legomen

Sorry. It is not an open source design, yet. I am using DRV8317 driver.

I agree with you that it is simply a matter of conversion. If there would be a servo motor with PU or PF connector and RC servo inside, I would use it. But there is not. GeekServo has 3 wire connector capable of connecting to RC radios directly. It can't be connected to the Buwizz or LBX or Lego Control box. People is using those Lego compatible boxes. My ESC is using PF signals to control the motor and from the user point of view, the LMX motor is completely replacable with Lego L Motor od Cada motor. But on the other hand, LMX has higher RPM and torque. And that is what I want.

When you stack PF connectors, the current through the first connector multiplies. So for example, you connect two Buggy motors on the same PF output, the Buggy motor can draw over 3A and then you will have >6A on the connector. Each PF connector has some impedance, which is not neglible and when you square the current and multiply it with the connector resistance, you will get a considerable power (remember you are squaring the current). The same goes with wires. Lego PF wires are 26AWG, I think. They can withstand 2A continuosly and even higher with short bursts. If Buggy Motor is not burning them, I think LMX will not too. Have you seen the battery wires inside the Buwizz? And now imagine you put two Buggy motors on Buwizz and 4 L PU motors on other 4 channels. It all goes down on internal battery impedance, which I asure you is not so small. And have a look to hpl502852-5c-3s1p battery specification (which I think it is used in Buwizz). That battery has BMS integrated and it will disconnect the battery at around 7A. But in that case the battery chemistry is already damaged, IMHO. There are also 8 PF channel Chinese batteries with 1000mAh inside a very small case. I would not dare to connect all of them at the same time:) This why, I chose 18650, because some cells are rated up to 30A of discharge, although 10A should suffice. I know, connecting them is another problem on its own and distributing that power to the ports.

You are right. It is a control unit with a battery box. Nowdays almost all battery boxes are control units also. Replacing the batteries in the model is one of the requirements, so without bottom (it is easier to take out the battery box and replace batteries) . Battery holder is usually tight enough that the batteries will not fall out, but normally the battery is not hanging from the model, it is sitting in the model, and thus batteries are supported somehow. Yes, I am also thinking to have a closed design, but this will come later maybe. PF and PU ports are on the same side because on the other side is a charging port. I have decided to use PicoW board for the first prototype and this limits thing a bit. Pico is a large board with USB on the side and needs to be put somewhere. With full custom controller board, price and development time could become an issue. Regarding the PU orientation, it depends how you look at it. Even Buwizz has one PF and two PUs on the same side, although they are looking upwards. The cables are then taking space on upper direction. If I am honest , I am designing LBX to be put into Formula 1 model, where battery would be sitting in the middle and two motors behind and everything should be placed as low as possible. Maybe this subconsciosly influenced on my decissions:) 10 stud limitation comes from the battery size itself. Regarding the size is like this: you can't have large energy reserve without sacrifing space. If you have tighter space requirements, go with Buwizz or Chinese clones. I am not trying to compete with them. If you put the battery deep into the model, so it can not be removed easily, then you need to buy quite a lot of batteries. In the case of Buwizz, this means a cca. 200 euros per model. I do not know for you, but for me is too much. My design decision was that one can reuse the battery for many models, but then again one need to design a model for easy access of the battery. 18650 cells are used everywhere (power tools, laptops, etc) and they are cheap. Yes, also RC pouch LiPo are good, but they come in different sizes and with different connectors. To get exactly right battery for my battery box is actually not as easy as it sound. And then you need to integrate the battery into a casing and when it needs to be replaced, you have problems. Tak a look at Buwizz. Quite a lot of problems with dead batteries I am hearing about. With 18650, everyone can buy a battery and replace it. Try to replace a Lipo in a delicate LTehnic model where connectors are so tight that when you pull it appart, everything goes flying. I did not say that my LMX motor is not working with other batteries. I am actually using it with original Lego Battery box and SBrick. It does not draw so much current that connectors are melting. PF connector can withstand 5A current easily. The problem with PF connector is that people are stacking motors on the same connector and then they have a problem. Why are they doing that? Because they can. I am designing a new battery box (controller) because I am not satisfied with existing solution. To drive 2 or more LMX motors you need much more power then you can get from single existing battery box. Also using thos controllers with Andorid or IPhone app is not for me. I like to drive them directly without an app in the middle. And lastly, because I took some satisfaction to design new things. Maybe you are right, maybe you are not. But GeekServos are using RC protocol to control them. They are not Lego world. For me, it would be much easier to develop a battery box controller with RC radio and RC servos and RC ESC. But this is not a point here. As I mentioned before mixing RC world and Lego Tecnic is like putting Marvel superheroes and Disney characters in the same movie Wonder what would happened? Again, for those who want a RC motors and Control, they can 3D print motor housing, put a LiPo battery and cheap ESC into a model and enjoy it. But this is not for everyone. Please don't get me wrong. I appreciate everyone opinion.

