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“WaterBone” design wins grand prize in ARPA-E LITECAR Challenge

The winning design: “WaterBone”. Click to enlarge.

Local Motors, in partnership with the Advanced Research Projects Agency-Energy (ARPA-E), announced the winner of the LIghtweighting Technologies Enabling Comprehensive Automotive Redesign (LITECAR) Challenge. The design challenge served to accelerate innovative ideas by using novel material technologies, structural designs, energy absorbing materials and unique methods of manufacturing to reduce vehicle curb weight while maintaining current US automotive safety standards. 254 conceptual designs were submitted. (Earlier post.)

The winning design, Aerodynamic Water Droplet with Strong Lightweight Bone Structure (“WaterBone”), was created by Andres Tovar, a mechanical engineering assistant professor at the School of Engineering and Technology at Indiana University-Purdue University Indianapolis, and his group of graduate students. The proposed design—which makes innovations in the structural layout, use of multi-materials, and the 3D printing manufacturing process—has the outer shape (envelope) of a water droplet with an embedded trabecular (graded porous) bone-like structure (spaceframe). The water droplet shape provides a low drag coefficient, while the spaceframe provides the mechanical strength and energy absorption capabilities (crashworthiness) required to protect the occupant in the event of a collision.

The envelope’s material is a polymer composite, which provides desirable characteristics of a monocoque design. The spaceframe’s material is functionally graded aluminum alloy foam. The layout of the proposed spaceframe is designed using a specialized and unique topology optimization algorithm (Hybrid Cellular Automaton, HCA) for crashworthiness. The monocoque-spaceframe design is built using additive manufacturing (3D printing) technology.

  • Novel multiscale structural layout. At the vehicle scale, the generated spaceframe has a structure similar to the one of long bone. In essence, the aerodynamic water droplet shape is protected by specialized ribcage that follows principles of Michell-type frame structures. At the component scale, each spaceframe tubular component is filled with a functionally graded bone-like cellular structure. Such complex, lightweight, multiscale structural layout is manufacturable using 3D printing technologies.

  • Novel lightweight multi-material design. The envelope’s polymer composite provides desirable safety characteristics of a monocoque design. The metallic (functionally graded cellular) spaceframe provides a level of protection similar to racercars that also use spaceframe design; however, the proposed design has less than 50% its weight with significantly lower part count. The result is a design of very light, strong, and safe (crashworthy) components with the possibility of utilizing a wide variety of plastics and metals.

  • Novel manufacturing process. Besides providing lightweight and innovative vehicle designs, 3D printing offers a number of benefits in comparison to current manufacturing processes: cleaner and environmentally friendlier operation that allows complex part production with minimal overall material wastage; free-form mass customization with reduced time to market; and low overall cost.

The concept vehicle combines the shape of a water droplet and the spaceframe design similar to a ribcage. Each structural component has a graded porous structure similar to the one of a bone. Click to enlarge.

The winning design was selected by a panel of experts in materials, crashworthiness, structures, manufacturing and safety.

HCA was proposed and developed by Dr. Tovar and collaborators with the support of Honda R&D Americas. Currently, the HCA algorithm is implemented by Livermore Software Technology Corporation (LSTC) in their commercial finite element analysis (FEA) software LS-DYNA. The topology optimization problem to be initially addressed is finding the material distribution that maximizes the internal energy (IE) and subject to a mass (M) constraint.

The main advantages of the HCA algorithm, says Dr. Tovar, are the proven convergence, its convergence rate, and its extension to solve a variety of topology problems. When applied to a single crashworthy vehicle component (e.g., a bumper), the HCA algorithm finds the material distribution that maximizes IE for a given mass target. However,while these designs may be sufficient for some vehicle components, this current strategy is not applicable to the design of crumple zone in the front and rear ends of the vehicle.

Other crashworthiness indicators must be considered: specific energy absorption (SEA); mean crushing force (MCF); peak crushing force (PCF); crash load efficiency (CLE); and progressive folding.

