Brushless motors in the lego world - general topic

[Ryokeen]

@Krzychups For the planetary gearbox, keep in mind that differentials also add up to the overall reductions. With most lego diffs that's another 28:20/22:14/28:12 reduction on the drivetrain.
So double planetary gearbox might be to much as then you need higher kV again and it might be better to get more torque with the planetary wheelhubs than with such an early reduction right after the motor.

1 hour ago, Krzychups said:

I'm worried about how will I do the metal axle adapter. At the moment I don't have any idea. 

You mean from the motors shaft to the first set of gears on the reduction stage ?

[Krzychups]

20 minutes ago, Ryokeen said:

You mean from the motors shaft to the first set of gears on the reduction stage ?

No, the metal adapter to a lego axle. My mistake.

[Krxlion]

Hi guys, I want to throw two cents from my side, regarding a similar matter. I was experimenting a while ago and trying to create something that was already achieved by @MaxBrix, but with 2838, 3200KV brushless motor.

On 1/21/2024 at 5:29 PM, Krxlion said:

Well done @Krzychups. I am so happy that someone from my own country is doing so much stuff with Lego Technic and now I can see that you are also moving towards the dark side of 3rd party components, haha. :D From my experience A2212 motors are more than enough for Lego Technic usage, more power might simply not hold other Lego components (if we are talking about pure Technic model and only power source with electronic is the only 3rd party component). Regarding your gearbox I believe going with planetary setup might be better. Just look at MaxBrix YT video. He powered old PF XL motor case with even stronger motor than A2212:

This man is very close to ideal motor (at least for me) - 1200-2000 RPM, but those RPMs are build with a lot of torque. What we would need to even spice things up is ESC with possibility to slowly speed up the motor, so we could create also crawlers with brushless motors. @gyenesvi mention about that part in different topic. :)

I want to also highlight the great advantage of A2212 motors (or similar to those) - those are 14-poles motors, which means you have more precise control instead of 4-pole, like the one in film above or those ZENE is advertising. I don't say those are bad (I have two of those) but in precise control of maybe offroad vehicles it makes more sense to go with as many pole as you have.

PS The shaft on the A2212 can be reversed, although you would need to create that little groove to hold the motor housing. Nevertheless, sometimes I go without it.

I found one crucial issue with that type of motors - poor RPM range. Likewise, I created a simple model (driving and steering) and hook up same thing as above in video. At first, I was pretty happy with the results, but after trying to work my way with throttle, I found there is very limited difference between low and high-speed. I think this is further noticeable due to transmission reduction, but all in all this effect does not take place when I do the same with A2212 motor. In all my tests I were using same ESC, transmitter and receiver.

Edited June 6, 2024 by Krxlion

[Ryokeen]

3 hours ago, Krzychups said:

No, the metal adapter to a lego axle. My mistake.

Depending on the metal part you want to connect(i assume it's some axle/driveshaft) you could try to mill an already available metal lego compatible axle to the needed diameter, like 3.2mm. You wouldn't get a a full round shape but that shouldn't matter much if you connect them via common RC shaft conectors(metal sleve with maggot screws).

[gyenesvi]

21 hours ago, Krzychups said:

After a break I want to come back to a planetary gearbox for A2212 or other 28 mm diameter brushless motors.

I still like this idea so will be monitoring the progress with interest!

Quote

I need to contact the factory that makes the planetary gearboxes to establish the parameters. Then when I have the planetary gearbox I need to make a preliminary model of the whole thing with the motor and gearbox. I will post here on the forum as to the design. 

Just out of curiosity, what company makes such gearboxes, how did you find one?

I think a double stage reduction between 1:16 or 1:25 could work out well for some use cases!

20 hours ago, Ryokeen said:

@Krzychups For the planetary gearbox, keep in mind that differentials also add up to the overall reductions. With most lego diffs that's another 28:20/22:14/28:12 reduction on the drivetrain.
So double planetary gearbox might be to much as then you need higher kV again and it might be better to get more torque with the planetary wheel hubs than with such an early reduction right after the motor.

Even with planetary wheel hubs, it all might end up in a good range for some purposes, like rock crawlers.

19 hours ago, Krxlion said:

I found one crucial issue with that type of motors - poor RPM range. Likewise, I created a simple model (driving and steering) and hook up same thing as above in video. At first, I was pretty happy with the results, but after trying to work my way with throttle, I found there is very limited difference between low and high-speed.

