Krxlion Posted January 9 Posted January 9 (edited) Hello Guys! Today I will be presenting yet another off-road model, capable of both crawling and cruising. If you are into details, skip the Backstory part, and go straight to overview. Backstory After losing in "Lego Truck Trial Championship" held in Poland, I've thought on ways of improving performance in my MOCs. My previous model (TRX-4) was having one major flaw - ground clearance. I started working right away on axles, that could offer better results in this area. On top of that, I knew that going with live axle, instead of double-wishbone can further increase ground clearance in central part of the model. Here, after 4 months of work, I present 4x4 Tarantula buggy/rock crawler, based on Injora Tarantula body for various rock crawlers/buggies, which I've been inspiring on through building process. General assumptions and features Large ground clearance Permanent 4x4 drive & locked differentials (to offer more off-road performance) Two-speed gearbox Model fit new 90mm RC tires, which I have learned about during LTTC Expand space between front and rear axle (this is beneficial for long steep climbs, but negative for short ones) Cover the bottom of the car Minimalistic body (keeping the car weight as low as possible) More mass on front than rear Brushless RC setup Trying other color than dark bluish gray for the body :) Model weights 1.49 kg Light bar on top of the car can be turned on, but I have not showed this feature here or in video Axles Front axle idea is an adapted solution from @gyenesvi. I bought couple of red steering arms (32195b) and started experimenting. They work great with TLG planetary hubs and other similar ones, but mine brick build were breaking, using this solution. I needed a way to hold both wishbones firmly, without connecting them one to another - this was impossible due to unusual angle the lower wishbone was placed in. This section have some slight stress connections (similar to one @gyenesvi had with his connection), but nothing that cause potential break of parts. On top of that, front axle features positive caster angle and ackermann steering geometry. Regarding linkages, it is triangulated 4-link. I was previously experimenting with 9L links like Viktor's Toyota Hilux had, but they were disconnecting like hell. :D I finally set on brick build links that create an angle, but I think better solution would be to define required angles first and then one long liftarm with steering arm with ball socket connected to it - again, I know a person that already done this couple of times. :D Suspension I finally got my hands on original Lego 9.5L hard yellow springs. I decided to use them only at front, as this section is much heavier compared to rear one. On top of that, front suspensions uses also rubber connectors(part 45590). That solution protects underneath of electronic box (where I store all rc components, except motor) when arms get close to that section, the rubber part gets squeezed, acting like a second-stage shock absorption. Rear axle suspension is using combination of soft 9.5L shock absorbers (part 2909c3) and 11L shock absorbers with internal spring (part 65151c01). Gearbox and driveline From my latest experience, using orange part 35188 (changeover rotary catch) for selecting clutch gears have far better results than red 6641 part. This is because of force pushing out the parts, trying to eject driving rings from gear clutches. Furthermore, the key for me to finally make really solid gearbox was securing it in all 3 dimensions, each time from both side. I wanted to achieve high speed difference between low and high gear. Final gear ratios (with motor planetary reduction and 90mm wheels to calculate theoretical speed) are: 1st: 50:1 - top speed: 4.275 km/h 2nd: 18:1 - top speed: 11.88 km/h Steering hubs I didn't want to go with usual planetary hubs, because of two factors. They do not offer additional ground clearance and are not as effective, because of how they are designed. Designing my own brick build steering hubs was the toughest part of the project. I went through multiple solutions to get the result I wanted. I don't want to reveal too much of how they are built, it will be a little secret for now. However, I suspect with some reverse engineering people around here will be able to re-create them. The key features of them are: Sturdiness (when I try stopping the wheel manually by hand, the spinning wheel ejects instead of destroying the whole hub) Offers multiple gear ratios Lesser offset than 92908+92909 hub Decent steering radius Works with heavy-duty CV joint Fits 49294 rim Can fit bigger tires like 107mm with additional half bush as a spacer (but creates bigger offset) Model with bigger 107mm tires Ground clearance - over 6 studs in the center of the car Notes Car have additional feature, which is snap on body. It holds firmly using 3 pins on each side. No need to remove them, just gently pull apart left and right side of the body and lift it. I have secured ball pins in various spots with 1L bar with tow ball on it (part 22484). Sometimes I do not include those small differences between actual model and digital Studio one. All universal joints are swapped to metal ones. Although, I am not sure if that is needed. The angles that they are working on are not great, so they should hold quite nicely. All driveline parts are lubricated, using silicone spray. Final thoughts It most likely not the end of this model. I am planning on brining it to next LTTC in the open category again. I want to test it out in field. I also want to share more crawling experience that this truck gives (I might create another video). Further improvements may be like making it 6x6 for even more performance or adapting it to BuWizz system as I have recently bought 4 their motors and still got two BuWizzes 3.0. Gallery: https://www.flickr.com/photos/197903409@N05/albums/72177720331372698 And finally a VIDEO of more speedy off-roading Edited January 9 by Krxlion Quote
vergogneless Posted January 10 Posted January 10 What a tough little adventurer! Really cool video in the snow, it truly shows it off. It would just deserve a better suspension system to make it more.. mature Quote
keymaker Posted January 10 Posted January 10 Looking forward for next time we gonna see you at LTTC :> In case of the model, great performance, we all know snow is problematic. I'm sure your machine will outperform standard LTTC participants in case of speed thanks to RC motor :D Quote
