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Old Aug 22, 2010, 05:41 PM
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I don't think that it would be much harder than this, right?
Weekend Project: Make a Vacuum Former (5 min 37 sec)
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Old Aug 22, 2010, 08:56 PM
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One of the challenges we always face when building an RC model is providing access to the equipment. After some thought regarding the Stinson I decided to use a sliding tray through the nose. The tray will hold the motor/gear drive, the receiver brick, and the battery. The challenge to making that approach work is making and breaking the connection between the servos and the control surface push rods.

Again, after some thought I decided to use magnets to establish the make/break control linkage connection. The one thing that had me stumped initially was how to connect the magnets to the servo piano wire linkages and the carbon fiber push rods. The magnets in this case are 1/8 in diameter and 1/16 thick. An idea finally came that suggested using a piece of 1/8 dowel to back the magnet followed by an application of heat shrink tubing all reinforced with some thin CA.

Prior to building the parts I developed some sketches to help evaluate the final configuration so today was spent at the computer rather than the building board.
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Old Aug 22, 2010, 09:15 PM
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I use ends like pictured. Easy to remove from the servo end with tweezers.
Might not be accessable in your sliding tray though.
Glenn
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Old Aug 22, 2010, 09:29 PM
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Paul- Nice work. It sounds as if you are taking the idea for the sliding tray from the world of electric free fight and the magnetic pushrods from the Snap-and-Fly airplanes. It sounds like a good mix!

-PC49
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Old Aug 23, 2010, 09:51 PM
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Glenn - That method is very good when you have access to the servos. My installation will not have servo access once the tray is in place. Hence the magnet joiners.

PC-49 - I have not looked at the Snap-and-fly models internally. I have only seen them in flight. I am not surprised that magnets are being used for their connections. It is a smiple and very effective way to make and break a connection. I know the sliding tray approach is not new by any means. It just seemed to be a perfect way to handle the equipment access for the Stinson.

With the control linkage make/break connection concept in hand the equipment tray was made up. It is simply a piece of medium hard 1/16 balsa that slides through slots in the cowl nose ring and two guides near the make/break connection. Each set of guide slots are reinforced with 1/64 plywood pieces. The shape of the cut out in the cowl nose ring disk was determined by the geometry of the equipment tray. The tray is held in place with a single pair of x 1/16 magnets. Again, plenty of hold power but also easy to separate when the time comes. The battery holder was cut from a replacement Blade MCX landing skid assembly. I have to thank my brother Ralph for that slick idea.

The push rods are held in place in the fuselage with balsa guides reinforced with pieces of 1/64 plywood where the push rod passes through the guides. This runs very smooth with little effort required for movement. To allow removal of the equipment tray without pulling the tail surfaces off, a piece of 1/8 dowel was CAed to each push rod behind the forward guide. The distance was just a tad more that the stroke of the receiver brick servos. These stops rest against the forward push rod guide when the equipment tray is pulled forward. The system works surprisingly well.

Weight at this point with the battery in place is 29.2 grams. My current weight projection suggests the final weight will likely be a bit above 50 grams. I would have liked to have made my goal but the model should still be ok at the higher weight. It has a wing area just under 84 square inches.
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Old Aug 23, 2010, 10:01 PM
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Clever pushrod arrangement Paul. I like the travel stops.
That's a brilliant idea, many models, one brick/motor tray.

How is the magnet held onto the pushrods?
Is there a piece of dowel glued on then the magnet glued to the dowel?

Glenn
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Old Aug 23, 2010, 10:29 PM
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Very slick, Paul. These are the ideas that stand the test of time, get published, and grab the attention and appreciation of modelers like Glenn and I! (You may know that builders are becoming hard to find on this forum with the advent of all the RTF Ultra Micros.)

Mike is using the module concept on his U.S. Abigail 2.4, but you have to leave the actuators behind. You've solved that problem. http://www.rcgroups.com/forums/showthread.php?t=1263139

-PC49
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Old Aug 23, 2010, 10:55 PM
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Yes indeed a very nice setup with the removable tray.
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Old Aug 24, 2010, 12:49 AM
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Yeah, like I used to think my stuff was cool until I saw this master modeling.
Thanks a lot!
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Old Aug 24, 2010, 08:59 AM
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Quote:
Originally Posted by glewis View Post
...How is the magnet held onto the pushrods?
Is there a piece of dowel glued on then the magnet glued to the dowel?

