STAINLESS STEEL 17-4 & 316L
17-4 stainless steel combines high strength, corrosion resistance, and hardness, making it widely used in aerospace, medical and petroleum industries.  We use it for assembly fixtures and tooling on the Mark X.

Also know as marine grade stainless steel, 316L stainless steel exhibits very good corrosion resistance and excellent weldability.

TOOL STEEL A-2 & D-2 (Beta)
A-2 tool steel is air-hardened with excellent impact resistance. We use it for punches, dies, and form tooling on the Mark X.

The high carbon and chromium content of D-2 tool steel provides great hardness and abrasion resistance (but not as tough as A-2).  D-2 is often used for cutting tools.

 

Blades spinning, blasts of fire, swinging weapons: this is the world of combat robotics. If designers want their robots to have any chance of winning, they have to design their bots to be sturdy enough to take dozens of hits, yet powerful and light enough that their robots can strike fast and hard. Many of these contraptions are built from hardened steel, heavy machined frames, and sharp edges. The designers themselves range from toughened veterans who know their way around the arena to fresh faces eager to send their bots blade-first into battle.

 

Re-Framing the Problem

His original design for the DDT was laden with a bulky, cumbersome frame: lots of fasteners, stacked plates, and plastic components. “The old chassis was manufactured using several stacks of UHMW Plastic, which were then bolted together with several long screws. This old design was cumbersome because it had so many different fasteners, it was a lot heavier, and because it was solid plastic it was actually very flexible, which isn’t very good for the design,” Go explained. This meant that Go had to dedicate a lot of his bot’s weight just to the unwieldy frame. “The old design did…ok. It definitely won a few matches, but I had to make compromises in lighter components, less powerful components, just because of the weight of the frame…as a result, in its last competition, it was totally destroyed.” Go took the opportunity after a particularly nasty battle to rethink his design: “DDT’s frame was done for and I saw this opportunity to revisit some of the design creeds that I’d been touting for the past year… and so starting with DDT, I will evolve each robot in my fleet”. Upon encountering the Markforged printer, Jamison Go saw an opportunity to use the Markforged to modify the chassis of DDT and make it a single, lightweight part. “This printer is unique because it has the ability to embed continuous strands of fiber within each layer of its print. Although it cannot place fiber in the vertical build axis, this is a monumental improvement in tensile strength… it prints nylon as its base material, which is mechanically superior to ABS in our application.” Go went on to describe how he would use the Markforged in his new design. “To further demonstrate the capabilities and applications of [the Markforged] technology, I have elected to print DDT as a nylon-kevlar unibody.” This would make it lighter and stronger so that he could add in heavier actuators and weapons to get an edge in the ever evolving world of combat robotics.

 

DDT v3 Unibody CAD

Reducing a multi-body assembly to a single part is no easy task. As Go describes, “many details about the parts, their connections, and their assembly order must be known ahead of time. CAD became an invaluable tool in this process; each part was modeled with excruciating detail and a detailed assembly order was developed for the rear component bay.” Pursuing his passion for both combat robotics and 3D printing, Go did away with many of the plates, bolts, and other fasteners that added unwanted material weight, and he designed the structure all in one part. “I was able to incorporate a lot of intricate design features to fit my specific components to make everything smaller, more compact, and more efficient.”

“Some of these chassis, they can take three days to complete, and the Mark One is the only printer I trust with a part this complex, and this long,” Go mentioned when describing the printing process. With the Markforged parts making the chassis even stronger and lighter than it was before, Go took DDT into battle with high hopes.

Grand Slam

DDT performed even better than Go had expected. By printing the part on the Markforged, the chassis weight was halved even though its strength increased: “All in all, I was able to make a frame that weighed 51% of the original design, yet was much stronger.”

 

Awards won with the DDT

This meant that he could use the extra weight he had to incorporate higher performance motors and electronics into DDT, making the bot even more of a threat. DDT’s new, lightweight chassis made it incredibly quick on the field, striking other bots fast and hard before some could even throw a punch. “The new design has performed phenomenally thus far. I’ve taken it to about four different competitions, and in every single one of them, it either won first or second. It’s currently the second ranked robot of its weight class in the whole world,” Go explained. “When I take this guy to competitions, the competitors, bystanders, are absolutely astounded. They can’t believe that this is 3D printed, and I tell them ‘this is what the Markforged printer can do.’” The new DDT quickly rose in the ranks of antweight combat robots and is now second worldwide. DDT’s success inspired Go to upgrade the rest of his iconic combat robots as well, designing Markforged unibody frames for all of them.

