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Futaba-RC . A Main Hobbies . Boca Bearings

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Main Discussion > Chinese weights on the tail grips
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

Yug, in that first picture you show that has a "bullet" on the leading edge of the tail blade, that seems to be opposite of what you want. What's that about ?

As for the longer blade bolts with heavy wall spacers, that's the way to go.
Post your numbers, spacer length, blade length, width, weight, etc.

What about measuring servo current ?

It may be a good idea to keep slightly short of the "sweet spot" to maintain a small bit of pre-load on the linkage to account for worn parts like the ball link.

Chinese weights - - - - - - - on a Raptor - - - - - - - and testing





Chinese weights at work on an SNJ,
http://www.planesoffame.org/featured-aircraft.php?ID=10
10-28-2007 Over year old.
HOMEPAGE  
 
 
Andy from Sandy
Veteran
Location: UK

So to make this work when just using the blade bolt requires the bolt to extend out of both sides of the grip?

Is there a generalisation for how much longer gives a percentage of reduction in load to the servo?

How do you know when it is working more or less correctly?

How do you know when you have overdone it with the length of the bolt or the amount of weight or is it purly down to bolt length?
10-28-2007 Over year old.
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

Quote 
Is there a generalisation for how much longer gives a percentage of reduction in load to the servo?

How do you know when it is working more or less correctly?

How do you know when you have overdone it with the length of the bolt or the amount of weight or is it purly down to bolt length?
That's where the experimenting comes in.
10-28-2007 Over year old.
HOMEPAGE  
 
 
Andy from Sandy
Veteran
Location: UK

Okay, I will start experimenting. How can I tell that adding the weights is actually doing something?
What am I looking for, so that I can see when I have gone too far?
10-28-2007 Over year old.
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

Yug ?
He's on your side of the pond.
10-28-2007 Over year old.
HOMEPAGE  
 
 
SkateFreak
Key Veteran
Location: Cambs UK/Luton

You can either try and figure out how much load the servo is taking or.....
The way Yug is doing it you will have to set up a heli that will spool up the tail rotor and move the tail pitch rod by hand (making sure the heli is secured) and judge it by feel

This was also shown in a talk by Collin Mill at the 3DM which was very interesting...
From what i can remember on your average R50 you just want to use a longer screw and an extra bolt...
Interestingly if i remember it correctly I'm sure it was just an extra bolt on the back of the blade grip, on one side... Hmmm

If anyone can confirm this I'll give it a shot at some point heh

-Jvr
10-28-2007 Over year old.
 
 
Yug
rrProfessor
Location: UK. Herts

That 1st picture was representative of when I 1st got into this several months ago. Then realised the correct solution using weights and 90 degrees.

I am not yet measuring servo currents - from the picture with the heli strapped down and a black and decker on the main shaft, i am moving the tail pushrod by hand as I rev up the tail. I can then feel exactly what is going on.

The screw length is 30mm and am using whatever I can find to act a spacers with a view to either side of the grip being just about balanced. A longer bolt (>35mm) and spacers seems to make it very over pitchy. In my photo, you'll see that the second nut is adjustable which provides some fine tuning although I'm not really sure that this is so necessary. I wish it was an electric heli so I could dial in the exact HS, but all I have is my hand drill and a tach on the tail blades. It is interesting to feel the effects of different speeds on the pitch forces.

Vegetable rights and Peace
10-28-2007 Over year old.
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

I would be real curious about the forces on the pushrod with the tail in the stock condition at operating speed on a 50, about 8,000 rpm on the tail, at full pitch that a servo would give.

A regular plane engine tach. can help to check the tail speed. Just have to watch out for the frequency of indoor lighting. When I check the rpm of my Dremel, I have to use a flashlight.