gyenesvi Posted January 11 Posted January 11 That's a massive and interesting build @Krxlion! I like the source material, in fact, I have been thinking I want to build a Tarantula since I saw it in RC test videos of the Injora motors when I was designing my brushless motor. Though I was thinking it would be a good target for a smaller scale build, something like 68 mm tires, I think the RC version is also around that scale. Of course I'd need some 3d printed parts for that small scale.. Anyways, back to your build, nice big suspension, and nice that you made brick built portals, I guess they don't use 3-pin hubs, just axles, are those holding up well at these speeds / powers? That would be quite reassuring, because I think there's much potential in brick built portals without 3-pin hubs, I plan to use them as well for crawling. The only thing I'd suggest improving is lowering the suspension and the body. For one, it is a bit off in comparison with the original, and also this way the center of mass is a bit too high, no? Lowering it would give it more stability and result in better climbing / descending. Quote
Krxlion Posted January 12 Author Posted January 12 On 1/10/2026 at 6:14 AM, vergogneless said: It would just deserve a better suspension system to make it more.. mature Ha! I think you mean RC oil shocks, right? :D Maybe I will dig into this topic, but I still believe I need to build overall better models to elevate their potential with further RC equipment. On 1/10/2026 at 3:08 PM, keymaker said: Looking forward for next time we gonna see you at LTTC :> In case of the model, great performance, we all know snow is problematic. I'm sure your machine will outperform standard LTTC participants in case of speed thanks to RC motor :D Speed, yes. Though you guys have very robust models, hard to beat in heavy off-roading. My model is still in the middle ground, as I pursue this dream of having one car designed for everything (though it mostly not work best in either scenarios - crawling vs cruising). 14 hours ago, gyenesvi said: That's a massive and interesting build @Krxlion! I like the source material, in fact, I have been thinking I want to build a Tarantula since I saw it in RC test videos of the Injora motors when I was designing my brushless motor. Though I was thinking it would be a good target for a smaller scale build, something like 68 mm tires, I think the RC version is also around that scale. Of course I'd need some 3d printed parts for that small scale.. Anyways, back to your build, nice big suspension, and nice that you made brick built portals, I guess they don't use 3-pin hubs, just axles, are those holding up well at these speeds / powers? That would be quite reassuring, because I think there's much potential in brick built portals without 3-pin hubs, I plan to use them as well for crawling. The only thing I'd suggest improving is lowering the suspension and the body. For one, it is a bit off in comparison with the original, and also this way the center of mass is a bit too high, no? Lowering it would give it more stability and result in better climbing / descending. I would like to see your approach with this body! Though it is designed for smaller off-roader, I usually aim at 1:10 scale, with my models. ;) I am not using 3-pin solution with my portals, the wheel holds just on one axle with two half bushes, acting as brackets for the wheel. They are holding well when crawling, when speeding my fiancee managed to lose one wheel after brutally driving it for 2 minutes. I was not a fan of using this one axle solution, but all in all it is acceptable. I thought that the wheel would slip much often. I believe that with bigger tire, that would require a half-bush spacer it would fall off much often, because there would be space for only one half-bush. Also, I don't know why, but yellow half bushes might be better for this job. I read in Sariel's book, that yellow color in Lego is more sturdy than others. This might be just a weird feeling, but I only use those whenever I can. I agree that the placement of shock absorbers isn't ideal. Initially, I was planning to put them closer to the axle, ideally above the driveline to each of wheels, but I wasn't able to do so. I also was messing a lot with geometry to achieve positive caster on the front, and changing shock absorber would most likely mean re-designing positive caster. Center of the mass isn't that bad. I would assume that with this amount of space under the chasis it will roll over a lot (for example just like in the video), but the angle when car no longer is able to stand, but rolls over is around 46 degree (this is side tilt). Regarding tilting to back, I couldn't go over 50 degree, because car kept sliding from plastic board, on which I was measuring all the angles. I think the car could have tilted a few more degrees before it started to fall backwards. Quote
Krzychups Posted January 13 Posted January 13 Hey! Nice build! That's good to see you've improved what you wanted to fix in your TRX-4! High ground clearance, good suspension - what a proper RC vehicle for crawling and cruising needs! I wonder how do you deal with driving in snow. When it comes to me, I can only drive my crawler for about a few minutes, then the wheels start to spin irregularly during rotation (sometimes slower, sometimes faster). Could be that water gets inside and freezes? I don't know. Winter is one of the best time to drive RC cars like this, isn't it? I must admit that my crawler is ready to show, but I'm delaying showing it... Like Victor, I think the body and suspension should be lowered slightly. Quote
Krxlion Posted January 14 Author Posted January 14 21 hours ago, Krzychups said: Hey! Nice build! That's good to see you've improved what you wanted to fix in your TRX-4! High ground clearance, good suspension - what a proper RC vehicle for crawling and cruising needs! I wonder how do you deal with driving in snow. When it comes to me, I can only drive my crawler for about a few minutes, then the wheels start to spin irregularly during rotation (sometimes slower, sometimes faster). Could be that water gets inside and freezes? I don't know. Winter is one of the best time to drive RC cars like this, isn't it? I must admit that my crawler is ready to show, but I'm delaying showing it... Like Victor, I think the body and suspension should be lowered slightly. I don't have to do anything special to drive my model in the snow. I haven't experience any issues like you with the tires. Maybe your 2nd brand tires are not perfectly fitting Lego rims? I do like cruising with my models in the snow, but this one handles it best, thanks to a lot of ground clearance. Looking forward to see your model, and thanks for the suggestions, I might take a look at those when designing new model. Quote
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