Let's talk about lego technic system power up limits, and how to make it higher

[dustblue]

Hey guys, recently I've been testing lego technic system power up limits, because I plan to make a 8 buggy motor drive trail truck, but I need to know if it is practical first. So yesterday I couple 4 buggy motors together, to drive my 4 sequential gearbox, to power a 5 blade propeller. I use this test setup because the power output and input is coupled very well, the output is powerful enough to suck in all the power from the input(you can see this from the currents the buggy motors draw).

Photos: ok this forum can only upload 30kb photos, maybe it's designed from 1999.

Use this: https://drive.google.com/drive/folders/1zjbJZIW18TFNwHwXXQR7grqEwignfjVb?usp=drive_link

This 4 speed sequential gear box gear ratio: 1.75; 1.2; 0.833; 0.57

So it's around the buggy motors' rpm, not much deviation from it. This gearbox is very effective, the propeller is setup to make down force, in gear 1 only 75g down force, gear 2 150g, gear 3 230g, and gear 4 would be higher but the orange clutch can not keep the driving ring in position. So these new gearbox parts are not powerful enough to handle this 4 buggy motor input, now this is the first problem, which should be easy to overcome: just don't use these new shifting gear parts.

 

The second problem is much more serious, after just a couple minutes testing, mostly in gear 3, which means the output rpm is 1.2* buggy motor native rpm. In this senerio the beam that holds the output carbon axle melted!!! I know the rpm is not the problem, the actual problem is the torque*rpm which is power output. In this gearbox design I can not make a symmetrical design on the output axle because I only have one set of the new parts from Lego 42159 so only 1 24 gear with driving ring input. However even if I can make a symmetrical design, it only eliminates output axle load problem, for the planet gear axles there would be still significant loads, in half, and still facing the melting beam problem.

 

Someone might thinks using lower rpm like L motors or xL motors, however there are much more hard to conquer pronblems in those setups, which is torque. I tested, in native output, xL motor torque is 2.5 times buggy motor, 3 xL motors coupled tegother would destroy carbon axle! 10-15 buggy motors coupled tegother can also do it. For lego plastic axles it would be much more easier. 3 buggy motors coupled could destroy 8 teeth gear! 5 buggy motors can destroy plastic lego axles.

 

So you see using buggy motors is to avoid the high torque situation, and leave it to the wheels( I use custom designed planet gear reduction on wheels, and wheel locks to prevent wheels comming off which is the no.1 problem of lego technic system).

 

And now, even buggy motors have limits.I have silicone oil and I would lubricate the parts when remembered. but is there anything else you can do to higher the system up limits? 

 

 

[dustblue]

I myself used direct drive a lot, like 1 buggy to drive 1 wheel, or 2 L motors to drive 1 wheel. That way can distribute system load, and get diffrentials/diffrential locks out of the car. However, it also significantly increased the unsprunged mass, also make it hard to use gearboxes, make the vehicle less real and hence less fun.

[dustblue]

detailed analysis photo uploaded, the one with many colorful arrows.

red arrow is input torque force direction, green is force on output axle, yellow circle is pivot point, purple arrow is the effect of green arrow axle force after the pivot, and it's the melting direction of the beam(the force is max on this direction hence friction max).

 

the lesson learned: you must use symmetrical output in high power situation, or try something to elimanate unwanted force on the axle.

Edited September 17 by dustblue

[Maaboo the Witch]

2 hours ago, dustblue said:

Photos: ok this forum can only upload 30kb photos, maybe it's designed from 1999.

You can use Flickr to host photos and copy/paste the URLs here.

[dustblue]

4 minutes ago, Maaboo the Witch said:

You can use Flickr to host photos and copy/paste the URLs here.

Thanks google cloud is better for me, let me know if you have troubles seeing those photos.

[howitzer]

51 minutes ago, dustblue said:

Thanks google cloud is better for me, let me know if you have troubles seeing those photos.

Google cloud works, but we have to click the link as the photos won't show up embedded in your post. Using Flickr or some other service like Brickshelf or Imgur will allow embedding the photos directly into your posts, which helps readability.

[dustblue]

1 hour ago, howitzer said:

Google cloud works, but we have to click the link as the photos won't show up embedded in your post. Using Flickr or some other service like Brickshelf or Imgur will allow embedding the photos directly into your posts, which helps readability.

