[MOC]Generic brushless Trophy Truck

[Ryokeen]

Well where to start, after i got back into building technic sets, the urge to create something of my own took over and i started to look around places where ppl discuss mocs, building techs and so on.
That's how i got to eurobricks and the topics about rc and brushless motors in the lego world took my interest, cause moving things are cool.

The eagle truck and in general the various mocs daniel-99 made gave me the motivation to create my own trophy truck and see how well bricks and rc components match.

It's currently still wip as it's lacking a proper bodywork and might change once i can test it properly(to rainy atm).

I'm not the best at presenting so feel free to ask.

Quick overview:

• 4-Link live axle in the back
• Double wishbone in the front
• 3250kv brushless motor on 2s Lipo
• Geekservo for steering
• All carbon axle driveshaft fully with ball bearings
• Metal gears and metal u-joints
• Strong chassis for serious offroad driving
• Underbelly protection

So far i'm using wheelhubs from zene with ball bearings and their closed metal differential. The whole driveshaft uses carbon axles, metal u-joints, metal gears and ball bearings.

I kinda tried to mimick tropy truck suspensions, so it got a 4 link live axle in the back and a double wishbone suspension in the front. Havn't figured out how i could add roll protection on the back axles as my first attempt didn't seem to help.

The use of triangle geometry gives the chassis enough strenght to take a fall from around 50cm without any damage. Another way i used to reinforce the chassis is the use of longer m3 screws and mathcing nuts as they fit perfectly through 3L pins and stabilize them aswell as preventing the connection to get apart. Good thing is they don't rly damage the parts, as they work
similiar to 3L bars inserted into pins, just better.

As i said i wanted to test how well rc components match with bricks so the first thing was using a brushless motor. The size is almost the same as a 540 brushed one so it was easy to mount using some m3 screews and 2x 32184 parts, for now. An mod 1 pinion gear with 12 tooths provides the connection to the drivetrain.
As the motor got quite a punch and high rpms i decided to only use metal gears on carbon axles seated in ball bearings. Additionally i lubed them with some lithium grease. Currently the total gear reduction is 1:10 including the diff. That gives me around 2500rpms on the wheels with a fully charged lipo and plenty of torque.

First i used 9L springs but in the first freefall test one of them broke, so i thought why not use rc dampers ? And 1:10 scale ones fit quite well. Their upper holes fit the pin diameter and the lower balljoint connection got a 3mm hole in them. Some screwing later they worked like a charm. Might even switch over to only use such shock absorbers as they can be tuned better.

So far that's all, if one got questions, just ask, if one got suggestions, pls let me hear them.
 

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[Aurorasaurus]

I would suggest trying to mount your rear shock absorbers in the middle of the arm. the way you have it right now means that the screw holding the shock in will experience more shear force than it needs to. while its unlikely to shear, you could pretty easily fix it by changing the geometry or mounting your shocks closer to the arm and closer in on the chassis. same thing at the front. if its AWD then try mount the shock above the arm, or add another small arm thats linked to the larger lower arm with the shock mounted between those, so its supported better. if its RWD then you should try mount the shock inside the lower arm and make your upper arm wider so the shock can go through it.  other than that im very impressed.

Edited November 9, 2023 by Aurorasaurus
add info

[Daniel-99]

Hey, man! 

You have used even more non-legoish parts than I did, and each of them has it`s own practical purpose! I really enjoy the closed differential and I do wana try one by myself. Also I have a couple of RC dampers like yours and your truck inspired me to give them a try. 

Do you glue metal U-joints to axes? I had to glue them from one side to keep the driveshaft from falling apart, but more often I glue 3L lego axes to connect U-joins with differential (cause I am using Lego parts here).

I have to admit, that your truck is much more powerful than mine due to the motor choice. Also I like the placement of the Li-Po battery, I use a similar scheme at Eagle V2 (it has not been published yet). Such layout helps to load the rear axle. 

Anti row-bar at the rear really helps with fast starts, As we know, cars with live-axes have a tendency to lift front right \ left wheel while accelerating. This may lead to an accident. I use a carbon-fibre 9L axe for the anti row-bar.

Keep up! I will keep my eyes on your progress!

[gyenesvi]

This looks interesting, so I do have a couple of questions :)

- I'm guessing it's RWD, and the motor output goes directly to the rear diff? Can you show some close-up pictures of how the motor is mounted?

- Are those complete RC wheels? Or lego rims and RC tires? It's a bit dark on the photos, but I am guessing the first.

- Did you buy parts from Zene one-by-one or did you buy a package?

- You seem to be using steered hubs in the rear axle as well, right? Is that on purpose, or is that because that's what you had from the Zene package?

