[MOC] Greyhound 4WD RC Buggy /w instructions - Improved rim-hub connection

[amorti]

As it's Chinese stuff, I'll ask @Jim his opinion first.

Does this come under the heading of improved PF parts like buwizz, or does the fact of it shipping from China (and specifically a moc stealing company) mean it's a no-go?

[Toshi]

Of course!

Forgot to say that you should of course adhere to forum rules! 

[benxz]

i tried to use sbrick and lego rechargeable battery today but it doesn't seem to be able to move the buggy. I connected each motor to each port on Sbrick, the wheels can spin when the car is lifted off the ground.

Edited June 29, 2020 by benxz

[amorti]

Assuming all wheels are turning the same direction, it's still a heavy model and maybe 1 S-brick can't manage? Or maybe the one rechargeable battery hits its limit first?

I know in Icarus, Madocca uses two rechargeable batteries and two S-bricks, maybe that's why.

[benxz]

35 minutes ago, amorti said:

Assuming all wheels are turning the same direction, it's still a heavy model and maybe 1 S-brick can't manage? Or maybe the one rechargeable battery hits its limit first?

I know in Icarus, Madocca uses two rechargeable batteries and two S-bricks, maybe that's why.

I thought each sbrick port outputs the same max current, maybe one battery is not enough?

[amorti]

30 minutes ago, benxz said:

I thought each sbrick port outputs the same max current, maybe one battery is not enough?

Yeh, probably the battery. Looks like it is fused at 750mA, I am pretty well certain the S-brick will deliver much more, and the 4x L-motors will certainly ask for more to beat a 2kg model's inertia.

As you have an S-brick, I think the answer might be to adapt a 2S lipo battery.

[benxz]

46 minutes ago, amorti said:

Yeh, probably the battery. Looks like it is fused at 750mA, I am pretty well certain the S-brick will deliver much more, and the 4x L-motors will certainly ask for more to beat a 2kg model's inertia.

As you have an S-brick, I think the answer might be to adapt a 2S lipo battery.

good idea with lipo. Any extra component needed apart from the lipo battery and soldering work? I just tried 2 Sbrick with 2 lego battery, it only runs for about 10 second then stopped moving.

Edited June 29, 2020 by benxz

[amorti]

10 minutes ago, benxz said:

good idea with lipo. Any extra component needed apart from the lipo battery and soldering work? I just tried 2 Sbrick with 2 lego battery, it only runs for about 10 second then stopped moving.

Don't know - I have not tried it myself. From a youtube video I saw, you need a spare PF plug, a 2S LiPo (you can use 3S but then you need to add a DC-DC transformer as a voltage limiter?) and a steady hand.

Not sure how you'd guard against excessively draining the LiPo. They don't like that. Maybe just make a special point to stop driving it when the vehicle starts running slower. IDK if there's an easy circuit or component that would do that function.

That may be thinking too hard though, apparently cells are OK down to 2.5v each. I think before Greyhound got down to 5v, it wouldn't be able to move.

[Toshi]

I would also assume that it‘s the battery that is holding you back!

I did some experimentation last week with a non-LiPo solution myself (the „can explode part“ of the LiPo still scares me somewhat).

My solution includes n regular 8-AA-battery holder, a 9V plug, a PF-Extension-Cable and 8 1,2V NiMH AA batteries connected to an sbrick.

The tracked vehicle I am powering with this has 4 RC-Motors and works nicely. The only problem is that the sbrick gets really hot and actually shuts down at 80+ degrees Celsius... ;)

My model is likely a bit lighter than the Buggy, but L-Motors draw less current than RC-Motors also...

At full charge the NiMH batteries provide about 10,85V which is also pretty nice!

I just think that the sbrick might not like that much power running through it for a longer period of time - I am likely going to reduce the load to 2 RC-motors and get a second sbrick...

Edited June 29, 2020 by Toshi
typo

[benxz]

1 hour ago, amorti said:

Don't know - I have not tried it myself. From a youtube video I saw, you need a spare PF plug, a 2S LiPo (you can use 3S but then you need to add a DC-DC transformer as a voltage limiter?) and a steady hand.

