New to the forum with a UH1-D 800 series

[sfcfury]

Astronome Is there a certain RPM range where the vibrations begin, or end?

Hey Alpha! Long time no see!

[sfcfury]

I know in there older mechanics sets, the main shaft bearings were suspect as well, but that probably seems to have been mostly corrected. Perhaps just a bent main shaft?

[Alpha]

Astronome Is there a certain RPM range where the vibrations begin, or end?

[Astronome]

Hi PawPaw and all the members

I check the front and tail bevel gear end play, all is OK.
I check and securise all the screws of the mechanic like my Vario's helicopters.

I changed the grease (SKF) of the 3 sets of bevel gears.


I took the opportunity to secure the fittings of the rigid transmission with a screw at each end, because the fittings are just glued and I don't trust.




After reassembling the mechanics: always these vibrations

I will have to wait for Roban to change the rotor shaft.

Daniel

[PawPaw]

If your finger rotation feels smooth, then just check the front and tail bevel gear end play. No need to remove the short tail boom for this. Reach inside the main frame and grab the horizontal tail drive gear and check for end play. Pull it back and forth as much as possible. Should be able to just feel a very small amount of play. Very small. In fact, if you did not install shims in the front transmission when you assembled your UH-1 I can almost guarantee there is too much play. Also, visually check to see if the vertical drop down gear is meshing properly with the horizontal gear. The back edges of both should appear 90 degrees with no offset in or out. There is no adjustment possible for the 45 degree angled gearbox, but check for gear wear and adequate grease. Check your motor pinion to main gear clearance. I set mine with a piece of thin receipt paper and it has worked well. Lastly, double check all the screws in the frame especially those around the tail drive unit. I had a bad vibration on my B407 700 that was found to be loose front transmission screws. Good luck!

[Astronome]

Dont think that this is normal .must be zero .

Hello Helikapoter,

I agree, but I don't think 0 is mechanically possible, there will always be a tiny tolerance.
But what its value?

[Astronome]

Thank you PawPaw

I did a hand rotation test: no hard point, but I'll disassemble the tail tube and check the 3 sets of bevel gears.

[PawPaw]

I agree the shaft should have be straight with no runout, but once mounted into 2 bearing blocks with only a slip fit then that assembly will have some + runout value. The shaft would need to be secured in an end mill, lathe, or other fixture to measure accurately.

[PawPaw]

Ok, my thoughts are your vibration problem is due to another issue. I have a couple of Robans with elevated tails and have learned that properly shimming the front and tail bevel gears is very important to reduce play. I also found that it is very easy to improperly mount the tail rotor assembly to the short tail boom which causes gear misalignment and vibration. To check this, slowly rotate your tail blades with one finger. If you feel “bumps” or “snags” during rotation then the tail gearbox needs to be remounted on the short boom. Let us know what you find!

[Helikapoter]

Dont think that this is normal .must be zero .

[Astronome]

..... Have you dialed a Vario shaft for comparison?....

Hello PawPaw,

Unfortunately no, I no longer have Vario mechanics.

Daniel

[PawPaw]

I have never measured a Roban shaft, but 0.05mm (0.00197 in) of runout on an installed shaft does not seem extreme to me. You could remove the shaft and measure it separately to get a more accurate number but that would require some precision equipment. Have you dialed a Vario shaft for comparison?

[Astronome]

Hello,

I have a technical question for ROBAN machine owners:

Big vibrations appearing from 1200rpm,
The blades are perfectly balanced and their center of gravity verified.

Have you measured the concentricity of the rotor shaft?
I made a measurement with a dial gauge
Result: 0.05mm of "faux rond" (in French) Is this normal in your opinion?

I have never had this problem with a VARIO mechanic

Best regards,

Daniel

[Astronome]

Exceptional work, Astronome! It would be nice to follow your next build in Hobbysquawk if you choose to share your secrets with us.

No problem PawPaw

[PawPaw]

Exceptional work, Astronome! It would be nice to follow your next build in Hobbysquawk if you choose to share your secrets with us.

[sfcfury]

Wow... that's a beautiful Cobra!!

[Astronome]

Welcome to the group Astronome! Parts are hard to come by now... MRC US and Europe get them sporadically... You can still hit up scaleflying.de via email and see if they have anything. RCAerodyne (www.scaleflying.com) used to be the US distributor and still have some parts floating around.

Like your collection! That's a nice AH-1P!!

Thank's sfcfury,

I have already looked at all the websites: nothing!

Some pictures of my Cobra

7000 drilling and rivets laid one by one




Modification of the fuselage and addition of the various hatches


Manufacture of armaments



First adjustment flights before finishing




Machine completed










Good flights

Daniel

[Astronome]

....I have had 2 successful parts orders from Roban last year but they have not answered my last emails......

Thank's PawPaw,

I made a request for parts for myself and a friend (about $700) to limit shipping costs.
Roban answered me and I am waiting for the invoice to make the payment.

Good flights

Daniel

[sfcfury]

Welcome to the group Astronome! Parts are hard to come by now... MRC US and Europe get them sporadically... You can still hit up scaleflying.de via email and see if they have anything. RCAerodyne (www.scaleflying.com) used to be the US distributor and still have some parts floating around.

Like your collection! That's a nice AH-1P!!

[PawPaw]

Welcome to the forum, Astronome! Yes, Roban parts are very hard to find here in the US. I have had 2 successful parts orders from Roban last year but they have not answered my last emails. Good luck!