A reprint from Additive Manufacturing
New Electric Dirt Bike Is Designed for Molding but Produced Through 3D Printing
Cobra Moto’s new all-electric youth motocross bike could not wait for mold tooling. Parts have been designed so they can be molded eventually, but to get the bike to market, the production method now is additive manufacturing.
Sean Hilbert, president of Cobra Moto, says manufacturers make a mistake in the way they justify additive manufacturing capability. “We cost it wrong,” he says.
If the expense of a production AM system is amortized across the parts it produces — the typical way to account for production capital equipment — then the unit cost of each 3D printed component is apt to be high. Additive manufacturing is often subject to bursts of activity, producing parts as they are needed.
But if the manufacturer accepts that AM is a necessary in-house capability for responding quickly to new opportunities and changing market needs, then the capability is an overhead cost. That is, it is a cost of doing business as a modern manufacturer, and the parts made with this capability are simply this quick response put into practice. That is Hilbert’s view, and this very advantage of AM has allowed his company to seize a new market opportunity a year or more earlier than it might have been able to if conventional manufacturing was the only option.
Based in Hillsdale, Michigan, Cobra Moto makes youth dirt bikes, including those used by young motocross competitors. Moving into production quickly proved vital to this year’s launch of an entirely new offering for the company: its first all-electric dirt bike. Cobra’s first departure from gas-powered motorcycles required numerous new components to be designed, many of which are now being manufactured through 3D printing even though they are fully suitable for injection molding. Indeed, the components in question have all been designed for injection molding — not for additive manufacturing. And in the future, they will be molded. But for Cobra to obtain all the mold tooling needed to go into full production with this bike, given the lead times it currently faces from its mold suppliers, might require a year or more, says Hilbert. Additive manufacturing allows the bike to be launched without this wait. Components will be made more cheaply through molding starting sometime next year or the year after, but right now, the chance to begin selling the new electric motorcycle is invaluable. The new all-electric motorcycle from Cobra Moto achieves the speed and performance of the company’s previous dirt bike models, just without internal combustion. Various components are manufactured through 3D printing.
Or, most of these components will be made through molding. Not all, because molding is not a certainty, he says. In a case such as the bike’s throttle housing, which is a small component that can be run in batches of 200 within the build volume of the company’s HP Multi Jet Fusion (MJF) machine, this part might continue to be produced additively throughout the entire commercial and production lifetime of the bike. Additive manufacturing is a bridge to full-scale production, but it is also a very good option for the way that might be taken on the other side of that bridge.
Bikes Are Not Like Drones
The company is no stranger to additive. It has a sister company, which operates in the same facility and is also led by Hilbert: Cobra Aero, which serves the unmanned aerial vehicle (UAV) market with drone engines made through AM. For Cobra Aero, the use of additive allows for lightweight small-vehicle engines that take advantage of design possibilities including complex geometry in the form of close exterior fin spacing for improved cooling of pistons, as well as part consolidation and features printed inside the exhaust that control noise. “The UAV engines are a relatively high-price-point product made at low volumes, so additive manufacturing is just perfect as a production method,” Hilbert says. Metal and polymer components are made using, respectively, a laser powder bed fusion system from Renishaw and the MJF system from HP. On the UAV engines, parts are designed for additive manufacturing.
And that is the most significant difference in the use of additive between the two companies.
Cobra Moto has now begun to leverage and apply what Cobra Aero has learned about AM, but it is doing so to make parts that are not designed for AM. One by one, 3D printed components of the new electric bike will shift to molding as molds become available. The parts were designed with this destiny in mind. But first, something like 250 bikes will be made, sold and shipped with the parts made additively.
One of the bike’s most central components is a visible example. The bike’s “injection molded” “gas tank” is, in fact, neither. The faux gas tank on this electric vehicle (which needs no fuel tank) is actually a component that directs air to the control electronics for cooling. And though it was designed for molding and therefore resembles a molded part, it is being produced in PA12 polymer through MJF for now.
Other parts being made additively include the bike’s throttle housing (previously mentioned), plus the kill switch, air diverter, skid plate and motor cover. All are made through MJF, but that’s not the only printing process used. Battery separators that hold the bike’s power cells in place are being made through fused filament fabrication on a series of desktop 3D printers from Prusa — a hint at the range of platform options that might be applied to bridge production.
The Design Can Still Change
Speed to market was invaluable for the new motorcycle because of the events where it might be ridden. “The motocross market revolves around a strict calendar of competitions,” says Hilbert. “If we miss a sale, we miss it forever.”
But the timing is right in a larger sense as well. The value of electrification for youth motocross bikes is not so much fuel efficiency, as in the case of other electric vehicles, but instead is in the nature of the rider and buyer. An electric dirt bike is quiet; parents can allow their kids to ride on their own property (if there is room) without this being a nuisance. Safety and teaching are easier because the digital control made possible by an electric motor allows the speed and power of the bike to be set at different levels for different riders’ skill levels. Plus, “We have a whole generation of younger parents who don’t know about the mechanical needs of bike maintenance,” Hilbert says. An electric bike is easier in this respect, as well.
Cobra Moto sells through dealers. Its top dealers were given a preview of the new electric offering earlier this year. They have begun promoting it. By the time this article appears, bikes will have shipped to some pre-order customers. And part of what will come from these sales, says Hilbert, is track experience. Real rider experience. That is, useful feedback — and with so many components made through AM, this feedback can be put to use.
“In the course of producing and shipping the first 250 or so units, we’ll discover areas for improvement. We’ll make design changes,” he says. The bike will get better because parts are being made with an adaptable process. Molding is definitely coming, which means hard tooling is coming. But because competitive riders are about to reveal how well the new bike and all its different parts perform, it is good that locking in the designs of all those molded parts can wait just a little while longer.