[WIP] Small Scale Defender with Brushless Motor (Video available)

[gyenesvi]

Hi! This thread is meant to document my first build using a custom brushless motor. If you follow the "Brushless Motors in Lego" thread you may have seen the motor design, but I give a quick summary here as well. Apart from the brushless drive motor, I am using a GeekServo for steering, and control them with an RC pistol transmitter/receiver.

So lately I started experimenting with 3d printing lego compatible mounts for brushless motors. I bought a small Injora Purple Viper motor with a corresponding ESC to control it; they come in a package for about 50 Eur, that includes a 11T gear and mounting screws as well. The idea was to make a motor that fits into a 3x3x6 space including a two stage planetary reduction, which is taken out from a 3rd party PF M motor (costs about 3 Eur on AliExpress). Apart from these parts, only the 3d printed housing is needed. The result looks like this, more info in this thread.

 

The key to this design is that it is possible to run a driveshaft right below the motor, furthermore, there's even space for heavy duty CV joints, as the motor itself is narrower:

There are two obvious gearing options, 16:16 and 20:12. I checked Injora's transmissions that are applied with these motors, and they also come in two options, the "normal" provides a 1:13 down-gearing, and the "underdrive" version provide a 1:24 ratio. Since the two stage planetary reduction from the M motor is about a 1:24 down-gearing, applying a 16:16 on the output results in exactly the "underdrive" ratio, while applying the 20:12 up-gearing on the output results in a 1:14.5 total down-gearing, which is roughly the same as the "normal" ratio with the Injora transmission, so there's a pretty good speed correspondence here with RC parts. By the way, these Injora parts are designed to be a drop in replacement for TRX4M Traxxas models.

So this was the starting point for my chassis, and I wanted to see first how small a 4x4 off-roader I can build, aiming for 56mm tires and two live axles. I also happened to have some soft and sticky Injora tires too that I wanted to try for a couple of years now..

For the front axle, I have been wanting to test this tricky wheel mount technique I have seen used by some builders around here, making it possible to use heavy duty CV joints at this small scale (9-wide axle between the pivots), combined with my linkage based steering techniques I used before:

This is a fairly slim and dense axle for what it achieves, quite happy with it, however it misses two upper links, and the panhard rod also proved to be a bit far away, so it became a bit wobbly under the power of the servo, so I had to use other tricks to make the axle stable..

For the rear axle, my aim was to make it as flat as possible to be able to run beams right above it without obscuring the trunk space. It is an often used negative caster (torque tube suspension) setup with only one CV joint and two links and a panhard rod for stabilization. The springs are also mounted on the back to be able to lower them and so that they don't protrude to the trunk.

A chassis that holds all these components together came out quite slim as well, I'm really happy that it actually looks somewhat like real RC chassis platforms!

The servo is mounted fairly low at the front, and there's just enough clearance for the drivetrain even when the axle is articulated. Another key element is that the servo is in between the springs, and right behind the front axle's cross beam, and it actually stabilizes the axle, not allowing it to move too much sideways or tilt forward/backward (just enough to let it articulate freely). These limiters together with the panhard rod make the front axle stable enough so that the servo does not pull it sideways when steering, resulting in a really good steering response and a quite high steering angle!

As you can see, there's plenty of space left for building internals / body and also for placing a battery and ESC/receiver to the trunk. For now, I have mounted these items with tacks onto the chassis for testing, it looks like this:

 

As for performance, I don't yet have a video, but I am pretty amazed by this little thing. Speed control is just very smooth at startup, and with those RC tires, it can climb steep ledges with such confidence that I never thought possible with lego parts. First I tried the 16:16 gearing, but I though it does have enough torque for the faster one, so now I swapped it to 20:12, which has the advantage that the gear below sticks out less, and it does not get caught up so much from the bottom. Also, this way the top speed is very good, like something with a buggy motor (or two), but with much better speed control (and steering). Will make a test video soon, just need to practise filming while driving.. :)

 

And the next step will be:

• building a bodywork; I'm thinking of a small Jeep, like a CJ or a Suzuki Samurai, but ideas are welcome
• printing some casing for the battery / ESC / receiver to enhance their placement / cable management (in the trunk)

Edited Saturday at 09:51 PM by gyenesvi

[Appie]

That's nice little chassis and I am sure it's a blast with these third party motors 

One thing for the front axle you might want to consider is to add a 9L liftarm at the bottom of the steering liftarm or even better at the bottom of the "hubs" (though would probably collide with the gears and would cost ground clearance). The wheels get a little bit of negative camber with the current construction when sat on the ground. You can leave it as it is since it is nothing major, but if it annoys you, that would help it a little (not completely).