What exactly do you mean by that? Is it that the minimal low speed is still too fast?

I have just recently managed to test a complete (brushed) setup in a real application, I will present it here soon in more detail, but I can already share some interesting details. I used modified motors: Lego L motors (so 1:25 planetary gearing), where the actual motor inside was swapped in from a buggy motor (they use the same sized motor, but the motor inside the buggy is about 2.5x more powerful). This results in a motor that is slower than the buggy motor because of the planetary reduction in the L motor housing, but it has more torque. I used two of these motors coupled, driving planetary wheel hubs with 1:1 gearing (no diff needed in a crawler, just 12:12 gears instead). All that built into a large scale 1.5 kg crawler, driven by a good quality brushed ESC and a 3s LiPo. The result is pretty amazing for me. For one, the system has very good low speed control, can easily crawl around the cm/sec speed, in a stable way. It is pretty powerful, moves the 1.5 kg model up a 45 degree slope with ease when it has good grip (or if the slope is steeper, it either spins the wheels under it or twists some axles in the drivetrain). At the same time, the top speed is pretty acceptable too, something like you'd achieve with two Lego L motors powered from a Lego battery but in a lighter model without planetary wheel hubs (like the Audi for example). Nothing really fast, but it definitely has enough punch required for some dynamic climbs, and to move across terrain in a non-boring speed.

Quote

I'm curious if anyone would like to buy it somehow.

I'd definitely be interested in buying such a thing as a finished product.

Edited June 7, 2024 by gyenesvi

[Krxlion]

15 hours ago, gyenesvi said:

What exactly do you mean by that? Is it that the minimal low speed is still too fast?

I have just recently managed to test a complete (brushed) setup in a real application, I will present it here soon in more detail, but I can already share some interesting details. I used modified motors: Lego L motors (so 1:25 planetary gearing), where the actual motor inside was swapped in from a buggy motor (they use the same sized motor, but the motor inside the buggy is about 2.5x more powerful). This results in a motor that is slower than the buggy motor because of the planetary reduction in the L motor housing, but it has more torque. I used two of these motors coupled, driving planetary wheel hubs with 1:1 gearing (no diff needed in a crawler, just 12:12 gears instead). All that built into a large scale 1.5 kg crawler, driven by a good quality brushed ESC and a 3s LiPo. The result is pretty amazing for me. For one, the system has very good low speed control, can easily crawl below a cm/sec speed, in a stable way. It is pretty powerful, moves the 1.5 kg model up a 45 degree slope with ease when it has good grip (or if the slope is steeper, it either spins the wheels under it or twists some axles in the drivetrain). At the same time, the top speed is pretty acceptable too, something like you'd achieve with two Lego L motors powered from a Lego battery but in a lighter model without planetary wheel hubs (like the Audi for example). Nothing really fast, but it definitely has enough punch required for some dynamic climbs, and to move across terrain in a non-boring speed.

So foremost, I am looking forward @gyenesvi to your project and happy to see you experimenting with other power sources. I have a working 2-speed model with brushless setup that I do my experiments on. I can within 3 minutes swap A2212 motor with 2838 BL in Lego XL motor housing (including planetary reduction). Furthermore, I was driving it today with both setup and my conclusion is:
1. I feel like 2838 has like 5-6 stages of speed, nothing in between. This is probably because those motors are 4-pole ones. A2212s are 14-pole ones - smoother work with throttle.
2. 2838 is getting hotter due to closed case in XL motor housing (though probably this can be further improved by creating some holes in the case.
3. 2838 is noisier than A2212.

I will try to not only speak, but also show you my experiments, but those probably will not be professional, just a video montage of me driving both setups.

[Ryokeen]

1 hour ago, Krxlion said:

1. I feel like 2838 has like 5-6 stages of speed, nothing in between. This is probably because those motors are 4-pole ones. A2212s are 14-pole ones - smoother work with throttle.

Could also be the esc or the size in general. I use a 4-pole 3652 motor and that one is pretty smooth even for a sensorless one.

[Krzychups]

On 6/7/2024 at 12:53 AM, Ryokeen said:

Depending on the metal part you want to connect(i assume it's some axle/driveshaft) you could try to mill an already available metal lego compatible axle to the needed diameter, like 3.2mm. You wouldn't get a a full round shape but that shouldn't matter much if you connect them via common RC shaft conectors(metal sleve with maggot screws).

