■ DIY Main Shaft of RC Heli.

[laodan]

     1. Returning to the RC Hobby: From Frequencies to Retro Repairs

     Quite a long time ago (around 2010), I developed an interest in RC (Remote Control). Back then, I practiced a few takeoffs at a temporary airfield on a riverside bank using an electric Mini Titan (450 class) and a Caliber 3 (550 class, 5.9cc GX36H nitro engine) before putting the hobby aside. Recently, I have become an enthusiast once again. Unlike today's 2.4GHz transmission systems, we didn't have that convenience back then. To prevent interference with other hobbyists, you had to announce your designated frequency band before turning on your transmitter, or you had to tune your transmitter to avoid the frequencies already listed on the bulletin board. When I picked it up again, my hands weren't used to the controller for a while, so the fuselage crashed into the ground quite frequently. Aside from the costs, the models were so old that spare parts were out of stock. While I could find some compatible parts, the most difficult component to match was the main blade shaft (main shaft).

     2. The Challenges of DIY Main Shafts and Tool Selection

     There were local manufacturers in Korea, but the cost was too high compared to other components. So, I gave up on buying them, decided to make them myself, and purchased a mini benchtop drill press (photo). It is the lowest-spec model among various products. Due to its low specifications, this machine lacks vertical alignment accuracy. When the drill descends about 2 to 3 cm, a misalignment error of about 0.1 mm occurs between the entry and exit points. Drill bits and carbon steel rods are easily available in various specifications and price ranges (via AliExpress). However, some caution is required. Carbon steel becomes extremely hard from the surface to a considerable depth during the chromium plating process. This makes it difficult to drill through, even with a solid carbide bit. Finding the right hardness is key. Preparing materials this way is significantly cheaper than buying finished products. However, there is a catch. Cutting the length can be done with a hacksaw and a file, but the real challenge is drilling a proper hole. Cutting it to length is easy if the diameter is 5 mm, but if it is 10 mm, it becomes pure labor. Now, I use an electric handheld rotary/grinding tool, which is very fast and precise (hand grinders are also very inexpensive). Drill bits also vary in price depending on size and strength. For instance, they range from a few hundred won to several thousand won, or even over 10,000 won per piece. At first, not knowing their characteristics or performance, I bought various cheap ones and went through a lot of trial and error. Even if labeled for carbide use, cheap bits often break or become too dull to use before completing a single proper hole. Generally, mid-priced ones are suitable; they can drill about 3 to 5 holes (based on a 10 mm diameter).

     3. Mastering 99% Drilling Precision and the Hobbyist's Philosophy

     There is another critical issue. In the beginning, it was extremely difficult to drill a usable hole. I could only salvage about one out of every three or four failed attempts. To be usable, the misalignment cannot exceed a 0.1 mm error, or the bolt won't fit through. To solve this, I now use a flat metal bar, as shown in the photo. It is a plate about 10 cm long, made by joining three straight hinges that can be easily found at Daiso. I place it roughly over the center of the rod to be drilled. Then, while gently lowering the drill lever to make contact, I adjust the drill bit left, right, up, and down until the metal plate becomes perfectly level, thereby finding the correct drilling position. When drilling from the position found this way, it is 99% accurate. The error in the true diametrical direction does not exceed 0.1 mm. By being able to manufacture the core main shaft this way, it becomes possible to increase the shaft diameter within the aircraft's limits (while upgrading the motor specs as well), allowing me to up-size a 450-class helicopter into a 480 or 500 class. Of course, I also prepare bearings that fit the new shaft. Bearings are also available on AliExpress in a wide variety of price and performance options. A few years ago, delivery from China to Korea took a month or even longer. After that, two weeks became the norm for a while, but nowadays, most items arrive within a week. If you use the "Choice" (budget-saver) section on AliExpress, it arrives in just three days. It feels almost like domestic delivery. They seem very conscious of shipping speeds to Korea. As I mentioned before, I cannot perform 3D stunts with helicopters. I am perfectly content with scale cruising or hovering, and I have become an enthusiast who enjoys hand-crafting and replacing various parts like this. You get what you pay for. For components like receivers and nitro engine glow plugs, it is best to use genuine parts. Counterfeit items often cause starting issues or incomplete combustion, which can severely hinder flight. They also have a short lifespan. Personally, I use Japanese hobby shops, which are relatively cheaper than Korean stores even when including shipping fees. The delivery takes about 5 days. In the next post, we will look into the issues that arise when upgrading other specifications accordingly as you scale up the helicopter class. I hope my post is of some small help to fellow helicopter users. Thank you.▮