[gyenesvi]

26 minutes ago, Appie said:

That's nice little chassis and I am sure it's a blast with these third party motors 

Thanks!

26 minutes ago, Appie said:

One thing for the front axle you might want to consider is to add a 9L liftarm at the bottom of the steering liftarm or even better at the bottom of the "hubs" (though would probably collide with the gears and would cost ground clearance). The wheels get a little bit of negative camber with the current construction when sat on the ground. You can leave it as it is since it is nothing major, but if it annoys you, that would help it a little (not completely).

Sure there's a little camber, but it's really nothing major, much better than I expected, and the goal here is definitely to maximize ground clearance, so I don't plan to add anything to the bottom.

[Krxlion]

This is becoming a very neat, small off-roader. One thing that I want to mention, is that it is much better for climbing purposes to have a battery on the front. I know that it is often very hard to do, especially in this scale. I don't say you should remodel it completely, but for a future projects, you might consider flipping the motor, so it's more on a rear side, then battery in the center (or as much to the front as you can do). Recently, I was building your Toyota Hilux chassis, but powered with BL setup and moved the motor to the back, so I can put a battery on the front and improve climbing performance.

[everybrickasculpture]

Great design!  I bet this will be a lot of fun when it's done.  It might be worth looking into some crawler shocks, as these can be oil filled and make a huge difference in performance.

[gyenesvi]

9 hours ago, Krxlion said:

This is becoming a very neat, small off-roader. One thing that I want to mention, is that it is much better for climbing purposes to have a battery on the front. I know that it is often very hard to do, especially in this scale. I don't say you should remodel it completely, but for a future projects, you might consider flipping the motor, so it's more on a rear side, then battery in the center (or as much to the front as you can do). Recently, I was building your Toyota Hilux chassis, but powered with BL setup and moved the motor to the back, so I can put a battery on the front and improve climbing performance.

Thanks, indeed, I agree with you about the weight on the front. The bigger problem however is the steering motor, moving that would be more of an issue. Maybe something can be done at a larger scale. Also, for this scale I actually plan to use a smaller battery.

6 hours ago, everybrickasculpture said:

Great design!  I bet this will be a lot of fun when it's done.  It might be worth looking into some crawler shocks, as these can be oil filled and make a huge difference in performance.

Thank you! Yeah, I have been eyeing on those too, but for now I don't want to get carried away too much with custom parts yet, only electronics and tires. I guess that will open another rabbit hole :)

 

Here are some short videos I made to showcase how it works. First, slow speed climbing:

https://bricksafe.com/files/gyenesvi/private/small-scale-brushless-chassis/DJI_20250908_132226_167_video.MOV

Then some high speed driving, it's only almost full speed towards the end because of the small space I had.. but it's surprisingly controllable, and the steering radius is great too!

https://bricksafe.com/files/gyenesvi/private/small-scale-brushless-chassis/IMG_7970.MOV

Edited September 8 by gyenesvi

[Krxlion]

The low speed control is even better with this one, than with the AM32 I was guiding you to check out! I recently burned mine AM32 ESC (don't ask me how, haha), and I know what I will buy next :D

The motor is so silent, I couldn't even hear it! I think it will suit bigger builds as well. Great showcase of your effort, Viktor!

[gyenesvi]

51 minutes ago, Krxlion said:

The low speed control is even better with this one, than with the AM32 I was guiding you to check out! I recently burned mine AM32 ESC (don't ask me how, haha), and I know what I will buy next :D

Good to hear that this looks great even in comparison, and sorry to hear you burned yours! But I definitely agree you should try this one. Also, I'm considering buying its bigger brother too, the Fat Viper, a 28x19 mm variant for bigger models.. :D

51 minutes ago, Krxlion said:

The motor is so silent, I couldn't even hear it! I think it will suit bigger builds as well. Great showcase of your effort, Viktor!

