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450 Class Electric Helicopters 450 Class Electric Helicopters manufactured by Align, Tarot, SYMA, Airhog, Chaos, HK and similar.


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Old 11-16-2013, 10:41 AM   #1
0veritas0
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Default T-rex 450L Dominator wobbles

I got problems with my 450L. During spool-up it wobbles a great deal but calms down a bit when it reaches higher RPM, but it stilll vibrates. When I'm in the air the tail wags, but it's hard to see if it is really the tail or if it is cyclic wobble that causes the phenomenon.

I'm using stock electronics, including 3gx with no updates made (probably v3.1). I can't find any play on the head, tail or main shaft that could, in my novice opinion, cause any vibrations (but question me if you like).

The 3gx is set up as instructed, main blades are tracking and both main and tail blades are balanced. I'm linking to my youtube video below. Is this a mechanical issue or is it the gyro?

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Old 11-16-2013, 10:49 AM   #2
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You might have a mechanical problem. The clacking sound right before lift off and the shaking- is either a mechanical problem... or...

What is your pitch curve in that flight video? You might have too much pitch which could cause the tail wag and low headspeed. And what scale is your TX curve? 0 25 50 75 100 or -100 -50 0 50 100 ?

I'm going to go out on a limb and further that by predicting you HAVE too much pitch. The helicopter should not make that much noise at hover. I realize you are in indoors... but that thing sounds like a fan... I think the blades are pitched too much, which slows the headspeed and puts more force on the tail, causing it to shake.

I also think the pitch is wrong because it bounces at spool up... which is the effect of the blade thrust forces pushing or pulling on the tail as the helicopter sits.

The manual does not give exact pitch values because your TX could have a different scale. But the three basic points of the pitch curve in normal mode should be Low Stick= -2* Mid Stick= 5* High Stick= 11*

I would guess you have significantly higher values for pitch. You can measure these with a pitch gauge or by calculation of your pitch range.

So my scale in my Futaba T8J is -100 -50 0 50 100 So if I setup my pitch range to have +- 13 degrees of collective......
at low stick -100... I would be using 100 percent of my negative pitch... which would be -13 degrees.

In normal mode, I don't want that at low stick. I want -2* at low stick. So I take a calculator and guess and check what value I need to get the correct degrees of pitch.

A value of -15 would be using 15% of my negative pitch range. So .15 x 13* = -2

Now I know that my first value in my pitch curve needs to be -15 to get -2* at low stick position.

There will be many opinions on how to setup the pitch and throttle curves... If you want to follow what Align would tell you... then program as such.

For a 0 25 50 75 100 scale-------------- Normal Pitch Curve = 44 52 74 84 93 -------Throttle Curve = 0 40 65 85 100

For a -100 -50 0 50 100 scale---------- Normal Pitch Curve = -15 6 40 69 87 --------Throttle Curve= 0 40 65 85 100

Again... this is a strong opinion based setting... but this is how Align sets up their RTF models.

Some may say these pitch curves will cause an altitude change at transition to idle up but by clicking into idle up during FFF.... you will not notice anything and it will be seamless.

Last edited by HighVoltage450; 11-16-2013 at 12:43 PM..
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Old 11-16-2013, 12:42 PM   #3
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Quote:
Originally Posted by HighVoltage450 View Post
You at least have a mechanical problem. The clacking sound right before lift off and the shaking- something is very wrong in the head.

What is your pitch curve in that flight video? You might have too much pitch which could cause the tail wag and low headspeed. And what scale is your TX curve? 0 25 50 75 100 or -100 -50 0 50 100 ?

I'm going to go out on a limb and further that by predicting you HAVE too much pitch. The helicopter should not make that much noise at hover. I think the blades are pitched too much, which slows the headspeed and puts more force on the tail, causing it to shake.

