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Home✈️Aircraft🚁HelicopterBeginners Corner › Trex 500 shake/guiver
04-02-2012 12:44 AM  7 years ago
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SGM Retired

rrApprentice

Toney, AL. USA

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Trex 500 shake/guiver
Well it's me again with my rebuilt 500. I now have upgraded to metal blade grips and torque tube. Just a update if you are just tuning in. These upgrades are after a major crash I had 1 week ago. The last couple of flights prior to the crash the Heli would shake to make the skids go left/right. This is not a nose/tail left right but a top/bottom shake.

The LHS said it might be static due to belt drive. So I did the grounding of boom to frame but this did not fix the problem. I thought the TT change over would have fixed that but for my first flight today after rebuild it did the same shake. There is no certain move I do to the Heli it just happens when it wants. During a 7 minute flight it will shake 5 or 6 times for a 3 to 4 second duration.

I don't have a clue what else I could replace unless its my ESC which is stock or the Rx (Spektrum) which is stock too. Can anyone shed some light on this subject?

PS. Today was my first flight after the crash and I must say I was shaky also for the first 30 seconds then all is calm. I'm back in the seat again.
Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-02-2012 12:48 AM  7 years ago
steve 01

rrProfessor

Grand Rapids MI

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Does it shake all the time or only with lower head speeds ?

Also does it go up and down gently while hovering ?
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04-02-2012 01:23 AM  7 years ago
dkshema

rrMaster

Cedar Rapids, IA

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Your receiver and/or ESC won't make your heli shake. Don't waste time or money replacing them.

The description of the shake is a bit confusing...skids go left/right and it's a "top/bottom" shake.

If it's somehow a shake induced by servos moving, perhaps you have a gear in a servo that's missing a tooth.

Recheck all wiring to eliminate the possibility that you've chafed the insulation badly on one or more wires, especially at points where they go through holes in the carbon frames, or around other carbon-frame corners.

-----

Another thought from left-field. Small probability, but you sometimes gotta cover the weird cases as well. The DX6i transmitter has had its share of stick potentiometer problems. These should have been solved by the time you bought yours, but one never knows for sure. Go to your TX "monitor" screen and watch the slider position indicators as you slowly move the right stick. If you see erratic movement, you'd need to have the TX serviced.

-----

Are you flying repaired side frames? (from another thread of yours). If so, did you get ALL the weak spots identified and repaired?

-----

Does the heli make any strange noises when the shake happens? Motor slow down, speed up, sound erratic?
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-02-2012 02:36 AM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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WOW, let me start at the top.

1. The shake happens at hover speed, now don't ask me what that speed is please. I have tried max throttle and back down thinking that might trigger it but it does not. The Heli does go up and down when hovering but I think thats me on throttle, Dx6i gimbal are not that good I think. Thanks Steve for your reply.

2. My good friend Dave, I agree on the skids left/right as though it was a boat and it is tipsy. As for the servos I do test those before every flight as to work them all directions with throttle hold on before lift off. They all act correct but I have not stuck my ear up to them for a sound check. Remember it just started doing this prior to the crash and I had never had a crash before.

3. I do a slightly smashed aileron wire, happened when I replace the frame. The wire is intact and works as what I can see. The frames were new but I hope to repair the others soon as a backup.

4. No noise that I can tell, I have had it within 10 of me when it shakes but I don't hear anything. Now let me quantify that, my hearing is not the best thanks to Army life of many years.

5. Well test Tx after I post this to check it out. Thanks Dave.
Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-02-2012 02:42 AM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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I checked Tx and they seem to move smoothly through the range.Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-02-2012 02:46 AM  7 years ago
dkshema

rrMaster

Cedar Rapids, IA

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You may not be able to hear the servos make a funny noise if you have a missing tooth, but you can slowly turn them from end to end by hand (power OFF, of course) and can feel the missing tooth.

What motor, how many teeth on your pinion? I assume a 6S battery pack.

