Embarking on the journey of building a drone for the first time can be both exciting and daunting. After countless hours in simulators and flying tiny whoops, I decided to take the plunge and construct my first proper FPV drone. My goal was to build a sub-250g drone, perfect for exploring urban parks and pushing my flying skills further. The foundation of this project was the brand-new AOS 3.5 V5 frame, paired with some powerful T-Motor AIO and 6S 1604 motors I managed to snag on offer. This guide details my experience, challenges, and ultimate success in creating a nimble and potent 3.5-inch drone.
Initial Component Selection and Weight Concerns
My initial plan included the Walksnail Avatar Pro VTX for video transmission. However, as the build progressed and I incorporated the TPU parts that came with the AOS 3.5 V5 frame, the weight quickly crept up to 194g. This realization prompted a necessary rethink, as maintaining a sub-250g weight was crucial for my intended flying locations. To shed some grams, I opted for the Caddx Nano v3 VTX instead. This single swap shaved off nearly 15g and conveniently eliminated the need for a separate BEC, as the T-Motor AIO provides both 3.3V and 5V outputs. Further weight optimization came from ditching the heavier TPU antenna mounts and instead, following community advice, securing the antennas directly to the arms with zip ties.
Assembly Challenges and Solutions
The assembly process wasn’t without its hurdles. I soon discovered that the Caddx Nano v3 VTX uses M3 mounting holes on a 20×20 pattern. This presented a challenge with the AOS 3.5 V5 frame, requiring drilling in several places to accommodate the VTX. Another significant issue was the center of gravity. With the battery mounted, it consistently sat too far back, impacting balance. This forced me to reconsider the XT30 holder, which I had initially intended to use to support the capacitor assembly. To shift the weight forward and improve balance, the XT30 holder had to go.
Facing these mounting and balance issues, I explored alternative VTX placement options. A breakthrough came when I realized I could mount the Nano v3 VTX at the bottom of the stack, utilizing the 25.5×25.5 mounting holes. By using nylock golden nuts and positioning the T-Motor AIO on grommets on top, everything fit snugly with a comfortable 6-8mm gap for airflow. To ensure a clean and secure stack, I added a TPU ‘strap shield’ attached to the standoffs, allowing everything to be neatly secured with 20mm stack screws. This central mounting strategy not only shortened motor wires, further reducing weight, but also effectively shifted the center of gravity forward, closer to the desired position.
Weight Optimization and Final Build
Through these adjustments, the weight of the drone without a battery was brought down to a respectable 164.3g. Pairing it with a lightweight 550mAh Tattu 6S battery, the total weight just barely exceeded the 250g limit, hitting just over. To enhance durability, I planned to add a skid plate and arm protectors. For true sub-250g compliance with these additions, a slightly smaller 450mAh battery became the ideal choice, and a couple were promptly ordered.
For a slightly heavier, more robust configuration when flying outside of strict sub-250g zones, using a 650mAh battery along with the skid plate and arm protectors brought the drone to 283.4g. This configuration offered a noticeably improved balance. This slightly heavier setup became my preferred configuration for less restricted flying locations.
Flight Performance and Updates
(Update: 08/05/2024) After several weeks of flying, this 3.5″ build has proven to be an absolute beast. Having recently built a 5″ drone as well, I was surprised to find the jump to the larger size wasn’t as significant as expected – a true testament to the power and agility of this 3.5″ setup. Initially, I experienced some video transmission issues, but these were resolved by switching to new antennas and repositioning the VTX antenna to a more vertical orientation. Mounting the antenna on the arm proved to negatively impact range and penetration in my testing. Securing the antenna to one of the rear standoffs with a cable tie significantly improved performance.
The trade-off for this impressive power is flight time. With a 550mAh battery (keeping it under 250g), I get around 3 minutes 30 seconds of energetic flying. Stepping up to the 650mAh battery extends flight time to approximately 4 minutes 30 seconds. For cruising, flight times are considerably longer, reaching up to 8 minutes on the 650mAh battery without issue. Propeller choice also made a subtle difference; I found myself slightly preferring the Gemfan 3520 props over the 3525s I initially selected, although it was a close call.
Looking ahead, if I were to rebuild this drone, the only change I would consider is opting for the newer mini decased VTX. Identical in performance to the Nano but without the casing, it promises to shave off another 10g overall. This would allow for even more robust TPU protection while comfortably staying under the 250g mark with the 550mAh battery.
This build has been an incredibly rewarding experience. Huge thanks to content creators like Joshua Bardwell, Oscar Liang, and Chris Rosser for their infectious passion and invaluable guidance that inspired me to embark on this FPV journey. Also, a shout out to Lee (3daqua on eBay UK) for providing excellent quality and affordable 3D printing services for all the TPU components. I’m excited to continue experimenting with battery configurations and flight characteristics as soon as the weather permits, but for now, it’s back to the whoop for some indoor practice!
