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Old 02-25-2008, 10:31 PM   #1 (permalink)
 

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Default B400 Gyro drifting

I have set my linkage up to where the bird holds great in Std Rate mode. But as soon as I flip the switch to HH mode the heli starts in a left turn which requires constant right stick input. Dialing in 11-13 clicks of right rudder trim in HH mode makes it lock in and hold a heading. Turn it back to Std and it holds again. I've set the gyros gain trimpot to 100, 75 and 50%, and it happens in all positions. My TX gain values are 67 and 64. If I go to 70 with gyro at 50% I get tail wag.
Does this sound like a jacked up gyro? I'm unsure which way to go with it.
Thanks for any input, guys.
~Ron
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Old 02-25-2008, 11:18 PM   #2 (permalink)
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We've found it likes to be trimmed out here as well. Holds well and doesn't drift that way. I found it extremely weird for a HH gyro. So it isn't just a jacked up gyro, imho. We just got our head around setting it up differently and fly it. Perhaps someone else has a different method, but it works. I haven't had a chance to find another way yet.

Mike
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Old 02-25-2008, 11:51 PM   #3 (permalink)
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Default "Oh good, then it's not just me."

Classic Austin Powers quote from AP2.
Thanks for the reply, Mike. Did you also set yours up to where in Std Rate mode you don't have any, or very minimal, nose drift? Also, is it normal to have to play with the trim once the battery starts flattening out and dropping on power? My tail will start drifting when power starts coming down. I think I have to go left trim back towards center (remember, it starts out at about 11 clicks of right). I'm still new to heli's so I'm still trying to let all the details soak in.

~Ronbo
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Old 02-26-2008, 01:10 AM   #4 (permalink)
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ave u tried setting up the tail
like how most of us did with the 401 you will find that you wont need any Tx trim
just adj mechanical and will hold
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Old 02-26-2008, 01:37 AM   #5 (permalink)
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We set it up mechanically in std and it still drifts in hh. To me that was what made it bizarre. But once trimmed out in hh it works reasonably well. We just wanted to find a cheap upgrade, like a tail servo, that would work reasonably well with the stock gyro and lock in. I haven't really had much time or the weather to go beyond that... so guys in the warmth may have gone further. I found the trim did change slightly throughout the flight.

Unfortunately most just swap out the gyro and servo, so the stock gyro doesn't seem to be getting a whole lot of attention. I think it could do pretty well with a little love and a good servo. The 9650 does turn it into a different animal. But I guess we'll see.

Mike
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Old 02-26-2008, 04:53 AM   #6 (permalink)
 

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Quote:
Originally Posted by ronbo422 View Post
Dialing in 11-13 clicks of right rudder trim in HH mode makes it lock in and hold a heading.
~Ron
That isn't holding a heading, thats just a substitute for a good deal of manually requested turn rate!

try moving the servo ball down to the 3rd hole (you need to open it up first before the screw will take) and to reduce binding move the servo mount up one hole as well, then chop the remaining servo arm off to stop it catching. Center the rudder in rate mode and then adjust the servo arm to be perfectly vertical, and eyeball the rear to be mid throw as well. Mid throw appears to give the right amount of pitch to counter main blade torque.

then boot it up in HH mode with zero rudder trim, and use sub-trim to dial out most of any creep you see at the tail (slider creeping).
reboot several times to check your sub-trim figure really is working. Also check it isn't creeping when idling at decent speed on the ground after boot up. Including a few hours , or the next day later! if the best sub-trim figure keeps changing there is no point setting it.

then boot up in HH mode and see if there is any drift with zero rudder trim in an actual hover.

i think sub-trim is finer than rudder trim by the way. I could find a solid heading with only 4 on subtrim and zero rudder trim. It still isn't perfect though, it looks solid but if I just hover hands off the rudder, the tail can be observed to very slowly move away from the compass point, maybe 1 or 2 degrees every second.

I guess the gyro has a slowly shifting idea of a locked heading that depends on one or more factors such as tail vibration, temp, battery voltage. It can't possibly be hooked into magnetic north, it must be based on guesses due to measured angular momentum. Maybe the process of trimming out the bird physically reduces vibration and ends up reducing gyro error?
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Old 02-26-2008, 05:21 PM   #7 (permalink)
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I installed a Spektrum DSP75 on the tail and also moved the servo arm linkage ball inward one hole, to the middle position. I was able to raise my gain to 74% in the TX.