I mean something like this:

I don't have any idea how to connect it to the planetary gearbox's shaft. Usually they have about 6 mm shafts.

On 6/7/2024 at 12:58 AM, gyenesvi said:

Just out of curiosity, what company makes such gearboxes, how did you find one?

If you search: 28 mm planetary gearbox, you will see some links to different factories that make planetary gearboxes and other stuff. I'm going to find a factory.

Edit: It doesn't have to be a planetary gearbox with a single ratio, there can be different versions of such gearboxes. 

Edited June 9, 2024 by Krzychups

[Ryokeen]

@Krzychups Hmm if the gearbox shaft is D shaped(so with one side more flat) you would just have an adapter that has an 1 stud axle hole on one side and on the other side a 1 stud 6mm hole with a place for a maggot screw. The screw presses on the flat part of the shaft and thus locks it. Problem might be that for 3D printed, it might need to be thicker than 1 Stud or it might break.

[Krzychups]

Hello,

I have written to the sellers of these planetary gearbox (the first planetary gearbox and the second one) if it is possible to change the diameter of the gear bore to fit the motor. I have received the replies that it is not possible. And that's the problem. Another option is drill 3.17 mm diameter bores if the gears' sizes are enough big. 

Edited June 15, 2024 by Krzychups

[HorcikDesigns]

Hi, I have designed 11:40 gearbox for motor A2212. Works great with 1000KV motor and 3S LiPo, even when tge hoising and gear are printed from basic PLA. Greased offcourse. 

https://makerworld.com/en/models/495158#profileId-409252

 

What do you think? 

 

[gyenesvi]

2 hours ago, HorcikDesigns said:

Hi, I have designed 11:40 gearbox for motor A2212.

This looks really interesting and well designed, promising candidate for 4x4 vehicles. Neat that the gear is spinning in bearings. Why is it required to print the 40T gear from two parts?

Unfortunately, I have one problem with these gearbox setups when it comes to integrating it into Lego builds, and I don't quite understand how real RC gearboxes solve it; maybe someone can enlighten me. The problem is that the main driveshaft ends up too high in the chassis. In this case, it's 2 studs above the bottom, which would result in high angles for the joints going to the diffs in case of smaller scales (shorter shafts). Furthermore, the large gear blocks the path for another axle, so it is not even possible to make a 2-stud step downwards with another gearing. How do RC gearboxes circumvent this? As far as I understand they use kind of asymmetric, multi-step gearing (possibly with extra spacing gears inserted) to arrive to the bottom to a not too big gear. Ideally, the main driveshaft should be about 1 stud higher than the bottom of the chassis. Do you think it would be possible to design such a gearbox adapter? How complex would it get?

1000 kv motor on 3s LiPo with this gearbox still results above 3000 RPM, which is still a bit too high for Lego to use safely I guess. Half of it would be enough, which would require more down-gearing..

3 hours ago, Krzychups said:

change the diameter of the gear bore to fit the motor

What does that exactly mean? At first I thought you'd want to change the outer diameter to 24mm instead of 28mm to fit 24mm motors, but it seems you are talking about something different?

[Aurorasaurus]

32 minutes ago, gyenesvi said:

This looks really interesting and well designed, promising candidate for 4x4 vehicles. Neat that the gear is spinning in bearings. Why is it required to print the 40T gear from two parts?

 

I think it might be to ensure a more perfect finish on both sides without the need for sanding or supports?

[gyenesvi]

3 hours ago, Aurorasaurus said:

I think it might be to ensure a more perfect finish on both sides without the need for sanding or supports?

That makes sense, thanks!

Upon giving it more thought, here is a sketch of the gearing that I have been thinking about, that might work out and would only be one step more complex. The upper (red) and lower (yellow) axles are in system, 4 studs apart, and the middle grey axle is out of the grid, but 3 studs apart from both axles. Actually, the red axle does not need to be in system, so that could be lowered or moved to the side as well, depending on the size of the motor. The down-gearing in this case would be 5x, which would result in the 1500 RPM range with a 1000 kv motor on 2s LiPo, still kind of safe for lego parts. The bottom axle could be 1 stud above the bottom of the chassis in this case, the complete height could be reduced to 6 studs, the width would increase instead (asymmetrically), and the thickness would also become 3 studs instead of 2.

