Open source Lego Technic battery box controller - LBX

[legomen]

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.

 

[Toastie]

Hi @legomen,

wow, this is a really educated approach! All things integrated that are >relevant< - as it tackles nearly all the "issues", which came up over the recent years if not decades.

But this is more a >powerful PF/PU controller< than (just) a battery box!

Open source = best firmware/software development possible.

Everything else: Totally cool!

All the best
Thorsten   

[Wapata]

10 hours ago, legomen said:

. I have deliberately omit battery cell cover in favour of easier replacing of batteries

I wonder if puting only batteries connectors (power and the other) can be a great idea for a variant product... Or if people will put way to big batteries 

 

It's a great design you have made here !! Is it a USB C port in the side ? 

[legomen]

Just now, Wapata said:

I wonder if puting only batteries connectors (power and the other) can be a great idea for a variant product... Or if people will put way to big batteries 

I do not understand what you mean with that.

 

1 minute ago, Wapata said:

It's a great design you have made here !! Is it a USB C port in the side ? 

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:)

[Wapata]

Big batteries pack have a power output and an output to check each cell individually (I'm not finding the English word right now) so instead of have a cell holder, one can put a very big battery pack.

[legomen]

Just now, Wapata said:

Big batteries pack have a power output and an output to check each cell individually (I'm not finding the English word right now) so instead of have a cell holder, one can put a very big battery pack.

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.

[Wapata]

Okay, it was just an idea floating around 

10 hours ago, legomen said:

NO Android or Iphone app

I hope you will make others devices like this one to control more outputs of on or the other type of connector. I'm soooooo disappointed by the lego compatibles apps. 

How can an output can be attributed to one or an other input of a gamepad controller by the way ? Do multiple devices can be connected to a single gamepad ? Are we only talking about the last Playstation and Xbox pads or there is a list somewhere (... I ... I Have wiimote with nunchuk  )

[legomen]

3 minutes ago, Wapata said:

How can an output can be attributed to one or an other input of a gamepad controller by the way ?

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.

 

5 minutes ago, Wapata said:

Do multiple devices can be connected to a single gamepad ?

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.

 

7 minutes ago, Wapata said:

Are we only talking about the last Playstation and Xbox pads or there is a list somewhere (... I ... I Have wiimote with nunchuk  )

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? 

[2GodBDGlory]

Ooh, I think there's some smart design choices here! I love the usage of 18650 cells! More pinholes would be great, but if there's not the internal space for them, it's not worth making it larger to incorporate them.

Will the firmware have support for at least basic servo modes for PU motors?

I'm looking forward to seeing progress on this!

[legomen]

6 hours ago, 2GodBDGlory said:

Will the firmware have support for at least basic servo modes for PU motors?

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

[gyenesvi]

I'm not sure I understand some design choices here.

First, this is not just a battery box, this is a controller unit. It just happens to have the battery integrated into it (halfway). By the way, it looks like those batteries would just fall out while driving off-road. Or do you plan to have a bottom? (I think you imply intentionally not). And why are the PF and PU ports on the same end? Won't they be in the way for each other in terms of internal (and external) wiring? Also, plugging the PU plug in from the long side is not the greatest position as it makes it even more space hungry and hard to integrate. The 10 stud size of this design is not a great match for technic builds, as even numbers are preferable. For example, batteries are often built in so that their longest edge goes sideways. That way the 10 stud size would effectively take up 11 studs of space, which is getting too much for many models.

Second, in many models, the battery has to be built deeper inside the model in a way that it's hard to take it out, so on-the-field replacement is not really possible. It's easier to make the recharge port easy to access. I'm also not much of a fan of those 18650 cells as they waste space because they are cylindrical. Flat LiPo cells are more space efficient, and they are not just for RC, but for anything rechargeable, so not sure why their use with Lego would be somehow different or worse than the use of 18650 cells.

Also, I guess the ESC  integrated into the motor also becomes a weird choice at this point. At first I thought that the rationale is that this way it can be integrated into the PF system. But then you realize that that's not going to work because the Lego batteries cannot provide the power anyway, so you design a battery as well, which turns into not just a battery but a control unit as well. At this point the ESC could be in the main unit too. Furthermore it is kind of pointless to use PF plugs that are known to melt under higher amps, which your motor will be drawing..

I guess next thing you'll realize is that PU servos are slow and imprecise, and GeekServos would be better ;) And that a pistol controller is far easier to control than an Xbox controller. At which point it's just easier to use proper, readily available RC electronics ;) (configurable ESC and receiver). Basically what I am saying is that if you redesign more than half of the system (motor, battery, control unit), then it's pointless to keep some parts of it (plugs, servos) that just keep you back (and better alternatives exist already, like GeekServos). It seems better to design the whole system from scratch.

What I think would actually be useful is a proper standalone battery unit. That is only that, a battery unit, has a charging port with a balancer, and an output plug that can take high amps. All in a slim, space efficient form factor. Or various form factors for different sizes / voltages.

