Misty’s Arms Pull Double-Duty

Misty II has arms! Believe it or not, this wasn’t a given. A lot of thought and discussion went into whether we would give her arms at all. Once we decided we should, even more thought went into what type of arms they should be.

Designing a robot for developers first

Throughout our decision-making process, we kept the following in mind: we are a developer platform and it’s imperative that you – the developer – have control. We never want to box you into what Misty can do based on our ideas versus what you think she should do based on your own. This is why we’re releasing CAD files for arm connectors, a trailer hitch, a backpack, and antennae. Misty’s expandability features, including her arms, are part of what will make her uniquely useful to you and right for the use cases you are building skills for.


Now, back to our decision-making process. We knew that planning for anything above eight motors would require a more complex control system, would add weight, and could become more expensive. So, we considered all of Misty’s articulation points and simply prioritized the capabilities we felt would deliver the most useful platform for you to build on (and how many motors it would take to make each capability a reality). Misty’s ability to drive, which requires two motors, was non-negotiable. This left us with six additional motor opportunities to use wisely.

We know that Misty’s personality plays a role in her appeal as a platform. For a robot to become an integrated aspect of your  life, consistent and frequent engagement is critical and that is certainly true for Misty. It will therefore come as no surprise that ensuring youget the most expressivity out of the mechanical and electrical requirements we were working with was one of the two majorfactors that drove  how we prioritized our wishlist for Misty’s capalities.

Because the ability to move her neck imbues Misty with an element of humanity, we knew we needed to give you a naturally moving neck to control; we immediately planned for pitch, roll, and yaw. Each of Misty’s neck articulation points requires a motor so those movements would require three motors total. With five of our eight motors spoken for, we had three left to decide how to best use.

Ultimately, we debated between either giving Misty a waist that could be articulated up and down or to having a pair of arms that could… well, communicate many things in many ways and perform more actions than even we could dream of. We opted for the arms. This is where you come in.

Look, Ma! I’ve got arms and personality

We included arms in Misty’s design to add another layer of communication to whatever she’s doing or saying. Programming her to raise her arms could convey excitement or fear. Having her raise one arm could signal a greeting or it could mean “stop”. Holding her arms straight out in front of her or repeatedly raising and lowering her arms could mean a number of different things depending on the context in which she’s making these movements. And that’s just the start of it.

Misty Arms Illustration

Is Misty driving forward or backwards while she makes these arms movements? Is she holding something? Do you have her say something while she does it? What is the expression on her face? For example, you can make her movement more expressive by adding color codes or flags to her arms. Want Misty to be fluent in Maritime signaling? It’s just your imagination and a small OLED that’s stopping you. You decide how to leverage her personality relative to the skill you are building; as long as the community flourishes with interesting and useful skills that incorporate Misty’s arms, there’s really no limit to what they can mean for her personality.

We’re in the business of building robots, not the arms business

The arms that Misty comes with fit her body aesthetically and can be highly effective in helping to express personality, but you’d be right to wonder what these arms can do, tangibly speaking. The TL;DR answer is not a whole lot – at least on their own. Again, we did this on purpose because (again) we knew it was a fool’s errand to try to design the perfect robot arms for all the different uses you will come up with. Instead, we focused on ensuring you will be able to implement your own ideas for her arms and hands.

We’ve done this in a couple of ways. First, we designed the arms Misty comes with to be easily removable. It’s as simple as unscrewing a single set screw and re-using that screw to attach your own arms. It was also important to us that you be able to 3D print or build your own arms without the need for exorbitantly expensive equipment. You can print your own Misty arms off a high-precision laser printer if you prefer it, but you can also print off any hobby 3D printer. One visit to a site like Thingiverse is sure to inspire you but here are a few ideas to help you picture some of the “arms” you can create for her: a drink holder, laser pointer, nerf gun, and dirty clothes “plow”. (We can’t wait to see how many people make that last one.)  

Size matters

Because we’re putting Misty’s arms in your hands, it’s important to be aware of the following arm-making considerations:

Weight: Misty is optimized for an additional pound or two of weight. If you exceed this amount, you will risk affecting her ability to move at normal speed and could potentially exhaust her drive motors altogether. You’re probably thinking it’s common sense that a six-pound robot isn’t capable of carrying too much weight, but we’ve all seen cars or trucks loaded down with heavy items that are obviously far too heavy… So it’s worth mentioning.

Balance: You may have noticed that Misty is taller than your average personal robot. This makes things like autonomous navigation and even our ability to interact and identify with her easier, but it also means her center of gravity is higher. This could make stable driving a challenge. To address this, we designed Misty to use track drive, enabling her to navigate different types of floor surfaces and even to go over some items that might be on the floor, such as clothing. However, if she is carrying something on one side of her body, this can affect her track drive and overall ability to move stably. Keep this in mind (and potentially a counterweight on-hand) when designing arms for Misty to carry things.

Size: Even if the object you have Misty holding is light, you should keep in mind how big it is. For example, will Misty still be able to move her neck, or will the object prevent her from doing so? If the object is tall, will it impede her ability to use the depth sensors or cameras located at the front of her head? If so, you could plan not to use those helpful features but we’d recommend you design a different object for her to hold instead.

There are many potential uses for Misty’s arms and the ways they will convey her personality. We’ve already seen some good conversations around this and are curious to see how the conversations and projects evolve as developers continue to build her skills.

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