Of course. That is the whole point of having PU ports. For servos.

Good question. There are numerous ways to do it. Firmware can have a special button on a gamepad dedicated to enter programming mode. Or a simple tty console on an USB port for programming. Anothe great one. I was thinking of that also. The easiest way would be to have one device as a slave to another. Master will be connected to the gamepad and channeling commands to the slave. Firmware would be supporting not just Playstation or XBox, but also other devices, if those are supporting universal Joystick protocols. There are some devices with proprietary protocols and those would need to be supported through firmware change. This way open source:) IMHO, mixing RC world and Lego Tecnic is like putting Marvel superheroes and Disney characters in the same movie Wonder what would happened?

Ok, I understand now. You mean a LiPo pack connector, like one used in RC world. Well, it is an option, but I think somehow against my principles to not use stuff from RC world in Lego Technic. If the battery would be encapsulated in the casing (like Buwizz), maybe. On the other hand, 18650 batteries are way easier to use, they are powerful (if proper type is used) and easily replacable.

I do not understand what you mean with that. No, it is an USB Micro. This is due to a fact that I am planning to use RPi Pico W for the main controller board. Why Pico? It is cheap and available. It has a good roadmap. I would also prefer USB-C. Maybe in the future:)

Hi Eurobrickers, Recently I have decided to develop a new battery box with controller for Lego Technic stuff. An idea emerged when I was developing brushless L Motor with integrated ESC, i.e. LMX (Lego Motor eXtreme) This motor demands more powerful power supply then ordinary Lego battery can provide. There are of course alternatives to Lego battery (e.g. Buwizz), but this motor can have even higher peak current than those batteries are comfortable with. So I have decided to set some basic requirements for the new battery system: 1. Replacable LiION cells. One can swap batteries in the field with new charged ones when needed. Look, a whole day of playing with Lego:). For storage, just remove the batteries and no worries. 2. 2S battery topology. Peak 8.4V, because most brushless motors of this size are specified for this voltage. 3. 2xPF connector and 2xPU connector. 2 LMX motors and 2 PU motors, acting as servo or not. 4. Full BMS and Charger integrated. 5. Open Source Firmware - direct connection to standard game consoles or phone (acting as console). 6. No, and I mean NO Android or Iphone app. Those apps need to be regulary updated and who has time to do it;) 7. Low price - of course. I came up with preliminary design and look for the new battery and I would like to discuss pros and cons. This is my first iteration of mechanics. Some details are still missing. I have deliberately omit battery cell cover in favour of easier replacing of batteries in the model. And it looks cool IMHO, especially with some fancy cells:) I chose the LiION cells instead of pouch LiPo due to high current demand and obtainability. Also 18650 format is somehow standard and you can buy those cells almost everywhere. Battery pack is 10x5x4 studs, a little bigger then Buwizz, but it has more then twice of energy (with 3000mAh cells 25Wh). Have fun.

Thanks. Yeah, this why I am now working also on my own battery, although Buwizz should have enough power to drive it.

And here is the test rig for the first prototype. I have used this rig to test Lego L motor and compare the speed with Brushless L motor. Later is more then twice the speed. The bottleneck here is the battery. Because of the voltage drop, the motor has only 6V to work with. Need to try it with Buwizz at 11V. That will most surely speed things up. I have decided to design a NEW battery system to be used with my brushless motors. It is in the working:)

It is using standard PF PWM signal to define desired RPM (in both directions). 100% duty cycle means highest rpm and 0% is stop. PF has two signals, one for each direction. The ESC is using FOC algorithm in order to maximize efficency at every RPM. From theory of FOC, the most problematic is startup, because the motor is sensorless and FOC can not estimate the proper rotor angle. For that ESC is using different technique to start the motor and once it is started it switches to FOC. Motor assembly with Kyosho XSpeed41. Expensive, but very high quality motor. and fresh ESCs.

It is in prototype stage. I am testing it with two different motors. 3500KV and 4100KV. Motor can draw up to 5A, but this are short spikes. Normally, it draws far less current. I do not think the wires are a problem. Also did not notice connector troubles. Motor with an ESC.

L Motor with brushless motor and integrated ESC. The motor uses existing L Motor housing and PF connector. It can be connected and controlled with existing batteries, like Buwizz or even Lego.

Some time ago, I played with an idea how to simplify a remote for kids to play. Food for thought. https://brickshelf.com/gallery/jturnsek/Remote/Motion.jpg