I also think the pitch is wrong because it bounces at spool up... which is the effect of the blade thrust forces pushing or pulling on the tail as the helicopter sits.
Thank you for your quick response. First of all, Ill give you the full story:

I made the setup of the 3gx as instructed and then went along and programmed the ESC. My throttle curve was set to 0-18-36-44-72. When I made the maiden flight I noticed that the heli started to wobble at approximately 40% of throttle stick. It also sounded as the headspeed was way to high (at least 3500rpm). I searched youtube for 3gx setup videos and found out that if I had to set up the throttle in the ESC after 3gx had to redo it on the 3gx again. When I recalibrated the throttle in 3gx the headspeed was a lot lower at this settings. But since I noticed the wobble I was afraid to set the throttle higher than 0-13-26-39-52. Could it be that I have to low headspeed? As you describes it, it seems to me that the throttle is to high for my headspeed and if I try a higher throttle curve it might solve, or at least reduce, the problem!
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Old 11-16-2013, 12:56 PM   #4
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You need to calibrate the governor/throttle in the 3GX with linear pitch and throttle curves.

So 0 25 50 75 100 across the board. After you are done with that step... you change them back to the flight conditions.

What was your pitch curve in the video though? What TX do you have?

Try my pitch and throttle curves from the above post... making sure you know which one to use for your TX...
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Old 11-16-2013, 02:08 PM   #5
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Quote:
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You need to calibrate the governor/throttle in the 3GX with linear pitch and throttle curves.

So 0 25 50 75 100 across the board. After you are done with that step... you change them back to the flight conditions.

What was your pitch curve in the video though? What TX do you have?

Try my pitch and throttle curves from the above post... making sure you know which one to use for your TX...
I used 0-25-50-75-100 on both throttle and pitch whilst setting up the 3gx. When I was done with the 3gx I programmed the ESC and then went back to recalibrate the 3gx throttle range. I use a DX8 and have it on 0-13-26-39-52 on throttle and 30-40-50-75-100 on pitch. Governor is not activated in the ESC since I wanted to be able to laborate with the throttle curve.

I use the low throttle curve since I was a little spoked of trying higher after the first take-off. On the first flight I used 0-18-36-58-72 on throttle with gov activated in ESC. Pitch was set as above (30-40-50-75-100). On aproximately 40% throttle on the radion the heli started wobbling. I kept trying and it lifted when the stick was about 60%. The effect was as on the video. I redused the throttle curve to 0-10-20-30-40 and the heli was quite stable, except for the tail that was wagging.
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Old 11-16-2013, 02:19 PM   #6
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Well your settings should work well enough.

Whats that massive shake in the head at lift off with the chattering sound?

Looks like something is bent.

Sometimes when you build a model- you put the helicopter on its side and push on it and unknowingly bend the mainshaft or other parts.

Its typical for a helicopter to straighten its main blades and bounce a bit... but yours seem to keep bouncing and never settle.

If you cant get it to settle on the ground... its not going to fly right in the air.
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Old 11-16-2013, 02:37 PM   #7
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I just tried 0-18-36-54-72 throttle and it sounds right now, but it still bounces. The sound you hear on the video is the landing gear bouncing from one side to another on the ground. It settles down before take-off, but the wobbling is way worse than you can see on the video (filmed with iPhone). It is almost as it tilts over and hit the blades on the ground.

Now I've double checked the main blades COG and it's fine. I'll check the pitch that it is 0 degrees at 50% pitch and that it is +-12 degrees on max/min pitch. If this is ok I'll check if main and feathering shaft is straight. It is a new helicopter, but it could still be bent.
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Old 11-16-2013, 02:44 PM   #8
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Originally Posted by 0veritas0 View Post
I used 0-25-50-75-100 on both throttle and pitch whilst setting up the 3gx. When I was done with the 3gx I programmed the ESC and then went back to recalibrate the 3gx throttle range. I use a DX8 and have it on 0-13-26-39-52 on throttle and 30-40-50-75-100 on pitch. Governor is not activated in the ESC since I wanted to be able to laborate with the throttle curve.

I use the low throttle curve since I was a little spoked of trying higher after the first take-off. On the first flight I used 0-18-36-58-72 on throttle with gov activated in ESC. Pitch was set as above (30-40-50-75-100). On aproximately 40% throttle on the radion the heli started wobbling. I kept trying and it lifted when the stick was about 60%. The effect was as on the video. I redused the throttle curve to 0-10-20-30-40 and the heli was quite stable, except for the tail that was wagging.
The takeoff problem sounds like it's mainly due to you not being at 0 pitch on spool up(since you say your pitch curve is 30-40-50-75-100). I am not positive but I thought the dx8 used a -100 to +100 scale for pitch, not a 0 to 100. (Edit: disregard that I am wrong about the dx8 using a -100 to +100 scale. But it does seem like there's too much pitch coming in before there is enough head speed to fly)

One other thing I noticed was your blades seem really loose, they folded back completely when you spooled up.