I think it works a little better than the stock setup but a still have a slow CCW yaw. I haven't made additional linkage adjustments yet but I think I can get it better. The pitch slider is almost halfway between center and the tail case but that may be due to the lack of thrust at my altitude (8,000FASL), I'm not 100% sure how much that plays a role yet.

Have any of you tried different positions on the physical gyro gain pot on the gyro?

I know the manual says it has no effect on the HH gyro but others around the web are finding that having it at full CCW or full CW makes the gyro hold better.
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Old 02-26-2008, 08:18 PM   #8 (permalink)
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Wolfpackin,
I've got my ball link on the 2nd hole out from servo shaft to tame it way down. I've tried the actual trimpot at 50%, 75% and 100% and still have the drifting CCW like you stated. I can trim it out with R rudder but it takes about 11-13 clicks to get it to hold where you put it. That's too much, in my opinion. I can see 3 or 4. But 13?
The TX gain is about 66 on HH and 64 on Std Rate.

~Ron
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Old 02-26-2008, 08:56 PM   #9 (permalink)
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I put the DSP75 on the tail when I stripped the aileron servo. I got the programmer, set it up as a tail rotor servo and switched the gyro to digital. I'm running 62% gain. At 63% I get a little tail shake. Checking the servo and gyro on he bench, there was a big difference in how much and how quick the servo moved when the gyro was in analog or digital mode. I can't speak to how well the tail holds in flight since the weather here hasn't been that good and what little time I've had flying was dialing the heli in and dialing me back in. It's been a long time since I flew helis.
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Old 02-26-2008, 10:39 PM   #10 (permalink)
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Ron,
Have you tried shortening the tail pushrod a bunch, at least 3-5 full turns?

I would go to the middle hole on the servo arm. Most agree it's the sweet spot. If you want to soften things up use D/R and Expo or even Travel Adj.
Both your gains are HH mode. You need to go below 50% to get into Rate mode.
I would think you could raise the gain to at least 70% with the linkage ball in the second or third hole without getting wag. Were you getting tail wag above 64%?

Sorry, didn't see you stated that you tried different gain pot positions in you OP.


Mike,

Same here, still playing with setup adjustments with the DSP75. But my gain is up to 73%. Probably because mine is not reprogrammed.
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Old 02-27-2008, 12:40 AM   #11 (permalink)
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Wolfpackin, did you put the gyro in digital mode. You can with the DSP75. Then I bet you have to turn the gain back down.

Actually, I got to setup the whole enchilada tonight. I'm using my DX6i to fly the simulator, my CX2, a foamie and the B400. Switching programs tonight somehow I lost the B400 programming. I knew something was up when the model type came up Airplane instead of Heli. Lost everything but the model name. I was going to put in new servos anyway, DSP75s on the cyclic. This just increased the hassle factor somewhat. Thank God I didn't fly it like that.

Anyway, here's the best part. The E-Flite servos are all reversed compared to every servo I have. OK, just reverse the servos in the TX. AIL & RUD are reversed in the stock setup, so now they are normal, ELE and PIT are reversed. Then I used the stock swash mixing. Wa-law, the swash is working correctly. Level the swash at neutral and at full throws, swash mixing is good.

I'm thinking all is good, so I decide to do a run-up on the floor with no blades to check for swash binding. First though, I checked the tail rotor. The stick is making the blades go one way and the gyro is doing the opposite. No problem, reverse the gyro right. WRONG! When I put the DSP75 on the tail and programmed it as a tail rotor servo, I also used the programmer to reverse it. So, I needed to reverse RUD in the TX and not reverse the gyro. Needless to say, I nearly crashed spinning it up on the floor with no blades. Oops! Man that tail got away from me fast. Easy to do when the gyro is working against you.

So, I get to go through the whole setup process again. Weather might be OK later in the week.
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Old 02-27-2008, 12:59 AM   #12 (permalink)
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I have Digital mode on the gyro, 73% gain in the TX and the linkage ball in middle hole of the servo arm.

