using this mod but may have not realized its true capability so i will be reporting it here.



Consider this. The tail has to quickly respond on the commands of the gyro and the rudder/yaw commands fed by the user. A motor driven tail has to rely on "quick" motor speed changes for a responsive yaw control. Speed changes has to be "quick" on both spooling up (counteracting torque for a positive yaw) and spooling down (deacceleration for allowing the main rotor torque to take over for a quick negative yaw). The problem with a motor driven tail is that the speed change is not that quick as the tail has to "accelerate" or "deaccelerate" first before the desired speed is achieved. The acceleration/deacceleration factor is heavily dependent on the weight of the tail rotor blades and the motor's shaft and armature. With a "dual motor" mod , you achieve a quick speed change but still it has to accelerate and it also increases the overall weight including the armature thus the opposite yaw would be slower unless you apply some sort of "braking" mechanism in there in order to have the same quick response effect on spooling down.

Some would even use a "brushless tail motor" or a ducted fan mod sort to speak but those motors need some time to accelerate and deaccelerate as well thus yaw control would still be a problem plus the fact the a duct itseld would even add a certain amount of momentum on the tail causing yaw overshoots and undershoots.

Well, the best tail rotor response would still be a belt drive option as you will only deal with a constant tail blade rotational speed, and you would only rely on the pitch of the blades to counteract the torque and with these much quicker pitch changes, no acceleration/deacceleration factor will affect the perfomance of the tail and your heli's heading will be tight.

But what about helis without a belt drive ? I am presenting this concept of having still a motor driven tail but with a constant speed and the yaw is still dictated by the pitch of the rotor blades instead of the usual motor speed changes.

The parts used on my mod may not be appropriate at this point but with lighter components, this should work;



I used the smallest brushless motor i could find and found this one. Its a "Blue wonder - 1100K/V" brushless motor. The shaft i used here is a CP2 main rotor shaft, yup - one of my spares.



Which is controlled by a small 10 ESC -



I used a HBK2 tail component for the adjustable blade pitch option. Here is how it looks when assembled;





Mounted on one of my "experimental" helis. Take note - NO beltdrive or Dual Motor mods....



Last edited by EQMOD; Sep 09, 2008 at 06:02 PM.
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Apr 20, 2008, 04:56 AM
Droner
SebastianJ's Avatar
Nice work, I'm working on a similar setup only smaller scale using EP100 parts to fit my 200 and 300 size helis.

can we have a video please? I'd like to see how much punch it delivers.
Apr 20, 2008, 04:56 AM
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EQMOD's Avatar
Ok, mod will not be complete without a test video. Take note of the last part of the video while i did some hover tests with random hard rudder inputs. You will see how tight the tail is;

The Brushless Direct Drive Tail Rotor with Servo Control (6 min 57 sec)


Some of the test results;

1. Brushless Tail Motor and ESC did not even get hot which means the weight of the tail blades plus the corresponding pitch controls are just right for the load requirements of the motor.

2. Tail control is very tight as the tail rotor rotational speed is being maintained. Yaw data is purely a blade pitch play.
Apr 20, 2008, 05:09 AM
Registered User
chench's Avatar
Nice work. I think the Trex guys something similar to this when working with scale fuses with raised tails, avoiding having to 'bend' the belt to get it to clear the fuse. I'm sure I saw one with a servo controlled tail but i can't find it now. This is a simple motor controlled tail.
https://www.rcgroups.com/forums/show...1&postcount=11
Last edited by chench; Apr 20, 2008 at 05:17 AM.
Apr 20, 2008, 05:56 AM
Droner
SebastianJ's Avatar
Power piro's, c'mon let's have em!
Apr 20, 2008, 06:43 AM
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EQMOD's Avatar
Quote:
Originally Posted by bas10an
Power piro's, c'mon let's have em!
To tell you the truth, i am not that good in executing those stunts. Although the tail speed is much faster than when it is rotating using beltdrive. So i guess the piros on these is much faster.