Not sure how you'd guard against excessively draining the LiPo. They don't like that. Maybe just make a special point to stop driving it when the vehicle starts running slower. IDK if there's an easy circuit or component that would do that function.

That may be thinking too hard though, apparently cells are OK down to 2.5v each. I think before Greyhound got down to 5v, it wouldn't be able to move.

Verified one 2s Lipo with 2 Sbircks did the job, actually I believe I can get away with one Sbrick, since the current is now big enough to push this heavy buggy. If you worry about the voltage drop on the lipo, you can buy an LED alarm you can plug into the lipo, it'll beep when the voltage drops to the value you set. thx for the lipo tip, will be using my lipo on lego technics from now on, much cheaper and powerful than lego rechargeable. 

[Jimrask]

7 hours ago, benxz said:

i tried to use sbrick and lego rechargeable battery today but it doesn't seem to be able to move the buggy. I connected each motor to each port on Sbrick, the wheels can spin when the car is lifted off the ground.

Just use 2 BuWizz'es, like the designer did?

[amorti]

Just now, Jimrask said:

Just use 2 BuWizz'es, like the designer did?

It's the best pure-ish Lego solution and it fits great in the model. But 2* buwizz costs 229€, which is a lot of money. It's especially a lot if you already have sbricks and lipos in the house.

[Toshi]

I have to add that even two BuWizz‘s don‘t seem to be able to cope with the buggy on ludicrous mode 100% of the time...

[benxz]

this thing is a U joint killer, need to wait for those metal ones before i run it again.

[benxz]

On 6/29/2020 at 7:49 AM, amorti said:

Assuming all wheels are turning the same direction, it's still a heavy model and maybe 1 S-brick can't manage? Or maybe the one rechargeable battery hits its limit first?

I know in Icarus, Madocca uses two rechargeable batteries and two S-bricks, maybe that's why.

I went back to Madocca's Icarus and used Amorti's suggestion, one 2s lipo with one Sbrick, Icarus runs very nice, saved one SB and 2 lego battery and reduced lots of weight. Great idea Amorti!

[amorti]

On 6/30/2020 at 2:56 AM, benxz said:

this thing is a U joint killer, need to wait for those metal ones before i run it again.

Well, they're a lot stronger than Lego's plastic u-joints, but due to poor design and cheap materials, they're still a wear part.

 

[benxz]

On 7/7/2020 at 9:40 AM, amorti said:

Well, they're a lot stronger than Lego's plastic u-joints, but due to poor design and cheap materials, they're still a wear part.

 

That's why I went to modify the Icarus' V joints to gear driven, I think the Greyhound needs that too.

[Didumos69]

8 hours ago, benxz said:

That's why I went to modify the Icarus' V joints to gear driven, I think the Greyhound needs that too.

I have only broken 2 universal joints over time, but maybe you guys are pushing it to the limit more, which is understandable of course.

Isn't the best option to use the new CV-joints like @amorti did?

 

Edited July 9, 2020 by Didumos69

[amorti]

8 hours ago, Didumos69 said:

I have only broken 2 universal joints over time, but maybe you guys are pushing it to the limit more, which is understandable of course.

Isn't the best option to use the new CV-joints like @amorti did?

So here's my findings after testing each solution, ranked in order of success and some embedded links:

