Cedar Rapids, IA
You don't find simple canned settings on line. Each heli is different, and even basic setup stuff is highly dependent upon servo type, manufacturer, how far out the links are on the arms, and a whole host of other variables.This is a giant, long post. But it covers 3GX setup from start to finish, and is viable for any heli in which it is installed.-----You have a DX8, and you have a 250DFC. The topic says 3GX -- are you using a 3GX unit, I have to assume it is this one:and not the MR or MRS version.AS such, I also assume you have at least one satellite receiver hooked up (that's all your 250 needs, by the way).If you have the 3GX connected to a Spektrum or JR satellite receiver, and your DX8, the first thing you need to do is to make sure your DX8 is set up to use Channel 7 (AUX 2) as the tail rotor gyro control channel. You MUST use channel 7 out of your transmitter in this configuration for the gyro gain to work, as in this configuration, the 3GX expects gyro gain control to be on Channel 7. You cannot change this in the 3GX, you have to configure the transmitter properly.-----On the 250 with the 3GX, the servo controlling the left-front corner of your swashplate is plugged into the PITCH output of the 3GX. The right-front corner of the swashplate is controlled by a servo plugged into the AILERON output of your 3GX. The center, rear servo of your 250 plugs into the ELEVATOR output of the 3GX. The rudder servo plugs into the RUDDER output and your ESC plugs into the THROTTLE port of the 3GX unit.The signal lead of all servos and the ESC are closest to the top of the unit, the ground lead, closest to the bottom.-----Your transmitter must be set for 3 servo, 120 degree swashplate control.-----The travel limits for each channel should be set to 100%.-----Next, you need to get the three swashplate servos moving correctly. This is done with the 3GX unit operating in DIRect (DIR) mode. In DIR mode the gyro functions are bypassed and all servo control goes directly to the servos without gyro interaction.Before you start, set your five pitch curve points to:0 -- 50 -- 50 -- 50 -- 100. You will have a big flat spot at 50%. As long as your throttle/collective stick is anywhere in the big flat spot, your three swash servos should be centered, at neutral. This will aid in the mechanical setup later.-----Enter DIR mode -- transmitter ON, hold the button on top of the 3GX unit down WHILE you plug the power into the 3GX unit. Watch the five LEDs on the 3GX unit. As soon as your TX and RX link up, the LEDs will begin to light in sequence. RELEASE the button during this period. The first LED labeled DIR will light up. The 3GX will remain in DIR mode till you exit by pushing the button again, or until you turn power off.-----All of the next steps are performed with the 3GX unit operating in DIR mode.-----In DIR mode you need to set your transmitter up so the three swash servos move correctly, just as if you were setting up a normal flybar, 3-servo, CCPM system.Use the Aileron and Pitch reversing functions in your transmitter to make the left and right front servos move correctly. When you move the aileron stick left and right, one servo moves UP, the other moves DOWN. It does NOT matter at this step if the two servos move in the correct direction with regard to the aileron stick, they just need to move one UP, one DOWN with aileron command.Next, move the elevator stick fore and aft. The two front servos need to move in the same direction (UP or DOWN), and the elevator servo needs to move in the opposite direction. If the two front servos move UP, the elevator servo needs to move DOWN. To fix this, use the elevator reverse function in the TX. Again, it doesn't matter if the movement isn't correct with regard to the stick, it is important that the elevator servo moves in the opposite direction of the two front servos.-----To get the swashplate moving correctly with regard to the stick, use the Transmitter SWASHPLATE menu.Standing behind the helicopter, if you move the aileron stick to the right, the right side of the swash should move DOWN, the left side should move UP. The elevator servo should NOT move at all. If the swash moves the correct direction, great. If it moves the wrong direction, find the AILERON number in the SWASHPLATE menu. It defaults to +60. Use the scroll wheel to change the AILERON number to -60. This will reverse the aileron direction.Move the elevator stick forward, the rear of the swashplate should move UP, the front should move DOWN. If it moves the wrong direction, change the sign of the ELEVATOR number in the SWASHPLATE menu from +60 to -60.You should now have the servos moving correctly with respect to each other, and with respect to the elevator and aileron function.Move the collective stick to its full up position, the swashplate should move UP the main shaft. If it moves DOWN, change the PITCH number in the swashplate menu from +60 to - 60.Now the swashplate should move correctly for left/right aileron, fore/aft elevator, and collective pitch.