Yeah, in sinusoidal startup mode the motor is really silent! Agree this could even move bigger models, like 62-68 mm tires. For 1:10 scale on 80 mm tires, I'd go for the bigger one, or the 2435 SurpassHobby motor. Hope that one won't burn down this ESC :D It is supposed to handle 25 A continuously and 60 A peak, while the 2435 motor description says it takes max 22 A, so it should be okay I guess.

[vergogneless]

Thank you for sharing, happy to see I'm not the only one wanting to miniaturize models powered by a brushless system 

Your build is really well thought out, and I think it's the smallest brushless crawler out there to date, congratulations! 

From these short video clips, it looks seriously functional and promising, can't wait to see more!

You should indeed use a more compact battery; I'm only running 450mAh 3S, and it's more than enough. Have you already found the one you're going to use?

Are you going to design parts with ball bearings? I'm worried that plastic won't hold up in the long term; play will develop, and it won't be as pleasant to drive.

Then again, maybe for a mini crawler, it'll be fine since you're not going fast, so there aren't too many friction issues!

I'd love to test your motor solution, but I'm afraid that in my case (bashing), the plastic gears won't last long! Do you think it would be possible to use it without a planetary reduction?

I'm currently working on a 1:24 scale mini 4x4 bashing build, and I'm designing a lot of 3D parts with ball bearings, along with carbon and aluminum transmission, metal wheel hubs on bearings, full metal gears, screw connectors, etc. It's a must for my setup 

[gyenesvi]

1 hour ago, vergogneless said:

Thank you for sharing, happy to see I'm not the only one wanting to miniaturize models powered by a brushless system 

Indeed, I also like to go small scale and test the limits of how much suspensions can be miniaturized :)

1 hour ago, vergogneless said:

Your build is really well thought out, and I think it's the smallest brushless crawler out there to date, congratulations! 

From these short video clips, it looks seriously functional and promising, can't wait to see more!

Thanks, glad you like it!

1 hour ago, vergogneless said:

You should indeed use a more compact battery; I'm only running 450mAh 3S, and it's more than enough. Have you already found the one you're going to use?

I actually have a 450 mAh version of the same Tattu 3S battery you see on the image. However, I have never really used it, and when I started using it to test this motor (yet with no load), it was working okay initially, but after a few minutes, one of the cells lost all charge, and now it does not even charge back with the LiPo charger, but the other two cells work, and now it's like a 2S.. I took it back to the shop and they said they might be able to revive that one cell with slow charging, now I am waiting for that..

Do you have any other good small 3S that you'd say is worth buying?

1 hour ago, vergogneless said:

Are you going to design parts with ball bearings? I'm worried that plastic won't hold up in the long term; play will develop, and it won't be as pleasant to drive.

Then again, maybe for a mini crawler, it'll be fine since you're not going fast, so there aren't too many friction issues!

I am thinking about using them, mainly want to experiment with portal axles (you can read about my ideas in another thread I made about those). But for now, I don't want to go too far with custom axles and bearings and gears everywhere, I think for slower models they are not needed yet.

1 hour ago, vergogneless said:

I'd love to test your motor solution, but I'm afraid that in my case (bashing), the plastic gears won't last long! Do you think it would be possible to use it without a planetary reduction?

Well who knows, it would be good to see the limits of those gears. I guess it is more difficult without the planetary reduction, the mounting points are 12 mm apart, so you need some custom part there anyway, and then the shaft is 2mm D shaped, so attaching a gear that can be used in connection with lego could be more difficult. And then you'd still need some down-gearing, but I guess you have figured a solution to that problem out already. 

1 hour ago, vergogneless said:

I'm currently working on a 1:24 scale mini 4x4 bashing build, and I'm designing a lot of 3D parts with ball bearings, along with carbon and aluminum transmission, metal wheel hubs on bearings, full metal gears, screw connectors, etc. It's a must for my setup 

Curious what comes out of it!

[vergogneless]

On 9/9/2025 at 10:02 AM, gyenesvi said:

Indeed, I also like to go small scale and test the limits of how much suspensions can be miniaturized :)

Thanks, glad you like it!

