Adjustable Wire Push Rods

by dharkless | January 20, 2014 | (22) Posted in Tips

Here is a quick tip on making adjustable control rods from unthreaded wire.  This is based on another hint that suggests using the wire from the small colored flags that you can get from Lowe's or Home Depot for about $7 per hundred.  If you use them you have to make the control rods a fixed length which is hard to do and get the exact length you want the first time.  It also limits your ability to make small adjustments to dial in the neutral position that can be done with threaded conectors or E/Z connectors.  This hint offers an easy solution.  

All you have to do is add an offset in the wire that can later be adjusted. I like to connect to the servo arm with a "Z" bend.  They are easier to insert than a modified "Z'.  Then use one width of the needle nose pliars gripping just after the first "Z" and make a horizontal 45 bend.  Go one more width of the pliars and make an opposite direction 90.  Then go one more width and make a second 45 back in the original direction.  You should end up straight with the first section after the "Z".  After that make the rest of the rod to length using a modified "Z" at the control horn.   The modified "Z" is easier to insert for the second end.  Simply grip it with needle nose, twist it a quarter turn, insert into the control horn and release.  It will snap right into place.

If you need a small adjustment just unhook the wire at the modified "Z" and either tighten or loosen the offest bends as needed, then rehook.  All 3 bends should be adjusted each time to keep it uniform. 

I like to put the offset bends just after the servo for appearance sake.

It should look like:

 

Here is another application where I used this idea:

This ia an Old Speedster to which I have added ailerons.  In this case I placed the offset bends near the horn which has a modified "Z" bend.  If you grip the offset bend firmly you can twist the wire enough to disconnect without using tools.  If you do use a tool the offset provides a convenient gripping position.  This is now my preferred position for the offset as long as the wire can be reached easily.

 

Update:

Someone asked if they would straighten in use.  I don't think so:

This is one of the push rods from the 60" flying wing that is hanging from it.   It weighs 460 g.  There is no hint of straigntening.  If you use the flag wires they are very stiff and do not need any middle support.  Mine are usually under 10" long.

 

Update:

Someone asked about my landing gear.  I am going to do a detailed article but here is a picture.  The whole set is made from one wire hanger:

 

Another quick tip:  

I install my embedded servos at an angle so that I can get at the control arm screw.  The arm end is just high enough to let a screw driver fit on the screw.  The other end is fully embedded to minimize drag.  The angle does not effect operation.

COMMENTS

Trippey on February 11, 2014
How much force can the bend in the pushrod withstand? It would not be ideal to have a pushrod unbend itself in a high-G maneuver.
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dharkless on February 11, 2014
These are pretty stiff. I re-drill the servo arms at 1/16" and they are snug. They do not need any middle support and the bends do not flex in use. I always keep the lengths of the bends pretty short, about 1/2" and they do not flex in use. I think you would tear out a control horn before these would straighten. They will definite take what a 9 g. servo will dish out. I just unhooked one on a model weighing 540 g. and hung the whole model from it with no noticeable deflection. I will add that photo.
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Holski77 on February 11, 2014
Please post a video of one of you wings flying! I would like to see how the undercamber performs!

Also, I would love for you to describe how you did your landing gear. If I could set up a decent pair of landing gear I would be a lot less stressed about throwing my flying wings and a lot more comfortable putting my fpv equipment on them. I like how you gear is integrated with your power pod. I have no landing gear on my wings and really need some. I am using an 8 inch prop on my versa wing because when I put the 9 inch prop that is appropriate for the 1100kv 15 amp engine it knocks the engine mount off durring landing. The extra power pod used to attach the landing gear would be great for, not only for landing gear and usage of a larger prop, but i could also put my fpv camera in it, along with a downward facing cloverleaf, that will provide clearer signal to my ground station below it, than if it was mounted upright on the top of the wing.

The last detail I need to attend to is the CG. WIngs like the versa wing, and the blunt nose flying wing I made, need so much nose weight to reach the appropraite CG. If I could find a planform that flies with the CG a bit further back from the nose that would be great. I know adding sweep will move the CG back. I imagine that the lack of trailing edge sweep I see in some of your wings would help with this. Just looking for a setup that wouldn't require any balancing weights.

One last thing, I love my electronics and am doing a pusher prop setup for all my planes for that reason. All that engine weight in the back has me putting my battery as far forward as I can and some lead upon that. I would like to take the lead out of the equation.
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dharkless on February 11, 2014
Unfortunately I am in western PA where we have not seen the ground for a while. I stared back into RC at X-Mas time after about 15 years off and have not had a chance to fly the wings yet. They sure "feel" like they want to fly and goodness knows I want them to but the actual flying part is all theory so far.

I will do an article on landing gear but I will add a couple of photos here to give you a hint. The power pods are already set up for gear on the front end (back in pusher mode). I just duplicated the set-up on the back. The coat hanger forked, spring loaded front gear is mine.

My wings also struggle to balance. You will notice that I have pretty generous cut-outs for the pusher motors and I still put the batteries way forward. I can get to between 20% and 25% of MAC but I would like to be at 15% for initial testing and set-up. I have a nose on one and some temporary weight (8 quarters taped on the nose) on another. I have redesigned both the single sheet and two-sheet no-waste designs to include more sweep including trailing edge which helps the balance. That has let me reduce or eliminate the big cut-outs. I have added the single sheet design to the article but not the two-sheet one yet (soon).

I am also contrary to adding dead weight for balance.
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Holski77 on February 11, 2014
Wow, thanks for the quick and detailed response! I will be trying this out very soon.
Maybe instead of increasing the sweep you could add a tail like the Ho229 (would require tractor or prop n slot motor). I will try a diamond shaped planform with a pusher setup.

Also, from experience try 20% MAC works fine for wings. 15% needs to much reflex, and you will have trouble guessing how much reflex you need. 20% with just a tiny tiny bit of reflex works great.
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dharkless on February 11, 2014
OK that is good news because I was having pretty good success getting to 20% but trouble getting to 15%. I thought some reflex would be needed especially with the under camber on the first two designs. I hope landing gear will make it easier to make those adjustments without banging into the ground.
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rickdavidson on February 11, 2014
Great Idea. !!!!!!!!!
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dharkless on February 12, 2014
Thanks!!!
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alibopo on February 12, 2014
From personal experience these little V bends work great. Don't make the V too big or it is more likely to 'spring' (open and close) under pressure.
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dharkless on February 12, 2014
Yes. I recommend just the width of the jaws on the needle nose pliers (3/8" or so). You can easily get 1/8" +/- adjustment with that amount. If you are careful about the original length you should not need any more than that. If the wire you are using flexes enough that you need to support it in the middle it is not stiff enough for this method. I recommend the wires from the marking flags you can get at Lowe's or HD for $7 - $8 per hundred. One wire usually makes two control rods so that is about $.04 each.
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Adjustable Wire Push Rods