Chinese weights at work on an SNJ,
http://www.planesoffame.org/featured-aircraft.php?ID=10
10-28-2007 Over year old.
HOMEPAGE  
 
 
Yug
rrProfessor
Location: UK. Herts

If I get time, I'll hook up a balance and measure the pushrod force. From what I've felt by hand, it is substantial and given the fact that servo loading has a dramatic effect on speed, then I believe a stock setup will severely compromise performance. At least, will not allow the full potential to be realised. Even if the servo is powerfull enough to largely overcome the forces, due to it's busy job, it will have to be working extremely and unnecessarily hard, which would impact on servo life among other things.

Vegetable rights and Peace
10-28-2007 Over year old.
 
 
Yug
rrProfessor
Location: UK. Herts

Just done a rough measurement on stock setup with the tail rotor at approximately 8000rpm and measured the force at near full pitch on an 18mm ball. It was somewhere around 3Kg. I must say I was also bottling out a bit and the test wasn't what you'd call controlled :- left hand on the drill trigger, right hand holding my balance which was coupled to the ball while watching the tach. Also noticed the belt slipped a wee bit at full blast. New belt and pretty tight. I don't mind admitting I chickened out after 3 attempts to repeat the readings as it was all a bit lively. Anyhow the force is loads. This heli has an 8700G, @0.09/3.5, which means the servo is really being abused, no wonder it's a bit whippy in piro manouvers.

Vegetable rights and Peace
10-28-2007 Over year old.
 
 
Barney
Key Veteran
Location: Inverness Scotland

The way Colin drove the tail was by pushing a small electric motor with a small piece of silicone tubing on the end of the motor shaft againt the shaft on the opposite side of the tail shaft from the blades.. i.e the tail boom was removed.

This allowed you to push pull the tail rod

I have no idea of the RPM he used though but may be an option to try

Meant to add it was a Raptor boom/tail
10-28-2007 Over year old.
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

Are you saying that the pushrod had a "push" on it of about 3Kg ?
10-28-2007 Over year old.
HOMEPAGE  
 
 
Yug
rrProfessor
Location: UK. Herts

yup

I used one of these tail setups and removed servo pushrod


Vegetable rights and Peace
10-28-2007 Over year old.
 
 
Vertrep
Heliman
Location: Sutherland,UK

Love your anti rotation clamp at the end of the workmate,gotta copy that. Just a word of warning, if you go over board with the chinese wieghts and you suffer any tail mechanism failiure the blades will not return to flat pitch and with a driven tail you will be stuffed trying to auto the cab
10-28-2007 Over year old.
 
 
Yug
rrProfessor
Location: UK. Herts

No worries, I'll have crashed long before then

I think the key is to use the weights to dramatically reduce the servo loading rather than eliminate it completely.

Vegetable rights and Peace
10-28-2007 Over year old.
 
 
Vertrep
Heliman
Location: Sutherland,UK

OK ,use a longer bolt, (QUK grips) and one ball each side, will try and post pics tommorrow, it is raining too hard to treck across to the workshop just now.
10-28-2007 Over year old.
 
 
Yug
rrProfessor
Location: UK. Herts

I thought of using balls but the only ones I have are for M2 bolts. Which do you use ?

Vegetable rights and Peace
10-28-2007 Over year old.
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

That's a bunch !
Let's see, 3Kg on an 18mm servo arm . . . . comes out to about 75 in.oz.

So . . . . what will it take to bring that load down to about 25 in.oz. ?

. . . . or about 1Kg on the pushrod ?
10-28-2007 Over year old.
HOMEPAGE  
 
 
Vertrep
Heliman
Location: Sutherland,UK

Sorry Yug, I should have said you need to ream them,if you do not have a lathe use two drills.
10-28-2007 Over year old.
 
 
Yug
rrProfessor
Location: UK. Herts

Very little. Using my 30mm bolt with spacers there is sufficient force for it to centre (overcoming friction) as it approaches operational rpms.

Vertrep - what do you see as being the advantage of using balls over a spacer ?

Vegetable rights and Peace
10-28-2007 Over year old.
 
 
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Main Discussion > Chinese weights on the tail grips
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