4B Robot

A 6cm 4-legged Ball Robot

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4B (Four-Ball) is a four-legged robot with 12DOF that folds into a 6cm ball! Although tiny it has three linkages on each leg and joints powered by micro servomotors. The overall weight of the robot had to be light enough for these tiny motors to have enough torque and lift it's on weight on at least three legs.

My plan is to also make it roll when folded. But first, 4B needs to take its first steps

4B is a hybrid robot that can be able to both walk and roll. It has three linkages (coxa, tibia and femuer) on each leg which folds into a 6cm diameter ball. That’s smaller than a baseball! To do so, every linkage had to perfectly align into the sphere while leaving space for the battery and pcb.

4B Robot

4B V1.0.rar

4B V1.0 - Gerber FIles, STL Files & Software

RAR Archive - 14.49 MB - 12/14/2019 at 17:49


  • 4B Issues

    Carl Bugeja12/31/2019 at 07:25 0 comments

    In this video I tried to explain all the issues I have encountered while building my 4B transformer robot.

  • First Test with an onboard battery!

    Carl Bugeja12/17/2019 at 21:43 1 comment

    This is 4B's first test with an on-board battery. In this video, I tested how it opens and closes into a ball, the walking algorithm and also a very rough open-loop rolling algorithm.

  • 4B is BACK!

    Carl Bugeja12/14/2019 at 14:57 0 comments

    This is the build video of 4B, a robot i started working on last year but had to stop because of the other projects that I had. This robot has 4-legs with a total of 12DOF, and what's special about it is that it can fold in a 6cm diameter ball!

    The full test video is coming next week :)

  • It's coming back!

    Carl Bugeja10/01/2019 at 21:05 1 comment

    After a long pause from this project, I happy to announce that 4B is coming back! Today I got these fresh new PCBAs! 

    I started this project last year, but I had to stop working on it because of all my other projects that I started 😂 As you know from my last log I had some issues with the soldering of this board. There was an issue with the plating of the old PCB and in fact the programming pads were even getting disconnected with minimal amount of heat (these PCB were order from a very cheap PCB manufacture which I will not mentioned). So now to make life a little easier and gain more time working on my other projects, my new PCB manufacture PCBway offered to sponsor its full assembly!

    Stay tuned for updates

  • PCB Assembly Update

    Carl Bugeja07/21/2018 at 22:49 0 comments

    Today i have continued debugging the pcb for any soldering bugs and test all the circuitry. The pcb ended up weighing 6.5 grams. This includes the programming header. This can be eliminated by designing a programming jig which will definitely be handy to have. 

    For now, i have soldered a temporary battery header until i configure the sleep mode. 

    Unfortunately one of the programming pads got disconnected while doing rework on the BLE module 😐 this means that i have to start over with a new pcb. 

  • PCB Assembly

    Carl Bugeja07/19/2018 at 21:54 2 comments

    All the components have arrived and today i started soldering the pcb! 

    I’m quite happy with the result 🙂 The only issue i have found till know is with the USB socket. For some strange reason the slots for its alignment pins were not generated in the NC drill files. So i had to chop off these pins from the socket and soldered them with the pad.

  • PCBs have Arrived!

    Carl Bugeja06/14/2018 at 18:33 2 comments

    The tiny pcb for my robot project has just arrived! Only a few components remaining to arrive so that i can start soldering the whole board.

    It seems to fit perfectly in place!

  • PCB

    Carl Bugeja06/04/2018 at 23:08 0 comments

    These are the 3d renders of the 36*36mm 4-layer PCB board for the 4B robot. It contain the CYBLE-022001-00, a tiny ble module in a 10*10mm package. The BNO055 IMU which has an internal fusion block and the VCNL4040M3O as the proximity sensor. Servo connector are all placed around the edge, closer to the servo motors. It also has a vertical usb connector and the MCP73831T LiPo battery charger with a status rgb led in the middle.

  • Electronics System Architecture

    Carl Bugeja06/02/2018 at 16:03 3 comments

    So this is where the fun begins. Design all the electronics of 4B on a 36*36mm pcb. To do so I needed to narrow down the number of components to the bare minimum. And these are the main modules:

    • MCU integrated with BLE Module
    • 9-axis IMU
    • Proximity Sensor for z-axis control
    • Connectors for the servo-motors
    • 3.3V LDO voltage regulator
    • USB LiPo battery charger

    The MCU will be responsible:

    • Bluetooth communication
    • Reading data from the IMU and proximity sensor on the I2C bus.
    • Calculating the inverse kinematic equations to actuate the robot kinematic chain
    • Setting out 12 PWM waveforms to the servo-motors

    That's a bit too much to handle for one MCU, but given the available space on the board it has to work.

  • Assembly

    Carl Bugeja06/01/2018 at 05:13 1 comment

    This is the assembly video of the 4B robot:

    I'm quite happy with the way the design turned out. 

    All parts are 3d-printed with nylon plastic and their finish looks beautiful. Some of the linkages feel a little flexible but that can be easily fixed by making a thicker edge. The servo-motor hubs that are integrated with the linkages fit perfect inside the servo splines and the tiny SMF681X-ZZ bearings snaps firmly in place.

    The next step for this project is to start designing the electronics and pcb. Having a custom pcb in place will tidy the wiring mess so that I could test the robot more easily. 

View all 14 project logs

Enjoy this project?



valvertulex wrote 06/20/2023 at 13:45 point

There has been a great deal of value to me in my involvement with the project. Would like to share it with the pickleball vs paddle tennis team so they can also read it and implement something new.

  Are you sure? yes | no

susuguetta wrote 02/15/2021 at 05:11 point

Hi, I am trying to create my own version of this robot. Could you please share the .STEP or  .SLDASM files? 

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[this comment has been deleted]

davedarko wrote 02/04/2021 at 21:20 point

delete this

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deʃhipu wrote 01/31/2019 at 10:47 point

Hi, are you still working on this? There hasn't been an update in a while, so maybe you moved with the project somewhere else? It's such a nice robot, it would be great to see it working!

  Are you sure? yes | no

Carl Bugeja wrote 12/14/2019 at 17:48 point

just made an update :) sorry for taking so long 

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solano.luca wrote 06/19/2018 at 11:19 point

very beautiful. will you share the .stl?

  Are you sure? yes | no

Carl Bugeja wrote 07/15/2018 at 21:45 point

Yes i will after testing the whole thing 

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JuPrgn wrote 09/18/2018 at 18:28 point

Hi do you have some results testing ? Do you still plan to share some files ? I would like to see more details 😉

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Chorcon wrote 06/07/2018 at 13:47 point


I clicked the project and thought to myself "It would be SO cool if he made it fold to a ball!". I then saw the animation in the description. I was positively surprised! :D

Thanks for sharing.

  Are you sure? yes | no

Dan DWRobotics wrote 06/02/2018 at 21:23 point

This is looking awesome. Look forward to seeing it walking and rolling. That IMU is going to come in handy when it comes to getting the legs to gently nudge it around to make it roll.

  Are you sure? yes | no

Carl Bugeja wrote 06/03/2018 at 06:30 point

Thanks :)

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Michael Graham wrote 06/02/2018 at 07:05 point

Very clever i love it! Reminds me of a star wars droidika

  Are you sure? yes | no

Carl Bugeja wrote 06/03/2018 at 06:31 point

Thanks! yes it looks kind of similar

  Are you sure? yes | no

deʃhipu wrote 05/30/2018 at 09:19 point

That looks great! I imagine it could be even able to roll when in the ball form!

  Are you sure? yes | no

Carl Bugeja wrote 05/30/2018 at 16:43 point

Yes it should :)

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