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HomeAircraftHelicopterMiniature Aircraft Whiplash & Fury 55 › Help with X-cell and 401
12-11-2004 10:44 PM  13 years agoPost 1
airriley

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Lynchburg, Va USA

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I would appreaciate some help with this as I am new. I got an x-cell graphite that I upgraded the gyro to a 401 with the servo package. Used existing arm, wich is working fine for hovering, however it seems short. Any of you guys using the same setup, could you tell me the length of the rudder servo center to ball-link hole? The reason I say its short is that when checking things on the bench in normal mode and I go full collective the 9254 actually reaches its limits and cannot go anymore. Seems to me that I need a longer arm and less revo mix so i have left servo travel to use. Also just checked the tail and at full collective there is about 1/8" travel left. Currently the rudder ball link is about 8.7mm from the center. Is this about right?
I am just probably mostly confused, but it seems to me that you would need to have leftover right yaw authority even at full colllective. Granted I am using it in heading hold mode for now, I'd still like to know if my revo mix is set up right.
Also I am confused on the trimming out of the 401 between the two modes. Currently in HH mode it holds well at mid trim, if I want to fly in normal mode I have to put in much left trim. Do i need to correct this mechanically first, or do I need to just trim out in normal, land and flip the switch three times?

Any help is much appreciated in advance.

Mike

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12-12-2004 03:37 AM  13 years agoPost 2
rcheliflyer

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calif., usa

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Seems to me that I need a longer arm and less revo mix so i have left servo travel to use.
Hi,
what gyro did you use before ? a non HH type ?
anyway revo should be turned off / inhibited when using a 401.
Do all your initial setup and mech trimming in N mode, then test fly in HH the 401 will compensate for revo.
You want the servo arm legnth to use about 100 % of the 401 limit setting for as much rudder travel as possible, it can only set both R and L together, using the adj pot on the gyro.
This travel limit and correct trimming in hover in N mode will allow the 401 to do it's job , great gyro
If your limit is way over 100 closer to 140 then your servo arm is too short.
As long as the setup is correct don't worry about where the tail linkage
is on the bench at full collective, those movements are just the gyro
trying to keep the tail from moving , so they don't mean the same as when revo mixing is used with the non HH gyros.

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12-12-2004 04:39 AM  13 years agoPost 3
Wyn

rrApprentice

Oregon, USA

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To add to what Howard already mentioned -

To switch the gyro from Normal to HH, you have to be able to switch off P>R mixing ("revo") off when you switch to HH mode. Many radios won't do this. Also, when you turn on the 401 in HH it memorizes that position as neutrol. So you would have to remember to be in HH when you turn on the RX (or remember to flick back and forth 3 times). It can be done, but it's a pain and not worth it. Did it this way when HH first came out - and then dropped the method in favor of HH all the time.

Regarding the travel limits: my preference is to adjust the arm length(s) so that with limits at 100 percent, the tail blades tilt about 20-25 degrees each way. On some heli's, the pitch slider alllows a lot more travel than that.

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12-12-2004 06:03 AM  13 years agoPost 4
Dr.Ben

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Richmond, VA, USA

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Indeed, the best way to set the gain is to start with a low gain setting of around 50%, and then increase it to the point that the tail holds acceptably well for your most demanding maneuver. This technique is kindest to your expensive T/R servo, since flying just below the wag threshold overworks the tail servo (it can get HOT).

A servo arm length in the 12-14 mm range works well for most X-Cells. Try to keep the limit set at or around 100%. It is important to set the limit for no binding at extremes not so much for any airborne reason but because it protects the servo for bottoming out and stalling if you pick the model up and turn it around while handling on the ground. This can also apply when you're carrying the model out to fly and the tail boom is boucing off your leg a little bit. Hard to describe the latter point in words, but I think you'll know what I'm talking about.

Ben Minor

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12-12-2004 01:33 PM  13 years agoPost 5
airriley

rrNovice

Lynchburg, Va USA

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Thanks guys and Dr. Ben for the actual number. Yes, revo mixing is turned off in HH mode and it does great.

What I am confsued on is the fact that if I go to normal mode I need a lot of left trim to keep it from tuning, whereas in heading hold mode the trim is center, wich makes sense to me.

The gyro that was in it before was a futaba mechanical. I got the whole bird off ebay, was showing it to a heli friend and he was worried about the excessive noise the gyro was making. So he lent me a new JR 1000 ( i think it was) also a mechanical. When changing it out I also changed the rudder servo to a digital. Well we found out that this was a bad combination, servo would never settle down. In troubleshooting the problem my help was cocerned that the servo was bad, so to check it we bypassed the gyro, and the servo started acting normal again. So he hovered it with no gyro, it did pretty well, so I tried it. Flew the whole weekend like that, man is that a lot of work. Realized I might as well get a good gyro, so thats when the 401 combo came in.

I'd just like to know how to get it trimmed out in both flight modes, I should be able to go between the two in hover without any change right?

Thanks

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12-12-2004 03:17 PM  13 years agoPost 6
Dr.Ben

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Richmond, VA, USA

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To an extent, the 401 in HH will hold the tail straight even if the mechanical trim is off in normal. At a certain point, though, it will cause drifting to occur when the degree of mistrim is excessive. Get the model in hover, tail comps still OFF and in normal mode. Adjust the trim with the pushrod just like in the days of mechanical gyros and until the tail stays straight. Make sure you have enough gain in normal (50-60%) to damp out spurious tail movements. Don't touch the trim on the radio. Once satisfied, either do the quick switch toggling to learn the new trim position, or land and reboot the system in HH. That should keep the model in trim in HH and normal. Remember that the tail still won't stay straight at any point but stable hover in normal unless you then go back and set up the tail compsl. Doing so is largely nothing more than an exercise, since you'll fly in HH all the time.

Ben Minor

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