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9253 Problem ?

Old 01-17-2003, 05:10 PM
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Fissy
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Default 9253 Problem ?

Hello,

When running the servo test, my 9253 t/r servo jumps. All the other servos slowly move from one endpoint to the other. As the 9253 moves to the left, it speeds up slightly just before it gets to the endpoint. When it starts to move back to the right it jumps from ~ 10% to 40% of the total travel back to the opposite endpoint. I have disconnected the control rod to no avail. When I turn off the power and rotate the servo by hand, it seems to move freely back and forth. I have set the 401 gyro travel screw to min and max and everything in between to no avail. I have the delay set at 0, the direction normal (reverse on the radio), and DS set to ON. I've only burned 3 gallons since I bought it. I recently crashed though and I can't remember running the servo test since I first put the heli together.

Any ideas
Old 01-17-2003, 09:31 PM
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Default 9253 Problem ?

Idea #1: test your servo without the gyro and you'll likely feel a whole lot better about it.
Old 01-19-2003, 07:24 PM
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Fissy
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Default 9253 Problem ?

321,
Great suggestion ! Yes, when I bypass the gyro, it tests out just fine. However....

The problem is still not cured because when I fire up the heli in HH mode, the gyro is not working properly. It rotates slowly (nose right) and the red light double-blinks which indicates that "... the rudder signal from the transmitter in the AVCS mode is different from the neutral signal memorized in the gyro ..." (according to the gyro manual). It initializes fine but starts to blink once throttle is applied. When I switch to non-HH, it works OK (albeit I probably need to adjust the mix a little). I have always kept the gain at 100% in the past and it doesn't make a difference what I set the gain to now.
Any ideas

Another issue I have is with the main rotor head. It wobbles. I have replaced the main shaft and bearings and the head itself. W/o the head the shaft rotates dead center perfect but when I put the head on (no grips, no links, just the head), it wobbles. I have tried putting it on several times. When I start the heli, it shakes a little until I get close to lift-off speed and then it's solid.
Any ideas on how the install the head so it doesn't wobble ?

TIA
Old 01-19-2003, 11:02 PM
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Default Concerning the gyro

The double light is telling you the gyro detects a rudder input from your radio. It happens a lot during operation. When the rudder stick returns to neutral position on the transmitter in AVCS mode, the light will go solid on again - provided that the gyro was last reset with the stick in this position. As you advance throttle, you're likely adding a small amount of inadvertent rudder and that will be enough to trigger the light signal on the gyro. It is normal while in AVCS mode.

When you say the nose rotates to the right, when is this happening? You're not using any Tx trim on the rudder are you? Does the tail drift in one direction while in normal mode with no Tx rudder trim? In case you don't already know, tail drift in normal mode should be minimized with linkage adjustments with Tx trim set to neutral. Don't use Tx trim on the rudder to compensate for mechanical issues! Drift issues should always be first addressed in normal mode. Finally, do you carry the model while in AVCS mode? If so, you should reset the gyro's neutral before engaging the clutch by quickly moving the rudder stick back and forth three times and then letting it snap back to neutral. Otherwise, it will immediately attempt to return the model to boot-up heading.

100% gain is most likely too much for that gyro/servo combo and excessive gain will overwork the servo. Because the 401 apparently doesn't hunt on some helis (on mine it does) when the gain is too high, use just enough gain to get the job done for your level and style of flying. 70% is a good starting point in my opinion. If, one day, you find the tail isn't holding during fast backwards in HH or the piroette speed is inconsistent during quick-traveling piros, try bumping up the gain a bit.

Hope all this helps.
Old 01-20-2003, 02:48 AM
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basmntdweller
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Default 9253 Problem ?

Be sure you don't have any revo mix. That may cause the inadvertant wandering.
Old 01-20-2003, 03:24 AM
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ralfhofm
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Default 9253 Problem ?

If you run the servo test with the remote gain connected, the gyro switches from normal to AVSC mode as the gain channel cycles through. That causes the irrate tail servo behavior.

Ralf
Old 01-20-2003, 03:47 AM
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Fissy
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Default 9253 Problem ?

My test is as follows:
1. Set the heli down on a concrete slab in my backyard
2. Turn on radio, turn on heli (gyro initializes as normal in HH mode)
3. Start heli (gyro light still solid in HH mode)
4. Apply 5% (25% total travel since I start at 20% throw for idle) throttle
5. Gyro light double-blinks. Any movement, or no movement, to throttle (left stick) and light blinks.
6. Only way to stop light from blinking is to return throttle to 0% (20% throw)
Without touching the radio, light blinks everywhere but 0% throttle.
Heli rotates right constantly when above 0% throttle (obviously since 0% means clutch disengages and rotors eventually stop) even when no input at all is given.
Tail does not drift/move in normal mode. It operates fine.
I do not touch the heli after turning on power, not to mention starting.
No trim is set.
No gain setting makes a difference.
The only revo mix is in normal mode which works fine. It's only HH mode that there is a problem.
HeliProz indicated that servo test mode on a HH gyro is inconsistent so I am not paying any attention to it.

Any other ideas?
Old 01-20-2003, 11:24 AM
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basmntdweller
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Default 9253 Problem ?

You are ahead of me as I haven't figured out how to change from HH to normal and have the revo mix shut off in HH. I always have mine off and don't use revo in either mode. Let me know how to set my 9c so I can turn revo on in normal without having it on in HH.
Thanks,,,basmntdweller
Old 01-20-2003, 12:01 PM
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Default 9253 Problem ?

The only way the gyro is going to detect throttle stick movement while in AVCS mode is if it is receiving a rudder command instead. And that would mean that the Tx is mixing throttle and rudder while in AVCS mode, which will automatically turn the tail. No amount of gain will stop the gyro from turning the tail when it's commanded to do so.

If the light is double-blinking after the throttle position is moved, the gyro is receiving a command to turn the tail. Period. Inhibit your revo mix and test for a steady light with varying throttle positions and neutral rudder. You need to find out what's causing the inadvertant rudder command and revo mix is the primary suspect.

Good luck and stick with it.
Old 01-20-2003, 08:20 PM
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Fissy
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Default 9253 Problem ?

321,
I'll re-check to see if there is any mixing occurring on one of the menus.

Anyone have any ideas on replacing the rotor head on a Venture ?
Old 01-21-2003, 12:37 AM
  #11  
Fissy
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Default 9253 Problem ?

Somehow I screwed it up I was using a switch to toggle HH mode but the mxing was not switching, instead it was staying on in both modes. I have changed it now to use an idle-up to toggle HH mode. It works fine now. I guess I still have some learning to do on my radio

Thanks for all your help

I'll go ahead and post the rotor head question in the JR heli forum. It'd be more appropriate there.

Thanks again

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