1. Plastic universal joints: when driven with the Chinese +30% motor M-003 on anything other than Slow, these last maximum of a few minutes. The rubber band trick stops them splitting, so they spread the yokes and the disc flies out, never to be seen again. The 30% extra torque of these Chinese motors might be the reason they're fine for @Didumos69 but no good for me. Anyone thinking about using these motors needs to be aware, they're heading down a rabbit hole of finding the next weakest link. I know I need to make a video of mine driving over rough terrain to show this claim, but it's not easy when you need your phone to run BrickController2.
2. AliExpress metal universal joints: These are sloppily built with a soft alloy body, the disc is brass/bronze, and the pins are steel. There is around 1/16 turn of play right from the start and on mine a few km of driving (driving Greyhound while walking Myhound  ) saw 1/8 turn of freeplay and a horrible noise, but at least they didn't fail catastrophically. However, some users have reported they can fail catastrophically, and the sloppy tolerances mean I can believe it.
3. Lego 42099 CV joints: actually these aren't bad .For any Lego purists, this is the best solution because they will not fail catastrophically like the two above, although they will wear down with use (image shows early stages!). I think a lot of the wear they suffer is because of the misalignment inherent in small ball-joints. In any case, only the ball part of the joint gets worn and it's not so hard to replace nor too expensive.
4. eBay metal universal joints: I've just ordered these and as they are made of plated steel, I have hopes that they'll be the most durable solution yet. They're 4mm RC universal joints bored out to 4.8mm such that a Lego axle fits snug. Seller told me it's best to use metal axles (which he also sells, I had to ask for 4L axles specifically and pay an extra £2.50  each as a custom machining fee on top of a 5L axle's normal price) as you need to screw the joint down onto the axle and even if that holds, your axle will be scrap afterwards.

 

Edited July 9, 2020 by amorti

[benxz]

7 hours ago, amorti said:

Seller told me it's best to use metal axles (which he also sells, I had to ask for 4L axles specifically and pay an extra £2.50  each as a custom machining fee on top of a 5L axle's normal price) as you need to screw the joint down onto the axle and even if that holds, your axle will be scrap afterwards.

 

These look nice, i think i need this for sure. I broke one of the lego axle running the yellow supercar, guess the power of lipo is really pushing the limits. I'm surprised the buwizz with ludicrous drive will still render not much damage to the U joints on Didumos' original set.

BTW, how do you embed the youtube video? I tried to follow the instruction with [media] [/media] but it doesn't work.

 

Edited July 9, 2020 by benxz

[amorti]

@benxz Just put the YouTube link in the text box, the forum software is smart enough to work it out.

Didumos has said he's broken 2 Lego plastic U-joints, and there's several reports of that happening in the thread.

As it's only 2, didumos clearly has more mechanical sympathy than we do, and no "leaden foot"! I don't doubt him, and happily accept that if you have original (less torque) Lego motors and you drive it considerately with gentle acceleration, the original U-joints will last at least a little while.

[amorti]

On 7/9/2020 at 8:44 AM, amorti said:

 eBay metal universal joints: I've just ordered these and as they are made of plated steel, I have hopes that they'll be the most durable solution yet. They're 4mm RC universal joints bored out to 4.8mm such that a Lego axle fits snug. Seller told me it's best to use metal axles (which he also sells, I had to ask for 4L axles specifically and pay an extra £2.50  each as a custom machining fee on top of a 5L axle's normal price) as you need to screw the joint down onto the axle and even if that holds, your axle will be scrap afterwards.

 

So, the postman came today.

 

The parts of DarkIce are not exactly cheap, as you can see here!

Shipping from UK to Malta costs £10, I guess other European destinations are the same.

 

But definitely quality parts:

 

The company only offers odd lengths of axles. I specially requested 2 * 4L axles, because it doesn't work with any odd length. Unfortunately they are about 2mm longer than Lego axles.

 

The colleague at DarkIce told me when I asked, that they add a 1mm rounding on both sides to protect plastic parts. Unfortunately, the 4L metal axles do not fit for this reason. 

No worries, I took a plastic axle. Either that holds or I'll grind away the 4 * 1mm roundings later.

 

The nice thing about this extra length is that in the end you have a 5.5L from a 5L axle and can mount the hubcap nicely.

So, do I recommend these? Yes! Either you can use these joints with plastic axles (which are then scrap afterwards because of the grub screw), or you order 2 * 5L metal axles with, and 2 * 4L which I'm sure they'd do to a specified custom total length of 32mm on request. If you're firing up the lathe anyway, what does it matter if it's 4L plus rounding or 4L including rounding?

