Brushless motors in the lego world - general topic

[Asakbar78]

On 9/2/2025 at 7:58 AM, gyenesvi said:

I decided it's time for me to enter the game :) So here it comes, my first brushless motor! A small one to start with.

A few days ago I bought myself a Bambu A1 Mini 3d printer, and started experimenting with making a housing for brushless motors.

Features

• Dimensions: 3x3x6 studs
• Weight: 34 gr
• Reduction: 24x down-gearing with 2-stage planetary gearbox of PF M motor
• Speed: around 1100-1200 measured RPM, but around 1500 on paper

Design

I decided I wanted to base my design on SurpassHobby 24xx motors, based on the ideas of @HorcikDesigns presented in this thread. For me, the ideal form factor is the 3x3 one, which those motors fit perfectly, and because with a planetary reduction, we can keep that form and get good amount of reduction.

So my key idea was to take apart a (3rd party) PF M motor, and take out the planetary reduction for my purposes. The PF L motors also has essentially the same reduction, but its internal housing has a bigger shape due to the L motors bulge, and so I could not use that. I went on and bought a SurpassHobby 2435 3300 kv motor. When I started looking for an ESC, I came across this super small Injora one, and since I used its brushed counterpart already, and I was satisfied with it, I decided to order one (it can handle 25 A continuous and 60 A peak current, 2-3s LiPo, has adjustable BEC output up to 3A, and is waterproof). I realized that there's an accompanying mini outrunner motor as well, they come in a combo, so I bought that as well (17x21 mm only, 2800 kv). The wiring is really plug and play, you just need a battery with an XT30 connector, and a receiver.

To my surprise, the motor comes with a 11T gear that's a perfect match to the gear inside the PF M motor, so it meshes perfectly with the planetary reduction. Furthermore, it also comes with a couple of 2M screws that I needed for the assembly, so I set out to print a housing for this one first.

The housing consists of 3 parts. First is the front face together with the planetary housing.

Second is the mounting wall.

And the third one is the back cover (it's optional, but good to have). The rear holes serve as ventilation openings, as well as they are inverse studs for mounting.

The assembly sequence is as follows. First, the wall is screwed to the motor from the inside with M2 screws that comes with the motor.

Second, the planetary reduction slides into the two horizontal slots of the wall (the planetary housing has two horizontal tabs on the back to fix it against rotation).

Third, the front face can be screwed on at the corners from the back using M2 screws.

And last, the back cover can be pushed into the slots on the wall mount from the back. It's a really tight fit, so it does not come off.

Optionally, the inverse studs on the back can be used to fix the motor or add further mounting points.

More pictures are available on my Bricksafe.

 

I haven't yet built it into any model, only tested the bare motor. The control is insane, it has super slow startup, it can go as slow as about 1 revolution per 25 seconds, but with enough power that I could not stop it with my hand.. And then it can go up to 1200 RPM. I'm really curious how it will perform in a model :)

 

I am planning to make a similar motor using the SurpassHobby 2435, but of course without the back cover, but first I need to buy some M3 screws for that one. Any ideas where to get them in various sizes?

This is absolutely sick I love it. Please let us know how it goes. 

 

Hi all, I have recently bought the whole starter brushless conversion gear. (A2212, 35A esc, 2x 1500mah lipo 3s, dumborc x6 controller/receiver)

I don't have a 3d printer or anything like that so I was considering just using a worm gear to reduce the speed from the motor. I went with the 930kv to reduce the amount of gearing I have to do. I make a lot of off road creations and was planning on making a really capable (but not too fast) model. Ive made them before simply using large motors and a buwizz and I use silicone spray lubricant to keep it all from binding. Do you think ill be able to pull it off without damaging anything?

[HorcikDesigns]

Not to discourage you, but using worm gear in offrad car at such speeds with plastic parts is great DIY project to learn basics of friction welding (buggy motor is enough to do this). I would recommend to find a different way to reduce the speed, or find somebody in your area with 3d printer. 