What is your throttle setting for your ESC at what you call "hover" where this happens?

What do you have for throttle "curves" and what might the throttle setting be when you notice the shake?

Is the shake FAST or relatively slow (as in a wobble, instead of things being a blur)?

Is the shake side to side only, or does the heli just kind of wobble around the mainshaft in all directions?

It might be something as simple as your head speed being too slow, or your rubber head dampers might just need some grease. They should not be dry.

-----

Double-check that aileron servo wire to make sure it truly is intact.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-02-2012 03:07 AM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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Ok Dave that's going to take some research to answer some of these Qs. As for the wobble it's slow where you can see it with no problem. It is side to side for what I can see from a tail-in hover.

The motor and pinion are stock and the heli is out in the shop so can't get to it to verify tonight. I do use 6S Pulse 65C 2600Mha batts.

The dampers were greased when I replace the new metal grips.

Here are the Throttle Curves:
Norm L: 0
2: 35%
3: 55%
4: 68.5%
H: 80.5%

Pitch Curves:
Norm L: 0
2: 25%
3: 50%
4: 75%
H: 100%

Hope this helps..
Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-02-2012 03:52 AM  7 years ago
dkshema

rrMaster

Cedar Rapids, IA

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Your throttle curve provides a clue...

0 - 35 - 55 - 68.5 - 80.5

The pitch curve really is meaningless, you have a 0 to 100% linear curve, but not knowing how much pitch you have at 0 and 100 leaves out much needed info.

I'll assume that you have properly calibrated the ESC to your TX throttle so that it knows what full low and full high throttle are.

If so, with the curve you have for throttle, you are WAY WAY WAY slow on the head speed, even at the 80.5 setting, you are just getting into where the motor is running well.

With a low head speed, most helis will show a wobble and in some cases, the wobble can be quite impressive and unsettling.

-----

I would recommend that you try the following:

1. Make sure you have properly calibrated your ESC to the throttle stick on your TX per the ESC setting procedure.

2. Set your Normal throttle curve (it appears that you are using only Normal flight mode at this point) to the following:

0 - 85 - 90 - 95 - 100.

This will let you set your throttle to low with low trim and the ESC will arm, but the motor won't turn. As a safety precaution, set your throttle hold such that with throttle hold engaged, the motor will NOT turn. Once you arm the ESC, engage HOLD to act as a safety when moving the heli.

Always treat an armed ESC and heli as safely as possible. Insure that the motor will not accidentally spring to life if you bump a switch.

3. Using a pitch gauge and a linear 0 to 100% pitch curve, insure that you have -12 degrees pitch at low stick, zero degrees at center stick, and +12 degrees at full high stick. Consider this a preliminary, starting point for all ensuing setups.

Make sure you have your motor disconnected from the ESC, or moved away from the main gear during all setup procedures so that if it should come alive suddenly, you don't get hurt.

4. For your Normal pitch curve, use the pitch gauge such that at low stick, you have about -2 degrees. At mid stick, you want 5 to 6 degrees. At full high stick, you'd want about 12 degrees pitch.

The small amount of negative pitch will ensure that the heli will not float as you attempt to land from forward flight.

This should get you hovering at a decent head speed and about 3/4 throttle. You should have a relatively high head speed, and the heli should not wobble or have any other bad tendencies.

Your motor is most likely a 1600 KV motor, and you probably have a 13 tooth pinion. Your gear reduction is 1:12.46. This, coupled with a 6S battery pack will give you the following ballpark head speed:

22.2V nominal battery voltage
1:12.46 reduction ratio
1600 KV motor
80% efficiency of the overall power system

((22.2 x 1600) x 0.8) / 12.46 = 2280 RPM with the motor running wide open.

