When it comes to skateboarding, flips and grabs are cool, but downhill longboarding is completely insane. Reaching speeds of more than 90 miles per hour, downhill longboarders combine skateboarding and surfing in an adrenaline blast that is all about speed. Clearly, keeping the wheels attached to the board is critical to these downhill daredevils.
The ‘truck’ of a skateboard is that piece on the underside of the deck that the wheels are attached to. Made of axles, bushes, and pins, the truck is the interface between the wheels and deck that gives the rider the necessary control through shifts in weight, bending and reacting to the board’s travel. It’s a pretty important part, to say the least.
And now, like aircraft parts, furniture, and so many other modern objects, skateboard trucks are set to change, thanks to topology optimization and metal additive manufacturing. Topology optimization is an algorithmic process that reveals the most efficient design based on a set of constraints or characteristics, often by removing material from the design.
Engineer and downhill skateboarder Philipp Manger applied his expertise to the skateboard truck because in his words, ‘it’s the only [skateboard] part I haven’t made before’. But his venture, Project T.O.S.T. (Topology Optimized Skateboard Trucks) was about a specific kind of skateboarding, downhill speed riding. Where the traditional skateboard truck design suits skating in the park or streets, a style called the reverse kingpin truck is built for longboarding and/or high speed skateboarding. After collecting load cases specifically for downhill riding, that’s what Manger designed his truck for.
An engineer with over 15 years experience in the automotive sector, Manger found his career after the kind of vocational training program that ensures his native home of Germany stays at the forefront of global engineering. He became a technical product designer, exposing him to CAD and 3D design and which he’d apply to work on – among many others – steering columns for the Mini Cooper.
But how did working on cars prepare him to redesign one of the most pivotal pieces of the humble skateboard? “It gave me a lot of preparation,” he says. “No matter what you’re doing, engineering is engineering. If you design a part for a car it’s not a lot different than for a skateboard – they’re both design, and I had the opportunity to learn a lot about design methods, what’s called parametrical constructions or parametric modeling. I tried out a lot of different CAD tools and it’s very hands on.”
Maybe the most interesting part of Manger’s project is how he got there – by telling the computer the parameters and constraints he needed to work within, pressing ‘go’ and letting the software do the work.
We’ve all seen those lattice designs inspired by nature in CAD – outlandish constructions no human could ever computer manually and which look like they’ve evolved over millions of years like a natural process. The improvements they offer in weight, performance, strength and countless other factors are capturing the imaginations of engineers and manufacturers across the world, but the first thing you might wonder when it comes to skateboarding is; why? A skateboard ins’t that heavy, after all – what kind of performance does a generatively designed skateboard truck offer?
“In terms of downhill skateboarding, if you try to brake from 80km/h on a board weighing five kilograms it’s harder than a board of three or four kilograms, so it makes the whole handling easier,” he says.” Even more gratifying, Manger is thinking about the whole experience, not just the fun part – you have to walk up long hills to skateboard down them, which means any reduction in weight will make it easier to carry.
Materials and methods
Most traditional skateboard trucks are made of aluminium, so you’d think Manger’s material of choice – the far heavier titanium – would add rather than remove weight. But the lattice pattern sees far less material used, making the truck much lighter than its aluminium counterparts. “Titanium has the double the density of aluminium, so it was kind a hard challenge,” he says. “But the big change was that the truck’s upper, moving part is normally a caster with a steel axle inside an aluminium body. My truck is made out of one part and the axle is hollow as well, with the lattice going inside the axis.”
Manger calls the process ‘topology optimization for organic like form’, and you might indeed be reminded of cross sections you’ve seen from biology class. Think of the bone design in any bird. Rather than being mostly solid (albeit with filaments for blood supply, marrow etc like those of large, ground-based mammals including us), the bones of birds are almost completely hollow, the result of millions of years of iterative design changes. They contain complicated networks of lattices that hold the bone together and provide structural integrity while using the least material possible to ensure low mass, a prerequisite for flight.
And the philosophy behind Project T.O.S.T. was indeed – as Manger’s presentation to potential partners said – an intention to ‘copy nature’ by using similar lattice structures.
As such, many generatively designed parts like Manger’s truck are simply impossible to manufacture traditionally. Milling or casting don’t have the finesse to remove material amid that tangle of detail . Some of the lattice beams in Project T.O.S.T. prototypes were less than a millimetre in width, which not only counted the traditional approach put, it gave the project a quantum leap forward. “It was kind of a goal to investigate the limit for metal additive manufacturing, the minimum feature size,” Manger says.
All of which made finding the right manufacturing partner critical, and he found it in Franhofer IWU, one of the big names in German production technology R&D and where the Institute for Machine Tools and Forming Technology has a department dedicated to generative and additive manufacturing that was perfect for Manger’s purposes.
“[The Institute’s] focus is on metal additive manufacturing and other lightweight designs, so it was the perfect partner,” Manger says. “I was happy to find such a big organization to work with and they supported me with the access to the building and manufacturing facilities, especially the concept laser tool, which is a laser beam making machine. It gave me a lot of know how.”
The next phase
After lining up a partner, collecting and synthesising data, designing and beyond, Manger says it’s been something of a dream job, working better than he thought and with only one hiccup. “We only had a single building process failure, but [the truck] worked the first time. It shows how good the software is, because I analyzed everything and prepared it for the build process from the beginning,” he says.
So with a market-ready product in hand, produced by the latest in cutting edge design principles and technology, what’s the next step for Manger and Project T.O.S.T.? “I find the less I plan the future, the better it works,” he laughs. Surprising though it is to learn, there are no formal plans to commercialise the futuristic new truck. Aside from the fact that it’s not yet economically competitive with traditional truck manufacturing (even if that was the plan, Manger says it’d take three to five years to get there), the aim of Project T.O.S.T. from day one was to enable a proof of concept.
He now says the project is bearing fruit because the industry contacts, the companies seriously interested in the technology, the attention focused on the project and the slew of awards he’s received at trade shows and conventions is kicking into high gear.
“The project wasn’t really about creating a skateboard truck,” he says. “It was more about finding new ways for lightweight designs for metal additive manufacturing. Project TOST shows new approaches from the combination of organic forms and lattice structures. The skateboard trucks just happens to be a demonstrator which everyone can understand.”
Telling a computer how to design
Note to ed: the pics from page 20 and 21 talk about this – the below is more suited to a caption accompany the image(s) rather than a section in itself.
The constraints and values Manger had to input into the generative design algorithm had to be designed and measured form the ground up. As well as acceleration, the weight of the board and truck as individual parts and other variables, the force exerted on the truck by various load cases had to be measured. Manger built a custom sensor box, added readings from various skateboarding moves and combined the data into a specialised formula that informed the topology optimization.