I actually have a 450 mAh version of the same Tattu 3S battery you see on the image. However, I have never really used it, and when I started using it to test this motor (yet with no load), it was working okay initially, but after a few minutes, one of the cells lost all charge, and now it does not even charge back with the LiPo charger, but the other two cells work, and now it's like a 2S.. I took it back to the shop and they said they might be able to revive that one cell with slow charging, now I am waiting for that..

Do you have any other good small 3S that you'd say is worth buying?

I am thinking about using them, mainly want to experiment with portal axles (you can read about my ideas in another thread I made about those). But for now, I don't want to go too far with custom axles and bearings and gears everywhere, I think for slower models they are not needed yet.

Well who knows, it would be good to see the limits of those gears. I guess it is more difficult without the planetary reduction, the mounting points are 12 mm apart, so you need some custom part there anyway, and then the shaft is 2mm D shaped, so attaching a gear that can be used in connection with lego could be more difficult. And then you'd still need some down-gearing, but I guess you have figured a solution to that problem out already. 

Curious what comes out of it!

 

I never would have thought a battery could lose a cell. I’ve always charged mine with a cheap charger that doesn’t show that kind of thing. So I just ordered a charger with cell display to do a little check-up on my stock 

I didn’t know about Tattu — I’m actually looking for new 450mAh packs, but with my current brand (Zop) they’ve become almost impossible to find or way too expensive. I’ll check AliExpress when I get a chance!

Yeah, with a crawler I think that’s fine. But once you start going for speed or acceleration, that’s a whole different world. I know that from experience 

I’d need to make an adapter to fit the D-shaft, but I think it’s doable. And for a planetary reduction, with such a small motor, if you’re aiming for speed (with 1:28 and small wheels), it’s not necessary. I’ve never actually used planetary reductions anyway, only the classic motor pinion to axle gear reductions.

[Ryokeen]

@gyenesvi great little model. As i happen to have a rc crawler in that scale (1:18) i would say, don't worry much about shocks. At that scale they can be oil filled but mostly aren't as you need a very thin oil and that won't then do much. 
2nd as a fun addition, crawlers mostly got counter rotating shafts to reduce torque twist. So the back and front driveshaft rotate in opposite directions. Maybe you find space integrating it, just an idea.
Anways awesome little model.

[gyenesvi]

On 9/10/2025 at 12:29 PM, vergogneless said:

 

I never would have thought a battery could lose a cell. I’ve always charged mine with a cheap charger that doesn’t show that kind of thing.

Actually if you have an electronics tool to measure voltage (digital multimeter), it is possible to measure each cell of the battery separately on the charging cable, it's a bit tricky though, you may look it up in google.

It seems that they could revive the 3rd cell of my battery, probably it was over discharged for some reason (maybe because it was brand new and should have charged it before use), I can pick it up tomorrow and see how it works.

On 9/10/2025 at 12:29 PM, vergogneless said:

I didn’t know about Tattu — I’m actually looking for new 450mAh packs, but with my current brand (Zop) they’ve become almost impossible to find or way too expensive. I’ll check AliExpress when I get a chance!

So far I was satisfied with my other Tattu battery, and it's not too expensive either.

On 9/11/2025 at 2:24 AM, Ryokeen said:

@gyenesvi great little model. As i happen to have a rc crawler in that scale (1:18) i would say, don't worry much about shocks. At that scale they can be oil filled but mostly aren't as you need a very thin oil and that won't then do much. 
2nd as a fun addition, crawlers mostly got counter rotating shafts to reduce torque twist. So the back and front driveshaft rotate in opposite directions. Maybe you find space integrating it, just an idea.
Anways awesome little model.

Thanks, glad you like it! I guess counter rotating shafts would require more space, not really possible in this small scale, but good idea!

[Krzychups]

Really nice RC car. Curious to see what will come of it.

[gyenesvi]

On 9/15/2025 at 6:50 PM, Krzychups said:

Really nice RC car. Curious to see what will come of it.

Thanks! Here is some progress on the bodywork.

When I saw in @Appie's video that the fender parts of the Icons Defender are available in white, and looked it up on Bricklink, I realized that they are also available in black, which are just ideal as they go well with many colors, I immediately decided that I need to get some and build a Defender with them because they seemed ideal for 56mm wheels :) Also, it's something that the Traxxas TRX4M platform comes with as a body option, so it's fun to replicate it in lego form. So here's the design I came up with, a pickup version that I have been planning for a while.