Wow, you took the long way around to set those up.
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Old 02-27-2008, 01:16 AM   #13 (permalink)
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Wolfpackin,
I shortened the linkage a little to get the tail to hold at 64%, which you say is still HH. Flipping the switch puts me at 66% and the nose drifts left (ccw). I just plugged stock numbers from DX6i into my DX7. Maybe at 50% gyro trimpot setting and 64% in my Tx my bird is happy 'cause that's where the tail holds. I'll play with turning the Std Rate value down to 50% tomorrow and see how she acts. Oh, and I was getting wag at about 68% Gyro Gain. 66 and it stopped. I've moved my linkage back out one hole to the middle and I'll test-fly it tomorrow, being wary of the tail getting away from me, which I don't think it will.

Thanks to everyone for the great info. I think I'll get this thing nailed down soon.
~Ronbo
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Old 02-27-2008, 01:37 AM   #14 (permalink)
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Makes sense.
Before I moved the linkage ball I couldn't get above 67% gain without getting a wag.
And I moved it and switched to the DSP75, in digital mode, at the same time so Im not sure which had more effect on being able to raise the gain to 73%.
I have read elsewhere that moving the ball makes a big difference. I don't know if the DSP's are much better than stock.

I still have adjustments to make so I think it will hold pretty good, I don't expect it to be a GY401.
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Old 02-27-2008, 07:05 AM   #15 (permalink)
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When I put int he DSP75 on the tail, I changed it to the 3rd hole on the servo arm and I still ended up at 62%. Going through the heli last night I may have figured out why. Remember I already reversed the DSP servo I put on the tail. I was also figuring out how the endpoint adjustment on the programmer worked. Initially, I lost almost all the throw from the servo. In getting the throw back, I probably maxed it out. So, even in the third hole on the servo I had too much throw and was binding at then end points. Stock servo ATV is 90%, I'm at 75%. Of course the gyro doesn't care about ATV, it just moves the servo. I bet if I turn the RUD ATV back up to 100% and reprogram the servo endpoints so it doesn't bind I'll be able to turn up the gain to where you have it.

No, I didn't mess with the endpoints on the cyclic servos when I re-programmed them because I wanted them to all move the same.

Tonight I'll put the blades back on and check the pitch. And, I'll reprogram the endpoints on the tail rotor servo so there's no binding at 100% ATV.

Just as an FYI, based on my observations, the stock servos appear to be 90* servos. i.e. at 100% ATV they move 45* in each direction from center (90* total). The DSP75s are also 90* servos out of the box; however, with the programmer, you can make them anything from 10* servos to 120* servos. I bet my tail rotor servo either is, or is close to, a 120* servo.

It will be interesting to fly it after putting in DSP75s all around. They may share the same case and gear train as the E-Flite servos, after that, all similarity ends. It's a much faster, more precise servo.
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Old 02-27-2008, 05:21 PM   #16 (permalink)
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the atv for rudd is for piro rate
i would leave at 90 both ways
and leave the gyro at 100 both ways

if u flip the gyro swith while in the atv menu you will see the diffren values in ieach position same goes for the all inputs

all mine are set to 100%

unfortunatly u will not be able to stop it from over throwing your tail slider unless u have a gyro in with has an limit adj

even when i had the stock setup the tail held well in a hover
with no trim or any adj just centered the slider on tail shaft
made sure control inputs were proper and gyro compensated right
and my gain was 65-66 depends on what i was doing but was ok
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Old 02-27-2008, 07:27 PM   #17 (permalink)
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Actually, I fixed it by programming the servo endpoints. The servo can't travel far enough to bind the tail anymore and the gyro can't overide the servos programmed endpoints. Plus I can set the RUD ATV to 100% now. After doing all this it will be interesting to see where the gain ends up. 65% will be a good place to start. After loosing the the program and replacing the servos I'm going to have to trim the heli again and track the blades again. Oh well.
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Old 02-27-2008, 08:21 PM   #18 (permalink)
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by lowering the atv in rudd it slows down turn rate
but hey its you bird fly what comfertable
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Old 02-27-2008, 08:35 PM   #19 (permalink)
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I actually have 100% ATV now. TR servo cannot bind because I used the servo programmer to set the end points. This way I actually have max piro rate in both directions, I cannot mechanically get any more throw. (Not that I need it I may have too much now)
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Old 02-27-2008, 08:37 PM   #20 (permalink)
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some peole set thier atv less one wat and more the other to make the heli rotate the same in both directions
since the heli has a natural tendency to counter rotate the blades
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