How Moto Mods went from concept to product

Motorola’s lead mechanical architect, Paul Fordham, chronicles designing a modular phone that has great performance and user experience

The Moto Z and Moto Mods announcement last month caught the attention of everyone who has followed modular phone designs like Google Project ARA. The intriguing Moto Mods are the most viable modular design yet because consumers can add features to their phones, simply and cleanly without stressing them with a complex interconnection procedure or having to wait for the phone to reboot. The magnetic interface intuitively explains how it works and guides the user the first time a Mod is added to the Moto Z.

I sat down with Paul Fordham, lead mechanical architect on the Moto Mods design team at Motorola, to talk about how Moto Mods were conceived and developed into a product. Interviewing software and electrical engineers can be tedious because of the high level of abstraction in their work. It was a pleasure to talk with Fordham, however, because mechanical engineers, like physicists, are tethered to the physical world, making for a very enjoyable and tangible conversation.


Steven: Smartphone designers face a dilemma. With each new phone design, features are incrementally better because components such as displays, processors chips, GPS chips get better, but they can’t really add a new hardware component that might add a game-changing feature without creating an overpriced device. How does Moto Mods change this?

Fordham: You can’t burden every phone with technology that perhaps only 10 or 20 percent of consumers might want. You are taxing everyone with the new technology cost of a unique component that may provide unique features but might not have reached the low price points from production at the smartphone scale of hundreds of million units. You can’t just roll out an intriguing phone design to the masses unless the price is intriguing, too.

That's literally what the whole Moto Mods concept was about. The design allows for customization for the consumers willing to pay for premium feature modules.

Look, if a premium camera is important to one consumer segment or really long battery life is important to another, they can pick and choose or they can choose both. They can decide what they want to use on any particular occasion without taxing everyone with the cost of building these features into every phone. It’s very similar to the concept of apps. Apps let you customize your phone with software. Moto Mods let you customize your phone’s hardware.

Steven: What were the principals you had in mind when you started designing Moto Mods?

Fordham: It has to function as a smartphone first. The Moto Mods concept would have failed if we didn’t design a phone with great performance and user experience. No one's going to buy Moto Mods for a phone they don’t love.

The design had to be hot swappable. Put the Mod on, take it off, again and again, simply without hanging Android. The design was meant not only for our inside Motorola engineering team, but for independent hardware engineers using the open-sourced hardware designs. We created a physical user experience when adding or removing a Mod that is really clean, simple and easy. And after a user does it once, he or she gets it. This is the clever part of the design.

This cleverness was the result of mechanical designers, working with software and electrical engineers to make the experience as clean as it is.

Steven: Please tell a bit more about how you designed this cleverness.

It was a unique situation. We were four mechanical engineers that started looking into how to modularize a phone. Three years have flown by because we've had a great deal of fun doing this.

We started experimenting with the Moto X. The Moto X curved back made the modules feel like an afterthought. All the attachment concepts we applied came out kludgey. Working with the three other mechanical engineers, we decided the first thing we have to do is make the phone light, super light thin and then you have to make it the back flat where the phone and module attach together. Not just connect, they have to attach and be one.

We started in about the August 2013. We added a few electrical and software engineers, but it was still a pretty small team. We released the first fully functional prototypes in December.

Note: At this point, Fordham produced the first prototype in one hand, a polished design, very thin—thinner than the Moto Z—and a thin battery module in the other and let them magnetically marry themselves.

This prototype amazed our colleagues and management. We’d let them hold the device with the battery attached and asked them “what do you think?” The answers were politely positive, which changed to jaw-dropping amazement when we pulled the module and the phone apart. Magnets were the right choice to invisibly and tightly connect the phone and module because people like and understand them. That convinced us that we had something worth developing into a product. There were some compromises, some of them a little painful. We made it thicker for a Type-C USB connector and settled on a camera bump so we could spec a high-quality camera assembly.

