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Home✈️Aircraft🚁Helicoptere-AlignT-REX 500 › Bobbing...
04-05-2010 02:35 AM  10 years ago
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darkfa8

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Brick, NJ - USA

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Bobbing...
I have a T500 and am running:

Phx ICE 100 (have tried lowing timing, changed PWM to 8KHz, SetRPM mode 2600/2800/2800, Medium gov gain)
PowerHD 1700kv outrunner
15t
Headspeed 2800-2900 RPM
425mm FRP main blades
all metal head
401-clone gyro on tail
PowerHD 3688 servos

I'm getting the headspeed I want, but the model just doesn't feel very crisp and when I give fast collective movements, the model bobs fore-aft slightly on stops.

Could the head dampening be too soft or might it be something else?
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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04-05-2010 03:12 AM  10 years ago
himaxkeith

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Atlantic City NJ. USA

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Maybe dampening. Are you using the gray bushings with the plastic tube also? OR. Are you using any plastic parts in the Head? Plastic seesaw or Mixing arms or blade grips. I have never heard of those servos. Just make sure your using some strong servo horns also that dont flex.
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04-05-2010 04:06 AM  10 years ago
hpilotrc

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NY--->>Mooresville, NC USA 8/2005

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Bobbing Trex 500
Dan,

If you Trex 500 is bobbing at slower head speeds I would think that your dampening is too hard. I had the same problem but was using the plastic tube and harder Align bushings. I eventually ended up getting rid of the tube and used the softer stock bushings that came with the kit. Also instead of the plastic tube I used a piece of large cut to length silicone fuel tubing over the axle.

Check out this link:
https://rc.runryder.com/t572921p1/?p=4731288#RR

Michael
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04-05-2010 04:11 AM  10 years ago
philip 01

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ft worth

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the softer the dampners the more 'bobbing' potential.
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04-05-2010 01:14 PM  10 years ago
darkfa8

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Brick, NJ - USA

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it's a full metal head, black rubber dampers - not sure of the durometer rating.

i may try changing to a harder damper and see what happens, or lowering the headspeed.
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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04-05-2010 01:37 PM  10 years ago
Fnity

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Denver, CO

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^^ ^^ +1 on the headspeed,
My 500ESP did the same thing till I raised it to around 2600. I'm now running 2850rpm, well over what align recommends, but it flies better than ever

P.S. usually when a heli has the bobble it needs more headspeed not less
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04-05-2010 01:58 PM  10 years ago
Richardmid1

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Leeds, England

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I would tacho your headspeed, you shouldn't be getting much wobble at 2800-2900rpm. Personally ide use a 13T pinion without governor at 100% throttle.60% of the time, it works every time!
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04-05-2010 02:55 PM  10 years ago
Fnity

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Denver, CO

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didn't read all your post, dampners might do it also, and timing
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04-06-2010 09:44 PM  10 years ago
Rogman88

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West Monroe, LA

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I had wobble as you described. Increased from 70% throttle to 85% and bobbing vanished!
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04-07-2010 02:35 AM  10 years ago
ChuckJrster

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West Monroe, LA - USA

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500s like higher head speeds since it's a relatively smaller heli when compared to a 600 or 700 which doesn't need (balls out) head speed to not bobble. Make sure that the blades aren't too too tight but that both main blade grips are relatively snug and the same tightness is apparent on both blade grips. Kick up the RPM some of whatever flight mode that you're in whenever you notice the "bobble." Yes, dampening is important as well. If it's not something else that's wrong, a higher head speed should fix the problem.Team Pilot for RCHeliWorkz
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04-07-2010 02:39 AM  10 years ago
Fnity

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Denver, CO

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^^ ^^ +1
usually a bobble is too low head speed, but you stated that you have a HS of around 2800-2900 so I would get a tach on it and make sure its actually near there... If it is then look into the dampners
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04-07-2010 03:43 AM  10 years ago
hpilotrc

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NY--->>Mooresville, NC USA 8/2005

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softer head/ dampner more bobble?
I am still confused. I would think that if you have a bobble at a SLOW headspeed the dampners could be too hard and not absorb the energy. And when the dampners are softer the bobbing and excessive energy would be absorbed by the dampner and not transferred to the head or heli as movement (bobbing)???

This is what I have found over the years...

Any experts out there?

Michael
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04-07-2010 02:07 PM  10 years ago
darkfa8

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Brick, NJ - USA

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from Ben Minor:
The first thing I would do is make the dampening pretty much as stiff as you can get it. The limiting factor will be how much or if it mast bumps in an autorotation.

Your motor set up has nothing to do with the lack of pop. You may need to steepen the pitch curve at least in the 1/4-3/4 stick range or the whole thing depending on what the logger data says about current, watts, and the power out of the motor.
I'm going to review my data files and also try and get a tach on it.
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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04-07-2010 02:52 PM  10 years ago
Richardmid1

rrProfessor

Leeds, England

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Softer head damping will allow a lower headspeed hover but any sharp cyclic inputs will cause the bobbing. Harder damping and higher headspeeds will stop the bobbing on fast stops etc.60% of the time, it works every time!
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04-07-2010 02:55 PM  10 years ago
blbills

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Provo, UT

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Dan,

I've been flying t500's for almost 2 years now (I've owned several and it happens to be my fav heli) and the head bobble has always been there at low RPM.

Regardless of head dampening it has always gone away when I'm in the higher RPM (2800-3100). It doesn't really bother me anymore as I just fly in stunt 2 so I never see the lower RPM range anymore.

Keep us posted on what you find out!
Brian
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