V911 Notes 02 - RC Groups
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This thread is privately moderated by Ribble, who may elect to delete unwanted replies.
Aug 16, 2012, 01:57 AM
Crash and learn

V911 Notes 02

Transmitters That Bind And Fly V911 Helicopter
V911 Wind-Surfing
Motor Overheating
Gyro Test
Spins nose-right (clockwise) problem
Rudder Fake-out
Mixing Arms Reversed
Troubleshooting And Other Information
Stuck Servo
Servo Repairs
V911 Helicopter Printed Circuit Board (PCB)

Transmitters That Bind And Fly V911 Helicopter
Stock V911 transmitter (and V929 quad transmitter), still best bang for bucks.
Turnigy 9x and clones
FS-CT6B - What I use when wind is steady, allows hands off hover pointing into wind.
Unconfirmed report that Trex 100 is "fully compatible"
FS-T6 reportedly

In my opinion, the best for price, performance, ease of use, is the stock V911 transmitter. But then I only fly V911's in low rates windsurfing outside, Elevator trim full forward.

V911 Wind-Surfing
For forward flight with the V911, push the nose down and add throttle. Throttle makes it go faster as well as maintaining altitude.

When playing in the wind, keep the nose down or the V911 will float away in the wind. Control forward speed with throttle. Practice nose-left (counter-clockwise) turns to circle around and dive back into the wind. Nose-right turns are easy but hard to pull out of because the V911 picks up too much speed.

Motor Overheating
To check for motors overheating, touch the main motor and kiss the tail motor. Touching tail motor to your nose also works quite well, but my nose isn't calibrated for heat. After you kiss the tail motor, get in the habit of blowing air into the tail rotor and get used to the sound it makes. Doing these things can save you a lot of headaches.

Gyro Test
Gyro only tries to correct an uncontrolled rate of rotation using tail motor.
Hold the helicopter in your hand
Apply throttle
Tail motor speeds up when helicopter rotated counter-clockwise (nose-left)
Tail motor slows down or stops when helicopter rotated clockwise (nose-right)
Tail motor speeds up when throttle increased.

Spins nose-right (clockwise) problem
Nose-right spin as viewed from tail indicates that the tail motor is too strong or that the main motor is too weak.
Push the tail boom into the main frame.
Push the tail motor towards the main frame.

Spins nose-left (counter-clockwise) spin.
Nose-left spin as viewed from tail indicates that the tail motor is too weak
There are brushes (electrical contacts) inside the motor that alternate the magnetic fields. The contacts get dirty or burned. Then sit idle for a week and corrosion starts. It never will get better. One hour in the air is a long time, but normally not a problem unless you overheat the motor. Kiss the motor or touch it to your nose to tell how hot it is. Blow into the tail rotor to make it spin and listen to the sound.

Still, you may get lucky. Remove the tail rotor (propeller) and imagine that there is hair or spider webs or whatever wound around the motor shaft (metal). Scrape this off going from motor outward. Replace the rotor.

"Recalibration" - Place the V911 on a flat level surface. Insert the battery. Quickly (within seconds) turn the transmitter on. This resets the electronic gyroscope inside the helicopter to see the flat level surface as the ground zero starting point. You have to do this every time you insert the battery.

You can test the gyroscope by hand hold the helicopter and run the motors. Rotate the V911 counter-clockwise and the tail motor speeds up. Rotate clockwise and the tail motor slows or stops. Yes, you first have to have a working tail motor.

Tail motor most times can be replaced by cutting the wires at the tail motor itself, then use same wires to connect new motor. Solder wires, then coat with nail polish to insulate and fix in position for crash protection. Not recommended, but some people scrape the wires clean, twist together, and do not solder.

If in doubt, a suspect bad motor can be tested by disconnecting a wire and jumper to a 1.5v battery. Possible (?) that this test could be done without first disconnecting a wire, but in the least, if you get the polarity wrong you will fry the snub diode on the printed circuit board.

Rudder Fake-out
Power off transmitter
Push rudder full left or right and hold
Power on transmitter
If you mess with the rudder potentiometer, then the transmitter knows and remembers

Mixing Arms Reversed
Reverse both mixing arms so that short-side goes to flybar, long-side goes to swashplate.
This makes the flybar dominate the V911 and makes it very stable. Oddly, it still flies quite well in heavy wind, just not as fast, and the wind doesn't bother it so much.

If only one mixing arm is reversed, the blades and balance bar tend to lock up due to different overall linkage lengths. Usually a result of replacing blades, then forcing the linkages back in place with one mixing arm reversed. V911 may hover OK, but there will be little if any aileron or elevator control. Correct way is long end of both mixer arms feed the balance bar and short end of both mixer arms fed from swashplate.

Troubleshooting And Other Information

Stuck Servo
Use a small screwdriver to slightly push the solder towards the three servo pins. Then test the servo. If it works, you may want to solder the pins. Photo is Aileron servo. Elevator servo is on the other edge.

V911-PCB Aileron servo pins

Back out 1/2 turn the screw holding the servo arm on the servo. (per Martyn McKinney)

Servo Repairs

V911 Helicopter Printed Circuit Board (PCB)
While here and looking at a clean V911 PCB, note the missing antenna.

V911-PCB-Parts V911-PCB-Parts
The parts, left to right...
Main motor FET
Antenna hole
16MHz crystal
Electronic Gyro
Gyro mixer ??
Tail motor FET
Tail motor snub diode

On the top (?) of the printed circuit board, below the battery connection, is a diode symbol and a bunch of missing parts. This was for a battery voltage boost circuit, or a negative voltage generator. My Yellow V911's still have this circuitry and one of my Yellows lost the ferrite core inductor.
Last edited by Ribble; Feb 23, 2015 at 12:46 AM.
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