-----With the swashplate moving correctly, the next step would be to get the mechanical setup correct.Move the throttle/collective stick so it is somewhere inside the big flat 50% part of the pitch curve and leave it there for the next set of steps.The three servos must be centered, their output arms must all be horizontal.You can reposition the arms on their servo output shafts to get the arms close to horizontal. Due to the arrangement of the splines on the output shaft, you may be able to get close to horizontal, but not dead on. Once you get the arms on so they are close to horizontal, use SUBTRIM for each individual channel to get the three arms horizontal.The left-front servo will be affected by the PITCH (channel 6) transmitter subtrim function, the right-front servo will be affected by the Aileron subtrim function, the rear elevator servo will be affected by the elevator subtrim function.In addition to having things moving in the correct direction with regard to each other and the sticks, you should now have all three servos centered, and their output arms horizontal.Next, adjust the pushrods supporting the swashplate so that the swashplate is level, perpendicular to the main rotor shaft.With this step out of the way, adjust the two pitch links between the swashplate and the main rotor grips until you have zero degrees of pitch in both main rotor blades.You now have the servos moving correctly with regard to each other and the sticks, the servos are at neutral with the throttle stick centered in the 50% flat line portion of the PITCH curve, your swashplate is level, and you have zero degrees pitch at mid collective/throttle setting.-----Next, move the throttle stick to its 100% position and measure the pitch. Use the PITCH number in the SWASHPLATE menu to set the desired full-pitch setting -- 12 degrees. If you need more pitch, adjust the PITCH number to be closer to 100%. If you need less pitch, move the PITCH number closer to 0. Do not change the SIGN of the PITCH number.Move the collective/throttle stick to its zero % (full low) position and measure pitch again. If you had set +12 degrees of pitch with the stick at 100%, you should see -12 degrees of pitch with the stick at its 0% setting.You now have everything moving correctly, a level swashplate at neutral and mid stick, you have zero degrees pitch at mid collective, and close to +/- 12 degrees of pitch with full stick travel.-----Turn the head so the feathering shaft is aligned with the fore/aft centerline of the heli. Move the aileron stick full left/right. Using your pitch gauge, set the aileron cyclic travel to 8 degrees for full aileron stick. Adjust the AILERON number in the swashplate menu to get the 8 degree of cyclic pitch value.Set the ELEVATOR number in the swashplate menu to the same value as the aileron number (leaving the sign properly set.-----You now have all servos moving correctly, moving properly with the sticks, a level swash at mid collective and neutral, zero degrees of pitch at mid collective, +/- 12 degrees of collective pitch travel, and 8 degrees of cyclic pitch in both aileron and elevator travel.This completes the DIR mode setup steps.-----Set your collective back to its center position, the 0 degree pitch setting and leave it there.Push the button on top of the 3GX one time. The E. Lim LED will light. Push the ELEVATOR stick to its full down (forward) position, then back to neutral.Push the 3GX button again. The E. REV LED will light. Lift up the tail of the heli while watching the swashplate. It should tilt in the opposite direction of the tail. If you move the tail up, swash should tilt toward the rear. If you move the nose up, the swash should tilt toward the nose. If the swash moves in the same direction as the nose or tail, move the ELEVATOR stick until the 3GX status LED changes color (red to green, or green to red). Recheck fore/aft movement to make sure the swash tilts opposite the nose/tail movement.Push the 3GX button again, the A LIM LED will light. Move the aileron stick full right and back to neutral.Push the button again, the A REV LED will light. Tilt the heli left or right, while watching the swash. It should tilt in the opposite direction. If it moves the same direction as you tilt the heli, move the Aileron stick to change the color of the status LED (red to green, or green to red). Recheck to see that the swash tilts opposite the tilt of the heli.Push the 3GX button one more time. The unit will go through a brief initialization sequence. You have completed the mechanical setup in DIR mode, gotten the servos moving correctly, have the correct mechanical setup and have set the correct pitch travel and cyclic travel. You have taught the 3GX that you are using a 3 servo CCPM setup, have set the aileron and elevator travel limits, and have gotten the 3GX to correct for pitch/roll movements as it should.GO BACK AND SETUP YOUR PITCH CURVES as desired. Don't leave that 0 - 50 - 50 - 50 - 100 pitch curve in your TX, that was a setup setting ONLY.-----If you have built your 250 correctly, right rudder stick will make the tail rotor servo PULL the tail rotor pushrod FORWARD, to the nose of the heli. If right rudder command makes the servo push the rod to the rear, REVERSE the RUDDER channel IN the TRANSMITTER.-----The next steps will set up the tail rotor gyro function.With the TX on and the 3GX up and running and initialized, hold the 3GX button down for a couple of seconds and it will enter the gyro setting mode.The steps in sequence set:Servo neutral pulse width (1520 or 760 usec)
Digital or Analog servo
Normal/Reverse gyro correction direction
Left/Right travel limits
Delay (heli size -- 450 or smaller, 500 or larger)
