HDX 300 Head Wobble

[Ron K]

I have been building my HDX 300 and when I finally got to spin it up there was an incredible head wobble but only as it slows to a stop or when it is accelerating to full speed...

When it is running wide open (clamped down) it is running a 2000 RPM on the head for speed and smooth....tracking fine

But like I say when I slow it down to stop it shakes like crazy.... I checked the main shaft and it seems ok...I don't have the tail rotors on yet so it isn't that...The main rotor blades balance perfectly AND I also even took the rotor blades off and spun it up....Same thing though Wide open it is smooth but ramping up and down the head and heli shakes bad! :arggg:

My gear mesh is very smooth with the motor and main gear when turned by hand as well...not too tight etc

Could use some help...can't get it all smooth...I have +/- 11 on the head and no binding of the flybar as per Finless videos...

Thanks for any help!

Ron

[Dan MacKay]

Hi Ron,

I just finished a build of one of these and the first flights were amazing except for a couple of glitches that were my fault any way. By the third lift off things were smooth as silk. I know that is not what you wanted to hear.

A couple of things you could look at are:

1. Are your bearings (both upper and lower) seated properly and functioning properly?

2. Is your belt tension correct? I never spun this bird up without the rear blades. If the belt tension is too loose it could be causing this, as well if the rear rotor is not attached even if you have the right belt tension the lack of drag input could be causing harmonic distortion with the belt.

3. How much slop is in the head? It could be that your feathering shaft has too much play in it or you have a ball link connector that may be causing you some grief.

These are only stabs in the dark. I caution you to only make one fix at a time then check the heli out again as you really do want to nail down what the problem is. If you make wholesale changes and the problem goes away you will never know exactly what the fix is.

I use about +9/-9 for pitch and that is tons coupled to the Park 370 4100 and a 10 tooth pinion. You may want to lower you pitch a tad. This will have the added benefit of picking up your head speed. I tach at 2400 at 85% which should my top rpm through the rest of the curve. You really cannot tie these down to a bench and get an accurate tach reading as you are loading the blades more than they would if it were flying all things being equal and you have your radio set up correctly. If that is your max throttle and pitch your motor is working awful hard and actually running under it's max rpm due to the blade load.

If you wish to discover your max rpm reprogram you radio for zero pitch at max throttle. Run it up and tach it. When you find the unloaded value it will give you a good starting point for setting your throttle/pitch curves. I found for example that the typical 85%/5-6 degrees of pitch at 50% stick for my 300 was way too aggressive (Perfect for my TREX) as it would take off like a rocket. I found that 5 degrees and 72% at half stick gives me almost a hands off hover at 5'.

Good luck with solving your problem. This little rice rocket will be well worth it by the time you are done so stick with it.

Dan

[Ron K]

I will check that stuff tomorrow then!

I hope I can get it ironed out

I missled you my RPM on the head...it is 2000 at 50%...If i moved the stick changing the pitch the heli would shke like hell clamped down even...The way i took the reading was put on throttle hold switch...Then put stick to 50% at o pitch and then let the TH switch off...and on etc

I will check these things..So I wil refraise at 50% and 0 pitch once it spools up it is smooth ramping up and down to 50 is horrendous shake...

Thanks for your help...
I have been working on this heli one heck of a long time...About 3 times longer than in took for My TREX SE....Still no text flight yet... :(