Hey all

Working on my first ARF assembly (Avistar) and having a problem with pushrod binding. I noticed the problem when my rudder / nose wheel servo was buzzing with no control input. Based on the pre-cut holes for the pushrod tubes, the tubes have to bend a little along their course to the servo, basically to accommodate the fuel tank. I figure the pushrods are binding in the tubes because the rods are straight and the tubes are not. Does that mean that the rods need to be bent exactly to match? Is there some kind of lubrication Ishould grease up thepushrods with? I tried to figure out a way to make the pushrods straight, but that would involve basically cutting new holes everywhere for them and that's not something I'm eager to do.

What kind of servo are you using? Digital?
disconnect the pushrods does the servo still buzz? If not, hook the pushrods up one at a time and see if the buzzing resumes...

If the rod is too strong, it may take some force to be bent while it slides back and forth.
Both solutions should help (silicone lubricant), plus reducing the diameter of the steel rod or switching to a cable.

Had a smiliar condition and corrected it by slightly bending the pushrod to a permanent curve to match the curvature of the sleeve in which the pushrod moves. Had to be gentle and slowly progressive in the bending so as not to overdo it. Matching the curve made all the difference. Mike.

It might help to replace that rod and sleeve with nyrod as it navigates curved runs much better than a solid rod. Also, tame down the throw, you only want that nose gear to turn about 5 to 10 degrees at full throw. Do that by connecting the nose gear push rod as close to the servo arm center as you can and as far out on the nose gear arm as possible.

On a light weight plane like the Avistar, Iuse gold in rod for the nose gear steering. You can make substantial bends in the push rod runs, andstill havesmoothbind freetravel of your control rod.

Rodney

I actually tried that but that particular configuration makes the rod bend even more acutely.

Start by bending the inner rod a little to match. I prefer not to lube this area as it will collect dirt. Plus I fly in the winter at times. The wrong lube when cold can make things tight.

David

Sounds like maybe the nose wheel is binding. Possibly it is too tight or the set screws are screwed in too tight, or the steering arm is rubbing or binding. If you haven't already done so, i would make sure the entire nose gear is free moving with no binding at all, anywhere. Mike.

With regard to the nose wheel - I have mucked around with this thing for awhile. The pre-drilled pushrod exit hole does not line up well with any of the wheel control arm holes, so that the pushrod bends within the exit hole during steering right or left, causing some resistance. If I keep the control throw minimal, there is less resistance. I just hope that little bit of throw is enough for useful steering during taxi. Guess I'll find out.

BTW, when either only the nose wheel pushrod or only the rudder pushrod are attached to the servo, there is very little binding / buzzing. However, when both pushrods are attached, that little extra bit of resistance is enough to cause buzzing at rest.

David,

I was gonna try some gun lube - supposed to be good in all temperatures and not thicken over time, also not supposed to degrade plastics. Do you think that would be a problem?

Resist from using any lube at all I assure you that you will have problems later on, Like Mike said if you was to carefully and a little bit at a time to put a bend in the wire to mimick the bend of the outer sleave you will feel less resistance and so will the servo. Using gun oil may or may not have a reaction to the plastics or the covering or the wood for that matter. If anything if you wanna use a lube, use vaseline, just put a little bit on your fingers and then slide the wire between your fingers but do not use a bunch as the more you use the more it could, can, or will collect dirt and junk on the wire and then you will end up with this same problem later on and then you will have to take things apart to clean out the junk out of the wire sleve and that aint no fun.
Try bending the wire first before any lube is to be used you will be glad you did.

It's not needed. If you're setup is right a smooth wire should slide well enough in a smooth sleeve. The nyrod really is the best solution when you have to go around some turns. Just anchor the sleeve in a couple of places along the way and you're done. If you're getting serious bending at the servo, the anchor point is too close to the servo.

There are some lubes out there that would help. I just think finding and fixing the problem is the better way. Lube will only mask the problem and could case other problems. If you plan on being in this hobby for a long time. Use this to learn the right way to fix a problem and it will help you down the road.
If your servo is binding only when both linkages are attached, I wonder if part of the problem is at the servo. Are you having to pull the arm over to the servo output shaft to get it on? If so, maybe a longer arm or a move of the servo is in order.

BTW, the nose wheel dose not have to move much to be effective. Matter of fact, too effective is worse than not enough. Flying on grass is not a problem, but a sensitive nose wheel on a hard surface can be a problem. I set mine in the drive way with the engine off. Just center the rudder and roll it down the drive. then adjust the linkage on the nose till it rolls straight.

david

http://www.rcuniverse.com/forum/fb.asp?m=10814229

I may actually try switching from rods to cables - sounds like that might help. So about cables - what are the downsides, if any? If they're better, why not just start with those instead of rods?

The down side of cables for a nose wheel is you need to have your tubes closer to the servo arm and control arms than you do if you use rods, otherwise the cable will try to buckle. You can overcome this by using two cables in a "pull"- "pull" arangement, but this is difficult and unnecessary to install on an Avistar's nose wheel.

I had the same problem you are having with my Avistars. The rudder tube comes out level and in pretty much the right spot to line up with the servo arm. The problem is the tube for the nose wheel has to come past the fuel tank and must stay right up against the side of the fusalage as well as rising upwards at an angle to meet the servo arm. The end of servo arm is 1/4" or so off of this line, so on all of my Avistars, I solved the problem by putting an extra "Z" bend between the servo arm the the end of the tube. This lines up the end of the rod right over the servo arm. I also bent the last 3/4" or so of the rod down just slightly to get it on plane with the servo arm and over come the "up" angle of the tube. This lets the rod line up better with the servo arm and still slide thru the tube without binding. You may have to cut 1/2" or so off the end of the tube to give room for the "Z" bend to move between the servo arm and the tube without striking it.

Thanks to all for your help. I'll keep tinkering.......

rob

Keep at it Rob. Do your best with the solid rods. I lot of guys use cables with great success. I am just not a fan. The cables have there own set of problems and getting the rods right will be better in the long run.

David

A small amount of rod travel is all that is needed on that nose gear, and will result in plenty of steering and a 180 turn on the runway. Small amount.