Pinewood and Plywood: Part 1

Ok! Now it’s time for the actual construction. Honestly, this is not an actual linear build like the posts in this project. For example, since the arrival of the third parcel I was start building the followings.

So, I decided to use wood for my build. It is a common material for the booms of multirotors and model airplanes in general but not the most common material for the body. For this part they tend to use plastic, carbon fiber, Plexiglas and other light/strong compounds.

I stick with wood, plywood for the body and pinewood for the booms, because it was really easy (and extremely cheap) to find where I live. Furthermore, is strong enough to handle the crashes that I was going to have in the beginning with a little bit of flex to cancel some of the vibrations.

The plywood is 4mm thick (you can find it in thinner/thicker variables as well) in the market and the smallest standard dimension is like the one in the picture below.

In my mind, the body shape was more complicated and pretty but because of the lag of cutting tools I ended up to use this design. The coffin style that looks like a bad joke!

I draw the first one with a ruler, measuring the needed dimensions, and then I’ve cut it with an old hacksaw. Then I’ve used the first finished part as a stencil to draw the next one and with the same procedure I made the parts two tricopter body parts.

The one will go on top the other on the bottom, sandwiching the booms on the middle.

From the dimensions I had in my mind that translated to the two body parts we have the center of gravity (CG), marked here with the tip of a philips screwdriver and a pencil. By reading more and more articles I realize that this point is not actual the CG point but the desired center of thrust (CT).

If those two points are the one on top of the other when the tricopter is completed then the balanced, and the flight characteristics oriented by that, will be great!

In order to have a better understanding of what is going to follow I’ve placed the flight controller (a KK2.5 board) on its estimated position and a rubber eraser on the bottom, playing the role of the receiver (an FrSky X8R).

Now, its time to start drilling! I own a small Proxxon electric hand tool (like the famous Dremel) that is more than enough to open some holes in the wood but instead of this I decided to use my old trusted motor tool! It’s made out of an old toy motor and a most of the times I am using it without supplying power to it. I am just spinning the rotary head with my hands! Currently, it has a 4mm iron drill bit, but this to wide for my project.

I’ve opened the small plastic draw with my old PCB drill bits and find a 3mm one. The perfect size for the steel bolts I’ve ordered from HobbyKing a few days ago.

But before start the actual drilling a few little bits and pieces. First, I’ve written which part will go one top and which on the bottom. Then I’ve places the two body parts on top of the other to sand the corners. The small little wood parts protruding from the ends can easily cut your hands.

To get a better perspective of the build three of my favorite pen type markers are playing the role of the tricopter booms!

And there is no better tool than the piece of paper! I’ve cut this with a 120-degree angle in order to draw the lines where the booms will fitted. The only problem with that is the paper itself. A thicker, less flexible material should be used the next time.

And because of this flexibility a ruler was supporting the edges of the paper and with a pencil I’ve draw the three lines. Each one with a 120 degree angle between them.

Here, I am going to place the FrSky X8R receiver. I draw a box with a pencil to get the dimensions right! After that I’ve marked the positions of the two holes that will hold the tail boom. You can see them where the “3mm” designators are.

And now its time for the booms! This is 12x12x600mm pinewood. It is from Sweden or at least this is what the carpenter told me! But despite the origin of the booms, the quality is great! Very strong and light! Exactly what you want in a multicopter build.

I’ve used my home caliper to measure the exact thickness and it seems that its 12.1mm tick. This is not a problem at all. The size is consistent and will not create any fitting problems with the main tricopter body.

You can use less thick or fatter wooden booms. For example you can go down to 10mm ones but not thinner ones as you are going to have problems with the strength. Like that, you can go to thicker ones but then the weight will be a problem. From searching and measuring I’ve found that the 12mm ones are the best (at least by using wood).

Again, by using my hand powered saw I’ve cut down the booms in length. The two arms will be 400mm long and the tail one must be 420mm long. This inconsistent in length is due to different mounting position on the main body. Have in mind that in an ideal setup the tips of every boom must be sitting on the perimeter of an imaginary circle.

The radius of this circle is critical! A big radius will make a more stable multicopter but not very agile and a small radius will have exactly the opposite results.

For my setup I’ve select the 40cm length in order to have a more stable tricopter. For now, as I am a newbie, stability is a want factor. Agile ability will come latter!

And it looks like that! The coffin looking main body looks great! With the electronics and cables will look even prettier!

The frond of the main body should have a supporting material. Since I have plenty of wood I will use it here as well. You can use PCB spacers to do that but in this case washer is a need component.

During the cut, it seems that I was holding the hacksaw in a small angle making the front body supporting wood piece a little bit longer on top. I can leave it like that without creating any problem but it will not be nice to the eyes!

A sand paper will do the job, making it exactly as I want it!

And finally! I’ve started the drilling! The pinewood and plywood are extremely easy to drill with a dit made for metal. Soft materials that will get drilled like butter!

For the booms, for now, I’ve just cut one hole in every piece. I will try to find the best placement for the next holes latter. I am doing that because I don’t have a clear electronics placement scheme for now.

This PCB spacer is paying the role of a “holder” for the booms. By doing that I can move the booms by holding their one end steadily and drawing the position of the next hole.

Since the front arms will move, going backwards for easily delivery purposes, I am not going to have four holes going through the front booms. Just a single one per arm, close to the beginning.

The next hole will be only on the body and will hold the booms steadily by just friction. By drawing the booms dimensions, I know where I should place those holes.

 

Next: Pinewood and Plywood: Part 2

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