The wobble you see when hovering is a cyclic wobble caused by the dampers being too hard for that low of a head speed, it's inevitable on that DFC head.
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Old 11-16-2013, 02:55 PM   #9
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I might have found the problem. I double checked the pitch and it was 0 on both blades when I had the blades along the tail boom. When I turned them 90 degrees so that they were facing sideways (not sure how to explain it in english) it measured +1 on one side and -1 on the other. This has to be a faulty setup swashplate, right? And I guess this might cause cyclic wobbling? I've been about a degree off at 600 size before and the vbar has warned about "raised vibration level", but I guess that aon a smaller sized helicopter that same degree could be devistating!
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Old 11-16-2013, 03:40 PM   #10
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I'm interested in this problem as I've read about it before in other forums.

Aside from a part being physically bent, its possible your head is not mathematically correct.

All the linkage rods from cyclic servo to swashplate need to be identically the same length. If they are different lengths, it will throw off the cyclic and collective geometry.

You first 90 the servo horn and use subtrim to perfect the 90 degree angle. Then you attach the linkage to swashplate to get 0 pitch midstick and keep all the linkage rods the same length.

I'm not sure that's the cause of your shakes though.

I think the tail wag is from the headspeed being too low.
Align wants you at 65-70 percent throttle at midstick (straight out of the manual).... you are at 20.
I think you have turned down the headspeed because you have a bent part or crooked setup. While this may reduce your shakes... the tail can't lock like that.

Lastly, there is a Rudder Delay Value in the 3GX software that should be a 0
But before you worry about software settings- the helicopter needs to be perfectly still and locked just before liftoff.

When a helicopter bounces around like that... its usually a bent part.
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Old 11-16-2013, 03:46 PM   #11
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How tight are your main blade grips, and are they equal tightness?
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Old 11-16-2013, 05:24 PM   #12
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Default T-rex 450L Dominator wobbles

First of all, I don't think my blades are to loose. I have tightened them enough som that they will not fold when I lay the heli in the side and shake it.

Are you sure about 65-70%? The ESC needs 75-85% for the governor, wich means I need to stay below that value. Am I supposed to set the curve somewhat like 0-30-60-67-74?

Tomorrow I will make the swash setup again and make sure my pitch is set up correctly. I will also check the shafts if they are bent.

Until then, thank you all for your kindness and will to help! It seems to me that you are all agreeing to low head speed/high pitch and possibly a bent shaft. I will update this thread when I have done the above.
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Old 11-16-2013, 06:20 PM   #13
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You said stock electronics right? Don't use the governor mode on the Align ESC.

At least not until you get it flying right. The Align governor is a joker card you don't want in your deck right now.

Read the throttle curve in the manual. It is as stated above. 65-70 at midstick depending on your liking.

The throttle curve will match up to the values of -2* at low stick 5* at mid stick and 11* at high stick.
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Old 11-16-2013, 10:03 PM   #14
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Default T-rex 450L Dominator wobbles

Quote:
Originally Posted by HighVoltage450 View Post
You said stock electronics right? Don't use the governor mode on the Align ESC.

At least not until you get it flying right. The Align governor is a joker card you don't want in your deck right now.

Read the throttle curve in the manual. It is as stated above. 65-70 at midstick depending on your liking.

The throttle curve will match up to the values of -2* at low stick 5* at mid stick and 11* at high stick.
That is what I was thinking. I turned the esc governor off after the first flight.

Should I have 5 degrees at middle stick? Shouldn't it be 0? When I switch to idle 1 I will get a 5 degree drop which sounds a bit much. So my pitch curve would need to be something like 40-57-74-87-100?
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Old 11-16-2013, 10:08 PM   #15
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You want 0 degrees at mid stick in every flight mode. What some do is have a pitch curve of 0-25-50-75-100 in IU, IU2, and Hold, but in "normal" mode maybe something like 32-40-50-75-100. Everything past half-stick should match in all the modes.

