Getting started

To keep these instructions simple to use, I’m focusing on the assembly rather than an in-depth explanation.

If you have specific questions on “why” rather than “how”, please post on our Petoi robot forum at or write to info@petoi.com.

You can support us by shopping at Petoi coding robot shop. Our social media (Instagram/Twitter/Facebook/GitHub) account is @PetoiCamp. Share your build with us by tagging #nybble #petoi #opencat so we can repost it for you!

1.1 Preparation

Prepare a clean desk and some small boxes to unzip the package. Take a picture of the kit contents in case you lost something later.

1.2 Tools and accessories

The actual kit contents and packaging method may be adjusted as we improve the product. This instruction will keep consistent with the current namespace.

Newest kit contents:

Early kit contents:

2.1 Cut body pieces off the baseboard.

There might be some tar residue on the wooden pieces from laser cutting. Use a piece of wet soft tissue to clean up the board.

The functional pieces are attached to the baseboard by lightly cut tabs. Though you could pop those pieces out by hand, it’s very highly recommended that you use a knife to cut on the backside of the tabs to avoid potential damage to the middle layer, where the fiber direction is perpendicular to the surface fiber.

After taking out all the pieces from the baseboard, you are encouraged to bend and break the remaining structures on the baseboard, to understand the mechanical properties of plywood, such as anisotropic strength, elasticity, etc. That will give you confidence in later handling.

2.2 Remove pointy fibers.

Use the sanding foam to clean up any thorns on the pieces. Don’t sand too much, or it may affect the tightness between joints.

2.3 Screws

There are five different screws used in the kit. I’m coloring them differently to indicate their locations better. Not all screws are required to assemble Nybble. Not all holes on the puzzle pieces need screws. Observe the assembling animation carefully to locate them.

● A is for attaching servo arms. D (sharp tip) is for attaching servos to the frame. A and D come in each servo's accessory pouch with plastic servo arms.

● B is for attaching servo arms/circuit boards to the frame.

● C (flat tip) is for binding the thighs.

● E (always the longest) is for attaching the battery holder.

2.4 Springs

There are three different springs: F, G, H.

● The eight spring F is used for elastic connection in the thigh. There’s one spare unit.

● The hard short spring G is for the neck

● The soft short spring H is for attaching the battery holder.

2.5 Servos

We are switching to a new servo manufacturer from recent batches. Previously, MG92B was used for the four shoulder joints. MG90D was used for other joints.

The new servos are differentiated by their cable length. Shorter cables are used for the neck, tail, and four shoulder joints. Longer cables are used for head tilting and the four knee joints.

3.1 Head and neck

3.1.1 Part list

3.1.2 Prepare ultrasonic sensor

We include an ODMed ultrasonic sensor with RGB LED in the Nybble kit. It doesn't require soldering, but you need to trim off the plastic clip residue of the connection wire on the head's end.

You can download the demo code at https://github.com/PetoiCamp/OpenCat/tree/main/ModuleTests/testRGBLedUlrasonic

BelowT is a tutorial video:

With the basic distance detection and some proportional reactions, you can achieve the following demo:

3.1.3 Trim the servo arms for attaching servos.

Most of the servo arms on the model are trimmed from the cross-shaped arm I. Since there will be more unused straight arms, you can practice trimming with them first.

An alternative method to trimming is using a half-burned knife to cut the plastic parts off. Leave a little bit longer because melted plastic will have a rounded edge.

As we switched servo suppliers, the servo arms also changed a little bit (as shown below). To reduce confusion, the servo arm I can be used for most of the joints, just trim it accordingly. Servo arm K is used for the tail. Servo J can be omitted.

3.1.4 Assemble the head group.

Watch the head animation to understand the assembling process, but don't assemble them all at once. Every part that connects to the servo's output shaft should not be fixed before calibration.

Notice how the servo wire is organized in the head.

3.2 Body

3.2.1 Part list

• NyBoard only

Note that without the Raspberry Pi, the NyBoard is mounted to the underside of y1 with the servo connections facing downward. In later versions, the y1 piece is designed to be symmetric so that both ends have two screw holes.

• NyBoard with Raspberry Pi

Use y1Pi to replace y1, and add Pi Stand. Pay attention to the location of the pink pieces. Note that with the Raspberry Pi, the NyBoard is mounted on top of y1Pi.

• Other controllers

I also included 5 x 1”/4 nuts for mounting other circuit boards.

3.2.2 Install the adjustable battery holder to the belly

After June 2022, we start to equip Nybble with a rechargeable Li-ion battery pack. It's also available at our online store if you get an earlier version of Nybble with a battery holder. Please add a note if you need the 3D-printed belly as well.

3.2.3 Assemble the body group

Pay attention to the long pins of the infrared receiver and FTDI port. They are designed to be bent in favorable directions. Don’t bend the pins too often or it will lead to metal fatigue. Observe the adjusted configuration if you want to mount a Pi.

Assemble the body group as shown in the body animation.