Glenn
Glenn - The sketch I provided does not do a good job of explaining this. The piece of dowel is glued to the push rod end. It has a hole drilled through the center axis that provides a nice gluing surface area. The magnet is then glued to the face of the dowel. The magnet/dowel assembly then gets an application of 1/8" heat shrink sleeve followed by a dab of thin CA. The combination holds the magnet very securely.

Paul Bradley
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Old Aug 24, 2010, 11:59 AM
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Uh, well, the diagram is actually very clear. If I had only looked at it first..
I have a stack of 1mm magnets, wonder if they would be strong enough, humm.
Glenn
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Old Aug 24, 2010, 11:22 PM
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Glenn - I am using magnets that are roughly 3mm in diameter by 1.5mm thick. They are stronger than needed. Not so strong you have a hard time getting them to part, but stronger than is actually needed. Depending on the application relative to the control surface sizes your 1mm magnets may work just fine ( I am assuming the 1mm is referring to the diameter).

I did not get much done on the Stinson today. Basically the landing gear wire was bent and installed. The parts for the landing gear were organized for installation. I plan on having the landing gear completed tomorrow. That will include making the balsa wheels.

Paul
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Old Aug 25, 2010, 06:41 AM
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Nice. Those landing gear parts look familiar!

You make your own wheels too?
Me too. I like making wheels. The sorta scale wheels I made for the Trojan came out well using neoprene cord tires. First time I made WWII style wheels.

Yeah the magnets I have are round, 1mm dia X 1mmm thick. Added them to an order from KJ magnetics and when I got them and saw how small they are, sort of had no use for them. Now I do!

Glenn
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Old Aug 25, 2010, 10:15 PM
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When I was young my Dad owned a Stinson Voyager that we flew all over the place. He gave me a few Stinson related items recently.

There are 8 sheets in the set. I have them in high resolution files on my computer but no real way of showing that on a forum so I only uploaded a scaled down image of 2 of the sheets. These are not model plans. I believe they are factory reproduction plans with some extra notes showing the differences between the different Reliant models. My Dad got these back in the 70's. I thought you would be interested in seeing these.



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Old Aug 25, 2010, 10:57 PM
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ckreef - Thanks for posting the drawing for the Stinson taper wing series. As it turns out I do have those drawings in my collection of airplane three views. Those drawings are the basis of my earlier comment that the Comet designer took some liberties when developing the plan for the Comet SR-7 kit.

I did have some time today to spend on my rendition of doing the Comet Stinson SR-7 as an RC model. Today was spent doing the fiddly landing gear stuff. The landing gear fairing parts were glued in place and then shaped using a piece of 220 grit sandpaper wrapped around a piece of 1/2" brass tubing. I used a larger diameter dowel when I did the Free Flight version, but found the smaller diameter brass tubing worked better this time around.

After the landing gear fairings were shaped I tackled the wheel pants. No real issues there. Just shape the profiles and then round off the edges. The inside faces of the pants received a piece of 1/64" plywood to act as a bearing face for the wheels. I will explain that in just a bit.

The wheels for the model were made from two laminations of 1/8" balsa with the grain of each lamination at 90 degrees to each other. I use a piece of 1/16" dowel as a wheel hub. The dowel is drilled along the center axis and is 3/16" long. The length of the hub allows the balsa to be turned down to form the wheel hub.

To make the dowel hubs I actually start with a piece of 3/8" dowel. The center hole is drilled. Since that part of the process is hard to do accurately without an appropriate machine tool, I start with the larger diameter dowel. That dowel is then mounted on my Dremel mandrel. The diameter is turned down to the diameter of the mandrel shaft that happens to be 3/16". Turning the larger diameter down allows the final dowel piece to be true relative to the drilled center hole.

Once made up, the hubs are glued in the balsa wheels. I run the wheels on a piece of 1/16" tubing to get them tracking straight and then apply a drop of thin CA to the hub. The tubing is removed and the wheels get mounted on the Dremel tool. They are shaped using a sanding block, an Exacto knife, and some 220 grit sandpaper. The shaping process goes quickly and is pretty easy.

The final step in making the wheels for this model was installing a piece of 1/16" aluminum tubing bushing. The length of the tubing is just a tad smaller than the inside width of the wheel pants between the two 1/64" plywood plates. The piece of aluminum tubing is glued in the hub and keeps the wheel centered in the wheel pant.

The wheels will be painted and dressed up a bit and then the wheel pants and wheels will be mounted on the landing gear legs. I can then get on with building the flying surfaces.

Paul Bradley
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