I get it, sorry for my misunderstanding. Would try flickr later if I would post frequently:)

[2GodBDGlory]

Yep, I think you're running into some of the same problems I've been fighting with lately! I've been trying to make powerful MOCs running off of a custom 3S lithium battery (similar to a Buwizz in voltage), but it's really a fight to figure out how to get maximum power! I tried one MOC with 4 XL motors, and had massive problems with snapping parts due to the high torque. I then tried a different one with two buggy motors, which still seemed to work better overall, but at some point there's the danger of melting parts due to high rpm!

Lego's system seems to be restrictive in both max torque and max rpm, which essentially limits the maximum power to the product of those two, unfortunately.

I think the only real practical solution to this dilemma is to build entirely parallel drivetrains, in which different motors drive different axles or wheels without any mechanical connection between them. This way, under no situation can you have too much torque on any given part of the drivetrain. The downsides to this approach are that for an off-roader, if you only have certain wheels on the ground, you may have a lot of power that you can't actually use, and perhaps not enough torque. The second disadvantage is the difficulty of building gearboxes. In my latest MOC I've built it with two entirely separate 2-speed transmissions, but like you, I'm finding that any normal driving-ring based transmission will lead to the rings skipping out under high power. Probably a better solution is to build a gearbox based on sliding gears, but this has issues of its own.

Frustrating stuff! I will say that putting a 4-speed like you have there in a performance model seems extremely challenging because of the relatively high friction involved, and so perhaps you could have better luck with a simple 2-speed? These new gearbox parts definitely offer potential for simpler 4-speeds, though, so maybe you can pull it off!

[dustblue]

41 minutes ago, 2GodBDGlory said:

Yep, I think you're running into some of the same problems I've been fighting with lately! I've been trying to make powerful MOCs running off of a custom 3S lithium battery (similar to a Buwizz in voltage), but it's really a fight to figure out how to get maximum power! I tried one MOC with 4 XL motors, and had massive problems with snapping parts due to the high torque. I then tried a different one with two buggy motors, which still seemed to work better overall, but at some point there's the danger of melting parts due to high rpm!

Lego's system seems to be restrictive in both max torque and max rpm, which essentially limits the maximum power to the product of those two, unfortunately.

I think the only real practical solution to this dilemma is to build entirely parallel drivetrains, in which different motors drive different axles or wheels without any mechanical connection between them. This way, under no situation can you have too much torque on any given part of the drivetrain. The downsides to this approach are that for an off-roader, if you only have certain wheels on the ground, you may have a lot of power that you can't actually use, and perhaps not enough torque. The second disadvantage is the difficulty of building gearboxes. In my latest MOC I've built it with two entirely separate 2-speed transmissions, but like you, I'm finding that any normal driving-ring based transmission will lead to the rings skipping out under high power. Probably a better solution is to build a gearbox based on sliding gears, but this has issues of its own.

Frustrating stuff! I will say that putting a 4-speed like you have there in a performance model seems extremely challenging because of the relatively high friction involved, and so perhaps you could have better luck with a simple 2-speed? These new gearbox parts definitely offer potential for simpler 4-speeds, though, so maybe you can pull it off!

Yes I am thinking the same, maybe 4 buggies to drive left and 4 buggies to drive right, thus no need of differentials and d locks. I guess that's why everyone is doing the same( at least madoca1977 do this in his bigger mocs) 

I also thought about using 3s RC battery but it's too much trouble, just buy more buwizz is my solution now. It's lighter and much more convenient with much more functions.

BTW did you try NiZn AA battery? it's better than NiMh and disposable AAs, and a tiny bit better than 2s Li like the ones from mould king & Cada. If you use power up control hub or lego AA battery boxes, worth a try. With many AA battery boxes and only one 2 channel control, you can simutanously control infinate motors at once. I didn't go that way though, because there is too much trouble and it would be too heavy. 

 

[Davidz90]

Maybe it's a stupid question, but how about adding a cluth that disengages the gearbox during shift, just like in a real car? As far as I understand, the biggest problems happen during shifting.

Second thought, the new splat gears have a huge teeth and can be attached with 2x2 round bricks with technic hole. A large-diameter axle made from 2x2 bricks with regular axle inside can handle some serious torque. Maybe some sort of transmission can be made with that?

[2GodBDGlory]

1 hour ago, dustblue said:

Yes I am thinking the same, maybe 4 buggies to drive left and 4 buggies to drive right, thus no need of differentials and d locks. I guess that's why everyone is doing the same( at least madoca1977 do this in his bigger mocs) 

I also thought about using 3s RC battery but it's too much trouble, just buy more buwizz is my solution now. It's lighter and much more convenient with much more functions.

