Ctan

Custom third party Universal Joint 3L

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Hi, as you probably know Lego Universal Joint 3L is not the strongest one in case of high power aplications. Some time ago I had modified my 9398 Crawler with 2 XL motors and they was breaking joints easily when one wheel stuck. I was looking for solution and found RC boats universal joints on aliexpress (3mm hole). It cost about 2-3$ each or less as far as I remember. So all in all it seems that it can work. Only thing you need to do is drill "X" openings to fit axle.

Here is a common view on my 9398

20180524_161239-e1527177948870.jpg

Axles are glued to joints and they are designed to replace original 9398 setup.

20180524_160811.jpg

they have same length using bushes (top part of 1L bush was cut and placed on axle)

20180524_160830.jpg

Hardest part of converting - drilling holes.

20180524_162607-e1527178092136.jpg

And here is a result:

20180524_161902-e1527178158987.jpg

After testing performance is now pretty cool, additionaly they're lubricated with silicone spray so I don't have to worry about friction and spare Universal Joints in my pocket when driving.

Hope you enjoyed my custom made cardans :)

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I actually tried making my own U-joints with these same brass boat parts a couple years ago, however I tried holding the plastic in with friction/set screws and it just wouldn't work. I didn't even think of carving out the cross section, that's obviously smarter :facepalm:

Great job! This is a must have for all RC MOCs.

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TLG  should redesign or improve 3l u-joints. They die like flies despite gearing and usage.

The part is a joke by itself. It has 4 weakest "sub parts" in it. 2 Bush parts on each side and 2 hubs with small holes. The strongest sub part is a crossy thingy.

Edited by Omikron

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1 hour ago, z3_2drive said:

I actually tried making my own U-joints with these same brass boat parts a couple years ago, however I tried holding the plastic in with friction/set screws and it just wouldn't work. I didn't even think of carving out the cross section, that's obviously smarter :facepalm:

Great job! This is a must have for all RC MOCs.

Thanks! First I was thinking the same about screws but it wont work for sure, maybe if you put an hard metal rod into axle it may work.

31 minutes ago, Zerobricks said:

What about changing gearing in the hubs to reduce the stress on the U joint?

It won't work, if wheel stuck no gears can help. All force goes to U-joint and breaking it. Also my crawler is powered by 3S RC LiPo battery with current limiter to 11,8V and SBrick so XL's always have enough torque to break U-joint :) Now this problem dissapeared. When wheel stuck engine just stalling. Also I like when RC models are speedy and powerful. Taking obstacles like on slowmotion is just boring for me.

 

15 minutes ago, Omikron said:

TLG  should redesign or improve 3l u-joints. They die like flies despite gearing and usage.

The part is a joke by itself. It has 4 weakest "sub parts" in it. 2 Bush parts on each side and 2 hubs with small holes. The strongest sub part is a crossy thingy.

Yes, this cross thingy is always lost outdoors when U-joint is breaking...

Edited by Ctan

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So next thing to upgrade - axles? As I think axles may twist since these are the next weakest link to be destroyed by might torque.

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36 minutes ago, zux said:

So next thing to upgrade - axles? As I think axles may twist since these are the next weakest link to be destroyed by might torque.

Nooo, just wanted to replace part that is too easy to break :)

I've ordered too much lego u-joints replacements and it's all about fun - less broken joints - more fun. :) Rest of bricks are pretty ok.

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Great improvement for the ones that need it.

Please be aware that some silicone sprays have a solvent that dissolves the weakener (or plasticizer) in the ABS making the parts brittle. I had a few 24 teeth gears broken until I figured this out.
So far I had best results with WD40 PTFE spray which doesn't seem to have the solvent that dissolves the weakener and keeps the 24 teeth gear in one piece.

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3 minutes ago, Berthil said:

Please be aware that some silicone sprays have a solvent that dissolves the weakener (or plasticizer) in the ABS making the parts brittle. I had a few 24 teeth gears broken until I figured this out.
So far I had best results with WD40 PTFE spray which doesn't seem to have the solvent that dissolves the weakener and keeps the 24 teeth gear in one piece.

That's very useful info! Thanks!