Obviously it will be a crazy tail if we use a direct drive 4900K/V brushless motor
Last edited by EQMOD; Apr 20, 2008 at 07:04 AM.
Apr 20, 2008, 07:34 AM
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EQMOD's Avatar
more video tests with a better view of the rudder tests;

Brushless Direct Drive Tail Rotor with Servo Control (2 min 28 sec)


From here you will see how "tight" the tail is even on a standard rate mode gyro. Such movement is not possible for "speed varied tail yaws" because of the time the motor needs to accelerate or deaccelerate.

In this case, the motor is kept at a constant rate and the tail servo still does the yaw control for the heli.
Last edited by EQMOD; Apr 20, 2008 at 07:52 AM.
Apr 20, 2008, 07:37 AM
Heli Hooligan
There was a guy here (Roffey) who did the same thing with his Walkera 52. He fitted a Baby Feigao brushless motor to the tail and used the pitch slider from the Gaui EP100. He lives not too far from me and I had atest flight with it. The tail held just as good as any of my other belt drives. I was well impressed with it.
Apr 20, 2008, 07:59 AM
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EQMOD's Avatar
Quote:
Originally Posted by mahbouni
There was a guy here (Roffey) who did the same thing with his Walkera 52. He fitted a Baby Feigao brushless motor to the tail and used the pitch slider from the Gaui EP100. He lives not too far from me and I had atest flight with it. The tail held just as good as any of my other belt drives. I was well impressed with it.
Exactly my point . Its not actually the belt that gives better tail control. Its the blade pitch that does the work. By allowing the blades to pitch positive or negative, the yaw performance on both direction is pretty much identical.

The Fiegao motors are 3900Kv right ? Those should perform better than the 1100Kv that i am using. Although a 1100kv should be enough for a good controllable tail. Higher KVs should give a better response.
Apr 20, 2008, 08:04 AM
Heli Hooligan
The Feigao he used was 5250Kv.
Apr 20, 2008, 08:48 AM
Registered User
EQMOD's Avatar
Quote:
Originally Posted by mahbouni
The Feigao he used was 5250Kv.
5250KV on direct drive ? Now that is one tight tail
Apr 20, 2008, 09:03 AM
Heli Hooligan
I think it was geared but not 100% sure
Apr 20, 2008, 09:12 AM
Victim of C.D.O.
murdnunoc's Avatar
Great, great mod!

I've been waiting to see something like this executed. I know it's been done, but I haven't seen it. Thanks for sharing!

Can you get an RPM reading on the tail at hover power?

That would help in motor selection, I'd think. Too high kv and you have to get a higher current motor to drive the DD rotor or gear it down, which I'm sure you don't want.

Most belt tails have ratios of 1:4 to 1:5, so if you could match your motor to give a ratio just a little higher than that, you'd have the killer tail with just as much motor as you need.

Have fun!
Apr 20, 2008, 09:37 AM
Registered User
EQMOD's Avatar
Quote:
Originally Posted by murdnunoc
Great, great mod!

I've been waiting to see something like this executed. I know it's been done, but I haven't seen it. Thanks for sharing!

Can you get an RPM reading on the tail at hover power?

That would help in motor selection, I'd think. Too high kv and you have to get a higher current motor to drive the DD rotor or gear it down, which I'm sure you don't want.

Most belt tails have ratios of 1:4 to 1:5, so if you could match your motor to give a ratio just a little higher than that, you'd have the killer tail with just as much motor as you need.

Have fun!
We can actually compute for this;

at 1100kv and using a 11.4V lipo and hover at 50% throttle, thats 1100*11.4*.5 (direct drive)

which results to 6270 less 15% tail load, thats roughly equivalent to 5300 revolutions which i think is pretty high considering thats only a 1100kv brushless in there.
Apr 20, 2008, 03:14 PM
Registered User
EQMOD's Avatar
I noticed one of the rotor blade is inverted on the above still images. Just ignore it as this was corrected during the tuning and test process


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