Push Rod Linkages - RC Groups
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Nov 03, 2017, 10:22 AM
God Created me to Create
The_Builder's Avatar
Idea

Push Rod Linkages


I had been kicking around the idea of doing internal push rods on the Epee for quite some time. None of the ways I had come up were as elegant as I wanted. In reality the current Snipe is probably one of the nicest as it requires no tools and is very reliable. The Epee is just too small of a plane to really make that system work and be easy to use.

I have now abandoned this idea as it kind of feels like putting a crystal chandelier in my garage. Sure it would look cool and make the plane super clean but I am not sure the effort to build the torque tubes and install them is really worth the return.

However, before I bailed on this idea I did come up with a method I would like to share. Feel free to use it, or maybe it will inspire some other ideas.

Here is the basic idea:
The vertical portion of the control rod that is inside the fuselage would have a steel ball on it. Ideally with is would be a small ball from a ball joint connector. It would be important that the ball be in the side of the vertical portion. A piece of tubing or piano wire with a 90deg bend with the ball slid on and glued in place would be ideal. This is the portion that would drop down into the fuselage.

The push rod would have a rare earth magnet on it. The rare earth magnet would be a disc with a counter sink. The one I looked at was .25" in dia and .125" thick and had a nice countersink designed for a #2 screw. The magnets would oppose each other because they can be ordered with the north or south pole on the countersink side. The magnet would be orientated vertically so when when the wing was dropped onto the fuse the ball would drop right into the countersink.

In essence you would end up with a magnetic ball and socket joint like a hip joint. This could also act as a servo saver in a hard crash. The tiny magnets I looked at had a pull force of 1.19lbs. I am not sure if this would be enough holding power or not but they do have larger versions.

I am pretty sure one of you folks who are smarter than I am could make something like this work. A 3-d printed holder for the magnet that the push rod slid into might be really nice.

I found the magnets at KJ magnets.
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Nov 03, 2017, 11:33 AM
Aurora Builder
It's a neat and relatively simple idea, I'll give you that. Even rare earth magnets are unlikely to be strong enough in the event of a medium force landing, or during launch loads. Build it and try it, I very well could be wrong!!
Nov 03, 2017, 11:35 AM
Just here for the pie.
randall_l's Avatar
Could you please post a couple sketches? I'm having trouble visualizing what you wrote. It's not poorly written, I just can't "see it" in my head.

Edit: Nevermind. I think after several reads and sketching I have it figured out.

Why not use a crank inside the wing, having a hole in the bottom for dis/connecting the control rods?

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It'd be simple to rig up a tool from a dollar store pair of eyeglasses or something to reach under and dis/connect the rods to the cranks when un/installing the wing.

Cheers!
Randall
Last edited by randall_l; Nov 03, 2017 at 02:28 PM. Reason: Lightbulb.
Nov 05, 2017, 09:11 AM
It's time for me to fly
JimZinVT's Avatar
Quote:
Originally Posted by samc99us
It's a neat and relatively simple idea, I'll give you that. Even rare earth magnets are unlikely to be strong enough in the event of a medium force landing, or during launch loads. Build it and try it, I very well could be wrong!!
Clever idea Paul, thanks for posting it. I'm also having trouble visualizing what the geometry of this linkage looks like. Is the concern that the ball will "sheer" off the countersunk face of the magnet? If so, maybe put a small strong magnet at the bottom of a "cup" (milled delrin or 3d printed?). That way the cup takes the sheer load and all the magnet needs to do is keep the ball seated.

I've been thinking about magnetic connections for the tail linkage of a light sloper (Ahi) to make it easier to remove the tails for travel. My ideas were too heavy. This gives me some other ideas to explore.
Nov 05, 2017, 10:44 AM
God Created me to Create
The_Builder's Avatar
Jim,

the idea of the magnet acting just as the retainer with no load occurred to me as well and I though of something similar to what you were thinking.