The questionable point in this is the 8T gear on the motor shaft, I know that that one is typically metal, but don't know if it is easy to find one, most motors I saw come with 11T. Do you guys know if there are smaller ones? Do you think this could be doable?

[Lixander]

29 minutes ago, gyenesvi said:

The questionable point in this is the 8T gear on the motor shaft, I know that that one is typically metal, but don't know if it is easy to find one, most motors I saw come with 11T. Do you guys know if there are smaller ones? Do you think this could be doable?

There might exist, but even so, there should be rare.

Also, Module 1 pinion gears (these mesh perfectly with Lego gears) with 8T are pretty much nonexistent.

Edited June 15, 2024 by Lixander

[gyenesvi]

3 minutes ago, Lixander said:

There might exist, but even so, there should be rare.

Also, Module 1 pinion gears (these mesh perfectly with Lego gears) with 8T are pretty much nonexistent.

They don't have to mesh with Lego gears, I only used them as illustration here, all gears in there would be custom non-lego ones, with any desired characteristic (diameter, tooth size) that fits (actually, a quick search shows that 9T gears don't seem too rare). The important constraints would be: 

• the bottom gear has to be in system, so it should roughly fit into a 3x3 area, including a thin covering bottom wall
• the bottom axle has to pass by the large middle gear, so the middle gear cannot get too large relative to the bottom gear

I wonder that if another gear mesh would be added to the current 11:40 setup (or for example to a 9:36 setup), in the above geometry, satisfying the above constraints, what would be the achievable final gear ratio. I think something above 5x could be reached, as those gears seem to have smaller teeth than lego gears.

[Ryokeen]

6 hours ago, gyenesvi said:

Unfortunately, I have one problem with these gearbox setups when it comes to integrating it into Lego builds, and I don't quite understand how real RC gearboxes solve it; maybe someone can enlighten me. The problem is that the main driveshaft ends up too high in the chassis. In this case, it's 2 studs above the bottom, which would result in high angles for the joints going to the diffs in case of smaller scales (shorter shafts). Furthermore, the large gear blocks the path for another axle, so it is not even possible to make a 2-stud step downwards with another gearing. How do RC gearboxes circumvent this? As far as I understand they use kind of asymmetric, multi-step gearing (possibly with extra spacing gears inserted) to arrive to the bottom to a not too big gear. Ideally, the main driveshaft should be about 1 stud higher than the bottom of the chassis. Do you think it would be possible to design such a gearbox adapter? How complex would it get?

First, on most RC cars the supsension is mounted ontop of the base chassis plate, that sets the overall diffs a bit higher. Then a lot of rc cars actually don't have one straight driveshaft, but 2 driveshafts going to the front and back dif from a center dif and they go down a bit. Next it's about scale, in my current car i use tamiya parts that are for 1:10 scale cars. Even there if the lower suspensionarm is on level with the bottom of the chassis you have the typical 5 stud high double whishbone supspension with the driveshaft in the center. That means even if the center driveshaft is on the same level, you can use a 36 gear meshing with a 12 thooth pinion. What some cars do(and what i did) is acutally having a cutout at that position in the base chassis plate.
So far what i've seen is that Rc cars that don't use an enclosed gearbox(motor to driveshaft) have such a cut out or use smaller gears with a different thooth pitch(mod 0.5 or dp68) and manage to stay on level with the diffs that way.
Rc cars that have an enclosed gearbox either have little connections going down to the diffs OR they are in another scale, means the ratio of the car to the motor is different, which along with bigger diffs, gives more vertical space.

[Lixander]

1 hour ago, gyenesvi said:

They don't have to mesh with Lego gears, I only used them as illustration here, all gears in there would be custom non-lego ones, with any desired characteristic (diameter, tooth size) that fits (actually, a quick search shows that 9T gears don't seem too rare). The important constraints would be: 

• the bottom gear has to be in system, so it should roughly fit into a 3x3 area, including a thin covering bottom wall
• the bottom axle has to pass by the large middle gear, so the middle gear cannot get too large relative to the bottom gear

I wonder that if another gear mesh would be added to the current 11:40 setup (or for example to a 9:36 setup), in the above geometry, satisfying the above constraints, what would be the achievable final gear ratio. I think something above 5x could be reached, as those gears seem to have smaller teeth than lego gears.