Among them is Charles Guan, an MIT graduate with a Bachelor’s Degree in Mechanical Engineering. His concoction of a go-kart is the Chibi-Mikuvan, designed to look like the 1986-1994 Mitsubishi Delica, made from “a hodgepodge of unrelated commercial and industrial parts,” says Guan, including the inrunner motor from an R/C boat and the gearbox of an angle grinder. Built for the previous year’s race, the Chibi-Mikuvan had recently undergone some important upgrades. His modifications to the Chibi-Mikuvan using the MarkForged printer helped him secure a victory.

One of the most essential parts of any automotive suspension is the steering knuckle, part of the linkage system that links the yaw of the wheels to the motion of the steering mechanism. The knuckle itself can be a fairly complicated part to manufacture, and has to deal with large forces from all directions, including the resistance from the road, the motion of the tires, and the weight of the driver. Guan wanted to replace his older steering mechanism design, a heavy, failure prone, metal assembly, with something lighter, easier to manufacture, and just as strong.

Designing to Win

 

When it comes to reducing weight and simplifying the fabrication process, 3D printing combines the quick, iterative design flow of rapid prototyping with the inexpensive yet complex additive manufacturing process. This allows for intricate, precisely dimensioned parts that would otherwise take hours to toil over in a traditional machine shop. Additive manufacturing provided Guan with an opportunity to vastly reduce the weight and bulk of his steering mechanism, but many 3D printing solutions produce parts that are too weak or too brittle to withstand the forces necessary for a steering knuckle.

When machining or 3D printing parts out of metal, the material properties of the piece are stronger, but nearly isotropic. Using a composite material, the fibers can be oriented such that the material properties can be optimized in certain directions along the part. However, composite materials can take many hours to set up, make, and perfect. The Mark One, with its nylon and composite Case studypg 3filament options, provided Guan with just the part strength and manufacturability he needed to design a compact, lightweight steering assembly for the Chibi-Mikuvan’s race at the Detroit Maker Faire.

The Grand Prints

Guan designed the parts to take advantage of the anisotropic nature of the Markforged prints, printing his parts with nylon and fiberglass. The nylon layers provided flexibility, while the embedded fiberglass provided strength about the layers they were laid down upon. “The new steering knuckle,” Guan explains, ”will be printed flat to have large C-shaped sections of fiber holding onto the axle stub”. The knuckle (shown in light pink in the CAD rendering below) has fiber strands running along the face of the “C”, maximizing the strength on that plane, making the part strong, light, and flexible in all the right directions. The knuckle could have been printed in one piece, but it was split into three, using the direction of the fiber in each part to optimize its strength and flexibility. The other two parts, the brake caliper (shown in purple) and the steering follower link (shown in red), were likewise designed to make use of the fiber direction to improve the part. Guan’s new improvements reduced the weight of the bracket’s weight by 40% and made for a more reliable steering assembly.

Printing the parts on the Mark One took about 24 hours. Guan then assembled and tested his new design, jumping on the Chibi-Mikuvan’s frame to make sure it could withstand the forces he needed it to.

In his first iteration of the design, Guan said that he “caused Version 1 of the kingpin bracket to buckle the fiber region where the part met the frame. It never failed…” The buckling only caused the wheel to twist a bit more. After slightly modifying the design, he went to testing again.

After the test, Guan explained “I think that one of the reasons it survives is that the nylon is very flexible. It takes quite a lot of shock. If I steer very hard, the whole bracket moves a little bit. I am deforming it right now with about 40 pounds of force and the assembly takes it.” The flexibility of the nylon and fiberglass parts lets the steering assembly absorb hard impacts, allowing it to easily handle an estimated torque of 5 N-m on the face of the axle stub. Confident in his design, Guan sped his way to first place

 

The Snotbot hurtled down toward the Ocean Alliance research boat, its operator hoping that he could get it back in as few pieces as possible. With the boat moving, the wind blowing, and the drone running low on batteries from carrying so much weight, all landings need to be quick. It’s pilot would be satisfied with any touchdown that at least saved the electronics housing , but that was not a guarantee. Ocean Alliance, a research organization that has studied whale behavior for nearly 50 years, has partnered with Olin College of Engineering, a unique engineering school in Needham, MA, to develop a novel method for collecting biological information from whales. Their solution, the Snotbot, flies over surfaced whales and collects the liquid expelled from their spout. The robot is much less invasive than the traditional tissue collection method, which involves shooting a biopsy arrow at the whale. While using the Snotbot is a much more effective method, landing the drone on a moving boat with rough wind conditions nearly always results in a crash. One of the problems the drone’s designers have to solve is that no landing gear thus far has handled impact reliably.