I will try and sit down and sketch something up to better explain my idea.

Randall, What you suggest sounds simple enough and has been done on a bunch of planes. In some cases the final connection was not quite as simple in the real world. The Snipe system is pretty nice for an open fuse where the push rods can be easily accessed and lifted up to connect them.
Nov 05, 2017, 11:04 AM
Transplant Chey WY from Reno
Thermaln2's Avatar
Paul,

Having experimented with small strong magnets , as disks, the pull apart axially is perhaps way too strong for you to easily disconnect two magnets, one on the bellcrank and one on the connection arm. Having the connection magnetic between contacts that are ball joints will be even more difficult.

What you are looking at is the shear forces for disconnects. If the idea is to pass a bellcrank connection axially into a ball joint connection, I do not think the linkage will ever come apart due to the motion of the servos and connects. What you might see is that as you attempt to take off the wing, one might damage the bellcrank or the flaperon .

The other issue is how can you connect the magnet to the bellcrank or pushrod such that it does not come off. These little magnets are really smooth and I found that grinding grooves with a dremel tool is hard to do. Then the epoxy does not bond well to the magnet metal. I tried this when I tried making a on-off magnet for my zipswitch (sp) in my DLG. I had to embed the magnet totally because it kept breaking free. So you need to get a small ring magnet and also have some way to hold it in place. So take a look here, because it shows a countersunk setup for a screw. Note the North-South alignments are different, and this will help the assembly: http://www.kjmagnetics.com/proddetail.asp?prod=R422CS-P

I can draw the way I would do it if you need me to.

Chris
Nov 05, 2017, 11:39 AM
Transplant Chey WY from Reno
Thermaln2's Avatar
Looking at the ring magnets, I would modify the ring magnets and make them like wheel collets. On the bellcrank wire, I would drill and tap the ring and slide it over the wire, then tighten. On the bottom, where the bellcrank would slide into the collet, tap in about half way and have the pushrod screw in. The pushrod would simply slide over the bellcrank wire and hit the magnet. The magnets will not slide apart but also may not be able to be disconnected unless one slides a razor blade or modeling knife between the magnet rings and twist.

What I read here is that people say it might not work because it will come apart, BUT I think the problem is not the coming apart during flight but coming apart when you want it to.

Sorry Paul maybe I'm beating the bushes to much.

Chris
Nov 05, 2017, 11:44 AM
Transplant Chey WY from Reno
Thermaln2's Avatar
I was thinking that the tap into the bottom ring might not permit bending as one might a ball joint. To get around this, glue a screw into the CF rod, then put a screw into the ring magnet. Cutting the heads off the screws and then connecting them with a short length of plastic , like a nyrod, will permit the flexing of the magnet to occur like a ball joint.

Simple.

I think you can mock this up fairly fast. Something I wish you could send me some bad center sections and a bas fuse saddle and we could glue it up to try.

Chris
Nov 05, 2017, 11:51 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Quote:
Originally Posted by The_Builder
The Snipe system is pretty nice for an open fuse where the push rods can be easily accessed and lifted up to connect them.
FWIW, the "stock" Snipe system is (IMO) a pain to deal with.
Most seem to have switched to carbon rods that are connected/disconnected at the servo end.
Mine is still stock, built it early before the carbon rod method became common.
Nov 05, 2017, 12:35 PM
It's time for me to fly
JimZinVT's Avatar
Quote:
Originally Posted by The_Builder
Jim,