- The lower links on the rear 4-link suspension seem to have an pin/axle connection at the axle and a towball connection at the chassis end. That way the rear axle does not have much freedom to articulate (no towball connection there). I believe it should be the other way round. Even the towball connection at the chassis end does not help much in the articulation, because that would require tilting the link, but that's held straight by the spring, so it cannot tilt. So this way I'd predict that there is not that much articulation in the rear axle. Or is that what you are looking for intentionally, so that the car does not roll?

1 hour ago, Daniel-99 said:

Anti row-bar at the rear really helps with fast starts, As we know, cars with live-axes have a tendency to lift front right \ left wheel while accelerating. This may lead to an accident. I use a carbon-fibre 9L axe for the anti row-bar.

I think the correct term is anti-roll bar. We want to prevent the car from rolling, a car does not row :) Of course I understand you are not a native speaker, but I just wanted to get the name right, so that we can explain the function correctly.

Do I understand correctly that anti-roll bars are mainly for fast vehicles? It is supposed to kind of hold back axle articulation when cornering, right? It wouldn't be so useful on slow rock crawlers, where axle flex is higher priority, right?

Also, I don't quite understand how it helps with fast starts in general? In a straight line start, isn't it the squatting of the vehicle that matters, instead of its roll? I'd think roll can be part of the equation in case of accelerating out of corners, no?

1 hour ago, Aurorasaurus said:

if its RWD then you should try mount the shock inside the lower arm and make your upper arm wider so the shock can go through it.

Sounds nice in theory, but how do you do that in lego? You can't just make the upper arm wider, there is no such lego part in existence, and you can't even build it from smaller parts in a way that gives enough space for a large shock absorber. Guess that's why everybody puts the shock absorber behind the arms.

[Aurorasaurus]

56 minutes ago, gyenesvi said:

Sounds nice in theory, but how do you do that in lego? You can't just make the upper arm wider, there is no such lego part in existence, and you can't even build it from smaller parts in a way that gives enough space for a large shock absorber. Guess that's why everybody puts the shock absorber behind the arms.

thats how ive done it. but your shocks are a lot bigger, so as you say it might not be possible. best of luck regardless.

 

my upper arms use 5m half liftarms with cross axle holes, and they seem to work on a theory level. i haven't built a vehicle to test that yet but i think it does work. if you google "goober reboot fastest trophy truck" you can see he used a similar setup, so it is doable with lego parts. just maybe not with rc shocks

Edited November 9, 2023 by Aurorasaurus
add detail regarding custom suspension arms

[Lipko]

Anti-roll bars are more for track vehicles than for offroad vehicles I read somewhere. You don't have that much cornering in the desert but have bumps that affect one wheel so it's not that good if both wheels are affected (hittinh a rock with one wheel with too strong anti-roll would flip the car). I guess it's a balancing act depending on the exact racing conditions.

[Ryokeen]

 

Wow quite a few responses :)
And i like the rowbar idea..amphibic offroad XD

 

@Aurorasaurus and @gyenesvi valid points about the rear axle swingarms, gonna redo that part. It's the first part on that thing i build anyways so it kinda was made on the rush :D. On the rear axle i can move the damper mount more in the middle of the swingarm, but at the front, no chance with those dampers and brick parts. The dampers are around 2.5 studs in diameter so an upper suspension arm would need 3 studs space and that makes the whole thing unstable, i've tried it. Oh and even most offroad RC cars, even the big ones have the dampers behind or in front of the upper suspension arms.

@Daniel-99 Well i just like to mix parts and techs to see how a project would benefit from it and if you got some rc parts or dampers go for it, might even help with finding the right spring stiffness or give you more suspension travel(and they won't break that easy)
So far i only glued 4 parts, wich are the 4 towball parts for the steering as the clutchpower there was simply not enough. The Driveshaft is made out of a 4L axle, a 6L and a 7L carbon axle. The 7L is the one connected to the diff and so far none of them moved a single bit. The metal gears sit quite tight on the axles.

One reason for that motor was the size, i've already used a 540brushed one and that here is almost the same size, so i knew how i could mount and connect it, but it is overpowered ;D
For the start problem i'm simply gonna use a gyro. An anti-rollbar would need a very stiff upper mount, but due to bricks being a bit flexible i'm afraid they might loose their purpose. Btw insted of gueing the u-joints and the axles you could also try fitting a smal spring in there to push the u-joints in place even if the axle moves a bit.

@gyenesvi So now for your questions :D
It is rwd and i do a bit of downgearing prior to the dif. 12t pinion to 20t, then 8t to 24t.