[legomen]

7 hours ago, gyenesvi said:

First, this is not just a battery box, this is a controller unit. It just happens to have the battery integrated into it (halfway). By the way, it looks like those batteries would just fall out while driving off-road. Or do you plan to have a bottom?

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.

7 hours ago, gyenesvi said:

And why are the PF and PU ports on the same end? Won't they be in the way for each other in terms of internal (and external) wiring? Also, plugging the PU plug in from the long side is not the greatest position as it makes it even more space hungry and hard to integrate. The 10 stud size of this design is not a great match for technic builds, as even numbers are preferable. For example, batteries are often built in so that their longest edge goes sideways. That way the 10 stud size would effectively take up 11 studs of space, which is getting too much for many models.

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.

7 hours ago, gyenesvi said:

Second, in many models, the battery has to be built deeper inside the model in a way that it's hard to take it out, so on-the-field replacement is not really possible. It's easier to make the recharge port easy to access. I'm also not much of a fan of those 18650 cells as they waste space because they are cylindrical. Flat LiPo cells are more space efficient, and they are not just for RC, but for anything rechargeable, so not sure why their use with Lego would be somehow different or worse than the use of 18650 cells.

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.  

7 hours ago, gyenesvi said:

Also, I guess the ESC  integrated into the motor also becomes a weird choice at this point. At first I thought that the rationale is that this way it can be integrated into the PF system. But then you realize that that's not going to work because the Lego batteries cannot provide the power anyway, so you design a battery as well, which turns into not just a battery but a control unit as well. At this point the ESC could be in the main unit too. Furthermore it is kind of pointless to use PF plugs that are known to melt under higher amps, which your motor will be drawing..

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.

7 hours ago, gyenesvi said:

I guess next thing you'll realize is that PU servos are slow and imprecise, and GeekServos would be better ;) And that a pistol controller is far easier to control than an Xbox controller. At which point it's just easier to use proper, readily available RC electronics ;) (configurable ESC and receiver). Basically what I am saying is that if you redesign more than half of the system (motor, battery, control unit), then it's pointless to keep some parts of it (plugs, servos) that just keep you back (and better alternatives exist already, like GeekServos). It seems better to design the whole system from scratch.

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. 

[gyenesvi]

1 hour ago, legomen said:

The cables are then taking space on upper direction.

In my experience that sounds like the best direction, because typically it's the direction that's not blocked by anything.

1 hour ago, legomen said:

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.

I agree that it's overpriced and I would not buy more just to be able to replace them in the field. Usually I'm just okay with playing until the battery goes down. Unfortunately the Buwizz goes down quite fast. But actually, a 450mAh LiPo lasts more than an hour with a brushless motor in a smaller model. For larger models, a 850mAh battery was more than enough for me, lasting more than 1 hour.

1 hour ago, legomen said:

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.

I did not know they can withstand that much.

1 hour ago, legomen said:

The problem with PF connector is that people are stacking motors on the same connector and then they have a problem.

Do you know why that becomes a problem?

1 hour ago, legomen said:

But GeekServos are using RC protocol to control them. They are not Lego world.

I don't understand why/how you see a difference between using RC servos and brushless motors. It's just a matter of signal conversion; a different technology. The same way your ESC converts the PF signal to control the brushless motor, the PF signal can be converted to a servo signal, and one guy here on EB made a quite small custom converter board for that exactly. Even the PF servo has some kind of a signal converter inside it, no?

But the good thing about RC servos, is that they work straight off the signal of an RC receiver. So you solve two problems at once; having a good quality controller (transmitter), and a precise steering control. Plus you can control 2-3 servos off of a 4/6 channel receiver. So for me it was a no-brainer to use them. Their downside is the closed communication protocol, I agree with that..

1 hour ago, legomen said:

Please don't get me wrong. I appreciate everyone opinion. 

Sure, I'm also curious about and appreciate your views, so it's good discussion :)

[legomen]

8 minutes ago, gyenesvi said:

Do you know why that becomes a problem?

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.

17 minutes ago, gyenesvi said:

I did not know they can withstand that much.

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.

[legomen]

31 minutes ago, gyenesvi said:

I don't understand why/how you see a difference between using RC servos and brushless motors. It's just a matter of signal conversion; a different technology. The same way your ESC converts the PF signal to control the brushless motor, the PF signal can be converted to a servo signal, and one guy here on EB made a quite small custom converter board for that exactly. Even the PF servo has some kind of a signal converter inside it, no?

But the good thing about RC servos, is that they work straight off the signal of an RC receiver. So you solve two problems at once; having a good quality controller (transmitter), and a precise steering control. Plus you can control 2-3 servos off of a 4/6 channel receiver. So for me it was a no-brainer to use them. Their downside is the closed communication protocol, I agree with that..

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.

[Wapata]

Well... Can't you also add two classical RC connectors output ? One could use a normal servo motor and why not a normal esc with at the same time 2 Lego motors of each types ? 

I mean... Theses 3pin connectors don't use too much space and a normal servo motor is a great option to have.