Arms Ahoy!

From grippers to battery packs, these custom arms have got Misty covered.

Misty Gripper Arm x
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A multi-purpose platform like Misty needs hardware that’s functional across a wide range of robot jobs. But when it comes to arms, designs that excel in one context might be invalid in another. This raises an important question. How do you provide useful arms without narrowing Misty’s overall utility? We think the answer lies in setting up developers to build their own robot arms.

Misty’s developers will invent uses for Misty that go beyond what we could ever dream up, and our notion of what’s possible shouldn’t bound anyone’s imagination. To get your creative juices flowing, this post lists a handful of custom arm designs that Misty’s already tried on for size. Without further ado, allow us to present:

The Cup Holder Arm

We always ask developers, “What would you code Misty to do?” Among the varied replies, we can always count on suggestions from a few parched programmers that Misty ought be able to bring them a drink. If we’re honest, we’ve had the same thought. Which makes the cup holder arm a good place to start.

Beer Cup Holder

This attachment holds a bottle, cup, or can in place with two prongs that curve around the container. It doesn’t make it any easier for Misty to open a fridge, and she’ll still need a hand getting the beverage in place. But the arm’s simple design and clear function prove the value of customizable hardware. Printing an arm like this doesn’t cost much, and putting it to use is scientifically proven to win friends at dev conferences.

Next up:

The Battery Arm

Misty battery arm
You can grab the STL files for left and right battery arms from Thingiverse.

The UART and USB ports embedded in Misty’s torso each provide up to 500 mA of power. In many cases, this is enough power for external microcontrollers and other hardware you might want to wire up to Misty. But if you want enough juice to operate hardware that requires more than 0.5A (like a Raspberry Pi), these battery arm attachments have got your back. Misty can use these holsters to pack along any extra batteries she might need for her skills.

Occasionally, we can tweak an arm’s design and put it to use elsewhere. Which brings us to the next entry – Misty’s “tin holder” arm.

The Tin Holder

We designed the “tin holder” so that Misty could carry smaller drinks, like a taster of your favorite IPA or an 8oz can of soda. This arm is a modified version of the battery arm – we removed the side walls and reconfigured the base to fit the circular shape of a can or glass.

Misty Small Tin holder

This arm is just about perfect when you’re coding Misty to deliver a drink. Just be careful about sending MoveArm commands with an open container on-board. (The STL files for this arm are also available on Thingiverse)

The Gripper Arm

While the utility a gripper provides is a far cry from what you could do with a truly dextrous robot hand, it does serve some of the less intricate hold-and-carry purposes you might think up for Misty – from picking up the mail to scattering flowers and candy on Valentine’s Day.

Misty gripper arm


Despite its industrial aesthetic, an arm like this is fairly simple to build on your own. There are dozens of small, low-cost robot grippers you can purchase online (Google “robot gripper” for a few options), and it’s a small task to print an attachment to connect the gripper to Misty’s arm socket.

Our version of this arm uses a gripper with a micro-servo that operates independently from the robot to control the pincers. You can control the gripper from the skill code running on Misty by wiring the arm to a microcontroller attached through Misty’s backpack. Misty sends commands to the microcontroller through her UART serial port to manage the gripper’s grasp.

The Laser Arm

Not all arms need to lift and carry objects to be useful. In fact, we think many of the first skills developers build for Misty won’t require her to move things around at all. They’ll focus instead on everything else she can do to be helpful, making use of her autonomous movement, her sense of sight/sound/touch, and her ability to communicate and express herself.

The laser arm — a simple attachment with an embedded laser pointer — is a great example of this. It shows what’s possible when you stray from the well-trodden path of robot jobs that involve holding, lifting, and transporting objects, and chart a course instead for the unmapped territories of robot expression and communication.

Misty Laser Arm
It’s also a really fun way to exercise your pets.

With an arm like this, you can code Misty to point at small, specific items from across the room. Misty could help out during presentations at the office, or even be the tour guide at an art museum. Or, if you’d like, you can take things in a more playful direction and code Misty to point out what you’ve seen in a game of I Spy.

The ______ Arm (Your Design Here)

DU students and Misty

Students at Denver University work with their own version of a gripper arm for Misty.

It doesn’t stop there. We’re releasing design files for Misty’s arm sockets, along with all the specs developers should keep in mind as they design custom hardware for Misty. Files for some of the arms in this post (and several other attachments) are already available on Thingiverse, and these experiments just touch the surface of what’s possible. The real fun starts when Misty puts her arms to the hands of the developer community.

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