BTW did you try NiZn AA battery? it's better than NiMh and disposable AAs, and a tiny bit better than 2s Li like the ones from mould king & Cada. If you use power up control hub or lego AA battery boxes, worth a try. With many AA battery boxes and only one 2 channel control, you can simutanously control infinate motors at once. I didn't go that way though, because there is too much trouble and it would be too heavy. 

 

Yeah, Buwizz does look really convenient! I haven't tried either it or NiZn, mainly because I'm cheap! My 3S battery was essentially free, because I was able to build it out of leftover cells from a dead hoverboard battery pack and a 3D-printed case, so I'm happy with it!

[dustblue]

1 hour ago, Davidz90 said:

Maybe it's a stupid question, but how about adding a cluth that disengages the gearbox during shift, just like in a real car? As far as I understand, the biggest problems happen during shifting.

Second thought, the new splat gears have a huge teeth and can be attached with 2x2 round bricks with technic hole. A large-diameter axle made from 2x2 bricks with regular axle inside can handle some serious torque. Maybe some sort of transmission can be made with that?

the shift is quick and efficient, never the problem, that's where the new parts shines.

If you want to handle torque just use carbon fiber axles, those can handle 3 times the torque than plastic ones. The problem is to handle torque*speed together, as 2GodBDGlory pointed out, which is equal to power.

7 minutes ago, 2GodBDGlory said:

Yeah, Buwizz does look really convenient! I haven't tried either it or NiZn, mainly because I'm cheap! My 3S battery was essentially free, because I was able to build it out of leftover cells from a dead hoverboard battery pack and a 3D-printed case, so I'm happy with it!

That's great! I used to make battery from A123 cells to power studio strobes, 600 Watts instant power, lots of fun:)

[Davidz90]

6 minutes ago, dustblue said:

the shift is quick and efficient, never the problem, that's where the new parts shines

Good to know.

I mean, 2x2 brick can handle much more than 3 times the torque of regular axle, so the idea was that it could be possible to transfer much more power before reaching axle-melting speeds. But that would necessitate some sort of bearings for 2x2 bricks.

 

To be more precise, I was thinking about something along the lines of the driveshaft in this pneumatic engine:

which powered real-life Lego car:

but that is total overkill for all but largest builds.

 

Edited September 17 by Davidz90

[dustblue]

41 minutes ago, Davidz90 said:

Good to know.

I mean, 2x2 brick can handle much more than 3 times the torque of regular axle, so the idea was that it could be possible to transfer much more power before reaching axle-melting speeds. But that would necessitate some sort of bearings for 2x2 bricks.

 

To be more precise, I was thinking about something along the lines of the driveshaft in this pneumatic engine:

which powered real-life Lego car:

but that is total overkill for all but largest builds.

 

WOW! Thanks for sharing! These are definately inspiring! Gonna find out how did they do it, I mean without metal axle?? Oh my...

[2GodBDGlory]

3 hours ago, Davidz90 said:

Good to know.

I mean, 2x2 brick can handle much more than 3 times the torque of regular axle, so the idea was that it could be possible to transfer much more power before reaching axle-melting speeds. But that would necessitate some sort of bearings for 2x2 bricks.

Hmm, it would be interesting to try to develop a whole ecosystem based on 2x2 round brick axles! The obvious challenges are how it would interface with beams and gears--after all, if you have to go down to a normal axle to get drive into an O-frame, there's not much point!

I'm not sure if it would be possible to build up a system that would work with that high strength and fit into MOCs of typical size, but the idea has me thinking!

[2GodBDGlory]

On that topic, here's a rough draft of what an O-frame housing could look like on a hypothetical 2x2 axle-based system:

I'm using splat gears, since they're somewhat heavy-duty looking, and interface nicely with the studs of the bricks. I'd like to use the classic, pre-Technic gears, but they can't directly interface with the bricks without having an intermediate axle, which defeats the purpose

I'm now feeling kind of inspired to try building some weird proof-of-concept vehicle with a mildly complex drivetrain, in which no torque whatsoever is transmitted by axles!

[Davidz90]

 

3 hours ago, 2GodBDGlory said:

On that topic, here's a rough draft of what an O-frame housing could look like on a hypothetical 2x2 axle-based system:

Amazing! Yes, that's exactly what I had in mind. Another thing worth trying is putting the 2x2 brick between 4 rollers in 4 corners.

[gyenesvi]

14 hours ago, Davidz90 said:

I mean, 2x2 brick can handle much more than 3 times the torque of regular axle, so the idea was that it could be possible to transfer much more power before reaching axle-melting speeds. But that would necessitate some sort of bearings for 2x2 bricks.