Otherwise, if you can drill out joints from the RC world to 4.8mm at home, this is also a good solution.

Edited July 23, 2020 by amorti

[amorti]

On 6/28/2020 at 12:10 PM, Toshi said:

Seeing @amorti talk about L-Motors with 30% more power made me very curious! 

Can you please share some more details about these motors?

To give an idea of the extra power these motors are drawing, if you give full gas from a standing start in Ludicrous mode, it'll trip the safety immediately even with two freshly charged buwzz units. Original Lego L-motors don't draw so much power to do that. I fully expect they're cheaper-made than Lego motors and waste more in heat and friction, but that extra wattage has to be going somewhere.

Anyways, some more mods have been made.

Sometimes Claas tyres just aren't big enough...

These are eBay China-special 1.9" x 120mm RC tyres. With them on, the model drives quieter as they're comparatively very soft rubber, relying on the foam inside to keep their shape rather than a hard rubber casing.

The circumference is about 12% increased, so speed should increase by about 1/8 if the motors have the power for it (the Chinese motors do have enough juice for that, I don't know about original Lego motors).

It now only barely touches the ground at full suspension compression, and has a little more clearance for e.g. driving up kerbs, which it will easily do.

I also added LED strips front and rear.

With all that extra power and extra grip, you can pop bevel gears at will by rocking the car back and forth in Fast mode. It's not a limit of the materials (yet) but the power exposing flex in the bevel housing.

I haven't broken any since doing this modification though. Swapping an I-beam into the rear of each swing arm gives more solid support for the rear of the prop-shafts than original solution. An extra 5L beam goes a little further still with form locking; the price is the swingarm then becomes one unit longer, but this isn't an issue for clearance.

The prop shafts are a 2L axle straight into a 2L axle connector, then an 8L axle which goes through a pin with hole connector being used something like a prop-shaft centre bearing.

The 8L axle is better-supported at both ends than the original solution, eliminating that flex and saving your bevel gears. You do lose the mechanical stop which was present on the 5.5 axle in the original solution, but for me it's worth it, and anyway it takes a fair while to creep any noticeable distance. If it does creep out, it'll escape the 2L connector first, but not fall out of the vehicle entirely due to the 1L bush. I guess you get enough warning and no catastrophic failure occurs.

I guess using an 8L axle with end stop would make it marginally quicker to change out a bevel gear if you still manage to break one. You might even manage to change out a pair without removing the wheel from the swingarm - I don't know, I haven't had to try.

Thinking about it, there's now no reason not to use a 10L axle to cover the whole length of the prop-shaft. I may yet do that, and add 2 more bushes in place of the 2L connector to give more clutch on the propshaft.

 

Again, thanks to @Didumos69 for the awesome design. It's a wonderful model, by far my favourite in the collection, and I just love to play with it, and make these little tweaks.

 

Edit: I did change for a 10L axle as a prop shaft. It does have more clutch, it's also a pig to assemble.

Edited August 11, 2020 by amorti

[Yoseep]

Hello. Built this years ago and when trying now, I noticed that the thin black 3l liftarms that hold the front L motors is supposed to hang on half of the black pin with pinhole which is also used to keep the steering mechanism in place.

http://imgur.com/a/sODbokH

"Problem" is, that is a friction pin and I really dislike it when friction pins are used as axles for moving parts. Doors and other cosmetics ok, but for suspended parts, I don't like it at all. Though Lego sometimes does it (9398 crawler suspension IIRC).

I now replaced the pin with pinhole with an axle with pinhole. I'm writing to ask whether the motor thin liftarm is actually supposed to rotate on that friction pin with pinhole, or did I misread the instructions, cause I really don't remember it being like that the first time around. But it was a long time ago. Also asking because if I get it wrong now, It'll be a slog to rebuild this part.

Thnx

[Teo LEGO Technic]

Amazing model as always, it's just so satisfying watching that suspension work  . How did you ever get it to run so smooth? Is it something to do with the geometry?