It is meant to be detachable as a single piece, just like in RC models.

I have built it partially (need to buy parts in the right color), and started testing it. The trickiest part is of course the front section, being able to make the wheel wells large enough so that the tires don't catch up in the edges. Unfortunately, with the weight of the body, the camber of the front wheels get more emphasized, and there's more play in the wheels, so it gets harder, more space is needed for the wheel. I went a long way trying to make the front face as thin as possible while not pushing it too much forward to keep the proportions more or less. Also, I tried to mount the fender parts as firmly as possible. Here's a close-up of the wheel well.

It's all supported from the top panels, and it actually came out sturdy enough. The face has a bunch of half stud offsets for the grille and lights, which are quite well possible with tiles and plates. Another area where I resorted to system plates and tiles is the wedged hood top / bulge, I think this is a good and simple solution. I managed to make a nice technic top (it is solid, and can be grabbed by the roof).

Here's how it would look on the chassis.

 

By the way, to make this possible, I had to make the chassis one stud longer. Now it's the same size as the new Bronco (also, I could have just used the Bronco's body on this chassis, but that would have been too easy). Furthermore, I added some bed sides to the chassis where the battery will be placed (I could not attach that part to the bodywork).

 

You can also see the mounting points for the body, maybe I'll add two more to the tail as well (for now it would just rest on the chassis).

[Appie]

Looks very nice!

Nailed the look of a little Defender. I also like how you did the little incline of the roof.

[Krxlion]

This is all going in a very good direction. The body is very detailed, you didn't let only your motor shine, but the whole assembly looks promising. I am awaiting a video, to see your MOC in action. Take your time, and polish every aspect if there is a need. Great work, Viktor. As always you keep us with clever solutions and catchy models. ;)

[2GodBDGlory]

Nice job! I look forward to seeing it running. Do you think it would be worth the effort to modify the Bronco body into an alternative body option?

[gyenesvi]

23 hours ago, Appie said:

Looks very nice!

Nailed the look of a little Defender. I also like how you did the little incline of the roof.

Glad you like it, indeed, I was happy how simple the roof turned out!

14 hours ago, Krxlion said:

This is all going in a very good direction. The body is very detailed, you didn't let only your motor shine, but the whole assembly looks promising. I am awaiting a video, to see your MOC in action. Take your time, and polish every aspect if there is a need. Great work, Viktor. As always you keep us with clever solutions and catchy models. ;)

Thanks a lot for the kind words :) Pushing the limits is actually inspiring!

8 hours ago, 2GodBDGlory said:

Nice job! I look forward to seeing it running.

Thanks! Have you checked the preliminary videos up there? (not embedded links)

8 hours ago, 2GodBDGlory said:

Do you think it would be worth the effort to modify the Bronco body into an alternative body option?

It may be worth giving it a try, I wanted to convert the Bronco to 4x4 and motorize it anyway :)

 

As a next step, I worked out a way to put the electronics components (battery, receiver, ESC) into a simple and versatile lego compatible casing. The general pattern looks like this, the base area and height varies according to the component.

The bottom is 2mm thick and has 5mm inverse stud holes in it. This way, it is possible to attach them to plates or half studs or attach plates/bricks with pinholes to them for mounting. It's a fairly generic and space efficient solution. My ESC and receiver both (separately) fit into a 3x4 area with thin walls. My small 450mAh battery (which got fixed and now is back and functional) fits into a 3x7x4 box.

Aaaand luckily I was able to pick up my parts order today in person (I ordered it 2 days ago, super fast), so I could finish the build! Here it is in all its glory, I even went all in and added quite some Injora stickers that came with the electronics :) I like the best the one on the top that says "Just one more part", as if it was meant for Lego :D

 

Here's a better view of how all the control electronics is packed into the trunk, it's neat and stable, everything attached to the 5x7 frame underneath with half pins. I'll try to print a top for the battery box but the cable is so short both on the battery and the ESC that it's a bit hard to connect them and let the cable be routed where I want it to be not where it wants to go..

 

Sooo, I'll go out and test and make some videos as soon as I can!