A simplification of this idea is when you connect short axles with 2L or 3L axle connectors, instead of using long axles. The connectors themselves already much stronger than bare axles, and in most situations you can get away with only using 2L, 3L or 4L axles, maximum 5L inside a gearbox. Those are much less prone to twisting and bending, especially since those are the points where the driveshaft is held securely in a pinhole.

[dustblue]

8 hours ago, 2GodBDGlory said:

On that topic, here's a rough draft of what an O-frame housing could look like on a hypothetical 2x2 axle-based system:

I'm using splat gears, since they're somewhat heavy-duty looking, and interface nicely with the studs of the bricks. I'd like to use the classic, pre-Technic gears, but they can't directly interface with the bricks without having an intermediate axle, which defeats the purpose

I'm now feeling kind of inspired to try building some weird proof-of-concept vehicle with a mildly complex drivetrain, in which no torque whatsoever is transmitted by axles!

wonderful demo!

 

52 minutes ago, gyenesvi said:

A simplification of this idea is when you connect short axles with 2L or 3L axle connectors, instead of using long axles. The connectors themselves already much stronger than bare axles, and in most situations you can get away with only using 2L, 3L or 4L axles, maximum 5L inside a gearbox. Those are much less prone to twisting and bending, especially since those are the points where the driveshaft is held securely in a pinhole.

Yes it would be stronger, I have tested it vs bare axle. but it would be still not as strong as a carbon axle, because the weakest ling of this system is still a thin plastic axle, not the connector

[2GodBDGlory]

3 hours ago, gyenesvi said:

A simplification of this idea is when you connect short axles with 2L or 3L axle connectors, instead of using long axles. The connectors themselves already much stronger than bare axles, and in most situations you can get away with only using 2L, 3L or 4L axles, maximum 5L inside a gearbox. Those are much less prone to twisting and bending, especially since those are the points where the driveshaft is held securely in a pinhole.

Yeah, that's definitely good practice, but even it can be maxed out! I broke many 2L and 3L axle connectors, and 3L and 4L axles in my Lada Niva MOC recently. I probably had more torque on those parts of the drivetrain than I could have, but if you need that level of torque, you'll need something tougher

[dustblue]

7 minutes ago, 2GodBDGlory said:

Yeah, that's definitely good practice, but even it can be maxed out! I broke many 2L and 3L axle connectors, and 3L and 4L axles in my Lada Niva MOC recently. I probably had more torque on those parts of the drivetrain than I could have, but if you need that level of torque, you'll need something tougher

you broke the connectors before the axles they hold broke first? did you use carbon axles on these? 

[2GodBDGlory]

1 hour ago, dustblue said:

you broke the connectors before the axles they hold broke first? did you use carbon axles on these? 

No, it was just standard 3L axles. The axles definitely twisted first, but didn't usually snap before the connectors

Here's the carnage from one day of driving:

No 2L connectors in the picture, but I did break them other days

[dustblue]

2 minutes ago, 2GodBDGlory said:

No, it was just standard 3L axles. The axles definitely twisted first, but didn't usually snap before the connectors

yes that's my thought. plastic axles generally deform first, so I won't use them in any situation with a torque higher than 3 buggy motors(or higher than one xL motor native output)

[dustblue]

So after the 4 sequential gearbox with new parts from 42159 failure on heavy load, I designed a new one, which is just 2 shifts, with symatrical planet gear like design to distribute the load, it successed on 4 buggy motors power! However today I wanted to push the limits and added 2 more buggy motors, it can generate 326 grams of down force! With a total of roughly 12A currents, that's 140 watts of electric power. That's the new record for me, but shortly after this run, when I run it again, it failed, turned out one of the planetary carbon axle melted the beams that holds it, 3 beams were destroyed. Just like I said earlier, even with symatrical design the planet gears would also cause trouble, but it is indeed effective, compare to my original 4 sequential gear box design, which is not symatrical.

This gear box has gear ratio of 1.8 & 0.6, so you can guess that I used 8 teeth gear, this is dangerous though, it can only work on the planet axle, because 8 teeth gear can handle max 3 buggy motor torque, any more than that it could be deystroyd instantly.

So my conclusion is, a lego gearbox can only handle 4 buggy motors power at most, any more than that, you need more gearboxes(Which is what I'm going to do on my next car).

 

Video:

Strange why it's not working? This is video on flickr, when editing I can see it, but after publish it's gone, wth...

Anyways the link: just delete the space

https: //flic.kr/p/2p4mrJL

 

 

 

 

Edited Thursday at 08:18 AM by dustblue