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4 Star 60 Pushrod Conversion...

Old 10-14-2005, 08:12 AM
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Sukhoi_Madness
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Default 4 Star 60 Pushrod Conversion...

This is a “How To” on changing over the 4 Star 60 braded throttle cable system to a solid push rod system.

This is my first build and so I am not an expert and the following example has not been handed down from God on a stone tablet… But it worked!!! And so I thought I would share it… Being that 4 Star 60's are very popular on this board...

For those who don’t know the 4 Star 60 has a “Snake” system for the throttle pushrod. This consists of a thin braded wire cable running through a plastic tube from the throttle servo to the carb of the engine.

When I saw this system for the first time I thought it looked dodgy… And I now hate it!!! It is very fiddly to install and a general pain in the bum!!! Although I know a lot of builders have used it with great success and some use the system exclusively.

The main reason why my Snake was not going to work was that I cut the plastic tube it runs through off at the fire wall, meaning that the braded cable had to run about 4 inches to the carb outside of the plastic tube causing the cable to flex and the connection between Servo and Carb to become sloppy and indirect. I realize at this point that it is my fault the system failed but I had only done what the plan pictured. To bad the plan was for a 4 stroke engine which has the carb against the fire wall. I put this down to inexperience after saying a lot of swear words…

To complicate things further I want to fly this Airplane in two days and my LHS is not open until next Monday so all I had to work with was what came with the 4 Star and the hardware pack that came with my GP RV-4 which I am building too.

Also… I have a 16 once fuel tank in the Airplane which cannot be removed. (I know I know) and the Engine mount, Engine, and Manifold are already Bolted, Double Bolted and lock tightened down which would be a 2-3 hour job to undo and redo and so this bash had to happen around all of those things…

For those that don’t know the 4 Star 60 has a snake because of where the fuel tank is in relation to everything else. It would be near impossible to route anything but the braded cable through the original whole in the fire wall to the servo. Even a Golden Rob would fail.
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Old 10-14-2005, 08:15 AM
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Default RE: 4 Star 60 Pushrod Conversion...

The first thing I did was to drill the new pushrod hole.

This is necessary as a solid pushrod will not work as explained above...

This was very difficult with the engine in but should be pretty easy with the engine out.

It is very important that you drill low enough in the fire wall so that you will not hit the tank or the floor which the tank is sitting on but at the same time you cannot drill too low or the new push rob will hit the wing when mounted.

Of course I could not reach the fire wall with a drill bit because of the engine so I took a piece of pushrod and soldered a drill bit to the end of it so that when mounted in the drill the drill bit would reach the fire wall. If your engine is not in at the time you do this there won’t be an issue.

See pictures…
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Old 10-14-2005, 08:18 AM
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Default RE: 4 Star 60 Pushrod Conversion...

OK with the new hole in my fire wall I was ready to install a new pushrod.

To my dismay I had to rob one of the nice pushrods from my RV-4… Not pleased but as I mentioned I want this Airplane finished.

A few bends need to be made in the push rod between it exiting the firewall and connecting to the carb. I can’t really explain exactly how to do this but it requires a bit of trial and error.

I used a piece of paper and pen first to measure the fundamental bends and then used a scrap piece of pushrod to practice on and ensure my bends and calculations worked.

I then worked out how long the push rod needed to be taking into account the bends and distance to the servo. Then I cut the pushrod. The length only had to be exact to the nearest inch because the servo end is threaded and so I have some adjustment in the clevis. I got it pretty much right though.

I tested everything and it all worked out. You may find you have to make very minor bends in the pushrod here and there to stop it binding but it is a pretty straight run to the servo after the difficult bends up to the card.

I also soldered a cross member where the major 90 degree bend is to stop any flex.

See pictures…
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Old 10-14-2005, 08:19 AM
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Default RE: 4 Star 60 Pushrod Conversion...

Sorry this is the best pic of the finished carb end of the pushrod I could get…
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Old 10-14-2005, 08:21 AM
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Default RE: 4 Star 60 Pushrod Conversion...

OK with that end done all I had to do was clean up inside…

I thought the pushrod system for the elevator and rudder was pretty good so I just used the left over scrap from those pushrods for the new throttle pushrod.

The white inner tube runs as far to the fire wall as it can without hitting it when the pushrod is operated.

The black outer tube runs all the way to the fire wall to stop flex in the pushrod and also to stop fowling of the pushrod as the Battery and Receiver are tucked in there too…

I also added a tag which you can see the outer tube running through to prevent flex.
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Old 10-14-2005, 08:23 AM
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Default RE: 4 Star 60 Pushrod Conversion...

All done… Works Awesome!!!

