Khajak REBOff is a new Ukrainian FPV kamikaze drone with fiber optic cable for communication instead of radio. This makes it immune to jamming , the most effective protection against small drones.
Russia has deployed similar technology with the Prince Vandal FPV used in action since August, and which has been lethally effective. However, Ukrainian expert Serhii Flash believes this is a Chinese model which the Russian suppliers rebranded and sold to the military (at a 750% markup), and which was not designed for military use.
By contrast 3DTech built the Khajak REBOff to operate under battlefield conditions. Oleksii Zhulinskii, Founder and CEO of 3DTech LLV talked to me about the development and why we are likely to see more fiber optics on the future battlefield.
The Jamming Challenge
Zhulinskii served in the Ukrainian military as a mortarman, where he gained a keen appreciation of the needs of soldiers at the front. He was fascinated by the Mavic quadcopters the team used to find targets and direct fire. In the summer of 2022 the vehicle Zhulinskii was riding in hit a mine, killing two of his team and seriously injuring him.
His injuries left Zhulinskii unable to return to active service, but he still wanted to help the war effort. FPV kamikaze drones were staring to have an impact, and Zhulinskii and some colleagues set up 3DTech to make drones. The company has worked with Ukraine’s BRAVE1 technology incubator and by summer 2023 they were supplying FPVs called Khajaks to Ukraine’s military. Unlike some of their Russian counterparts, 3DTech have constantly refined and adjusted their design in response to feedback from the front.
“New methods and technologies emerge every month, and we need to keep up,” says Zhulinskii. “We are actively searching for, testing, and implementing new technologies, as modern warfare evolves very quickly. “
Jamming as always an issue as both sides filled up their front lines with portable electronic warfare gear to interfere with drone communications. This rapidly became a major problem. In March, General Schill, the French Army’s chief of staff, said that jammers knocked out 75% of drones in Ukraine, and he expected the number to rise.
“Soldiers reported that in some areas of the front, there is a very high concentration of electronic warfare (EW) systems, particularly intense where the enemy’s important targets,” says Zhulinskii. “Many high-value targets were completely unreachable due to these powerful EW systems.”
Ukrainian (and Russian) developers have used a variety of techniques to make their drones more resistant to jamming. But every move is met by a counter-moves by jammer developers, and constant upgrades are needed just to keep the drones flying. The ideal solution would be able to beat any jammer.
“We turned our attention to the only communication channel that can be used in such conditions — fiber optics,” says Zhulinskii.
Fishing For Cyclists
Zhulinskii says some developers experimented with fiber optics earlier in the war, but there was then little interest as radio communication still worked well. As jammers saturated the front, 3DTech took another look at the technology.
One of the biggest challenges was the cable, which, like other types of glass, is strong but fragile.
“We encountered issues during transportation and use of the drones, as fiber optics can easily break or snap. This prompted us to create specialized systems for evenly winding and unwinding the cable during flight to prevent sagging and tangling.”
Mounting the spool on a drone brought its own challenges, given the need to avoid contact with the drone’s propellers and preventing it from catching on obstacles.
The fiber optic cable could be surprisingly tough. Zhulinskii relates an incident during the first test flight. A group of cyclists were riding rode across the drone’s path; Zhulinskii, piloting the drone misjudged the distance. The next thing he knew he felt a tugging on the cable like a fish on an angler’s line. The line had caught one of the cyclists and brought him off his bike.
“The cable didn’t snap, proving its strength, but we had to apologize extensively because the cyclist wasn’t happy with the situation,” says Zhulinskii.
The early test version only had 1 kilometer [.6 miles] of line, but it proved that the technique worked.
“We were impressed by the speed of data transmission and the absence of interference,” says Zhulinskii. “The only challenge is the weight of the spool. Later, we assembled working versions of the drone with a 5 kilometer [ 3.1 mile] spool and took them to the front lines to get feedback from our military personnel. They were very impressed with the product and provided several recommendations for improvement, which we have begun implementing.”
Piloting Challenges And Opportunities
The cables unspools as the drone moves so there is no tension (unless a cyclist runs into it). But while the cable has good tensile strength, there are piloting challenges it is fragile if bent more than 45 degrees, or of it become knotted.