Whether the 3GX is installed right side up, or upside down.Each setting step will time out after a short time if you do nothing. You can easily re-enter the gyro setting mode by holding the 3GX button down for a couple of seconds, then stepping through the seguence by pushing the button till you get to the desired sequence step.The rudder stick will be used to set up all gyro related functions, moving it left or right while watching the color of the status LED.Enter the gyro setting mode...Your rudder servo most likely uses a 1520 usec wide neutral pulse. The STATUS LED should be green. (If your servo uses a 760 usec neutral pulse, move the rudder stick til the status LED turns RED).Push the button one time. The gyro will be in Digital/Analog servo select mode. If you have a digital servo (again most likely) the STATUS LED will be GREEN. (To select analog servo mode, move the rudder stick till the STATUS LED turns RED).Push the button one time. Pick up the heli and turn its nose to the LEFT while watching the tail rotor servo. It must PULL the pushrod FORWARD, to the nose. If it pushes to the rear, move the rudder stick until the STATUS LED changes color (from green to red, or red to green). Verify that the servo now pulls the rod forward when you turn the nose of the heli to the LEFT.Push the button one time. You will now set the left and right travel limits for the rudder. Move the rudder stick to the right while watching the pitch slider. When the slider reaches its limit of travel, let go of the stick. If you over shoot a bit and the servo is stalled, move the stick slightly back until you just stop the binding. Wait until the STATUS light changes color (I believe it goes from green to red -- doing all this from memory). Then move the rudder stick the left, to move the pitch slider to its other limit. Stop just before the slider bottoms out (or if it does bottom out, move the stick just a bit the other direction until the binding is gone. Let go of the stick, again wait for the STATUS LED to change color.Push the button again. You will select the DELAY. Since this is a 250 sized heli, move the rudder stick so the STATUS LED turns RED. This will select small heli mode.Push the button again, if the 3GX is mounted right side up, the STATUS LED should be GREEN. If the 3GX is mounted upside down, move the rudder stick to change the STATUS LED color from Green to Red.Push the button one more time, you have completed the rudder gyro set up.Turn everything off.
-----Finally, set a straight line, 0 to 1005 pitch curve, and a straight line 0 to 100% throttle curve in your transmitter.Have your transmitter ON, throttle stick full low, full negative collective.Hold the button on top of the 3GX unit down while applying power to the 3GX system. Watch the LEDs as they sequence. Let them continue to sequence till all five turn ON. Let go of the button.Move the throttle stick from its full low position to its full high position. After a couple of seconds, the 3GX unit will reset. Move the throttle stick to full low and turn everything off.-----You have now set up your heli correctly in DIR mode, taught the 3GX unit its basic travel limits and correction direction, you have set the tail rotor gyro functions correctly, and you have calibrated the 3GX to your full throttle/pitch range.This completes the 3GX setup.-----If you plug in the PC link and have the unit powered up, transmitter on, and your PC software running, you can look at the current settings (and write them to disk, or recall previous settings and set the 3GX to those old settings). You can make setting changes, you can look at the maximum pitch, roll and yaw rates you have set, you can see the current elevator and aileron gains, and change some flight parameters.You can verify that the unit is in SMALL heli mode and that it understands if it is right side up, or upside down.You can also see which version of software is loaded, and either update to newer software, or revert to older software.-----I would suggest that you find the CYCLIC EXPO setting slider in the 3GX PC software and set that to ZERO. (Hit the WRITE button after setting the value to ZERO). Use your transmitter EXPO for aileron, roll, and rudder functions.-----The 3GX stock settings generally work well without furhter tweaking. Fly the heli before screwing around with other settings.Settings that MIGHT need tweaking after flight --Torque precompensation. If you romp on throttle and the nose swings left or right, adjust this parameter to fix that. The 3GX PC software tells you how changing the number affects the result.Cyclic precompensation. If you romp on throttle, you want the heli to ascend vertically, without dropping the nose or tail. Adjust this value if the nose or tail drops when you apply sudden throttle/collective.
-----You should have set your DX8 gyro control to run using Channel 7/AUX 2 as noted way way way above.If you use your GYRO SENSE menu, make sure it is set to use Channel 7/AUX 2. Numbers in the menu for each flight mode go from 0 to -100, and from 0 to +100. Negative values put the gyro in RATE mode, and the STATUS LED will be RED. Positive values select Heading Hold operation and the STATUS LED will be GREEN.Note that in the rudder gyro setup stuff, if you have the gyro in RATE mode, setting the left and right travel limits is much easier to do.-----Finally, if you are using software Version 4.0 or 5.0 -- set the rudder gyro to RATE mode operation. Hover the heli. Adjust the tail rotor linkage until your heli does not want to yaw left or right in a hover. RESET your LEFT and RIGHT travel limits to prevent binding. You should be able to run a fairly high rudder gain with version 4.0 or 5.0.-----
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