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Old Jan 27, 2012, 10:36 AM
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Razzor111's Avatar
United States, TX, Amarillo
Joined Jan 2012
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Dh 9104

Hey all I got my new DH 9104 and would like to know why the Heli will go in nose in circles. I know to expect the slide to the left but after the copter gets up it starts to go in a right nose in circle. I have tried to trim the tail rotor to make it stop but I'm not able to get it to work. The nose does drop down as it starts the circle any help would be most appreciated.
Thanks
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Old Jan 27, 2012, 11:42 AM
Crash and learn
United States, PA
Joined Dec 2011
1,605 Posts
The helicopter nose pitches down and helicopter tilts to the right, ending up in a slow right moving forward circle?

The helicopter moves forward, but wants to rotate on a horizontal plane (yaw)?

The circles are more than once every few seconds or less? Any wind at all will cause tilting on lift off and uncontrolled flight.

Have to see if this is yaw due to tail rotor or gyro, or tilting due to forward speed and not being able to correct or maintain heading.

A good check is to unplug the main rotor from the electronics board. Throttle up, and the tail rotor speed should increase with throttle. With throttle up, test gyro by rotating helicopter, tail rotor should increase and decrease speed as electronic gyro tries to correct rotation (yaw).

Do the rotor blades flop down when you tilt the helicopter? Both blades should seem very loose and adjusted the same.

Your first message here on rcgroups, so can't tell if you have prior experience with helicopters. Your description of flight suggests prior knowledge.
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Last edited by Ribble; Jan 27, 2012 at 11:55 AM.
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Old Jan 27, 2012, 11:44 AM
LearningFast
United States, LA, Denham Springs
Joined Jan 2012
410 Posts
Congrats! Some can fly out of the box and some cannot. Did you charge the battery really well before use. I have found that when the batter starts to go low, the rotor gets less power and cannot compensate very well. If it is charges well, you should have 8.4V. I did not like the Li-Ion battery, so I switched to LiPo and fitted the copter with matching plugs as the battery. Check the TX for the trim knob is at center before starting. Check to make sure the trim slider is centered, also. If the motor is good, it should compensate. My motor went bad and would actually stop.

To stop the left drift at start, you can actually cut off each end of the rear rotor blade about 1/4 inch. You have an extra, so give it a try if you want. I can throttle up and take off with hardly any left drift at all now. If you can't go forward, take off the servo link at the swashplate and turn counter clockwise to level out the swashplate or put it in a slightly forward slant. Make sure the link on the servo is in the last hole. Also, you can put some plummer's putty in the front of the nose just to make it a little nose heavy, but just a little. You have to experiment.

Read and look at some of the mods in this thread. I would order another tail boom which includes the motor. Also, the tail motor is encased in plastic with no hear relief, so I drill holes top and bottom to let some of the heat esscape. I might make it last longer, but not sure yet. I will post a picture later. Enjoy!
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Old Jan 27, 2012, 12:15 PM
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United States, TX, Amarillo
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The helicopter nose pitches down and helicopter tilts to the right, ending up in a slow right moving forward circle? [B]Yes the nose pitches down then it goes is a right hand turn.
The tail does work as I have tested the gyro moving the tail ether direction and it counters to move
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Old Jan 27, 2012, 12:22 PM
Crash and learn
United States, PA
Joined Dec 2011
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I never tried to correct a tilt to the right. A slight tilt to the right and very slight nose pointing right is necessary to correct the tendency to drift left caused by the rotor rotation and tail pushing left (viewed from rear).

Bent flybar.
A link is pushed in toward rotor shaft instead of riding on ball.
Anti-rotation pin (swashplate forward) is not in slide guide.


Ken is tilted to the right and is the expert on swashplates.
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Old Jan 27, 2012, 12:45 PM
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United States, TX, Amarillo
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Quote:
Originally Posted by Ribble View Post
The helicopter nose pitches down and helicopter tilts to the right, ending up in a slow right moving forward circle? Yes this is what it is doing

The helicopter moves forward, but wants to rotate on a horizontal plane (yaw)?

The circles are more than once every few seconds or less? Any wind at all will cause tilting on lift off and uncontrolled flight.

Have to see if this is yaw due to tail rotor or gyro, or tilting due to forward speed and not being able to correct or maintain heading. I have checked this and the gyro is working fine

A good check is to unplug the main rotor from the electronics board. Throttle up, and the tail rotor speed should increase with throttle. With throttle up, test gyro by rotating helicopter, tail rotor should increase and decrease speed as electronic gyro tries to correct rotation (yaw).