Then there are some 8T pinions for sale out there, but, for the other things, I don`t know what to say :/

Edited June 15, 2024 by Lixander

[HorcikDesigns]

Well, the 2 piece gear is due to printability on FDM printers - this way it could be printed without supports and each half can be printed with different angle of infill that should improve strength of the narrow section that connects to the axle. Regarding the offset from the ground, there is second version with 2-step gearing in planning, but for my current application in big scale Tatra 8x8 trial truck it works well, and I wanted to keep the housing 5 studs wide with as many mounting points as possible). It might be too fast to be a trial truck, though... (see video on my IG profile https://www.instagram.com/reel/C8O6w2wo4e6/?igsh=eHNxb3gzaHo5NjBl )

I plan to make more similar parts, but it needs more time. :) 

Edited June 16, 2024 by HorcikDesigns

[gyenesvi]

42 minutes ago, HorcikDesigns said:

there is second version with 2-step gearing in planning

That's great to hear! Curious what you manage to bring out of it! Is the idea similar to what I proposed above?

42 minutes ago, HorcikDesigns said:

but for my current application in big scale Tatra 8x8 trial truck it works well, and I wanted to keep the housing 5 studs wide with as many mounting points as possible). It might be too fast to be a trial truck, though... (see video on my IG profile https://www.instagram.com/reel/C8O6w2wo4e6/?igsh=eHNxb3gzaHo5NjBl )

Oh, I see. Indeed, that seems a bit too powerful :) Could try with 2s LiPo only.. What scale / wheel size is that? About 80mm?

[HorcikDesigns]

1 hour ago, gyenesvi said:

That's great to hear! Curious what you manage to bring out of it! Is the idea similar to what I proposed above?

Oh, I see. Indeed, that seems a bit too powerful :) Could try with 2s LiPo only.. What scale / wheel size is that? About 80mm?

Yes, the scheme is similar, but terth numbers will be different. I hope to bring to reduxtion at least to 1:6 and the offset from ground to 1:8. I also consider direct coupling of the housing with 24 tooth differential. But I have to do some calculations first. 

The wheels are similar in size to big tractor tires, so approx. 110mm

[gyenesvi]

1 hour ago, HorcikDesigns said:

Yes, the scheme is similar, but terth numbers will be different. I hope to bring to reduxtion at least to 1:6

Sounds good!

1 hour ago, HorcikDesigns said:

and the offset from ground to 1:8.

What does that mean?

1 hour ago, HorcikDesigns said:

I also consider direct coupling of the housing with 24 tooth differential.

What would that do? Just to be able to have a center diff, or something more?

1 hour ago, HorcikDesigns said:

The wheels are similar in size to big tractor tires, so approx. 110mm

That's huge, and that small motor rips with all that to carry! Serious power!

[HorcikDesigns]

4 hours ago, gyenesvi said:

Sounds good!

What does that mean?

What would that do? Just to be able to have a center diff, or something more?

That's huge, and that small motor rips with all that to carry! Serious power!

A Typo. Huge one. I do not understand it either.  I meant that there will be 1 stud (1 x 8mm, aha... maybe... :D) between the axle and bottom of the housing (12mm actually, maybe littlebit more) 

Yes, just central diff. But some clever minds will find some other uses. 

I am almost scared from the power output of the motor of this size. 

[NoEXIST]

@HorcikDesigns This gearbox is sick! Imo that's how we should put BU motors inside Lego builds, not using planetary hubs.

I personally would like to have a version with center diff!

[Krzychups]

On 6/15/2024 at 9:46 AM, HorcikDesigns said:

Hi, I have designed 11:40 gearbox for motor A2212. Works great with 1000KV motor and 3S LiPo, even when tge hoising and gear are printed from basic PLA. Greased offcourse. 

Wow, good job! You have done something I tried to do (look here), but much better. I'll try it. What I'm concerned about, are mounting holes - there aren't many of them. 

Edit:

@gyenesvi I cannot quote while editing. You said: "What does that exactly mean? At first I thought you'd want to change the outer diameter to 24mm instead of 28mm to fit 24mm motors, but it seems you are talking about something different?" Regarding it, I meant that these planetary gearboxes are made for motors which have got about 2 mm shafts, for example the A2212 motor has got 3,17 mm shaft, so it wouldn't work. I hope you undestand it.

Much easier would be using 3650 motors, but they are big and powerful. 

 

Edited June 17, 2024 by Krzychups