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17 hours ago, z3_2drive said:

I actually tried making my own U-joints with these same brass boat parts a couple years ago, however I tried holding the plastic in with friction/set screws and it just wouldn't work. I didn't even think of carving out the cross section, that's obviously smarter :facepalm:

Great job! This is a must have for all RC MOCs.

I did something similar, but tried to glue cut down axles to very similar swivel joints. They were useless and kept breaking at the glue joint.

Very nice idea.

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2 hours ago, nerdsforprez said:

Dont forget there is a legal way to strengthen universal joints....

I am a member of Team Illegal (:devil:) so i am often confused by what is and isn't considered legal... but how is wrapping a part in cotton etc legal? Now don't get me wrong, i'd use the brass ones tomorrow as i'm not a purist by any stretch, but it does seem odd that from a purists perspective, wrapping it in something is ok? Not being argumentative, and its a fairly light hearted question, but it does confuse me... 

Anyway, i love the modification to the brass ones. How long does it take to do each one? Is the working angle as good as Lego's? I'm looking at using the metal axles that are available as i've got some BIG tractor tyres that twist lego axles something terrible.. those plus brass UJ's on the front axles would see me with a lot of torque/pulling power..!!!!!

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Look at the whole post not the picture. The picture on the post is from someone else.  Personally, I don't really know how helpful thread would actually be.

 

The trick is to wrap it with official Lego silicone elastics.  This keeps it legal.  Elastics have a exponential holding force.... unlike string. 

@Didumos69 used it on his recent build and I have used it successfully on many of my prior builds.  But as you mentioned, if you are team illegal..... then ignore this and continue on!

Edited by nerdsforprez

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This is by far the strongest solution I've come across that still fit the 1x1 cross-sectional size. But I don't quite like the amount of drillings and cuttings :laugh:.

So far, I've tried larger solutions - either with Lego pulley wheels, or with brass-joints measuring 12x24 mm (and 5mm holes that fits an axle nicely). With the brass-joints, I would do what @z3_2drive did - made use of the tiny screws, but applying glue additionally, to make sure they don't unscrew themselves out over time.

On 25/05/2018 at 3:50 AM, zux said:

So next thing to upgrade - axles? As I think axles may twist since these are the next weakest link to be destroyed by might torque.

What I've experienced so far is that Lego axles are VERY STRONG, so long as you take care of their rpm and friction - make sure they turn freely, and limit rpm to below 4k (max 5k), so that they don't get the chance to heat up and turn soft.

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On 24.05.2018 at 10:33 PM, kieran said:

Not for the purest, but a fantastic mod to improve the strength 

I do illegal mods, I cut bricks, paint them and modifying them if it's needed to get better results. For me they are just pieces of plastic and sometime they can't handle enough stress :)

On 25.05.2018 at 9:14 AM, MOMAtteo79 said:

great job

Thanks, hope it help to make stronger creations!

On 25.05.2018 at 10:15 AM, Berthil said:

Great improvement for the ones that need it.

Please be aware that some silicone sprays have a solvent that dissolves the weakener (or plasticizer) in the ABS making the parts brittle. I had a few 24 teeth gears broken until I figured this out.
So far I had best results with WD40 PTFE spray which doesn't seem to have the solvent that dissolves the weakener and keeps the 24 teeth gear in one piece.

Thanks for the info, it's very helpful!

I used silicone spray from Lidl market. As far as I've using it no brick melted (about 2 months of intensive using especially with RM8's trophy truck (with 2 buggy motors and 9V constant LiPo). No brick melted and dissolved, so I think it's also good one.

23 hours ago, TeamThrifty said:

I am a member of Team Illegal (:devil:) so i am often confused by what is and isn't considered legal... but how is wrapping a part in cotton etc legal? Now don't get me wrong, i'd use the brass ones tomorrow as i'm not a purist by any stretch, but it does seem odd that from a purists perspective, wrapping it in something is ok? Not being argumentative, and its a fairly light hearted question, but it does confuse me... 

Anyway, i love the modification to the brass ones. How long does it take to do each one? Is the working angle as good as Lego's? I'm looking at using the metal axles that are available as i've got some BIG tractor tyres that twist lego axles something terrible.. those plus brass UJ's on the front axles would see me with a lot of torque/pulling power..!!!!!

