Post #3: Thoughts, Ideas, and Planning become reality.
My airframe came as a ready- to- fly remote control trainer package. It has a PVC fuselage with carbon-reinforced foam wings, elevator, and rudder. The setup is supposedly a very solid flier, but we’ll see as soon as the snow melts. I assembled it in a matter of an hour, and the finished product is below.
Overall, I’m quite happy with it so far. The plane kit came with “everything to fly included”, but there were many things I wanted to change immediately. I want the finished product to be a capable UAV, not a foam park flier.
The first thing I replaced were the stock servos. They are super cheap, have thin plastic gears inside them, and look like they will break just sitting on the table. I bought some 9 gram servos, which are also cheap but better than what came on it, for $2 apiece. Two went inside the fuselage for the rudder/vertical stabilizer and two went in the wings for the ailerons. The old ones were fairly simply to remove: the ones inside the fuselage could be unscrewed and removed, and the wing ones could be pried out of the wing with a simple flat head screwdriver and some foam for leverage.
The 9 gram servos ones seem much more solid, even if they are still inexpensive and have plastic gears. They fit perfectly into the mounting holes, as seen below.
After replacing the servos, the next step was to replace the electric motor. The one that came with the airframe was extremely cheap, so I replaced it with a NTM 28-26 1350 KV prop drive motor. After spooling it up, there’s a considerable difference in the overall quality of it. It is much stronger, the internal bearings are much better, and I am incredibly happy with it.
It was an awesome surprise for now, but we’ll see during flight testing whether the housing can withstand the additional tension and torsional/ bending forces caused by the better motor. There’s a good chance it will have to be modified for strength down the road. Also, the opening for the motor drive didn’t have to be widened at all.
When the motor housing was bolted back up to the fuselage, I replaced the prop with a 3-blade Master Airscrew 8×6. The stock one is super cheap, out of balance, and I don’t want anything to do with it. An 8 – inch prop is as big as I could go on the airframe without modifications, so I stuck with it.
As outlined in my last post, I want to keep everything on my project legal, so choosing correct frequencies for the electronics was a good first step. My R.C. receiver is a 2.4 ghz Spektrum DSM2 spread technology setup; the serial data transfer link to the autopilot is 915mhz; my video transmission feed is 5.8 ghz. All of the above have the correct wattage to keep transmission distances relatively close (and legal). A photo of the control-side electronics is below.
The power-distribution electronics consist of a supply module for the autopilot, an air-cooled 50 amp electronic speed controller (ESC), and a battery elimination circuit (BEC) for stepping the servo-supply voltage down to 6 volts. The reason for separating everything is so that the ESC can fail, but the plane still be operational so to land safely.
The on-board video transmission consists of a 200 mW, 5.8 ghz transmitter. I’m still not sure whether or not I want to put it in the airplane, but here’s a photo of it.
So what are you doing now?….
Currently, I’m in the process of doing the final electronics layout. There are many factors to consider when deciding where to place everything into the aircraft, such as:
- Electromagnetic interference (EMI) within the fuselage
- Aircraft’s center of gravity (COG)
- How much wire I want to use
- Desired total weight
- Optimal antenna location
It’s going to take a little bit of time to make an optimal layout with all of these factors, but I plan to have it complete by the end of this week. By next week everything should be soldered, interfacing with each other, and into the airframe. Also as a disclaimer, I have decided not to outline everything I’m learning in the Coursera class on here and focus on the UAV instead.