View Full Version : 6HV FBL Ground Resonance solution

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Dave Ketelhut
04-19-2011, 08:59 PM
alright, so i have been spending alot of time on the 6HV trying to get to the bottom of the ground resonance issue, and i have come across a solution that isnt quite conclusive because of the amount of people that have tested it. what i did was raise the head block on the 6HV to the lower hole raising the head up 5mm. in doing this i had to lengthen my delrin rods and move my swash plate up to adjust for the head. i split the difference with the servo rods and the delrin rods to make sure i wouldnt lengthen one to much.

in testing, i landed multiple times on concrete, landing with power, without power on angles ect. i also made the tracking of the blades go out over an inch to simulate a bad vibration. even in doing that i could not replicate the ground resonance issue.

for people that still have this ground resonance issue i would recommend trying this at your own risk. if you do want to do this make sure the ball links are all secure on the rods, id hate to see own lose a ball link in flight. but im very positive that this is the fix to our issue. along with the new landing gear.

and if anyone does get to try this, if you could report back and let me know your outcome i would really appreciate it.

04-20-2011, 03:25 PM
That's great info Dave! Was your 6HV having ground resonance problems before your fix? If that's the case then you have in fact solved it, correct? How does it fly after this small change, any difference at all?

Dave Ketelhut
04-20-2011, 03:30 PM
After I rebuit it from a crash it did but never ate itself. I was able to give full negitive collective and would stop it. But once I raised the head there was no sign at all. Flight charectoristics didn't change much at all. I would need to fly back to back to maybe see a difference

04-20-2011, 04:23 PM
What effect do you think it has on flight characteristics? I would think it would put the COG a little lower, so maybe reduce roll rates a tiny bit? Does it add any more stability to it? Also, do you think it was just the height difference that helped? Maybe having taller skids would help with it as well?

Dave Ketelhut
04-20-2011, 04:38 PM
I think the skids help prevent it. But my 6HV before I did the mod would start the shake in Thr air. So I believe it was just having the CG so close the head giving the issue. But I really couldn't tell a difference in how it flew. Still felt like my 6HV :)

04-20-2011, 04:58 PM
Yeah, I wouldn't think you'd notice a 5mm lower CG.

04-20-2011, 08:21 PM
I just built a 6HV and have been test flying it. I had some serious ground 'shaking' problems like others during the spooldown. I tried the blue KBDD dampers, no different. I would even get some shaking inflight at various times. I looked at blade balance(perfect), tried different blades, no change. I did add some Velocity black stock dampers, a bit undersize for the stock compass head, but it solved my problem of shaking during spool down. I did see some shaking inflight with these also.

So I bought a new velocity FBL head, it's very nice and weights almost 3 oz. less. I have no shaking during spool down, or in flight. It flies wonderful! It still needs a good HS(2050) min., if slow you can get some shaking inflight during hover. I could use a bit softer damper if available.

I'm still working on some Jive esc program issues to get the proper throttle % settings, and I may go to a lower KV motor, like a -500 Hyperion or Scorpion, as my throttle settings are way to low 30% (2060) HS to govern properly. I'm shooting for a 2150 HS, with mellow 3D at 2000.

Question?? Will a Scorpion 4035-500, or Xera 470 fit the 6HV? I would like to hear from someone who has used a different motor, and used the stock pinion support.

I will shown some pics for you guys, on some of the small changes I have made to make my 6HV a better heli (pem nuts, Furion 6 tail pushrod guides and wire) to start. After I get some of these issues solved.

Brian Rasmussen
Louisville, KY

Dave Ketelhut
04-20-2011, 08:27 PM
How much higher does the v50 head sit over the stock head

04-20-2011, 09:06 PM

I measured the stock head, then adjusted the V 50 head to match it. The V50 head even on the highest setting, was 1mm lower than the compass head.

I do think that the Compass head has some issues with the one piece arms, just a gut feeling. I am going to reinstall the compass head without the arms, using some double MA balls will get the blade grip arms delta correct, and I will use the Velocity swash follower. It will be interesting to see how the head behaves.


Dave Ketelhut
04-20-2011, 09:09 PM
if you get a chance to use the stock head on the lower hole please let me know. as the compass head does work great. i dont think the head itself is the issue becuase there is not one person that has this issue with the compass head on the 3D+ or other machines with a higher profile.

