Pushrod support

Just like a Bowden cable, if the sleeve is anchored at both ends, what happens in the middle doesn't affect precision, only friction.

IMHO no. If you don't like the rods that came with you can replace them with carbon rods or make some better ones. I like gold-n-rods but I must support them at intravals all along the length to keep the slop out. mk

Firmly fixing the rods at two points will be OK.

The trouble I've had with the plastic pushrods is that they seem to be very temperature-sensitive--and here in Buffalo, we tend to fly in weather that ranges from pretty chilly to moderately hot (for me nowadays, from early spring to late fall).

The recommended fix, I think, is to make an S-curve between the two attachment points. I've never tried that myself and don't know how well it works.

Where I am able, I've gone to arrow-shaft pushrods with a Y for the elevators (once I did a pattern setup where the arrow shaft was supported in brash bushing BEHIND the elevators), or servos in the tail of the plane with short, stiff pushrods, or pull-pull for the rudder, or two servos for the rudder (GP Wagstaff Extra setup).

Kits are available for the arrow-shaft pushrods and for pull-pull setups. If you move the servos to the rear, standard pushrod hardware will work (4-40).

Let us know how your experiment turns out!

Marty

"Martin X. Moleski, SJ" wrote:> > ... (once I did a pattern setup where the arrow shaft was

Now that was a problem! Those brash bushings are always on the alert to cause some trouble.

Tom

If you can anchor the end close to the servos you should be OK. The middle won't go anywhere as each end is supported.

On Sat, 22 Oct 2005 12:03:16 -0400, "Tom B" wrote in :

Hmm. Looks like the brass turned brash when I wasn't lookin'. :o)

Marty

The consensus seems to be that if I anchor both ends I should be OK, so I'll try it on the workbench (not in the plane) and see what happens.

If there is a flexing problem, it will probably be with the "push", not the "pull". I'll post the results of my test in a day or two.

Thanks for all your replies.

Bill

Bill:

I very much like the Sullivan pushrods, and they aren't affected by temperature. I use them in my Ultra Stick 40 and my Duraplane T-40. You might note that the rods come in rigid, flexible, and semi-flexible models. I'm using the semi-flexible anchored on both ends. In fact, the rods come with a sleeve to perform this function - works great!

Most of the hardware that come with kits or ARFs is generally junk. Also the method of attaching the control rods to the servo and control horn is to use a 90 degree bend with a plastic connector. This involves drilling out the servo arm and control horn which is a very poor practice. With the Sullivan rods, you don't have to do this which makes for a better setup.

Ciao,

Mr Akimoto

I used 30 cm of gold-n-rod to control the throttle - supported only at both ends and it works like a charm - but of course not much resistance

David

Storm's Hamburgers wrote:

Sorry Marty,

All the S-curve accomplishes is to add drag to the control system. Guess how *I* know...

On Sun, 23 Oct 2005 05:55:40 GMT, "Six_O'Clock_High"

Thanks for the feedback from your experience, Six!

Much appreciated.

I like it when I can learn from others' mistakes!

Marty

True...

But I would also nail down the middle somewhere..

Vibration can cause the unsupported section to "buzz"...fracturing/loosening the end attachments and causing slop/loss of control... (usually "up" in a dive....)

Don't ask....

.....electric fliers can disregard the above... :)

Dave

OK -- test done, not too scientifically but OK for pragmatic me.

I locked one end of an an almost full length outer sleeve (35") and clamped the end of the inner rod to the workbench so it couldn't move. I then applied 5 lb of pressure to the free end of the rod using a kitchen scale to measure the push. I looked for twisting/bending of the assembly but could not see any.

The servos I'm using are Hi Tec HS-422 which can develop 46 oz-in of torque at 4.6V or just under 3 lb of push at the end of a 1" servo arm. So, I guess I'll be OK without middle support, especially since the unsupported length will only be about 16".

But Dave makes a good point about vibration. I'll have to think about that.

On 23 Oct 2005 14:03:45 -0700, "Bill D" wrote in :

Cool. When I experiment, I install stuff in my planes and go fly. :o)

I've used lots of Golden Rods without intermediate support. They've never torn out.

Vibration can be a big problem with wooden pushrods or arrow-shafts. They have only two points of support--at the servo arm and the control horn. Your setup would have four: servo arm, bulkhead, fuselage side, control horn.

Marty

Nice job! If more people actually tested their theories, there'd be a heck of a lot less bullsh*t flying around on the newsgroup. :-)

I prefer a carbon arrow shaft, myself. As for the vibration, I recently found a solution for rattling control rods in my Unionville Hobby 6' Beaver: I glued a small bracket at the rear of the fuse that supported the end the shaft in a small ring of scrap EPP foam.

Good flying, desmobob

On Sun, 23 Oct 2005 22:35:17 GMT, "Robert Scott" wrote in :

Wait, wait, wait--the foregoing is an untested theory! :-P

That is what I was talking about when my bushings turned brash. The arrow rod is supported from the servo arm to the bushing in the tail of the plane.

Marty

One simple test is worth a much more than a lot of simple minded opinions. Good job!

I'll still put in supports every 8" or so when installing this type of control linkage - only when I think ahead and install them prior to closing up the fuselage. Servo on left exits fuselage on the right, and right servo exits on the left. Gives you a chance to get nearly straight runs with only gentle curves offering the least amount of resistance in the system.

Red S.

I'll second that.

Untested theories and brash bushings! LOL

Bill