Might be not the most stable approach due to parts 32184 used as screw mounts, but so far it hold up. The motors weight is supported by a liftarm in the back, it just lays on it.

I use rc tires on lego rims, think those are some 1.9" crawler tires, a bit wider than the rims but even with the foam layin they fit well.

Yes the diff and the wheel hubs are from Zene and i bought them separately as i didn't need the u joints, receiver and so on. I just wanted to give those parts a try and so far they work. The diff was interesing cause it's closed, lubed and got bearings. That's also the reason why i use steered hubs in the front and back. Their 1:8 hub pack is like that and i didn't want to be limited to rc wheels only as rc on-road tires have just a few to small sizes(mostly 68mm)

About the 4 link system, as i said i'm gonna redo that, it's just a bit complicated as i don't want to use the 3D printed diff as a structural part, so i have to somehow build around it.

[Aurorasaurus]

if you have flip flop beams, they are very useful for that sort of thing.

[Ryokeen]

5 hours ago, Aurorasaurus said:

if you have flip flop beams, they are very useful for that sort of thing.

You mean on the rear suspension links ? I got plenty of them in almost ever lenght :D But i don't rly see how they would help there.

[Aurorasaurus]

i mean for the rear axle, since they are easy to reinforce vertically and horizontally at once

[Ryokeen]

I see i use them there already, the printed diff casing probably would also be fine, but don't want to risk it.
But i changed the lower links at the rear a bit.

Also i'm currently adding small plastic sheets to protect the electronics and gears from dirt and smaller rocks.

Had a few more test-runs with a few non lethal crashes. Only one steering arm broke as i drove with the left wheel into a wall haha
I hope i can make a video soon, but it rains almost each day atm. And while it's still wip and not fully stress tested i don't want to have to clean it that much :D

Might also post another RC / display model soon, once i got the wireing a bit better looking and hidden.

[Aurorasaurus]

that rear suspension is looking much better now. im excited to see how this progresses, keep up the good work!

[Ryokeen]

Thx :)

Atm i'm redesigning the mid section as i need more space for a bigger lipo and i don't want to place it over the back axle. Might get damaged to easy on a rollover.
Also gonna lenghten the wheelbase by 1 stud and make it 2 studs wider

Edited November 20, 2023 by Ryokeen

[Ryokeen]

I had the time to redesign the truck as i now know better how big components are, how heavy everything is and so on. Also the 1800mah Lipo i used proved to be to small for this motor, as after 10-15 mins the juice was gone.

In the process of a redesign, i made the whole truck wider, front and rear axle both 2 studs wider and the mid chassis section 1 stud longer. That way i hope to have a bit more stability and as i moved the motor gearing from the rear to the front i can not fit lipos behind the motor, low on the mid section. That way all rc componends are well protected and give the truck a low center of mass.
I could also construct the 4 link rear spuspension in a more clean and robust way so that the shocks are properly aligned in a straight line.

As some asked how i mounted the motor and how the gearing is done, i took some pics this time.

So it's first a 12:20 reduction then a 8:24. That gives me quite some options in case i want to change that. I use 2 liftarms with some half-stud 7.8mm holes drilled into so i can fit some ball-bearings there. The gears are protected from smaller rocks from all sides with panels and some cut out thin plastic sheets.

As i could better plan where each component would be and what parts/structures need reinforcement, this iteration became stronger but also lighter.

As said, now i have the space to fix quite bit lipos behind the motor and have them shielded from rocks and debris without raising the center of mass. Even more, the bigger lipos help to get some weight to the rear axle.

One problem did arise, because the main driveshaft is now 1 stud lower the driveshaft part between the mid section and the rear axle needs to expand while the rear axle moves up.

Currently i use a pure lego sollution, but that might get replaced by an metal RC part, same for the center driveshaft, it's a braced carbon fibre axle, but with a lenght of 18studs i might need a metal one.



The 2 sides of the extendable driveshafts are pushed outwards by a small spring that sits on one of the connecting 4L axles. That way it won't slipt out.
But so far a 60cm/2ft drop was no problem, nothing moved, the truck just bottomed out, but the rc shocks are adjustable so i'll do that once everything was fully tested.

And last, a pic how lipos are gonna fit

[Aurorasaurus]

all looking very good. only think id recommend is adding a beam on the other side of the lower point of your front shocks, so its supported on both sides. then attach that to the lower arm so the shock is supported better

[ZENE]

Very beautiful structural design, as well as site protection, it looks like you have done very detailed planning.