04-21-2011, 12:40 AM
Its such a rigid airframe its hard to get rid of the shakes,I have a carpet peice I land on or in the grass so its no big e. To everyone I suggest you completely avoid takeoffs and landings on concrete as the heli will auto destruct,lol. The first time I spooled down I bout sh!t myself when this thing started shakeing. Couple of local pros had theirs explode on the ground.

04-21-2011, 03:10 AM
about the FBL head from Compass, it is'nt the head, all my shakes that i had where with the stock flybarred head that sits higher then the FBL head btw...

now with the FBL head i only had one shake and that was during the first spoolup that the blades couldn't seat properly during spoolup because i overtightened them.

04-21-2011, 09:06 AM
Raising the head as Dave suggested certainly cured my head shakes. Since I am still trying to get my V-Bar settings adjusted, I've avoided T/O & landing on the tarmac, since it's still a touch unstable. The first time I was hovering, I scraped the tail blades and ruined them as I was getting a feel for the controls. However, since it now has zero tendency to shake on spool-up or shutdown on hard ground, I am confident my issue was resolved completely. There's not even a particular speed as it ramps up or down where it acts like it might shake any more. Most of my other helis do that somewhat.

I am painfully awaiting a decent Michigan weather day to flog it a bit. I never thought I'd have a machine as smooth running and quiet as my Outrage 550, but I do now.

Thanks to Dave so much for his help. I am really pleased with Nankin and Compass!

Quick update 4/21/11, 4:00 pm
I tested takeoff and landing, power off and on over tarmac today. Zero wobbles! Smooth as glass, just like from grassy ground.

05-01-2011, 05:42 PM
Just moved the head block on my 6hv today and the shake on spooldown is gone. I fly alomst exclusively off asphalt. Before I would have to be careful when landing because anything other than zero pitch during spooldown would cause the heli to bounce around violently. Thanks for the advice.

Dave Ketelhut
05-01-2011, 07:47 PM

05-02-2011, 12:27 AM
i landed on asphalt the other day, long story short : i demolished my tail blades during spool down :face

the other 3 packs i landed on gras without a hitch ! :thinking

Jason O'Connell
05-02-2011, 11:14 AM
Are you guys having resonance issues with take off and landing on grass? Or does the problem only show up with take off and landing on pavement?


05-02-2011, 11:22 AM
I'm getting vibe issues on grass, both on spoolup and landing. Landing and keeping it at 0 pitch keeps it fine but spoolup is a little iffy. It was fine until I put the green KBDD's in, and those are what caused my blowup on landing last time so I am starting to be a little suspicious of the dampeners.

Jason O'Connell
05-02-2011, 11:25 AM
I wonder if I should go with the blue ones to start? I have the greens instaled now with plenty of grease. The spindle turns freely with an allen wrench so I am hoping it will be ok.

05-03-2011, 09:08 AM
I didn't notice any difference in mine on spool-up/down with either the Blue or Greens. I had mine on the lower setting as well and only ever saw a slight wobble when bringing it up. I normally auto land, but even on powered landings I never once saw a single wobble on my machine. I was experimenting around with all the dampeners and the Blue ones ended up being my favorite, but the green ones are gaining my interest because they do give a little more snap to the controls.

05-03-2011, 09:23 AM
I haven't raised the head on mine yet, but my experience is the same as Tim's, i.e. I only get a wobble midway through spool-up.

Are you all just raising the swash plate when you raise the head?

Dave Ketelhut
05-03-2011, 11:10 AM
yea, i raised the swash plate, and extended the delrin links

05-03-2011, 11:14 AM
I have the stock dampers in. I get a some wobbling on spool up but it goes away quickly if I accelerate a little faster. On spool down over asphalt I get absolutely no shakes or wobbling regardless of having 0 degrees pitch or negative :).

05-03-2011, 12:32 PM
+1 :thumbup:

05-03-2011, 12:35 PM
yea, i raised the swash plate, and extended the delrin links

I was just wondering about only raising the swash plate without affecting the Delrin links. Are there not enough threads in the servo-to-swash linkage rods to do that?