Edited Wednesday at 08:51 PM by gyenesvi

[2GodBDGlory]

15 hours ago, gyenesvi said:

Thanks! Have you checked the preliminary videos up there? (not embedded links)

I just did now, and wow! That's a huge performance spread for something without a gearbox! With Lego motors you could get that much speed or that much torque, but no way could you get both with the same gearing!

It will be more fun to watch it with a pretty body on it, though! :)

[HorcikDesigns]

Nice idea to make boxes for the components! Can they be snapped onto studs? 

[gyenesvi]

1 hour ago, 2GodBDGlory said:

I just did now, and wow! That's a huge performance spread for something without a gearbox! With Lego motors you could get that much speed or that much torque, but no way could you get both with the same gearing!

Exactly, that's the key here! And I don't think it's actually due to the power of the motor, but rather the control electronics, that's able to control it at such a low speed with such good torque.

1 hour ago, HorcikDesigns said:

Nice idea to make boxes for the components! Can they be snapped onto studs? 

Yes, that's the idea, 5mm wide and 2mm deep holes have a firm grip on studs or half pins, and in the flat orientation they get printed perfectly. Here every box is fixed with 2 half pins to the chassis, and now all is really stable and tidy, easy to turn it on or plug cables in and out.

[thekoRngear]

Cannot wait to see it in its full glory in video! 

[gyenesvi]

On 9/17/2025 at 8:16 AM, Krxlion said:

I am awaiting a video, to see your MOC in action.

On 9/18/2025 at 2:20 PM, 2GodBDGlory said:

It will be more fun to watch it with a pretty body on it, though! :)

On 9/18/2025 at 6:55 PM, thekoRngear said:

Cannot wait to see it in its full glory in video! 

So I had time to shoot a video in the weekend, it was a lot of fun, here it is! Also, due to the magic of 3d printing, I managed to fix my selfie stick and phone to the bottom of my transmitter, hence taking low shots while driving became super easy :) Hope it shows!

 

A few take-aways:

• It's fast for this kind of terrain, and this kind of suspension; it can easily flip over in sharp turns.. I probably flipped it over more than I would have liked to, also on the rocks while climbing.. I think soft live axles don't help much with stability at high speed
• A bit of a negative of the motor is that it can cog sometimes when moving slowly and getting stuck a bit, it can be seen occasionally on the video. Often a bit of throttle helps. But I find the transition between slow speed sinusoidal motor control, and normal motor control a bit abrupt, and it often starts moving faster when I'd need a bit more slow speed; I miss kind of the sweet spot. Maybe this transition is tunable in the ESCs software, which I could not yet try because it requires a Windows PC, will try to test later. Does anybody have experience, understanding of this phenomenon, and cogging in general? Is it natural to brushless motors?

By the way, do you think I should make a new thread for final presentation?

[N1K0L4]

Awesome little model! It may use RC components, but it's still a clever build with a great looking body :)

29 minutes ago, gyenesvi said:

A few take-aways:

• It's fast for this kind of terrain, and this kind of suspension; it can easily flip over in sharp turns.. I probably flipped it over more than I would have liked to, also on the rocks while climbing.. I think soft live axles don't help much with stability at high speed
• A bit of a negative of the motor is that it can cog sometimes when moving slowly and getting stuck a bit, it can be seen occasionally on the video. Often a bit of throttle helps. But I find the transition between slow speed sinusoidal motor control, and normal motor control a bit abrupt, and it often starts moving faster when I'd need a bit more slow speed; I miss kind of the sweet spot. Maybe this transition is tunable in the ESCs software, which I could not yet try because it requires a Windows PC, will try to test later. Does anybody have experience, understanding of this phenomenon, and cogging in general? Is it natural to brushless motors?

Well.. it's not meant for high speed, is it? I think if you gear down at the motor (12:20 instead if 16:16) you could solve the cogging and the too fast top speed issue.

 

31 minutes ago, gyenesvi said:

Also, due to the magic of 3d printing, I managed to fix my selfie stick and phone to the bottom of my transmitter, hence taking low shots while driving became super easy :) Hope it shows!

It does! Really liked the shots. Can we see the setup? I wonder how low does it go.

 

35 minutes ago, gyenesvi said:

By the way, do you think I should make a new thread for final presentation?

However you like, maybe just rename this topic.