Hope to see more follow-up content. Our differentials are also evolving and we hope to provide more valuable accessories

[Ryokeen]

@ZENE Thx for the compliment and for the parts aswell. So far the hubs and diff hold well. I've just changed the greasing in the diff itself as there. Also i've noticed that maybe in another version of the diff you maybe could work on how the input ball bearing is secured(side ones to the wheels are fine). So far it's only secured from getting pushed out but not in, giving it a lot of play, at least for me. It might not be an issue if the input axle is more secured, but in case of a live axle it lacks a bit of support.

@Aurorasaurus yeah i think i know what you mean, i've tried it but it's a bit difficult for the big suspension travel i have(currently almost 7 studs) and since the supporting part would be quite far away from the wheel connection itself, it won't provide much support. Next week i'll just shove a 40mm m3 screw through the whole lower suspension arm, that should be enough.

Also got some additional parts, receiver protection and a metal extendable driveshaft. So far RC components with 5mm holes and screws from both sides to fix an input axle fit lego axles quite well.

The tape is just some teflon fibre tape to protect the parts a bit and seal the pinholes below the motor and esc(even if both are waterproof/protected)

[Aurorasaurus]

looking better every time. i think now it might be time to start thinking about bodywork.

[Ryokeen]

I'm afraid so. Made one full car and the bodywork took me weeks and is still not where i want it to have :D
But first i need more testrides, in case it ever stops raining -.-

[Daniel-99]

Hey, man! I love to see the progress on this project. Whole chassis become cleaner and properly-designed! Keep up!

[Lixander]

I know the pain when you made a good chassis and you still have to do the body-work.

Some months ago, I started to look for inspiration for my body-works, especially for the techniques not the shape or the pieces themselves.

So, I put here some videos and a Rebrickable baja-truck that might help you with the body-work.

https://rebrickable.com/mocs/MOC-4874/RM8 LEGO Garage - BrickGarage/baja-trophy-truck-double-trouble/#details

 

 

 

 

 

[Krzychups]

Yeah, chassis for serious offroad is something that I want have got in my cars too. Is there a big difference between rc shocks and lego shocks? I will be happy if you tell me after the tests.

[Ryokeen]

@Lixander Thx a lot, i was looking through rebrickable for some inspiration.

So far i got 2 main criterias for a bodywork.

1. it must be isolated from the chassis so i can just take it off by removing a few pins
2. No soft axles or expensive parts or stuff that can fall off easily

I set those cirterias cause if i'll go offroad and the chassis holds, i don't want to have to collect falling of pieces from the bodywork :D
Also in care of a crash/ropll over the bodywork should either hold, or only loose larger pieces that can be attached back quickly

Edited November 28, 2023 by Ryokeen
Site bugged out

[Lixander]

I see. I would suggest to start a simple body-work, but taking in account that you made a  pretty complicated chassis, I dont know...just build and test :)))

Good luck anyway!

On 11/28/2023 at 3:12 PM, Krzychups said:

Is there a big difference between rc shocks and lego shocks?

Yes it is. The RC shock absorbers have a larger suspension travel and can be adjusted to the desired stiffness and height, from what I know.

Also, the large Lego shock absorbers are expensive, especially the 9.5L hard and extra-hard ones.

Edited November 30, 2023 by Lixander

[Ryokeen]

On 11/28/2023 at 2:12 PM, Krzychups said:

Yeah, chassis for serious offroad is something that I want have got in my cars too. Is there a big difference between rc shocks and lego shocks? I will be happy if you tell me after the tests.

RC shocks can be bought in a lot more sizes and different spring stiffness than lego shocks. The springs also have way more variety like simple ones as i use or dual spring setups or progressive single springs. And you can change the springs, or the damper oil so that you can adjust the springs according to your needs.
But the biggest advantage is, proper RC shocks are oil filled, means they dampen the impact on compression aswell as on relaxing. Lego springs tend to bounce, rc shocks don't and that makes the whole suspension actually work as it should. In my initial tests, rc springs setup had way more traction then with lego springs and a more stable behavior(curves, small bumps)

Oh and as Lixander said, RC shocks can be cheaper. usable oil filled non progressive shock sometimes are cheaper in a 4 pack than one single 9.5l lego shock absorber.

So for me the realistic behavior, the possibility to adjust the pre compression and in general the possibility to customize them make the disadvantage of the slightly wider size neglectable.
 

2 hours ago, Lixander said:

I see. I would suggest to start a simple body-work, but taking in account that you made a  pretty complicated chassis, I dont know...just build and test :)))

Good luck anyway!

Thx, i have some time now to plan it as i need to change one long axle from a carbon fibre to a metal one. Had to combine a 3L and 16L axle with a metal connector. That connector only screws into the axle from one side, seems like the axles didn't like that on full throttle