Do the rotor blades flop down when you tilt the helicopter? Both blades should seem very loose and adjusted the same. Yes they do

Your first message here on rcgroups, so can't tell if you have prior experience with helicopters. Your description of flight suggests prior knowledge.
Yes I do have some knowledge of Helicopters as I was a UH-1 Mechanic in the Army for 6 years.
Sorry I'm a noob on forums
In the 1980's I flown the FP 3 channel gas "Cricket" Helicopter
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Old Jan 27, 2012, 01:27 PM
Crash and learn
United States, PA
Joined Dec 2011
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I am at a loss to suggest what to do. I'm reading it as a tilt right and inability to correct using tail (rudder).

There is the obvious, like center of gravity is off due to weight distribution or bent tail boom. Something not assembled correctly - the anti-rotation pin out of the guide is almost impossible given the sturdy two fixed forward links holding the swashplate fixed plate. Just looking for something that would favor the DH9104 unusual right tilt.

Main rotor turning too slow or tail rotor turning too fast would cause the problem. That is main rotor speed relative tail rotor speed.

OK, suppose something crazy like the tail rotor is wired backwards.

Normal (for my DH9104):
- Right rudder (right stick right) makes the nose turn right.
- Forcing the nose left, the gyro causes the tail rotor to speed up.
- Forcing the nose right, the gyro causes the tail rotor to slow down (can't hear this while main rotor turning).
- Turning the "LEFT/RIGHT TURN" knob in upper right clockwise causes the tail rotor to speed up.

As to forward flight:
- Right stick up causes pitch forward (servo pushes rear of swashplate up).
- Turning "BACKWARD/FORWARD" knob in upper left clockwise causes pitch forward.

Ken has the best ideas. Trimming the tail rotor by 1/4 inch is a good try. Poor Li-Ion battery is possible.
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Last edited by Ribble; Jan 27, 2012 at 02:52 PM.
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Old Jan 27, 2012, 07:18 PM
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United States, TX, Amarillo
Joined Jan 2012
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Thanks for your input guys.
Now I found something with the Transmitter if I put a little right yaw in to correct for the torque letting the stick go back to center the transmitter will hold that input until I make make an other input to stop it from turning to the right. I think this is why it makes the right turn and then make the nose drop ?
Now how do I get the Transmitter to stop doing this? The stick is not sicking it springs back to the center.
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Old Jan 27, 2012, 08:00 PM
LearningFast
United States, LA, Denham Springs
Joined Jan 2012
410 Posts
I have not experienced any TX abnormalities. Guess I am lucky! I was unlucky today, though! Flying good with just a little wind, which I can now work through. The copter seems to respond rather well with the swashplate mods. I was getting ready to install the direct drive tail rotor and snap, I grounded against the mainboard as I was checking polarity on the tail motor. Well, the tail rotor is now stuck in full throttle, so the PCB(mixer) is shot. I have another on order. Another thing is the modded swashplate is seperating, which I have only one idea why. It is possible I have to make up a new side mount for the swash that may be 2mm longer. Or, just go ahead and order the metal swashplate I found. Hmmmm.
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Old Jan 27, 2012, 09:05 PM
Crash and learn
United States, PA
Joined Dec 2011
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Quote:
Originally Posted by Razzor111 View Post
the transmitter will hold that input
The transmitter uses 40 year old technology and doesn't have the brains to hold an input. In real flight, pulsing a right rudder will cause the helicopter to yaw and not return (but it should not continue to increase yaw further).

To confirm what is happening, unplug the main rotor from the Electronic Speed Controller (ESC), and concentrate on the tail motor (rudder). You can hear a change in speed and hear the tail motor hold the last speed or drop back to stick neutral.

On mine, right rudder causes tail rotor to speed up (forcing tail left) and returns to normal speed after stick neutral.

Further, with full right rudder the tail motor spins faster and continues to spin faster for 1 second after I switch the transmitter off - loss of signal causes control hold for one second, then stops (failsafe mode). Not that this tells you anything more than what happens when you fly out of range.

OK, anyway, if right rudder causes tail rotor speed to increase and it doesn't drop back to normal after stick neutral, then I would think that you have a mechanical problem with the stick in the transmitter. Potentiometer mounting is loose, etc. The "LEFT/RIGHT TURN" knob can also move the stick rudder into a range where left rudder does nothing (on mine) though I haven't seen the opposite where the knob allows left rudder to work and fails right rudder.