 

Devynn Diggins, a mechanical engineer in her junior year at Olin, has accepted the challenge and has worked on the Snotbot for over a year. As part of Olin’s Intelligent Vehicles Lab, Diggins works under Drew Bennett, a professor of robotics and systems, to discover new ways to improve the drone with each prototype. From making the Snotbot resistant to saltwater, to designing landing gear that can handle rough landings, to protecting the blades from rough waves, the pair have faced their fair share of challenges with this drone. Efficient design of the drone is a critical balancing act: a heavier drone will waste more battery life, but a light drone may be too fragile to succeed.

Toughening Up

“The original landing gear we had were traditional carbon-composite layups, and they all shattered on landing…,” Bennett explained. “We needed something that had more give, more flexibility, more compliance. But it also had to be really strong.” Traditional carbon fiber layups just weren’t strong enough. The landing gear was just too brittle to handle the impact, even when testing on land, so the team needed a different solution, and they needed it fast. The window of good conditions for whale research was shrinking, and Diggins and Bennett didn’t have the time to wait for another order of spare parts. “Because we were having these problems during testing, we were even more worried about if we were to go over a whale with our vehicle and something went wrong, then the landing gear could snap, preventing us from retrieving the vehicle and possibly harming the whale in the process.” Diggins described. “When we heard about Markforged, we realized that there was a way for us to 3D print new copies of our landing gear based on our existing design, that was just as light but even stronger than what we were currently working with.” The fiber options on the printer provided room to experiment with different designs and materials with a quick turnaround time, as Bennett recounts: “We didn’t know what the right landing gear was, and with the Markforged, we could try different materials, we could try different geometries on the landing gear, we could run out and test them out back…we could make changes to the design, and that allowed Case studypg 3us to create the necessary landing gear fast enough to meet Ocean Alliance’s needs for their operations.” They soon created a lightweight solution with the Markforged printer’s nylon and embedded Kevlar. “The Kevlar gave us the strength we needed for the shape, but at the same time it gave us the flexibility we needed to absorb the force of the impact,” Bennett described.

The Markforged, while initially only used as a quick landing gear fix, provided many more opportunities to shine as a prototyping and learning tool over the course of the project. “Moving into another phase of designing for our vehicles, we realized that when we’re flying our vehicles just above the surface of the water, we run the risk of accidentally submerging the motors and possibly damaging our systems,” Diggins explained. “Keeping this in mind, we decided to redesign the arm assemblies of our hexacopters with Markforged parts so they’d be able to safely navigate our vehicles close to the surface.” The arms were redesigned to protrude out from the body of the drone at an angle, raising the motors higher above the water. Just like everything else on the Snotbot, the arms need to be light, but strong enough to support the body of the multicopter. The standard carbon fiber arms provide a great balance of the two requirements, but bent carbon fiber tube is expensive to come by. Diggins used the Markforged printer to reduce manufacturing time and part weight while still conserving strength: “The parts we wanted to make…would require machining in order to create the precision and strength that we needed. However, the weight of the machined parts would be far too great for us to be able to accurately fly our vehicles above whales. The 3D printed strength of the Markforged came in handy.” Once again, the printer served as a great prototyping tool to produce the parts necessary to succeed.

Taking Flight

The pair of engineers couldn’t be happier with their upgrades. “We never had to worry about our vehicle coming backin more than one piece,” Diggins described. The Snotbot hasn’t had a single landing gear failure since the modification. While the new arm adaptors have not yet been tested on the Snotbot, the success of the landing gear has given the team high hopes for the other components. Bennett, proud of his student’s accomplishments, was very satisfied with her work: “without the Markforged, she never could have built the right assembly.” With the help of the Markforged printer, the Olin Intelligent Vehicles Lab can prototype faster, stronger, and cheaper not only for just the lab’s fleet of drones, but for the entire school. The printer has opened up as another manufacturing resource for students in need of high strength parts, and Bennett is amazed at how the students have used the printer in creative ways. “We’re really happy to have the Markforged and we’d like to keep working with it, pretty much forever, at this point. Every time I think we’ve figured out how to use it, some student will come in with a brand new idea to use the device in a way we never thought.” The printer’s reputation has spread far and wide in the semester it’s been running, and now the Snotbot is just one of a wide collection of projects the Markforged printer has helped succeed.