Building a Quad – Frame Change

After my first real flights ended with a broken battery lead and a fried flight controller and messed up video transmitter, I decided that since I was going to have to take everything apart anyway, I might as well change the frame I was using. While I liked the Phreak it really wasn’t suited well to having a four high stack, and rather than getting taller standoffs and screws to raise the top plate I decided to switch to an Acrobrat.

An Acrobrat is a 3″ frame designed with three mounting positions and a top-mounted battery, where the Phreak only had one mounting position and a bottom-mounted battery. That meant I could separate out the boards in the flight stack and have the camera and HD board up front, the flight controller and ESC in the middle, and the VTX and receiver in the back. Having the battery on top also meant I wouldn’t be landing on it.

Since I was moving to a new frame, I also got a new set of 3d printed accessories from Brain3d. They had a nice kit that included arm guards, front bumpers, and a nice rear mount to handle both the VTX and receiver antennas.

Of course switching the frames meant taking everything off of the original and moving it over to the new one. But more than that, I had to lengthen the motor wires since the Acrobrat’s layout had a wider length from where the motors mounted to the ESC on the center stack. Fortunately I had saved all of the wire I’d originally trimmed, so it wasn’t too difficult to solder and heat shrink extensions on and retrim and solder back onto the ESC. I also decided to add a capacitor to the build to help smooth out any electrical noise, and taped it down to one of the arms.

With that done I was back to the original repairs I would have needed anyway. I soldered the wiring harnesses back up to the new flight controller board and reseated it on top of the ESC. Then I got the camera and VTX both hooked back up and mounted. The receiver I ended up loosely zip tying to the VTX, which I’m not sure was a good idea even with the Kapton tape to keep them electrically isolated but I haven’t tried changing that around yet.

While it didn’t take me as long as the original build it was still a few hours worth of work to move all of the electronics over to the new frame. I have to say that it was worth it though. It was much easier to fit everything in the Acrobrat than it was the Phreak, which just wasn’t designed to have that extra board in it for HD capture from the FPV camera.

Battery leads securely zip tied to the side-plate of the frame.

It took me a while to get to this point, but I’m pretty happy with the second iteration of my 3″ quad build. I have to put a 60% throttle cut on it in order to fly it around my yard, but that power is nice to have when I go to my in-laws farm or take it to a nearby park.

Building a Quad – Assembly

After picking the parts the first thing I did was take the flight controller and plug it into USB and connect it to Betaflight to check two things. First just to make sure that it powered up before I started doing any soldering on it. So in case I got a defective part I would be sure that it wasn’t something I did on the workbench that broke it, and I’d more easily be able to get a replacement. The second thing was to see if it was to record the firmware target that the flight controller was using and make sure it was the most recent firmware version.

Then next thing to do to prepare for the build was to flash the receiver with the most recent firmware version from FrSky. This was a new process to me and involved downloading the firmware from the vendor, storing it on an SD card that I inserted into my radio, and then plugging the receiver into the radio using a wiring harness that the receiver came, then flashing the firmware.

Finally it was time to start building the quad, starting with the frame. I’d already watched a video of a more experience builder putting one together, but seeing it done once and doing it yourself tend to be very different experiences. For fun and to try to stay organized, I started out by organizing all of the pieces.

There’s four arms, blue standoffs, a top plate, a pair of bottom plates that sandwich the arms, and miscellaneous screws. Putting it together wasn’t too much different from assembling a Lego kit or any of the various children’s toys that I’ve had to put together after a birthday party or on Christmas morning. I think it took me about 20 minutes to get the bottom plate and arms assembled and be ready to starting on installing the motors and the electronics.

Before I started installing any of the electronics, I needed to tin all of the pads, and I figured that would be easier to do before I put them on the frame. In all of the build videos I’d watched to get ready for this, the builder would just put the board on the frame and then add the solder from there, but I was coming into this with just a little bit of soldering experience and I wanted to give myself the best chance at success. So I laid out all of the boards in the flight stack and made sure I knew which wires ran to which pad.

Then I tinned all of the boards at once: flight controller, four-in-one ESC, and VTX. The Caddx HD capture board on the camera had plugs and didn’t need any soldering.

Putting the ESC onto the frame as the base of the flight stack and installing the motors marked the first real part of the build for me as the quadcopter started to take shape. The process itself was pretty simple: screw a motor onto an arm, run the motor wires to the ESC, measure and cut the wires, solder them to the ESC. But cutting wires like that was a bit nerve wracking for me, as I was paranoid about cutting the wires too short and too long. On the one side I’d end up without enough slack and have to solder additional wire back on along with heat shrinking the joint, and on the other side I was trying to have a clean build plus extra wire would also contribute to extra weight. Which a few grams doesn’t sound like a lot but for a small 3″ build like this every gram counts.

After that the next step was the battery lead. As often seems to happen to me with this hobby, the part I was thinking was going to be easy turned out to be pretty difficult. It took a lot of work for me to get these two leads soldered onto the main battery pads of the ESC board. The heavy gauge wire and the big soldering pads on the board required a lot more heat than I’d been using up until now in order to get the joints flowed together properly.

Soldering the rest of the electronics was pretty easy. The hard part had been getting the documentation online for the various parts and making sure I knew which pads to use on the flight controller for the camera and the VTX. It had a pin header that plugged straight into the ESC board which made assembling the rest of the flight stack pretty easy.

Then came the big moment, plugging in the battery for the first time to see if it all worked. After going over all of the solder joints with a multimeter to see if I had shorted anything, I took the battery and plugged into a smoke stopper before plugging that into the battery lead on my new quadcopter. A smoke stopper is basically a fuse that will trip in the case when there’s a short somewhere so that you don’t release the magic smoke from the electronics. I’d bought one with a light and a reusable fuse at the same time that I ordered my parts.

The smoke stopper lit up green and the leds on the flight controller, receiver, and VTX are lit up as well. The best part though was hearing the startup tones playing as the flight controller and motors synced up.

After the battery test I connected it to my computer and went into Betaflight to check that all of the motors were spinning the right direction, and then change the settings on the two that weren’t. Then I plugged in a battery again and I checked that my radio would connect, and that I was getting a video signal in my goggles from the VTX.

At this point I figured I was just about done, I just needed to put the top plate on and the props. Which naturally is when I ran into the one problem that gave me the most trouble in the whole build.

When I picked out all of the parts, I remember adding up all of the heights to make sure that it would fit inside the frame. But I was looking at the height of the standoffs on the frame and not the length of the screws for the flight stack which were a couple of millimeters shorter. That makes sense to me now since you don’t want those touching the top plate and transferring impacts from the top plate into the flight stack, but it meant that I was just a couple of millimeters short on getting the top plate on my brand new build.

It took more time rearranging the parts and trying difference spacers between the boards to get everything to fit than it did to do the whole rest of the build, or at least that’s what it felt like to me, but in the end I did manage to squeeze everything in. I wasn’t completely happy with the solution but it would do until I could order slightly taller standoffs and longer stack screws.