Boston Dynamics builds robots that go where people shouldn’t. MES manufactured a critical magnesium component that helps make it possible. Here’s what it took.
Boston Dynamics’ Robot Dogs Walk into Danger. Here’s What Keeps Their Electronics Cool.
Summary
A magnesium electronics plate sits in the belly of Boston Dynamics’ quadruped robots, a product line that includes Spot®. The plate secures, protects, and cools the processors, communication modules, and power systems that keep the robot moving. Magnesium is about 1/3 less dense than aluminum, but its fine chips and dust can ignite, and its castings are prone to porosity and cracking. This post shows how MES cast, machined, and inspected the plate to meet strict flatness and tolerance requirements. AZ91D-F alloy adds strength and crack resistance. High-pressure die casting with controlled temperature gradients produces each casting in 45 seconds while preventing defects. Machining on a 5-axis CNC cuts the electronics pockets in 15 minutes per piece. Flatness drives heat transfer, and matching machining and inspection fixtures keep every measurement on the same datum.
KEY TAKEAWAYS
- Boston Dynamics robot dogs carry their electronics on a magnesium plate that MES die casts and machines.
- Magnesium cuts weight in mobile robotics, but its fine chips and dust can ignite, and its castings are prone to porosity and cracking.
- MES paired AZ91D-F magnesium alloy with high-pressure die casting and controlled temperature gradients to prevent casting defects.
- Flatness was the most critical requirement, because greater surface contact between the electronics and the plate improves heat dissipation.
- Matching machining and inspection fixtures held a consistent datum and constrained-state inspection with gauge pins verified every plate before coating.
ARTICLE
When the job is checking out a suspected bomb or a chemical threat, the best person to send is … nobody. Better to send a four-legged robot to take the first look.
Boston Dynamics builds just that kind of robot. Its quadruped robot, Spot®, is designed to navigate stairs, uneven terrain, and hazardous environments. Equipped with cameras, sensors, and specialized payloads, Spot can investigate hazardous environments while keeping people at a safer distance.
You’ve probably seen the videos. A robot dog trotting up a flight of stairs is hard to look away from.
What you don’t see is the magnesium plate mounted in the robot’s belly. It’s an essential piece of hardware, even if it isn’t nearly as exciting to watch as the robot itself.
MES manufactured that plate. And producing it to Boston Dynamics’ specifications presented some serious challenges, starting with the choice of metal.
Where Powder Coat Works Best
Electronics need stability and a way to manage heat. A robot dog makes both more difficult.
The magnesium electronics plate provides a secure foundation for critical components as the robot walks, climbs, and navigates rough terrain. It serves several important functions:
The challenge for robotics manufacturing is delivering all that functionality without adding unnecessary weight.
Boston Dynamics specified magnesium for the plate. And that introduced a new set of manufacturing challenges.
Why Magnesium? And Why Is It So Difficult to Cast?
Magnesium is about one-third less dense than aluminum, a significant advantage when every gram rides on four legs. But its lighter weight comes with manufacturing challenges that demand careful process control.
The tradeoff? Magnesium offers important performance advantages, but it also demands careful manufacturing controls.
Magnesium Die Casting: Benefits and Manufacturing Challenges
| What Magnesium Offers | What Manufacturers Must Manage |
|---|---|
| Less weight | Porosity and cracking risks |
| Complex cast geometries | Precise casting process controls |
| Precision-machined features | Tight tolerances and accurate fit |
| Lightweight structural support | Safe handling of combustible machining chips and dust |
For MES, those challenges were especially important. The finished plate needed precise recessed pockets and mounting surfaces, dimensional accuracy, and the durability to withstand a robot’s constant movement.
Magnesium Die Casting: 45 Seconds to Cast, 15 Minutes to Machine
MES selected AZ91D-F magnesium alloy for its strength and resistance to cracking. But material selection was only the beginning.
The team used high-pressure magnesium die casting with carefully controlled temperature gradients to minimize porosity and cracking. Each plate took just 45 seconds to cast.
Using 5-axis CNC machining, the team created recessed pockets for the electronics and achieved the tight tolerances and surface finish required before coating. That process took 15 minutes per plate.
The plate also featured integrated heat-sink fins to help dissipate heat generated by the electronics.
One important detail was the tooling. MES designed the machining and inspection fixtures around consistent datum references. In practical terms, the plate could be measured from the same reference points used during machining, helping ensure dimensional accuracy through production and inspection.
Why Flatness Matters for Electronics Cooling
A magnesium plate can meet its dimensional specifications and still struggle to transfer heat efficiently if its contact surfaces aren’t flat enough.
For Boston Dynamics, flatness was especially important because the electronics plate also serves as a thermal conductor. A flatter contact surface helps maximize contact between the electronics and the plate, reducing thermal resistance and improving heat transfer.
Bud Abraham, Senior Project Engineer at MES, explains: “One of the most important aspects is the flatness of the part that the electronics go into. It’s the substrate used for thermal conduction, so we achieved as much contact as possible to dissipate the heat.”
Even small variations in flatness can create air pockets between mating surfaces, increasing thermal resistance and reducing heat transfer.
Precision Inspection from Machining Through Coating
Manufacturing the magnesium electronics plate was only part of the challenge. MES also needed to verify that each part met Boston Dynamics’ specifications before it moved to a third-party coating supplier.
The quality team inspected plates in constrained states, using specialized fixture gauges to hold them in a controlled position. Gauge pins verified critical diameters, while pneumatic measuring instruments supported dimensional checks.
The inspection process required coordination among Boston Dynamics, MES, and the coating supplier.
“It was all very precise and required a lot of coordination between the customer, MES, and the third-party coating supplier,” says Abraham.
For a component with demanding fit and thermal requirements, consistent inspection helped ensure the plate was ready for the next manufacturing step.
Your Part Doesn’t Have to Walk
Most manufactured parts will never climb stairs or approach a suspicious package. But plenty face similar engineering challenges: reducing weight, managing heat, and maintaining tight tolerances through casting, machining, inspection, and finishing.
For Boston Dynamics, MES brought together specialized die casting and machining capabilities, coordinated suppliers, and managed quality through inspection and coating to deliver a precision component for a demanding application.
Read the full Boston Dynamics case study for more details.
Working on a component with weight, thermal management, or tolerance challenges? Talk to an MES project engineer.
Frequently Asked Questions About Magnesium Die Casting
Why is magnesium used in robotics manufacturing?
Magnesium is about one-third less dense than aluminum, making it useful for robotic components where reducing weight is important. It also supports complex die cast geometries and precision machining for applications requiring structural support and tight tolerances.
What are the biggest challenges in magnesium die casting?
Common challenges include controlling porosity, preventing cracking, maintaining dimensional accuracy, and managing fire hazards associated with machining chips and dust. High-pressure die casting, controlled processing conditions, and precision inspection help address these risks.
Can magnesium die cast parts help manage heat?
Yes. Magnesium conducts heat and can be used in components designed for thermal management. Features such as integrated heat-sink fins and precisely machined contact surfaces help transfer and dissipate heat from electronic systems.