3.3 Shank

3.3.1 Part list

3.3.2 Attach the rubber to the tip of the shank.

The serrated structure on the tip of the shank is already good for walking. The rubber toe is optional to increase friction and soften each step.

3.3.3 Insert the servo into the slot on the shank.

Pay attention to the direction that the wire is twisted. The small dent on the long edge is designed to let the wire go through. Think about the symmetry of the four legs. Assemble the shank as shown in the shank animation.

3.4 Thigh

3.4.1 Part list

In later versions, we will use plastic pieces for thigh2.

3.4.2 Trim the servo arms for attaching servos.

The location has been shown in the Head and Neck section. The trimmed narrower servo arm is designed to be inserted into spring F.

3.4.3 Assemble the thigh.

Before closing thigh1 and thigh2, put the wire of the shank through the slot in the middle of the thigh. Think about the symmetry of the four legs.

When installing the screws, pay attention to the directions you insert them.

The servo arm should be able to slide in the track on thigh2 with subtle friction after thigh1 and thigh2 are screwed together. You can tune the tightness of screw C to achieve proper friction. If you need more control over the tightness:

• Scratch the track using a flat screwdriver to reduce friction.

• Apply a little paper glue to the track and let it dry to increase friction.

Assemble the thigh as shown in the thigh animation.

3.5 Tail

3.5.1 Part list

3.5.2 Assemble the tail.

The screw D is installed in the third hole counted from the center of the servo arm K. Pay attention to the order that every piece is stacked. The wheel (tail2) should be able to rotate with little friction, and the whole tail should be able to tilt by a small degree.

Assemble the tail as shown in the tail animation.

4.1 Joint map

Nybble's servos are connected to NyBoard's PWM pins symmetrically and resemble the nerves along the spinal cord. Though Nybble doesn't have shoulder roll DoF, those indexes(4~7) are reserved for the full OpenCat framework.

4.2 Plug in the servos

Even though the PCB layouts vary on different NyBoards, the wiring pattern is the same. You don't need to read the indexes of the servo pins when plugging the servos. The joint mapping is done automatically in the OpenCat code. You just need to select the right board version when uploading the code.

4.3 Wiring

4.3 Prepare for calibration

Install the head, tail and leg components as following picture:

You can install the legs with the reference of a triangle ruler or the L-shaped ruler included in the kit.

4.4 Wiring

After calibration, troubleshooting and final assembling, It’s time to think about wiring routes to make Nybble look neat. There are multiple slots on the frame designed as a wire organizer. Feel free to develop your own style for connecting future accessories. Make sure the wires don’t get in the way of the servos‘ movement.

Below are the wiring routes.:

NyBoard V1_* :

There are two methods to config the NyBoard:

• The simplest method is to use the Petoi Desktop App. No programming is involved. You can play with some preset modes.

• If you have some programming experience, you can use the Arduino IDE. You will be able to modify the open-source codes for your new projects.

If you are using the BiBoard, please refer to this Arduino configuration instruction.

• The simplest method is to use the Petoi Desktop App.

• If you have some programming experience, you can use the Arduino IDE.

The joints of the robot have to be calibrated before future use. Make sure all the servos are connected to the right spot on the circuit board in the right direction, the battery is powering (the yellow LED in the cat's logo is lighting up), and all the legs and head/tail are NOT attached to the servos so that the servos can rotate freely.

Our calibration routine will send a calibration signal to the main board and rotate all the joints to known positions. Then you can attach the legs close to the reference posture, and fine-tune the angles using the software.

There are three methods to calibrate Nybble:

• Use the mobile app Petoi.

• Use the Petoi Desktop App.

• Use the Arduino IDE.

See the Getting Started guide.

There are 4 methods for users without any programming experience to control Nybble:

• Use the IR Remote Controller.

• Use Petoi Mobile App.

• Use Petoi Desktop App.

• Use Petoi Coding Blocks.

If you have some programming experience or want to explore more advanced features, you can try the following methods:

• Use Arduino IDE.

• Use Python.

• Use MicroPython.

• Use ESP8266 + Python.

• Use Raspberry Pi.

• Use the extensible modules.

8.1 Understand skills in InstinctNybble.h.

8.2 Example InstinctNybble.h

8.2.1 Defined constants

8.2.2 Data structure of skill array

8.2.3 Suffix for indicating Instinct and Newbility

8.3 Define new skills and behaviors

8.3.2 Add more skills in InstinctNybble.h

There are two ways to create new skills for Nybble:

• Use the Skill Composer in the desktop app

• Write Arduino code

🔬It will make another textbook.

The controlling framework behind Nybble is OpenCat, which I've been developing for a while. You can read more stories from my posts on Hackster.io.

It's too much work for now 🤷🏻‍♂️ but you are welcome to discuss it with me on the forum or through email. Good thing is, I will keep the code compatible with future OpenCat models, and even your own DIY robots! Hopefully, the documentation will be completed during the processes.

Please refer to the Extensive Modules in the Doc center.

To be written by 👉 YOU!

Share your knowledge and creativity with the community at https://www.petoi.com/forum.