“Pilots do need to be more cautious,” says Zhulinskii. “While our spool mounting system minimizes the risk of cutting the cable, pilots still need to remember the trailing fiber-optic cable and avoid sharp or fast maneuvers that could cause the cable to be cut by the propellers.”
There is also the added weight. The spooling mechanism weighs 300 grams and 5 kilometers of cable weigh 1.25 kg, so a system with a 10-kilometer range carries an extra 2. 8 kilos, significantly reducing the available payload. Hence Zhulinskii says for longer ranges they used larger drones. A 13 -inch drone can carry enough cable for 10 kilometers as well as a 2 kilo /4.4-pound warhead. Longer ranges would be possible with bigger drones like the Queen Hornet.
Fiber optic control also opens up new opportunities. Because radio control relies on line-of-sight, FPVs have stay high to maintain contact before their final dive.
“Certain parts of the front line have difficult terrain, including elevation changes, valleys, and forests, which make radio-controlled drones difficult to use. Fiber-optic drones eliminate these issues entirely,” says Zhulinskii.
As the Russian Vandals have already shown, fiber optic drones can fly at extremely low altitude – right down to knee height – and come from unexpected angles.
“The enemy often expects the drone to attack from above, so they tend to watch the skies. Fiber-optic-controlled drones, however, can approach targets from outside the enemy’s field of vision, flying at low altitudes, which increases their effectiveness and adds the element of surprise.”
Fiber Optic Urban Warriors
The line-of-sight limitation means that most drones lose contact when they are more than a few feet inside a building.
“The fiber-optic control provides a stable connection even in enclosed spaces where regular radio signals may be blocked by walls or barriers,” says Zhulinskii.
Working in tight spaces without breaking the cable requires a sophisticated unspooling mechanism to avoid tangling.
“After refining the attachment system for the fiber-optic spool, we achieved very high maneuverability for the drones. They can hover, turn on the spot, and navigate around both small and large objects at low and high speeds,” says Zhulinskii. “This maneuverability allows the drone to easily explore every room in a building or access more complex shelters.”
The Russian Vandal drones have already shown how they can hit targets inside buildings, REBOff can go far deeper.
This opens up the possibility of drones for urban or underground warfare going in ahead of, or even instead of, footsoldiers, checking out buildings and engaging targets while their operators remain at a safe distance. (Israeli company XTEND are developing a similar approach using fiber optics for their drones. Others are likely following suit.)
Fiber Optic Drones In Action
The RebOFF has successfully completed military testing, and 3Dtechg are preparing the first batch for delivery. These are likely to be used in action as soon as they are delivered.
At the same time the drones are going through certification so they can be acquired via the standard military procurement process. Zhulinskii says that with their current resources they can produce a thousand RedOFFS “in a relatively short timeframe.” After that, it depends on how demand takes off.
Meanwhile a number of other Ukrainian developers working on fiber optic drones, and the German company HIGHCAT has demonstrated their technology to Ukraine. The technology is not expensive, and while there are technical challenges it is likely to proliferate rapidly.
3DTech are already looking at enhancements for the next generation. These include thinner, lighter-weight fiber optic cable, giving longer range or greater payload. They also plan to integrate an AI terminal guidance system to increase the hit rate and reduce the need for a skilled pilot. Fiber optics mean the expensive AI unit can be located in the operator’s control unit rather than being lost with the drone.
Other developments include combinations of radio and fiber optics for operational flexibility , and implementing fiber-optic communication for drone motherships. These are drone carriers which will be able to extend battlefield operations by carrying unjammable FPVs to the enemy’s rear.
Zhulinskii says that the same technology could be applied to ground robots and remotely operated weapons like the ‘Death Scythe.” Fiber optics are likely to be invaluable anywhere that high-intensity jamming makes radio-controlled drones ineffective.
“Fiber-optic controlled drones are an innovative and promising technology that can solve tasks beyond the capabilities of traditional drones. Our goal is to make this technology as accessible and effective as possible to assist our military,” says Zhulinskii. “But this project isn’t just about technology; it’s about making a real contribution to the safety and effectiveness of our military on the frontlines.”