Thread on u-joints bushes is very helpful when you're using for example 2x L motor for driving and have 2 in line u-joints (for example combination of: liftarm > axle > u-joint > axle > u-joint > axle > liftarm) It can be easily disconnected on stress and thread or tape really help to keep them on place. 

It took me about an hour of drilling, cutting, fitting to make 4 brass u-joints. I did it without vice (which can shorten this time a lot) holding this tiny stuff in my hands. Dremel was set for 5000 rpm and brass was hot on acceptable level when drilling :)

Working angle is a bit smaller than lego original one but didn't have any issues of 9398 steering. 

I use RC4WD 1,9" rock crusher tires on but it need more stress tests in outdoors. For sure 1 stalled XL (11,8 V)  is not able to break brass ujoint or twist axle. Actually lego shorter axles are pretty damn hard to twist so you can try to make longer sections from shorter axles (maybe additionaly taped) connectors. 

 

Update:

Today after really 1h of hard crawling, stalling XL's, and harcore play no u-joint was damaged, no axle twists or any damages so all in all mission is completed!

20180526_135942.jpg

And here are a couple of additional pics of power setup:

20180526_140121.jpg

3s LiPo' s with current limiter to 10,8V to not burn Sbrick. 1800 mAh can handle this model for about 3h of intensive playing. 

20180526_143249.jpg

And dirt is always welcomed on the model :)

20180526_135909.jpg

20180526_135823.jpg

Edited by Ctan
Update

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Great job with the U-joints, they fit perfectly. 

So perfectly, in fact, that I need some for my own crawler project.

You see, I am currently building a relatively large lego rock crawler with huge wheels (these 2.2" bully comp tires with Lego porsche rims). Unfortunately, I am not using portal hubs for this crawler as the wheels are large enough, so I cannot gear down to reduce stress on the U joint. Thus, I have been looking for a metal alternative to lego U-joints and you seem to have made it.

Could I buy some of those modified lego-compatible U-joints from you? If not, could you please give me more information regarding the U-joints you bought as well as the drill you used so that I could create them myself?

Sorry for the slightly off-topic reply. What can I say, your post was inspiring.

(I didn't want to hijack this thread at all, but eurobrick's apparent lack of a messaging feature somewhat forced me to) 

Edited by PunkTacoNYC
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Here is a seller of brass joints (I've ordered them there). It took about 3 weeks to get them in mailbox so relatively fast. 

https://m.aliexpress.com/item/32671992611.html?aff_trace_key=ec1ccf5b136247a19c917ba87564be7b-1526836074823-02011-FuvFYny&aff_short_key=FuvFYny&aff_platform=msite

Milling cutter is from Dremel set, nothing really special, diameter is about 1,5-2 mm. It's a triangular shape so you can control the size of the hole. I drilled it at 5000 rpm and it wasn't too hard to remove brass. 

According to this picture it would be great to have 1,7mm cutter.

v4G9S.png

I left tighter hole and pushed axle with force.

Before you push axle sand joint flat surfaces with grainy paper, it will help to make stronger connection with 1/2 bush because it also hold axle in place. 

When you have axle in hole add a 1/2 bush and check if it fits well. If bush is outside the circle it need more drilling. 

Later glue it with superglue (any cyanoacrylic glue will be ok) and spray with instant hardener. 

Now you need a correct length (3 studs) and top part of bush fit there perfectly so just cut it and glue to the axle.

That's all you need. Also if you're worried that you'll have shorter axle you can use for example 4L black/red axle and cut it to desired length later. 

@PunkTacoNYC

Edited by Ctan

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@Ctan once you get 10 posts you can PM, recommend you don't post your e-mail add on public forum. By the way  great fix, not for the purist though. 

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What does the little display measure in your lipo setup?

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Just now, MAB said:

What does the little display measure in your lipo setup?

It's cell voltage checker with buzzer. You can set there voltage when alarm is on  For example if voltage is below 3,1V on on a single cell)

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15 minutes ago, Ctan said:

It's cell voltage checker with buzzer. You can set there voltage when alarm is on  For example if voltage is below 3,1V on on a single cell)

OK, thanks. Just found them on ebay.

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