We learned to compromise. We just would say, OK, how do we make this design work? How do we evolve the design so that it will really work for consumers in everyday life? And when the Moto Mods designs are made available under an open-source license, how will we attract independent hardware designers motivated to create an ecosystem of unique add-on modules?

Steven: This reminds me of Google’s Project ARA, a concept modular phone.

Fordham: We were aware of Project ARA because Motorola was owned by Google at the time, but we had a different idea. We didn’t think that the typical consumer would be able to make—or care about making—modular choices like processors and displays.

Steven: Three Moto Mods were released with the Moto Z: an LCD projector Mod, a JBL stereo speaker Mod and a battery Mod. What were some of the other concepts you worked on?

Fordham: We built a battery module that had a full QWERTY keyboard inside. I could show it to you; it's almost like a slider type concept for people who like the tactile feel of a real keyboard. We had all these different ideas that we hadn't even partly developed.

But we don’t have a monopoly on all the possible ideas for modular phone applications. Our developer program lets other hardware design teams build intriguing Moto Mods that consumers want. I think there are some good ideas that are coming in. It certainly is different; it's a new revenue stream that Moto Mod brings for Motorola and our hardware and carrier partners.

Steven: How did you choose magnets?

Fordham: Magnets really turned out to be the only real choice. We looked at mechanical snaps, drop-and-slide type stuff. These were kludgy, not a good experience. So, when we started, magnets came into focus, not just because of the mechanical properties but because people actually gravitate towards magnets—they understand them, there's something unique about them and they're super easy. People immediately understand how the Mods work and don’t stress about damaging the phone or Mod putting them together or taking them apart.

We hit some bumps in the road—we learned a lot—we were not experts in magnets. We worked with KJ Magnetics They really helped us realize our design. They were intrigued by our questions, I think, because while magnets aren’t new, the application is pretty unique.

The engineering challenge wasn’t so much driven by the magnet connection of the Mod to the phone back, but a strong enough magnetic field to counter the force of the 16 pins that make consistent electrical contact. We designed the phone that would marry tightly with a Mod up to about 200 grams. Each of the connector pins on the back imparts a 60-gram force against the opposing contact, and there are 16 of them, so we engineered the magnets to counter the force of the pins.

We would have preferred to build the phone with Cobalt stainless steel because it has the best magnetic properties, but we chose a Series 400 stainless steel because it is much better for decorative surface coatings applied with physical vapor deposition (PVD). We also had to design in tolerance for slight warping of the phone or Mod. It all turned out well, but there were a few dark moments during which we went back to mechanical snaps for three days.

Steven: The electrical interfaces, RF, things that keep engineers up late at night—what were some of the challenges you ran into in doing that?

Fordham: We had a number of constraints that we had to accommodate. The most important to be considered in the final design were optimizing the antenna functions without interference from the high-speed data going over the 16-pin connector and what position on the internal system board was best for interfacing the internal phone bus with the bus in the Moto Mod. We tried different pin configurations, too—8, 14, 16. Some team members would want fewer; others would have been happier with 40. This interface achieved our goal—one we believed was essential—making a connection that would not need a reboot like the LG G5 does.

We [mechanical, software and electrical engineers] were pretty happy with the design, and we didn’t lose too much sleep. The design performs well, transmits high-speed data across a reliable connector and bus. The phone doesn’t have to be rebooted when Mods are attached, detached and exchanged, and the design is future-proofed.

Steven: When did you think the Moto Mods design was far enough along to include manufacturing engineers in the discussion?

Fordham: Each member of the team had experience designing for manufacturing. Together we had many years of experience. We started meeting with the manufacturing engineers early on. When we saw a point of contention coming with the manufacturing engineers, we would meet, push back and forth, explain that we had to evolve a really thin phone design and a dead-simple method for attaching Mods.

We took some risks and mitigated them, found the middle ground with the manufacturing engineers that allowed the design to continue to evolve. Drop testing and accelerated life testing produced the new flagship design of Moto Z family that is robust, manufacturable and provides the end user with a good experience.

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