BπBO: My New Mecanum Wheel Droid Has Arrived

Added: 2026-05-31

[00:00:00]I built a droid that can drive sideways, tilt its head, and look you in the eye, all on ROS 2.

[00:00:08]Let me introduce you to B Pi Bot.

[00:00:12]I've been inspired here by my success with Rex B1, my other droid project, and the work I did on the Mecanum wheel drive.

[00:00:21]You might remember that from an earlier video.

[00:00:24]Thinking about the examples of Mecanum drive droids, particularly in sci-fi, I got drawn to um B2EMO from the Andor TV series. You remember that? This is a very much inspired, rather than screen-ready replica. After all, B2EMO is really a remote-controlled puppet, and I wanted a bit more autonomous capability here. So, different things.

[00:00:52]The central control system for a B Pi Bot is the Robot Operating System, and that really sits on a Raspberry Pi 5 for me. Not actually a 4 as in this photo, but uh a 5. And then that's talking out to a number of um microcontroller-based uh control boards. They're all based on RP2040s or RP2350s, and they control all of the subsystems like the motors, uh the head motion, the servos, the lights, well, everything.

[00:01:24]And we'll talk about those as we go on.

[00:01:27]Um and the interface between those two is something called micro-ROS. And I've looked at micro-ROS and a set of videos before, so I won't talk too much about it, but um it really just allows us to take this whole topic publication strategy of uh distributing messages around the world um into the world of microcontrollers from the world of ROS, and gives me access to that reliable communication.

[00:01:54]Now, in actual fact, on this robot, uh one board was not enough and one Raspberry Pi was not enough. So, I've actually got two. And the reason for that, you'll see as we go along, is basically the head rotates and running data signals up to the head through a slip ring proved challenging and problematic, which I kind of expected. So, these two boards uh Raspberry Pis actually talk by Wi-Fi and they share the Ross messages across by our Wi-Fi. That uh the Raspberry Pi 5 also allows me to do some other tricks and I'll talk about those when we get to talking about the eyes within uh the Pi-Bot.

[00:02:39]Of course, for this demo and this video, I'm actually controlling all of this just using a DualShock 4 from Sony uh and it's talking via Bluetooth into one of the Raspberry Pi 5s. That isn't a long-term plan, but that at least allows me to explore the capability of the droid before I start automating stuff.

[00:03:00]So, let's talk about the drive system.

[00:03:03]It's important we can actually move the Pi-Bot around and we can. He's based on this uh chassis that I had already had and I looked at with these mecanum wheels and it's driven by four JGB37-520 motors. And that's what we're going to use as the main power house for for driving him around.

[00:03:28]And he suddenly can drive then in any direction.

[00:03:32]But, you know that cuz I've looked at this uh chassis before. And in fact, I built this quad motor controller to do just that and we explored that in a previous video. And this uses two 88236 dual motor controllers. And the reason it does it uh uses that is so that I can nicely integrate that onto a single circuit board and use uh basically daughter boards on that to control it.

[00:03:59]And that I works really well, and I explain um a lot of that in in this other video.

[00:04:06]The way of controlling it uh and being able to move in any direction, well, any direction on the ground, that is, um I explain in this other video where we show how we can take twist messages saying move uh linearly on the X or the Y axis and angularly on Z, so rotate, and how there's a whole bit of mass that we can do in order to actually control it and actually give us the ability to move these devices around and give us, you know, life for our droid.

[00:04:43]Before we dive deeply into the robot build, a quick thank you to today's sponsor, wolfSSL.

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[00:05:10]wolfSSL provides a lightweight, high-performance TLS and crypto library designed specifically for embedded systems.

[00:05:19]It runs beautifully on microcontrollers, small single-board computers like my Raspberry Pis, or anything you typically use in a robot.

[00:05:28]With wolfSSL, you can encrypt control messages, secure your Wi-Fi or cloud connections, and protect sensitive files or configuration data without slowing your system down.

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[00:05:53]But, it's not just about moving around.

[00:05:56]We also have a head on this droid, and that head is actually controlled with the ability to rotate it and to raise it and tilt it, which is really quite neat and quite nice.

[00:06:09]And that's all driven by a Stewart platform or a simplified Stewart platform cuz I'm using three servos to actually give me the ability to raise and tilt that head.

[00:06:23]And they're bus servos from Hiwonder, they're LX-224HV's, and they work really well. And I've looked at these before cuz we did look at a video about the Stewart platform and how that works.

[00:06:37]And the controller I'm using for this is actually one that I built for REX-P1. Um and didn't really use significantly. I used it a bit, but not significantly because I moved away from using these sorts of uh bus servos in the first version of REX-P1.

[00:06:57]Now, the whole Stewart platform and the head, of course, rotate, which means I couldn't actually run all the control systems uh from the main boards and the main chassis. So, they're all actually sitting inside the head, and there's another Raspberry Pi 4 sitting in there, which actually provides then comms to the main Raspberry Pi 5.