This way when you first spool up, you don't have a lot of negative pitch pushing the heli into the ground, but you don't have any pitch changes once you liftoff and change into IU.
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Old 11-16-2013, 10:24 PM   #16
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Quote:
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That is what I was thinking. I turned the esc governor off after the first flight


Should I have 5 degrees at middle stick? Shouldn't it be 0? When I switch to idle 1 I will get a 5 degree drop which sounds a bit much. So my pitch curve would need to be something like 40-57-74-87-100?

The Align manual calls for +5 degrees at midstick. The Futaba manuals call for +5 degrees at midstick.

Like I already stated before, this is matter of personal preference. The reason I set it up this way, is that the collective is metered and progressive in pitch while still maintaining a consistent headspeed. I dont use governors on 450s... so I like the pitch to meet the throttle with precision in normal mode.

From midstick on up, the collective feels so much better in normal flight mode ( because I have no governor keeping RPM)

Its really up to you how you want to do it.

The real way you are supposed to be doing this... is measuring the actual blade pitch in degrees with the stick at the three basic positions. Low Mid High . Then tailoring the other values to transition.

If you change your full collective range.... then your pitch curve has now changed. Getting -2* at low stick position requires a different value when the max collective changes from 13 to 14 degrees total.

So when someone tells you to use X X X X X pitch curve- the actual blade pitch in degrees will vary at the stick positions depending on your max and min collective throw.

If you take 50 percent of 14* (collective pitch) ---- it will be different than 50 percent of 9* (collective pitch) One gives you 7 degrees of actual pitch and the other gives you 4.5 degrees of actual pitch. Big difference.

To be clear, I dont think any of this is relevant to your problem.

You have a nasty shake that isn't going to work while spinning at 3400 rpm.
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Old 11-16-2013, 11:04 PM   #17
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If you're wanting to fly 3D, you want zero at mid stick, with equal positive and negative at high and low stick.

I've never went with the 5 degrees of pitch at mid stick...seems more suited to scale flying, in my opinion.
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Old 11-16-2013, 11:20 PM   #18
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Theres pros and cons to both.

The way Align, Futaba and myself recommend- you have a jump at the transition to idle up from normal mode. But you gain a very smooth application of pitch and throttle while in normal mode without a governor. The helicopter just feels better for some people this way. This is the standard that can be found in nearly every manual from every manufacturer.

Your way, you slide easily into idle up with no pitch change, but the collective feels terrible when simply flying around and landing.

I fly 3D. That has nothing to do with it. We are talking about normal mode here.

Im curious Jimmy- if you have ever actually tried -2 degrees low stick 5 degrees at midstick 11 degrees at high and given Align, Futaba and many others the chance. You know, those guys that actually design and build all this stuff...You say you never have, so how can you form an opinion of it?

If you are just taking 5 sets of numbers that someone else has told you to use- your helicopter isn't tuned. If you tried setting it up by actually measuring the pitch of the blades instead of just plugging in 5 sets of numbers- you might experience a revelation in how the helicopter feels at takeoffs, landings and general accuracy in flight.

Ive tried both ways several times. I'll gladly take the jump into idle up versus the horrible collective feel. The pitch change is easily resolved by either changing into idle up during forward flight (the pitch change is nullified) or by using the delay function in the TX.

Im not trying to be rude... Just a bit curious how you can disregard what the actual manufacturer of this exact model recommends- and you've never even tried it.
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Old 11-16-2013, 11:20 PM   #19
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Default T-rex 450L Dominator wobbles

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Originally Posted by jimmy77611 View Post
If you're wanting to fly 3D, you want zero at mid stick, with equal positive and negative at high and low stick.

I've never went with the 5 degrees of pitch at mid stick...seems more suited to scale flying, in my opinion.
Yeah, that's how I've been setting up my helis ion the past.

But as HighVoltage450 says, I got massive vibrations which I need to resolve first. I will spool up without blades and check the feathering shaft and without head to check the main shaft. And as I understand, the tailwag should most likely disappear, or at least reduce, as soon as I get higher HS?
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Old 11-17-2013, 01:15 AM   #20
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It seems as the main shaft actually IS bent. Its hard too se on the videos, but take a close look as the motor is about to stop.


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