Saurabh, please note I really meant no offence. If taken, I humbly apologise.

The fact is many newcomers do ask their queries, and sometimes without thinking the whole matter through, blindly follow that advice, irrespective of how qualified it is.

Sure, use a sparkler wire....... but what length can you safely use?

I continue this explanation in the next post........

Quote from: GP_Freak on May 19, 2015, 02:44:31 PM
Guys, IMHO, experimenting doesn't need experience. On contrary, it is those very experiments which builds up experience.

In continuation, an aeromodel is a potential hazard. Experimenting is indeed very well, for you learn, but when you are dealing with a hazardous object and/or activity, you never go blindly into it. Not at the risk of injuring anyone; nor at the risk of losing/damaging your equipment.

Take the case of a low cost foamie. The modeller has used a 1 mm sparkler wire as the elevator pushrod with a length of 8 inches. In flight it deforms permanently leaving the elevator in the down position. The model weighing (All Up) 500 grams comes diving down at a speed of 40 mph.

This is enough to

a) Injure someone
b) Destroy the battery, motor, Rx, servos plus model. A loss of thousands!

And for what? Saving Rs. 5 on a cycle spoke?

Go ahead and experiment: there can be no development without it. But, understand in depth the science and practise of what you are doing, and carry the responsibility of the same. Irresponsible acts give the whole community a bad name. Use other's experience as your textbook.

The hobby has enough risks as it is; we should try to systematically and scientifically reduce these to the maximum extent possible. I too have been guilty in my time of taking unnecessary risks, and now do try to eliminate these, as should all of us.

+1 to that.
In today's age, we should use CF rods as far as possible, with an adjuster at the servo, and a support in the middle.
Using jhadoo ki teeli etc is a hangover from the days of scrounging for alternative as stuff like Goldenrods, clevises etc were either not easily available, or we could not afford them.
Cycle spokes are, in my opinion, unnecessarily heavy and too thick to fit the servo/control horn.
Traditional pushrods used to be balsa with wire ends, but do not use unless it is is really hard/stiff balsa, and is not less than 1/4" sq. (I know from recent personal experience that a 1/8" sq will flex and ultimately break even in a foamy)
What Rai saheb says is doubly important as i see many modellers building HUGE control surfaces, imitating 3d designs.
Two other avoidables:
1. Aileron pushrods angled out significantly from a single servo
2. V bends in wire pushrods to allow adjustments

BTW, the single thread method i used is intended for lightweight, slow gliders. Mine is 200gms and flies at 5-6m/s (~20kmph). It is actually a specialist method, not intended for regular powered models including foamies.

A simple test.
If you can move the control surface by hand without the servo turning, the pushrod is inadequate!

@Sanjayrai55, no body is contesting that people are trying to save a couple of bucks and you jumping to conclusion that people are irresponsible is not appreciated  .  One has to employ all necessary precautions and testing needs to be done in a place where even such mishaps doesn't endanger others. That is common sense right ? Not sure how that is going to endanger people 

GP Freak: I'm sorry but I do not think your post is worthy of a reply

Quote from: K K Iyer on May 19, 2015, 08:25:20 PM
+1 to that.
In today's age, we should use CF rods as far as possible, with an adjuster at the servo, and a support in the middle.

Cycle spokes are, in my opinion, unnecessarily heavy and too thick to fit the servo/control horn.

Iyer sir, well said.

Flexible outer/inner pushrods (snakes) are an excellent option for longer lengths. But the ones with an inner plastic tube-rod are useless. The ones with a 1 to 1.2 mm inner wire rod are excellent up to a 40 size model. Just make sure it has adequate support and anchoring of the outer at frequent intervals - like every 100 mm or so. That way, effectively the unsupported length is never more than 100 mm.

Remember. buckling (the cause of failure here) is a function of the length. If you will notice large models usually have the empennage servos fitted in the tail, with push rods less than 3" long. I prefer (where possible) to fit the elevator & rudder servos in the tail section with short pushrods even on smaller models. I say "where possible" because of CG constraints in design.

On cycle spokes, you get 2 mm spokes, which fit (threading included) into standard clevises and linkage stoppers, and are good for up to 4" with standard Servos or 6 Kg-cm torque. I normally use them for ailerons.

Flexible inner/outer pushrod



Rear mounted Servos (17 gram)

Need to properly glue the outer at all contact points to prevent bending/buckling

Rear mounted standard servos

Cycle Spoke (2 mm) as Aileron PushRod

Reading some of the previous post from some people...  I would only say going for an alternative is only perfect if its well proven over the time, its not a question weather you are flying a electric or a engine powered airplane, talking about model airplanes these are not toys & over the years I have seen many disasters here in India, why not simply use a CF rod..  which can cost just Rs. 100/-

The cycle spokes are well proven & are used worldwide since many years... especially all my engine airplanes for 0.15 & above I have used them & never had issues with it 

Carbon Fibre rods are nice. The only problem I face is with 3 mm rods or higher, the end fastenings is an issue. A clevis normally is good for M2 threads, and Linkage Stoppers too take 2 mm dia rods.

So I use a CF tube, 3 mm OD & 2 mm ID and glue metal rods inside. In the photo below I have glued a 2 mm Cycle spoke about 60 mm long into the CF Tube



I would be happy to know what others do for this

Personally, I have used only cycle spokes on all my builds (on Sanjay Sir's advise). They are pretty stiff and fit easily into the linkage stoppers. Never faced a problem with them. However, I have heard of people using piano wire (available at music shops) successfully. Never tried them myself though.