BAH - Bay Area Heli
It seems there are quads everywhere these days, at my work, at the Suynnyvale Baylands Park where I sometimes fly, even at our field, not to mention on the news, spurring a bit of controversy. Some are ready to go as you buy them and a bit pricey, others are in kits, still others can be built from the pieces. They can be as small as the little estes proto (we call this pico, 1.1” square), to hubsan to blade nano, up to the size you can use to deliver pizza and supposedly amazon.com shipments. This last one seems more like a publicity stunt to me, but I might be surprised. Of course, I had to do one from the pieces as you might expect. Here’s my BAH.
BAH, 250mm Quad
While I’m far from a heli guy, I have to admit to a certain curiosity. I have some of the little ones, the pico, several hubsans, the blade nano, but thought it would be interesting to go through the build process. One of my friends has a BAH and was very complementary and knows the frame designer, so I decided to build one of those. This one is foldable for easy transport. The 250mm is the center to center measurement on the motors.
BAH Side View
For the BAH, you build it up from the frame which is made of PCB materials and buy all the parts separately. I liked the idea of also being able to incorporate FPV elements.
The framing on this BAH is particularly interesting as there are two distinct parts; the dirty assembly houses the motors and ESCs and the folding arms. The clean assembly houses the gyro, rx, video stuff as well as the batts. These two assemblies are connected with vibration isolating mounts, which are a couple of screw studs vulcanized into a shock absorbing rubber spacer. Below is the frame initially fit together.
Below shows the ESCs mounted in the dirty assembly. While I started with some Castle ESCs, I did not end up using them. More on that later.
Stats below with FPV gear.
AUW with 3S2200 batt is 620gr=22oz.
3S2200 = 175gr=0.62 oz. 3S1350=120gr=0.35oz.
23A at full throttle. So ~5.5A per motor
11v * 23A = 250w, 180w/lb
Rear View BAH
Above is a rear view. The donut thing is the 5.8Ghz antenna for the FPV downlink. Right in the middle so the props don’t hit it. Orange props in front for visibility, 3S2200 batt on top.
Left side view
Above you can see the camera on the left between the top two plates, Naze32 board in the middle and on the right are the OSD and vid tx. The Naze32 board takes in the RX outputs for pitch, yaw and roll and converts to throttle drive for the 4 motors.
OSD is On Screen Display, which measures the battery voltage and puts this on the FPV screen for active pilot viewing. Very convenient.
Right side view
Above you can see camera on the right, HK orange receiver in the middle and vid tx OSD on the left in the back.
I also included a buzzer that activates from an aux channel. If it goes down in the weeds need a way to locate it.
Here is a pic of the BAH opened up clean assembly.
On the FPV side, I installed the Fat Shark with a 250mw 5.8Ghz video TX for the downlink. I wanted to use a better performing camera than stock and chose the PZ0420-L28-N from security camera 2000. www.securitycamera2000.com This camera is 12v instead of 5v like the stock Fat Shark one. So, I had to make a custom cable to hook everything up.
To make the video subsystem easy to disconnect, I took advantage of the power module on the Fat Shark shown below. This module allows fat shark tx to be powered from 2s, 3S or 4S batts; I’ll be using 3S batts and leaving the others open. The needed cable supplies 12v for the camera as well as the OSD which puts the battery voltage on the FPV video screen. Below is a pic of the Fat Shark power module. To power the video subsystem, I just plug in the custom connector into the unused 4S slot.
Fat Shark Power Module
Below is the switch settings for the vid tx for changing the channel. Of course, this channel needs to be the same as the goggles.
Video TX channel Selection
I originally started with a Castle Quad pack ESCs, specifically designed for quads. It contains 4 Castle Talon 25A ESCs, only one has a BEC and the other three don’t. You only need one BEC to power the gear. It was more expensive than the other guys were using, but I have always had pretty good luck with Castle. I later found Castle luck had run out.
Initial check out showed the quad to oscillate in hover (sort of shake) and drift around. This was very surprising and unexpected. I went through a lot of gyrations, changing settings in the FlipEZ controller board as well as timing settings in the ESCs. Unlike typical Castle ESC settings list, the settings for quadpack were few and there was only one firmware version available. Oscillations never went away. Called Castle tech support and they told me to email a guy named Clint, he said he had no experience with the controller board I was using, so really wasn’t much help. I also started a thread in rcgroups under Castle Creations. I used the flipEZ because a friend had good luck with it, but he was using a different brand of motor, sunnysky. I used Tmotor MN1806 2300kv which should be stronger.
The controller board also contains PID coefficients that can be changed through an interface to fine tune quad performance. PID is a control system thing that stands for Proportional, Integral and Derivative type of closed loop control. I played with some gains on the flipEZ board and the coefficients but no joy, so went back to default settings.
Getting a bit frustrated, I then changed from the flipEZ controller board ($18) to the current Naze32 board($25). Oscillations stayed. Ok, not the controller or the ESC settings.
Finally, I changed out the castle ESCs for some $8 each ESCs with special SimonK firmware, link below. This is what most quad guys are using. Oscillations went away and hover is solid as a rock. Woo hoo!
So, it seems that ESCs for multi rotor use might not be as simple as just using 4 airplane ESCs and handling the BEC issues. It would seem that Castle is a bit early in their quad ESC deployment and maybe they need to progress a bit more to meet today’s competitive product performance levels.
Below is a link that talks about the Simon Kirby firmware improvements for the ESCs, with tradename RapidESC. There is a nice demonstration video showing the differences and an Interesting discussion.
The bare openpilot link also has an amazing level of depth and some interesting stuff from the controller board viewpoint, including the mathematical model of the quad and how things change with the PID coefficients.
FPV. The FPV front was interesting as well. Getting all the info from the goggles instead of line of sight, I found it challenging to maintain any given altitude. Later I settled down a bit and about 10ft from the ground seemed comfortable. Another element that I didn’t expect was that, while on FPV, the visual comes from a different place than the sound. I found this to be a bit distracting initially, but am sure I’ll get more used to it with practice.
Stand along camera for recording. Later I bought a stand alone camera to use on the quad. It is HD quality and contains its own battery. The quality is excellent, pics and link of the camera are below.
HD Wing Camera II from Hobby King
Manual is above and pic is below with a small swiss army knife for scale.
HD Camera and Swiss Army Knife
Below is a pic installed on the quad. The stand alone camera is up top, and the fpv camera is between the two top plates.
HD Camera Installed
Overall, I learned a lot from this build, which is always the intent. It was a bit more frustrating than I initially expected, but I now understand quads a lot more. On with some fun!
So, if you’re interested in building a quad, recognize it might be a frustrating experience. But as with anything worth while, perseverance pays off. Never give up!