Tricopters are a rare sight in 2021, they are as scarce as commercial flights are. This is because they are inferior in flight to quadcopters and other multirotors. It was not always this way though, as the tricopter used to be the premier drone for capturing aerial footage. The main issue with quadcopters is that they could not yaw quickly, this was due to a multitude of factors, but most of them were software-based.
This was the first tricopter that I built at age 10, as can be seen, it was an extreme fire hazard held together by tape, hot glue, and zip ties.
Quadcopters’ software problems were stifling their performance. A quadcopter yaws or turns about its Z-axis but changing the torque applied by the props, this is done by spinning up opposite sides of the drone’s motors and decreasing the other two. This change in torque applied rotates the drone.
Originally yaw on quadcopters was sluggish or would change the drone’s altitude drastically, this was due to software limitations on the flight controllers (FC), and electronic speed controllers (ESCs). The flight controllers could not compensate for other factors while yawing as there were not enough tuning parameters, the introduction of the Yaw-specific parameters allowed the aircraft to become more stable. It still could not yaw quickly, as the ESCs could not respond quickly enough. The original ESC’s used on multirotors were only capable of performing at a relatively slow rate. Then multishot firmware came out and began to increase the responsiveness of the motors. Both software solutions proved to be the effective way forward for multirotors.
What about tricopters? Well, this was the hardware approach, instead of fighting the escs and flight controllers for quicker response times, they go about vectoring the thrust of the rear motor with a servo to yaw. This was initially superior to quads when the ESC and FC response was slow, as vectoring the thrust gave a direct force that could push the tail about without decreasing and increasing the throttle significantly. This hardware-based solution made the best of what was available at the time, but it was quickly passed up and even suffered from faster software being developed. The improved speeds of modern ESC’s have worsened the tricopters ability, as there a distinct yaw wiggle, as the servo tilting the tail motor cannot respond to the flight controller fast enough. This is really challenging to tune out, and most of the time that it is tuned out, the tricopter feels lose and the tail can skid about.
A modern quad is a superior aircraft, but is there still a place for tricopters? There are still a few unique situations that a tricopter is better suited for. One of these is endurance, as an RCexplorer LR tricopter can fly for over an hour, as they are more efficient than quadcopters. With 3 motors, and one servo you can fit larger props and lower kV motors in the same frame base as a quadcopter. Tricopters also are generally quieter than quads as the motors are not fighting each other as much like a quad when yawing. While tricopters are currently down in the fight for the superior multirotor, I wouldn’t count them out yet.