the idea of the magnet acting just as the retainer with no load occurred to me as well and I though of something similar to what you were thinking.
Something like this is often done on "wingeron" slope planes. Carbon tubes are embedded in the wing halves, with a magnet glued onto the outboard end of the tube. These slide over a steel joiner/pivot rod. The magnets keep the wings from sliding off but allow them to pivot on the rod. My thought was a miniature (and much shorter) version of that. It wouldn't allow for multi-axis ball & socket type motion though.
Nov 07, 2017, 10:20 AM
God Created me to Create
The_Builder's Avatar
Quote:
Originally Posted by JimZinVT
Something like this is often done on "wingeron" slope planes. Carbon tubes are embedded in the wing halves, with a magnet glued onto the outboard end of the tube. These slide over a steel joiner/pivot rod. The magnets keep the wings from sliding off but allow them to pivot on the rod. My thought was a miniature (and much shorter) version of that. It wouldn't allow for multi-axis ball & socket type motion though.
Jim we are thinking the same thing. The countersunk magnets came to mind first because I knew they were available. It would be the cup with the small steel ball on the torque rod. My idea was that the ball would snap into the cup but I really like your idea of a carbon tube with a tiny magnet glued inside. This could be smaller, have the same holding power and be even more reliable.

If not for the pain of making and fitting the torque tubes or horns I would look at doing this on the Epee.

Two of the guys I was hanging out with in Farmville had Snipes and they made hooking up the flaperons look pretty simple.
Nov 08, 2017, 04:42 PM
Aurora Builder
Quote:
Originally Posted by pmackenzie
FWIW, the "stock" Snipe system is (IMO) a pain to deal with.
Most seem to have switched to carbon rods that are connected/disconnected at the servo end.
Mine is still stock, built it early before the carbon rod method became common.
I think this is why the fork system pioneered by Kristoff in the XXLite and used elsewhere (perhaps with more popularity due to limited XXLite availability) has taken over. I also like the system engineered for the Evolution 3.1, but it has a lot of custom machined parts and wouldn't scale down to the 1m class so readily.
Nov 09, 2017, 03:04 AM
Registered User
B75Driver's Avatar
Quote:
Originally Posted by samc99us
I think this is why the fork system pioneered by Kristoff in the XXLite and used elsewhere (perhaps with more popularity due to limited XXLite availability) has taken over. I also like the system engineered for the Evolution 3.1, but it has a lot of custom machined parts and wouldn't scale down to the 1m class so readily.
Sam,
I came to DLG after the popularity of the XXLite, so I am not familiar with Kristoff's system. But I just finished building Roy Dor's Vortex 3 and I think it's a better solution than the Snipe. (I made the carbon rods and disconnect at the servo end on my Snipe. It's a bit fiddly at first before one gets the hang of it.) The
Vortex uses a forked aileron horn that mates to the pushrods through slots; and the pushrods are held in place through a carefully designed rib system that is glued in the fuselage at the factory. There are careful adjustments to make in the initial build, but after that the assembly at the field is instantaneous.

Jim
Nov 09, 2017, 08:17 AM
God Created me to Create
The_Builder's Avatar
Quote:
Originally Posted by B75Driver
Sam,
I came to DLG after the popularity of the XXLite, so I am not familiar with Kristoff's system. But I just finished building Roy Dor's Vortex 3 and I think it's a better solution than the Snipe. (I made the carbon rods and disconnect at the servo end on my Snipe. It's a bit fiddly at first before one gets the hang of it.) The
Vortex uses a forked aileron horn that mates to the pushrods through slots; and the pushrods are held in place through a carefully designed rib system that is glued in the fuselage at the factory. There are careful adjustments to make in the initial build, but after that the assembly at the field is instantaneous.

Jim
Jim, You hit in a key to the forked system. If the push rods are not very rigid and locked in place very well that system would be a mess. If the pushrods can move up and down at all in the slot throws will not be very consistent.
Nov 10, 2017, 07:52 AM
Registered User
B75Driver's Avatar
Quote:
Originally Posted by The_Builder
Jim, You hit in a key to the forked system. If the push rods are not very rigid and locked in place very well that system would be a mess. If the pushrods can move up and down at all in the slot throws will not be very consistent.
Yea, it certainly would seem so. Roy Dor's design seems to account for that. The forks are carefully machined and he uses steel clevis' on the pushrod so that there is no slop. It may be too complicated for your needs.-- Jim


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