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bouncing like a basketball


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dnipper
Hopping Maniac
Hopping Maniac


Joined: 03 Apr 2012
Posts: 24
Location: Tennessee

PostPosted: Wed Jul 04, 2012 8:32 am
PostPost subject: bouncing like a basketball
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When I hover for a minute or 2, sometimes maybe longer, just a few inches to a foot off the ground, the helicopter will drop like a rock to the ground and bounce back up and fly a few more seconds and drop again. If I don't cut the throttle it will bounce up and down like a basketball. The motor never changes sound and the rotors seem like they never slow down. However I do hear a different sound from the blades after the first bounce. Once or twice the tail started spinning so fast it threw the battery off but I it never crashed.

Any ideas?

Thank you...
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tombo242
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Joined: 04 Nov 2008
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Wed Jul 04, 2012 5:56 pm
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Yes! You're flying in ground effect and that's what happens if you don't control the height with the throttle.

Being close to the ground increases lift as does any horizontal movement. With no throttle movement, as you rise the lift decreases and the heli drops, as it falls the lift increases and it may rise again before hitting the ground. The effect is just like that of a bouncing ball.

Wind gusts can do the same. As it gets blown away the lift increases, then as the airspeed drops the lift decreases giving a bobbing effect that you have to cancel out with the throttle.

In flight your sticks are rarely still, unless you have smooth air and a few meters altitude, then you might get a few seconds hands-off with a very well set-up heli.

Tom.
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dnipper
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Joined: 03 Apr 2012
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Location: Tennessee

PostPosted: Wed Jul 04, 2012 8:56 pm
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I understand the concept of ground affects and I'm afraid to take the heli up too high for fear of crashing until I get this sorted out. What I'm talking about is the bird drops like a rock and then takes off again. It looks like the blades loose their lift and then once it hits the ground it might stay there a couple of seconds and then takes off again without me moving the stick. After a few bounces, the bird starts spinning wildly.

Can not figure out what is causing this problem.
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pjdog
Extreme 3D
Extreme 3D


Joined: 12 Jan 2010
Posts: 2073
Location: Hudson, Florida, USA

PostPosted: Wed Jul 04, 2012 11:34 pm
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You never say what kind & brand RC Helicopter you have?

Jack
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chopper54
Extreme 3D
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Joined: 15 Jan 2010
Posts: 990
Location: suffolk UK aged 61

PostPosted: Thu Jul 05, 2012 1:03 am
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You may have some slop in the rotor head allowing the blades to adjust pitch. Check it over and make sure everything is correctly set up and tightened.
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dnipper
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Joined: 03 Apr 2012
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Location: Tennessee

PostPosted: Thu Jul 05, 2012 1:38 am
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I have a Blade 450 3D with a Spektrum DX6I. I am using a E-Flite 440 4200Kv motor and a E-Flite G210 Gyro.
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pjdog
Extreme 3D
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Joined: 12 Jan 2010
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Location: Hudson, Florida, USA

PostPosted: Thu Jul 05, 2012 2:02 am
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dnipper:

That's a real good combo you have. Best bang for the buck me thinks.

I don't know what to tell you.

Today my B400 did a little hopping around when I spun it up after main blade replacement to check for vibration. I know if I had given it just a click more power it would have lifted off and flown low.

Give it a shot.

Have you flown a 450 before? Do you know what to expect?

Jack
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admiral
Extreme 3D
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Joined: 20 Mar 2009
Posts: 1100
Location: Brisbane, Australia

PostPosted: Thu Jul 05, 2012 3:05 am
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Hi Dnipper,

Seems strange to me that it hovers OK for a couple of minutes and then starts bouncing. Thombo is right about the ground effect if you could try hovering at about 3 or 4 feet up you would get a better idea what is going on and you would probably find it easier a helicopter hovers much better in clean air.

The other thing I would try is to emulate the problem on the ground, I had a problem once with a 450 that would fly OK for a couple of minutes and then start dancing all over the place, I weighted it down and the run it a 30% throttle for a couple of minutes, all of the time putting in small stick movements, after a couple of minutes the aileron servo twitching, replaced the 3 servos and it's flown well ever since.

Maybe not your problem but it's worth a look.
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dnipper
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Location: Tennessee

PostPosted: Thu Jul 05, 2012 4:43 am
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I have been flying this 450 for about a month now and it seems like I've replaced almost every part on it several times around. Between repairing the helicopter and this site, I am becoming very familiar with this bird.
Something I just noticed when testing again this afternoon, I used 5 batteries with 10 - 15 minutes between flights, 4 of the 5 flights were without a drop or bounce but the 1 time I had several drops was with the cowling. Could the ESC be getting hot and causing the problem?

Thanks,
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tombo242
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Joined: 04 Nov 2008
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Thu Jul 05, 2012 5:07 am
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Hi David,

Looks like you've got it there, sometimes the ESCs' can be real tempermental. Worth trying another one to check.

Tom.
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dnipper
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Location: Tennessee

PostPosted: Thu Jul 05, 2012 8:40 am
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I'm not sure if I found the problem or not but I turned down the Pitch to - 50% in the Swash Mix and it stopped bouncing. I turned it up to -85% and it started bouncing again.
I'm still learrrning how all these settings affect the helicopter.

Thanks for all your input..
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tombo242
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Joined: 04 Nov 2008
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Location: Santo Estêvão, East Algarve, Portugal. Now 82, but still feels 22.

PostPosted: Sat Jul 07, 2012 12:39 am
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dnipper wrote:
I'm not sure if I found the problem or not but I turned down the Pitch to - 50% in the Swash Mix and it stopped bouncing.


That would increase your head speed at hover as the collective pitch is reduced. It may be that this is reducing the ground effect. I wouldn't attempt any 3D with that amount of pitch tough, it should never go below -60%. (Halfway pitch point, Swash Mix goes from -120% to +120% which half you use depends on head and servos.)

Tom.
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