You need to use the longest servo arm you can without hitting the side of the fuse to ensure full open and shut throttle…

This is by no means the only way to do this, or the best way… And considering the conditions I was working under it took some time but anyone who decides they don’t like the snake should give it a go…

Let me know if anything is unclear…

And sorry all you Snake users HAHAHAHA….
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Old 10-14-2005, 01:39 PM
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Default RE: 4 Star 60 Pushrod Conversion...

Great mod and write up, well done. But being a kiwi you should have used some No.8 fencing wire
Old 10-14-2005, 01:56 PM
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Default RE: 4 Star 60 Pushrod Conversion...

Nah... I save that for "repair" How To's...
Old 10-14-2005, 03:19 PM
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Default RE: 4 Star 60 Pushrod Conversion...

No duct tape?
Old 10-15-2005, 01:35 AM
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Default RE: 4 Star 60 Pushrod Conversion...

No Duct tape sorry... But I tested the system with the motor running and it works very well...

Nice smooth action and in my opinion much better then the original snake...

[8D]

Matt
Old 10-15-2005, 03:35 PM
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Lowlevlflyer
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Default RE: 4 Star 60 Pushrod Conversion...

I had the same problems with the cable throttle on my 4* 60 ARF. I had an unrelated crash that tore out the firewall (good ole ARF glue) so I figured it was the perfect time to do away with that terrible little setup. I actually put my pushrod tube in the same place that the cable tube was, by just enlarging the holes. Besides that, my setup is pretty much the same as yours- solid wire rod, bent to fit just right. 100% reliable so far. As far as you cutting your cable tube off at the firewall, that probably wasnt the problem. I left mine long, within about an inch of the servo on one end and an inch of the carb on the other end, and it STILL didnt work right. It's just not a reliable design in my opinion, the cable isnt strong enough.
Old 10-16-2005, 12:35 AM
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Default RE: 4 Star 60 Pushrod Conversion...

I agree...

And if you still had slop in the system even after you ran the outer sleave to the carb then it is worse than I thought...

I just can't stand slop in pushrods... What ever sort... I hate delays or bad movements in control surfaces it drives me nuts!!!

I'm interested that you got a solid pushrod through the original hole though... You must have had to bend it just right...

Matt
Old 10-16-2005, 10:37 AM
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Default RE: 4 Star 60 Pushrod Conversion...

Yup, it took me a few tries and three pieces of wire to get it just right, but I finally got all the bends in just the right spots to make it work. If I was going to do it again, though, I would reposition the tube to make it a bit easier.
Old 10-16-2005, 10:16 PM
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Default RE: 4 Star 60 Pushrod Conversion...

Can't understand why you don't like the flex cable system.. I have one on a 4*60, a something extra, a Hog Bipe and a 1/5 scale cub.. never had the slightest problem with either. Did cut a sleeve too short on one, and simply slid a short section of sleeve over the cable to stiffen it between where I cut it off and the throttle arm, leaving enough gap to handle the required throw... Worked fine..Fred123[&:]
Old 10-16-2005, 10:54 PM
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Default RE: 4 Star 60 Pushrod Conversion...

Didnt say I dont like a cable system, in fact I've seen some planes where that is the only way to run the throttle linkage. What I did say is that the "stock" cable throttle linkage that comes with the 4* 60 ARF (and I am assuming that it is the same one that comes with the kit version as well) is NOT a quality setup. The cable is flimsy, I dont care how much tube is used. I set mine up EXACTLY as the directions stated, and the cable would kink at the servo end almost EVERY time it was actuated. There was no binding or friction interfering with the cable, it just simply was not strong enough to work without kinking up. After fiddling with it I did finally add a larger tube over the stock tube on that end to try and stiffen it up. Also added a piece of light ply with a hole in it to run the tube through, as an extra support between the throttle servo and the fuselage former directly behind the fuel tank. Still no dice, it would still kink up. I jacked with it and finally got it working about 90 percent of the time, but as soon as I used the throttle cut function on my transmitter to kill the engine, the cable would kink as soon as the throttle was advanced again, EVERY time. For me, it just wasnt worth the headache. I know for a fact that the linkage I have now will work EVERY time, and I dont have to worry about it.
Old 10-17-2005, 04:37 AM
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Default RE: 4 Star 60 Pushrod Conversion...

ORIGINAL: fred123

Can't understand why you don't like the flex cable system.. I have one on a 4*60, a something extra, a Hog Bipe and a 1/5 scale cub.. never had the slightest problem with either. Did cut a sleeve too short on one, and simply slid a short section of sleeve over the cable to stiffen it between where I cut it off and the throttle arm, leaving enough gap to handle the required throw... Worked fine..Fred123[&:]
They may have changed wire used since you built yours...

It could just be me, but I found the wire to be a piece of crap which would never have worked even if I did not make the mistake with the outer tube...

It is my first kit so I don't have much experience to go on...

The point of this post is to demo the mod though... Not rip on the wire system...

Matt

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