[00:07:17]Um it's also going to run a camera, and I'll tell you about that in a minute, but it's really for this bit of the story about providing connectivity to my servo control board, and it's that servo control board then then lifts the head and allows us to do all those motions.

[00:07:34]Now, this servo control board is the same servo control board that's sitting inside REX-P1. It's actually rotating the dome in there.

[00:07:42]And um I've done another video talking about how that board actually controls bus servos directly and how all of that works without needing to use any of the intervening driver boards. So, if you want to know about those, go check out those videos.

[00:07:59]The head rotation for B Pi Bot is actually based on a stepper motor and it's on a completely separate control board. Cuz this control board actually down on chassis level and actually controls the whole thing from there.

[00:08:15]And it's basically using a NEMA 17 uh stepper motor and a DRV8825 uh stepper motor controller. And that stepper motor controller happens to be sitting on an identical board to the one that's actually controlling the bus servos. Cuz actually I put both of those capabilities on the board. But um yeah, they are two separate boards and two separate places on the board.

[00:08:41]Um I use the same board and the same uh DRV8825 to control the dome in Rex B1. And I've previously talked a bit about that story.

[00:08:53]Also in the head, we have two eyes. Um they're different sizes, much like um B2 Emo from uh Andor. And uh they are basically just LED WS2812B LED rings. And we've looked at those before on the channel. In fact, I did a whole video where I showed how you can actually animate different patterns on these sorts of rings. And I've done some other clever stuff on that. Um I actually have a course that goes through how to drive these in some detail over on the Udemy platform that you might be interested. It's called the MicroProjects course for the Pico. Um and that's a good place to to leap off from into this journey if you want to play these sorts of games. Now, for B Pi Pi, this is based on the same controller board that I'm using in the head to control of those bus servos for lifting and tilting the head. And they're of course connected to a Raspberry Pi 4, which I'm using for comms to connect it to ROS. Now, that allows me to also place a camera in the head. And so I've got a Raspberry Pi camera up there, and that Raspberry Pi camera is actually sitting in the middle of one of those LED rings.

[00:10:16]And you can just see it's the little cutout I've put into the front lens disk. So, that's we can actually take forward pictures. So, that's quite useful, and I may do more stuff with that as time goes on. I might actually even look at replacing it with one of the AI cameras from Raspberry Pi. Um, what do you think? Do you think that's a good idea? What do you think of those AI cameras? Let me know in the comments.

[00:10:46]Power.

[00:10:47]With a Raspberry Pi 5, a Raspberry Pi 4, um, these servos, the stepper motor, the motors to drive him as round, and a bunch of LEDs, he's going to be consuming quite a lot of power.

[00:11:02]And therefore, to handle all that, I'm going to need some fairly chunky batteries. And I'm going to once again use these LiFePO4s, 6 amp hour batteries that I used on Rex Pi 1. Now, that's really good strategy for me, because it means that I can actually use the same uh control structure for power management that I'm going to use on Rex Pi 1. So, I'm actually using the same relay board that actually controls the power, so I can choose whether I get power from each of the batteries to either the electronics or the motors.

[00:11:40]I can actually uh choose to also take power from USB.

[00:11:45]Um I can monitor the batteries state. I can monitor the voltage coming from those batteries and the amps being uh released and used on from those batteries all the time.

[00:11:57]And I can even have a separate charging board, which is actually allows me to charge the batteries in situ.

[00:12:05]Plus the ability to actually use USB-C PD to actually power the unit. And that's I've talked about at some length in a video on the RockPi 1 droid's Lifeboat 4 journey.

[00:12:19]The one that I haven't talked about, which is the board that's just on the top here, is actually the charging board. And I do need to do a video about that, and that's coming soon. There's just a few bits more work I want to do on uh understanding how all of that works before I start explaining to you.

[00:12:38]But it's already actually sitting on BPi Bo, and actually providing me to uh USB power to actually run the whole unit on my desk or indeed put those uh batteries onto charge.

[00:12:52]So, a demo. Meet BPi Bo, my uh new droid.

[00:12:59]At least partial project. We can rotate its head, we can lift its head, and we are able to tilt its head either uh to the side or front forward and backwards, as well as of course um drive him around. So, he is already a completely mobile uh capable little droid. Now, everything at the moment is being driven by me remote controlling him. There's not a lot of automation on there yet, but that's all stuff that I want to get into. First of all, let's make sure we understand the capability of how he can move, the limitations, and then I need to add a little bit of bodywork as well, I think, cuz we've got rather a lot of boards exposed, but he's certainly on his journey.

[00:13:50]Beep-Boop has come to life quite quickly, and that's because there's a lot of carryover from Rex B1 design.

[00:13:58]Though they look nothing like each other, a lot of the subsystems are based on the same code or very similar code bases and the same PCB designs.

[00:14:09]Yes, there's a lot more to do, including a full body case.

[00:14:14]Right now, I'm checking his capabilities out and starting to refine the control systems.

[00:14:20]So, make sure to subscribe so you can keep up with the journey.

[00:14:25]And why not check out Rex B1 project, too, my other droid? Link's right here.

[00:14:31]See you on the next build.