[Krxlion]

1 hour ago, Asakbar78 said:

This is absolutely sick I love it. Please let us know how it goes. 

 

Hi all, I have recently bought the whole starter brushless conversion gear. (A2212, 35A esc, 2x 1500mah lipo 3s, dumborc x6 controller/receiver)

I don't have a 3d printer or anything like that so I was considering just using a worm gear to reduce the speed from the motor. I went with the 930kv to reduce the amount of gearing I have to do. I make a lot of off road creations and was planning on making a really capable (but not too fast) model. Ive made them before simply using large motors and a buwizz and I use silicone spray lubricant to keep it all from binding. Do you think ill be able to pull it off without damaging anything?

Maybe trying to use planetary wheel hub to reduce rpms. Its not ideal way of reduction, but as a start it will work. I remember combining myself that method with same motor model, and using small plastic card part (take a look at my message before).

[Krzychups]

On 9/1/2025 at 11:58 PM, gyenesvi said:

I decided it's time for me to enter the game :) So here it comes, my first brushless motor! A small one to start with.

Nice! I wonder if the problem is that the motor casing can become hot and melt, as well as restrict motor cooling.

[Asakbar78]

13 hours ago, HorcikDesigns said:

Not to discourage you, but using worm gear in offrad car at such speeds with plastic parts is great DIY project to learn basics of friction welding (buggy motor is enough to do this). I would recommend to find a different way to reduce the speed, or find somebody in your area with 3d printer. 

Thanks. I was wondering why no one had talked about it previously on here so there must have been a reason lol. I will probably go for 2 or 3 sets of 8 tooth to 24 tooth to see how it works, and if that doesn't work I will try find someone with a 3d printer. 

[gyenesvi]

20 hours ago, Krzychups said:

Nice! I wonder if the problem is that the motor casing can become hot and melt, as well as restrict motor cooling.

Thanks! The back section is completely optional, not necessary for functioning, so it can be left out to allow more cooling.

However, there's a slight other problem with the back section: it cannot be taken apart without breaking off the mounting tabs (they kind of get jammed in the hole and rather break than slide out). Also, it is just in the way for the large head of the HD CV joint as I am building my 4WD off-roader.. So I might just do away with the back for now.

[Tup4n]

@Krzychups here is photo. As you can see, it uses standard hole for Lego axels. 

 

[gyenesvi]

Version 2 of my motor housing! :)

As I started to build, I realized that it would be good if the sideways mounting holes would be vertically in the middle of the motor, because then it would be possible to hold it between two beams that are just the right height for dropping the output shaft right under the motor with one gear mesh; the simplest ever driveshaft (see below). So I designed another housing, where I could add pinholes in a row, and even round off the whole thing, and change the assembly so that it requires less screws, holding the back panel from the side. I also removed the back cover to prevent the motor from overheating. This version looks like this, as slim as it could get:

The first pinholes (towards the face) are full stud deep, while the rear ones are only inverse studs for half pins.

The new mounting points hold the whole 3L front section firmly, so there is no need for stabilization on the back. At the same time, it can be assembled using only the screws that come with the motor, and it is easy to disassemble and assemble again multiple times (the wear of the screw holes does not matter, because it is actually the head of the screw that holds the back wall). Another advantage is that now the wire can come out in a diagonal, allowing the motor to be tilted 90 degrees and mounted from the front without the wire interfering with the beam that runs next to it. The motor can also be mounted so that the wire comes out on the top, if needed.

This is how it looks in more detail:

Of course, it is possible to combine the two designs, and make a square version that has more mounting holes than the first version had:

Now as for building, this is how the most compact 4WD off-roader driveshaft for live axles could look like (two gear ratios are possible):

I have built this into a small scale 4x4 chassis and the performance is just great, super smooth control, great top speed! I guess I'll just open a new WIP topic for showcasing it!

 

Edited 3 hours ago by gyenesvi

[HorcikDesigns]

Good job!