Brushless Whoop Build – Part One

It took me a while to actually sit down and do the build for the brushless whoop parts that I got for Christmas.

The first thing I like to do on a new build is test the flight controller. Especially before any soldering is done, it’s good to make sure that the flight controller works, so that later on if it doesn’t I know that it’s because of something that I did and can troubleshoot it instead of wondering if I just got a bad one from the factory. It’s easy enough to do. Plug it into a USB cable to make sure it gets power, and then make sure that Betaflight will connect to it. Test out the gyro by turning and tilting the board and make sure that the movements match up with the animated diagram in Betaflight.

At that stage, it’s not critical to do, but since it’s already connected, I like to download the latest firmware and flash it to the board. It’s just a couple of steps to do, and isn’t any harder or easier to do now or wait until later. But since it’s already connected I figure why not.

The last step I took care of before really starting the build was binding my radio. I don’t always do this part so early, usually because for anything bigger than a whoop build, I don’t use a flight controller with a built-in receiver. So there’s some soldering that normally has to take place first. But in this case since the receiver is built into the board, it’s much easier to do now where the bind button is easier to get to, than to wait and do later.

Binding the radio took me a bit to figure out since I had to find the built-in receiver specifications. I couldn’t find anything about telemetry being available or not, but it would only successfully bind when I picked the radio setting without telemetry, so I’m guessing it’s not supported. Not a big deal for a small whoop like this, but something I’ll have to keep in mind if I ever decide I need to go hunting for it outside.

With the flight controller testing out of the way, I was ready to start figuring out the build. This involves dry fitting the flight controller to the whoop frame and trying to get an idea for where the canopy, camera, and VTX were all going to sit. I found the wiring diagrams for the flight controller on BetaFPV’s site, and used those along with the printed manual that came with the VTX to figure out how everything needed to be wired together.

The only part that wasn’t immediately obvious to me until I’d studied it for a couple of minutes was that the signal wire of the camera needed to go to the camera pad on the flight controller. This would apply the OSD information, and then a wire from the VTX pad to the video in pad on the VTX would take the signal for broadcast. I also didn’t need one pair of the 5V and ground wires on the VTX since the camera already had its own.

Once I figured all of that out, then I rechecked it by fitting all of the pieces together to make sure I knew which wires to cut, which to desoldering, and what was getting soldered to what. I could always fix any mistakes, replacing or lengthening any wires that I cut too short, but I didn’t want to have to mess with that if I could avoid it with a little extra care up front.

After checking a few times though, it’s usually time to just commit and do it and hope I’ve thought through everything I needed to. In this instance that included trimming all of the VTX wires to be just a bit longer than the camera wire lengths. Trimming the plug from the camera, which I wouldn’t need, and then desoldering the two wires from the VTX that I wasn’t going to need.

Desoldering is quite easy. It just requires me to get the piece set up where I can get some pressure on the wire that I’m trying to remove, so that I can have a minimal amount of time for the soldering iron on the board. In this case the extra 5V and ground wires that were going to be replaced by the corresponding wires on the camera.

After getting the wires cut to length, I was ready to tin the wires and the pads on the VTX and flight controller. Tinning just means to prep exposed wires and any copper pads on PCB’s that I’m going to be using with solder. Ideally so that when it comes time to solder a wire to a pad, I don’t have to add any additional solder, I can simple touch them together with a bit of heat and I’m done.

Soldering a small build like this is a bit of a challenge just because of the sizes of the pads involved. I’ve found using the lowest heat setting along with a lighted magnifying glass, and a very small soldering iron tip helps tremendously for this. I’ve also applied some tricks I picked up in painting miniatures for keeping my hands steady by moving the piece to the iron and keeping my arms are my sides.

Once everything has been tinned and then soldered together, the easy part is over. With the camera, VTX, and flight controller all wired up, it’s time to check for shorts and then plugin in a battery.

Before plugging in a battery and risking releasing the magic smoke, I like to use a multimeter and check that there’s no continuity between the various connections. For example the yellow wire from the VTX to the flight controller should have continuity between the ends, but if I touch a probe to one end and then touch the other probe to the ground then I shouldn’t have any connection. If I do it means there’s a short somewhere, and on a tiny build like this it’s probably because two pads are bridged.

In my case I did have a solder bridge on the VTX between the video signal and the ground. But that’s just a matter of adding some flux to the board and using a soldering iron to try to clean up the bridge. It only took me a couple of minutes to get it cleaned up in this case, and afterwards all of the connections passed the multimeter test.

Which brings me to the last part before assembly and that was plugging in a battery and testing that everything booted up, that the VTX was broadcasting, and best of all that I was getting an image through the goggles from the camera. It’s good to do all of that before assembling everything just to make sure that there’s no more soldering fixes that need to be made, and it’s a good chance to make sure I know which way the camera needs to go so that up is up.