-----

Running your motor with the ESC much less than about 85% is operating the motor way outside its best efficiency zone, and will also affect the amount of torque available. RPM out of the motor is a function of voltage, torque is a function of current. Electric motors just don't "throttle" as well as nitro counterparts. Keep your ESC at 85% or above, your motor will thank you, your ESC will thank you, and your heli will thank you.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-02-2012 04:42 AM  7 years ago
highrpm

rrApprentice

Shelby Twp,Mi

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Every time you write we all get a little smarter...Thanks for being a great ambassador of our hobby dkshema
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04-02-2012 04:51 AM  7 years ago
Stephen Born

rrElite Veteran

USA

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it's a "top/bottom" shake.
Check the tightness of your blades. Might be that they are to tight.
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04-02-2012 03:47 PM  7 years ago
Pistol Pete

rrProfessor

Seffner, FL

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Does it shake with blades off as well?

Next suspect would be the paddles and or flybar rod possibly not centered.

Paddles same weight?

Indeed throtle curve needs to be looked at.
~~Enjoying the hobby one flight at a time~~
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04-02-2012 05:30 PM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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Thanks Dave, will plug those numbers in when I get back this afternoon after Turkey Hunting. I believe I'm at -3 to +10 and zero at center stick but will check again.

Pete, how will it shake with the blades off?? Are you saying to spin up with just FBs on?? I have new KBdd blades on and had them centered but will check again.

ASC, I have the blades where they pull back for storage just like the last blades.

Thanks guys for helping me out, don't want this thing to fall apart on me.
Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-02-2012 10:34 PM  7 years ago
airdodger

rrElite Veteran

Johnston USA

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Did you replace the thrust bearings in the blade grips?Chris
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04-02-2012 11:26 PM  7 years ago
RaptorRob

rrApprentice

hamlin P.A.

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I would have to say its the headspeed way too low

mine shakes like its going to fall apart till i get into the 80% throttle and above range

my 2c
no babe i swear i sold my other heli to buy this one :)
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04-03-2012 02:51 AM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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Airdodger, I did replace the thrust bearings and main bearings.Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-03-2012 06:35 PM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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Houston we have lift off!! I took it up just now with new throttle curve and did not see any wobble as before. That head speed is hauling butt! The tail started kick a bit but that might be due to on the rebuild I repositioned the gyro to on top of the tail boom. I used only one layer of tape and I think it might need to.

Thanks Dave for the help, I might tone down the throttle curve to maybe max of 90 instead of 100. That thing is scary at the speed it's at. When spinning up I thought it would never lift off. Would 0-80-85-90 be a ok throttle curve or do I just need to stay as is a just hang on?
Trex 500FB Trex 600ePro McpX. Synergy E7SE
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04-03-2012 06:52 PM  7 years ago
dkshema

rrMaster

Cedar Rapids, IA

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That curve would be fine ... just get above 85 for best performance.-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-03-2012 07:19 PM  7 years ago
Pistol Pete

rrProfessor

Seffner, FL

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Pete, how will it shake with the blades off?? Are you saying to spin up with just FBs on?? I have new KBdd blades on and had them centered but will check again.
One of the plus things of electrics when building is that you can spool up motor at anytime in between adding items to check for vibs.

Ie: first spool up with main and rotor shaft installed checking for meshing, then add grips,spool up, then flybar rod w/paddles, spool up, so by the time you add blades you have a vib free bird.

Great that only throtle speed was the culprit.

You can also use 0-85-85-85-85 on Norm.
~~Enjoying the hobby one flight at a time~~
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04-04-2012 11:32 AM  7 years ago
SGM Retired

rrApprentice

Toney, AL. USA

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Leeson learned yesterday after first flight, when you increase throttle curve you lesson flight time. Did my usual 7 minute hover flight and when I took off I noticed it was warmer than usual. When I checked it only had 9% left in batt. Flew next batt pack for 5 minutes and it came up at 35% so now I know my limits.

Pete, will take your advice and pull off blades and FB and check for vibration. Seems there is some vib somewhere on spool up. Tail is really unstable on spool up.
Trex 500FB Trex 600ePro McpX. Synergy E7SE
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