In order to address this crashworthiness problem, we have proposed a design algorithm that uses the “gray” design generated by HCA that is then clustered and optimized using sequential metamodel-based genetic programming. The multiscale design offers an optimal spaceframe design that maximizes internal energy, and the internal functionally graded cellular structure to manage the impact by extremizing crashworthiness indicators. The loading conditions for the optimal space frame two frontal pole impacts (full frontal and offset) and three side impacts (central and two offsets). The result is a lightweight structure that satisfies all safety standards.

Tovar will receive the $60,000 grand prize for his pioneering vehicle design concept. The remaining $90,000 in prize money will be divided between five additional submissions that were recognized for their ideas by both the Local Motors’ online community and LITECAR judging panel.

  • First runner up ($40,000): Sumit Lakhera and Feyzi Aras, Skeletos

  • Second runner up ($20,000): Wilburn Whittington, David Francis and Kyle Johnson, Metal Matrix Metallic Composites

  • Innovative design component ($10,000): Yuqing Zhou, Kazuhiro Saitou and Jeff Xu, Manta

  • Innovative safety component ($10,000): Alexander Rivera, Modular Sprung Pod Car

  • Community favorite ($10,000): Anthony Kim and Sheetanshu Tyagi, Apalis

The LITECAR Challenge launched on 2 January and voting concluded on 20 March. The submissions were evaluated on four main criteria: vehicle curb weight reduction, vehicle safety, innovation and supporting evidence.


Roger Pham

Looks just like the Citroën Deux Cheveaux, which was also very light-weight and had skinny bicycle tires, and about 15-25 hp.


Will this be enough to guide the majors in the right direction towards future lighter more efficient cars?

Will we see 1000 to 1500 lbs e-units in the not too distant future?


a: I'd rather crash in it than a 2CV

b: How long will it take to print one ?
(Days, I'd say)

c: Looks like a 3 door Opel Corsa.

d: Looks more like a supercar construction style than an econobox.

e: 1-1.5K lbs e-units - no, the batteries would weigh too much (if it was a 4 wheeler)


This thing sets a new standard for UGLY. It would be more like a rain drop if was running in reverse, except that a raindrop only has that shape as it drips off of something. Once it is free, the surface tension pulls it into a sphere. You can get the same effect of the so called bone structure by separating 2 skins with either foam or honeycomb material which is how most race cars and contemporary aircraft are made. If I was grading it, I would give it a D at best.


I am all for 3D printed body panels of cars, though currently I don't think I'd feel safe in a car that weighs only 300lbs.... even if that is without the powertrain it gets a bit confusing.

My biggest concerns with the legitimacy would be the weight of the amenities (seats, trim, radio), weight of glazing/glass, and weight of powertrain. Part of me also doubts the crashworthiness, mass does play a bit in the safety of the occupants... this vehicle weighs less than some motorcycles.

back to 3d printing... if it becomes part of the industry, there is no need for costly repairs or paint. Someone cracks your bumper with their trailer hitch, print a new one at the dealer. The old one can be ground up and recycled. All the dealer would have to have is colored plastics/resins.

I was watching TED talks and they have this new type of 3D printing that is not so much additive as it is drawn out up of the goop, it is also accurate to something like 40nm. Also this process is like 2000x faster than some of the current additive methods. (since it doesn't use thermo curing plastics, they could use it in most automotive applications).


@Cheese, I agree, there are about 30,000 parts in a car and to make it really light, you have to make all of them light, which would be an enormous task.

On the other hand, it is an idea / demo rather than an actual vehicle to be sold so we have to cut them some slack.

I am not sure you would be able to print large parts in the dealers, the printers would probably cost $1-10 Million. Also, the would probably paint the printed parts.

Aerodynamics is very much about the details of the surface, so you have to get everything right, wipers, handles, door gaps, underneath etc. - again, a very big task.


One important advantage of 3D body printing is to be able to incorporate model changes overnight instead of every 4 to 6 years.

It should therefore be easier to progressively reduce weight and drag with computer optimized modeling.


Not so long ago, many people bought their vehicle by the lb/Kg. Everybody were falsely lead to believe that 4-ton units were better than 3 tons.

Ultra light vehicles are more efficient and can be as safe if not safer. Race cars are good examples.

However, manufacturers were not interested to build light more efficient vehicles. Even today, they manage to sell 4-ton large pick-ups by the millions because of higher profit margins. It is ridiculous but true?

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