rcFp

I have to connect the engine throttle to the the servo on my profile but the only available servo is quite far from the body (see attachment).
this requires to bend the pushrod to extent of 2 inches in order to get close to the body.
is this a good practice or should i use any other technique

thanks

rorywquin

Should not be a problem - as long as nothing is catching or binding the load is negligible - an alternative is to use a flexible (bowden cable) arrangement!

rcFp

do i need some kind of plastic tube housing

Flypaper 2

Use Nyrod. A tube inside of a tube. Comes with the end fittings.

mulligan

A little more explanation...

Bending pushrods adds flexibility to the link, and you will lose control authority. On a control surface, this would definitely be a no-no; you would lose control power and possibly cause a flutter problem. On the throttle, you're not as concerned, but you will lose a little precision on throttle control due to the added flexibility. Unless you are looking for competition type precision, this would not be noticable.

- George

foxx

My Feedback: (2)

You may also consider using a bell-crank .

Rodney

You should have no problem using nyrod providing you can anchor the outer sheath every few inches. Make any bends as shallow as possible.

klhoard

My Feedback: (10)

I've lost a couple airplanes to bends in pushrods that were connected to flight controls. Try your best to make a straight shot from the servo to the control horn. I even avoid Z-bends because they create weak spots in the pushrod.

Nyrods are the best bet for the throttle. You usually have to snake it around the fuel tank and thru the firewall anyway. . .

rcFp

I thought of one more option.
the dazzler arf comes with some kind of flexible metal wire .
will it be better to use one of these wires or this over flexibility will cause harm.

majesticmonkey

Or you could slip two one-inch pieces of pushrod tubing over the pushrod and glue these to supports. This would prevent flex and would be workable solution.

CafeenMan

I like using 1/32" music wire for throttle pushrods with a Z-bend on each end. It's the lightest throttle pushrod I've come up with and is more precise than cable pushrods. But I'm not sure if you'll be able to make it do what you need due to the servo and throttle being so far out of alignment. You might want to consider relocating the servo if possible.

Flypaper 2

RCFP
The flexible cable in plastic tube will work fine. Just cut the plastic tube close to the throttle arm within reason to help stiffen the cable.

mulligan

majestic, that set-up will not offset flexibility caused by the bends (it would only provide the normal resistance to flexing for the straight portions).

- George

majesticmonkey

To flex the pushrod tubing supports must move appart which will not be possible if they are fixed. On the diagram I mean that they must move apart in the horizontal axis since any bending will cause the diagonal section to force itself into a more horizontal level which would make the horizontal spacing between the supports longer. Hope this helps...

mulligan

Yeah, I see what you are saying- the geometry is right. But I'm not sure that it will be as rigid as the geometry suggests.

For example, the horizontal displacment caused by flexing in the bent section would be very close to zero if the bends were close to 90 deg., and the fit between the rod and the supports would have to be very tight and very rigid. Even with that, the rod is still free to bend upward (axis out of the page in your diagram) to allow the flexing.

This is probably getting a little too theoretical. I'd be curious to know if anyone has tested a set-up like this to see what the flexibility is.

- George

rcFp

I got a lot of views on whether this connection method will work.
at the meantime i don't see any way to move the servo closer to the body .
i will try first to setup a pushrod connection with the bending and check for any flexibility (including upward bending)
otherwise i will have to move to one of those flexible wires

anyway i will let you know the outcomes

pinball-RCU

The throttle connection has to be more precise than you may think. The difference between a nice idle and cutting off the engine (both are necessary) is very tiny, and you'll go nuts with the 2" bend. It wouldn't cost much to try majesticmonkey's solution (nice picture by the way), but I think you'll find there's still too much slop in it. It may work OK from idle to full, but when you come back to idle, who knows where it will stop?

I would suggest a visit to the LHS, and take a look at all the different control rods. Personally, I think the best bet is the braided cable inside the plastic tube. It will be very flexible (more than nyrod I think), but very precise. The hassle is that you have to wick in solder in the last inch or two of the cable, where it's not inside the tubing. You can use EZ connectors on both the throttle and the servo to avoid having to solder on the clevis connector.

patternwannabee

My Feedback: (1)

Any reason you can't switch the Rudder and Throttle servos?

Just curious.

rcFp

the reason i can not make the switch is because i used pull-pull for the elevators and left the rudder with a pushrod connection.
the closet servo will be used by the rudder and the farther one should be for the throttle