What are the design challenges of developing a car that can walk? Hyundai Motor engineers recently set about exploring that idea and developed a prototype vehicle called the Elevate. The goal was for the car to have several types of locomotion–reptilian, mammalian, and the more familiar passive suspension.
The Hyundai engineering team was keen to find out how generative design software could help with the design. They turned to the Autodesk Research team in London to help. The generative design program used was Autodesk’s Fusion 360.
We interviewed Andrew Harris, Engineering Manager, Autodesk Research, London, about the Elevate and what his design team faced in the development of the prototype. Here are highlights from the interview.
“Generative Design is very good at understanding material performance and using that to optimize a structure,” says Harris. “It’s a bit more challenging to design parts that will be affected by isotropic properties of some materials in an additive manufacturing prototyping process.”
But the Fusion 360 program helped Harris and his team analyze complex materials in a more detailed way that showed the isotropic tendencies. Harris found the generative design program to be a “design exploration tool that will optimize multiple designs and then help you choose” from the offered solutions. “After that,” he continues, “further simulation lets you analyze assemblies of components, which is what we were doing using Fusion. We had to analyze the mammalian and the reptilian type movements that it was going to do and we did all of that in Fusion.”
Generative design software offers capabilities not found in traditional CAD design programs. For example, the ability to explore hundreds of concepts quickly. In Harris’ experience, other programs offer a limited scope of solutions with potentially a couple of materials. The issue, however, is that you’re not considering other possibilities that may work better.
The ability to deliver so many potential solutions, “is the strength of generative design, says Harris. “It opens your mind to all the possibilities and you can start to experiment with materials that you’re comfortable with, materials you’ve never used before but have been interested in, and you can start to say, this new material is very interesting and actually, it kind of costs the same, just giving me better performance or lower mass. And you can start to look at those.”
In addition, generative design helps you explore the trade-offs with various manufacturing methods. In effect, Harris and his team generated many designs overnight, selected a few in the morning, took them through CAD modeling to further analyze the designs, materials, and loads, to find those that worked best with the desired manufacturing process.
Load calculations were critical to the design of a car that can shift from traditional suspension locomotion mode to mammalian and reptilian. Multiple load requirements were entered into the generative design program, along with Hyundai aesthetic needs. One of the last factors entered into the calculations was manufacturing processes. “Generative Design, to a large extent, considers a lot of the additive manufacturing processes that we actually applied within this technology,” notes Harris.
Generative design proved helpful in developing a wheel suspension system that had to support other types of motion. The engineering team also worked with Sundberg-Ferar engineers who looked into the robotics aspects of the various motions.
“With each of those motions, the programs analyzed a position that the leg would hold, then applied a load, and we would study the motion that would occur,” says Harris. “So maybe it’s stepping up onto a rock and then lifting the vehicle up using the leg that’s holding onto that rock. If you look at some of the positions that the leg has to hold, it’s reaching out quite far, and yet it still must carry the weight of the vehicle with that leg. That’s a lot of load going through the leg and through the motors, and the motors have to be high torque to give the leg the capability to actually complete these maneuvers successfully. With each of those load cases, we were able to capture within generative design and then use that to generate a large number of designs that we discussed with Hyundai to choose the ones that were aligned with the kind of aesthetics they wanted, and some of the advanced manufacturing processes that we wanted to exploit in this project.”
An interesting design challenge involved applying the novel materials available for FFF 3D printers. Some of the continuous carbon fiber materials display isotropic behavior. “With the FFF process,” says Harris, “you have an isotropic behavior in some places, and in other places it’s not isotropic. The fibers conform with the structure and not necessarily going in an X or a Y direction. So it can be harder to predict the mechanical performance of a part made with such materials. It took a lot of simulation to be confident that the part would cope with the loads. And at the moment, we’re going through a lot of testing of the components. And so far, they are behaving well and they’re meeting the mass requirements and they’re very stiff, which is good.”
With the FFF process, it can be important that the fibers align with the X and the Y directions, conforming within the part. But then you also have the Z direction to consider. In some cases, as the layers are built up in the Z direction, you can have a different strength within the material than what you may have in your X and the Y directions. It’s important that the fibers align well with the load direction, so that you do not have a load being applied effectively in the Z direction across the build layers, which could cause a failure within the matrix of the material. “That was one of the considerations we focused on as we explored these novel materials,” adds Harris.
For this project, generative design software proved to be a powerful tool for developing concepts. Noted Harris, when you are working on a brand new design, it’s a good practice to try and explore as many options as possible. Those options should include different materials, different manufacturing methods, and different aesthetic outcomes. You can also explore more detailed aspects of a design, such as cost.
Harris and his team explored a range of materials and manufacturing processes, focusing on those that were compatible with each other. “We looked at possibilities in CNC machining, and materials compatible with CNC machining, and then also additive manufacturing, where we would look at some of the matte metallic processes and some of the polymer processes, and we even looked at composite processes. Generative Design helped us make some of the decisions, and we actually went down a process of using a lot of additive manufacturing. We explored metal powder bed processes using selective laser melting, FFF processes with short chopped carbon fiber filaments, and continuous carbon fiber as well as dual extrusion type machines where we needed the very high performance, high stiffness and low mass materials for the legs.”
Hyundai Motor plans to make a full-size Elevate large enough to carry people–that’s the main intention. One of the planned functions of Elevate is as a search and rescue vehicle. But there is also the possibility of planet exploration with NASA.
For Harris and the team, generative design also indicated whether it was cost effective to stay with additive to make parts or to add a little bit more manufacturing complexity with multiple components through separate leg parts that required assembly. “Those are the type of questions we can use generative design to answer as well.”