The Köhler Story

The eldest, Frank Köhler (41), was already running an engineering firm at the time. The two younger brothers, Jochen and Reto, were still in school at the time. They had become fascinated with electric flight back when they were all still living with their parents in Pfullingen, in southern Germany, in the early 1990s. In their free time, they would go to the model airfield together and fly electric gliders, as well as electric-powered model airplanes—to the extent that this was possible with the Japanese Mabuchi motors. As luck would have it, they got their hands on an AVEOX motor early on—the top innovation from the U.S. at the time. Frank Köhler recalls that they were frustrated by how little torque it provided—

cost so many dollars (which were still really expensive even back then).

From then on, the idea started to take shape in the brothers’ minds. Shouldn’t they—no, wouldn’t they simply have to move the air gap of this motor further outward...? The best way to do that would be to just turn the whole thing around. Inside out, as the Americans would have said. The first outrunner was something like a Mabuchi with a cut-off commutator, where you simply let the housing rotate. The initial measurements,

results, of course, were sobering. They were still a long way from the 90% efficiency they’d dreamed of. Yet it was precisely this long-term percentage goal that fueled their discussions over lunch. At some point, the Köhler brothers appeared at an electric model aircraft meet in southern Germany with an electric tractor whose large propeller brought the attached glider up to altitude with surprising agility, even though there was no gearbox

could be heard. It was one of the first major appearances of the so-called NEWTOR, an elusive 4-pole power motor that, however, was still partly based on off-the-shelf parts (e.g., commercially available 12-slot stator laminations). This was followed in 1995 by their first, highly acclaimed trade show appearance in Stuttgart.

The Köhlers continued to innovate, designing their own new stator laminate cuts and finally presenting the 8-pole ACTRO around the year 2000. A year earlier, they had teamed up with the local company Aeronaut, which from then on took over the administrative “paperwork” and, gradually, the distribution of Köhler motors as well. The plan was to focus on inventing in the future. Of course, things turned out differently! At the end of 2000, for example, the assembly instructions for the LRK motor were published. Suddenly, everyone was talking about outrunner motors. The DIY trend that followed gave wings to the entire electric aviation scene. After all, not everyone who had started such an ambitious DIY project actually saw it through to the end. Demand for motors rose considerably, not to mention the sudden need for brushless controllers. The ACTRO-C (compact) was developed as the company’s own response to the “Multipol” craze. Unfortunately, the previously successful brotherly collaboration soon became increasingly difficult, as both Jochen and Reto had to, after completing their studies in

pay tribute to professional mobility. Frank Köhler, who still runs an engineering firm near Stuttgart, now works on his own. He is pleased with the strong demand from helicopter customers for the recently developed 24- and 32-ACTRO models and is currently working on a helicopter modification for the larger 40-series model. He is equally pleased that the 60 series—with which the team has since achieved the once-elusive goal of 90 percent efficiency—is well-received by aerobatic pilots.

Nevertheless, he must also admit that the wave of Chinese competition

means that, as a German manufacturer (with in-house winding), he can only survive in the premium niche. So the company is working hard to maintain its quality standards and build on the efficiency advantage that ACTROs demonstrate, especially during “partial throttle” operation typical of helicopters. Industrial contracts also ensure the company’s continued existence.

And how often does he still get to fly models? Once again, Frank Köhler points to the photo wall in his office. Well, there don’t seem to be a striking number of new photos among them.