Again, if you are actually flying the DH9104 and the helicopter yaws and holds that yaw, then that is normal. In fact, the electronic gyro will try to hold the yaw - actually momentarily tries to correct an uncommanded yaw change or heading change. Stick neutral from right rudder should cause no change to the helicopter heading and the yaw should hold where you stopped.

OK, I am guilty of complicating my explanations. So, if you make the helicopter fly sideways and release the stick, the helicopter should continue to fly sideways until the inertia wears off.

Heading Hold vs. Yaw Rate Gyros
http://www.rchelicopterfun.com/rc-helicopter-gyro.html
http://www.rcgroups.com/forums/showthread.php?t=1016943
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Last edited by Ribble; Jan 28, 2012 at 12:24 AM.
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Old Jan 28, 2012, 02:41 AM
Crash and learn
United States, PA
Joined Dec 2011
1,605 Posts
Ken - As best as I can see the ESC board circuitry, battery positive goes to the printed circuit board (PCB), through the main motor connector, red wire to main motor, back from the main motor on black wire to connector, to switching transistor which pulses the black wire (motor negative) to battery negative, completing the circuit. Ditto tail motor, different color wires.

However, the snub diodes are connected directly across the motor connectors on the PCB and the exposed leads are battery positive.

The switching transistor heat sink tabs appear to be connected to the motor negative (black wire) and while I haven't tried it, shorting the tabs to ground should cause the motor to spin.

The only decent ground that I found to poke a voltmeter lead is on the forward left corner of the PCB. The tab on the +5 volt voltage regulator (3 leads and heat sink tab soldered between mounting screws) is at +5v output to receiver, gyro, mixer, etc and is switched by the side mounted orange on/off switch.

A litlle late, but you don't want to short the exposed snub diode leads to anything.

If the PCB LED lights when the receiver gets a signal from the transmitter, then your damage may be limited to a shorted switching transistor next to the tail motor connector (likely a 50 cent low voltage high current switching FET).

"The little 8 pin guy next to the main motor FET" (((( EDIT: Probably not a FET driver))) is a FET driver similar to FDS8812NZ-20AmpMOSFET, rather rugged for how small it is, but then the drain-source resistance is only a few milli-ohms and they don't dissipate much power except during the transition from short to open.

However, since you have the good fortune to actually remove the PCB, would you be so nice to post a picture of the underside, please. And get some numbers off those FETs. Thanks. My eyes are too old to read those small numbers.
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Last edited by Ribble; Feb 02, 2012 at 09:09 PM.
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Old Jan 28, 2012, 11:39 AM
LearningFast
United States, LA, Denham Springs
Joined Jan 2012
410 Posts
9104 pcb picture

Here is the picture of the board front and back.
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Last edited by Ken59; Jan 28, 2012 at 11:39 AM. Reason: forgot to upload pictures
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Old Jan 28, 2012, 11:40 AM
LearningFast
United States, LA, Denham Springs
Joined Jan 2012
410 Posts
Try it again

Pictures!
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Old Jan 28, 2012, 03:01 PM
Crash and learn
United States, PA
Joined Dec 2011
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Ken - Thanks for the photo's. They enlarge nicely and making brighter/contrast brings out unseen details. Far better than using a magnifying glass, lots of light, and flipping the board constantly to compare top and bottom.

I should have borrowed a camera and done that with the DH9104 transmitter instead of having it in pieces for a week.

So nice! I never saw so much detail just looking at my PCB.

---
Nagging questions about 4th channel ghost on DH9104
Older April 2011 version of DH9104 PCB. Note full heat sink tabs, newer version has 8 pin dual FET driver (?) at "Missing FET". Somewhere mixing is done to add throttle and Gyro to rudder and the 8 pin FET may be where.

In the same series of Killbucket older photo's, the transmitter "Missing Pot" is only a connector for a DC recharging jack that isn't there, hence D1 isn't needed either and only robs power (0.6v drop from battery voltage).

As to the "Missing Servo". I couldn't find any transmitter signal that ends up on this servo signal land.
http://www.rcgroups.com/forums/showp...8&postcount=41
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Last edited by Ribble; Jan 28, 2012 at 04:12 PM.
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Old Jan 28, 2012, 03:19 PM
LearningFast
United States, LA, Denham Springs
Joined Jan 2012
410 Posts
Thanks! Let me know what part you want the number off of. Just post it again with an arrow and annotation.
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