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JLiu15

[MOC] Race Buggy (INSTRUCTIONS AVAILABLE)

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Posted (edited)

LEGO Technic Race Buggy

An off-road race buggy model powered by BuWizz. Features a drivetrain containing 2 RC buggy motors and a 4-cylinder piston engine, full independent suspension, and working headlights and taillights.

Functions:

  • Drive
  • Steering
  • 4-cylinder engine
  • Full independent suspension
  • Working headlights and taillights

Instructions available on Rebrickable: https://rebrickable.com/mocs/MOC-185091/JLiu15/race-buggy/#details

All my MOCs containing RC buggy motors so far have had the motors connected straight to the wheels or tracks (either directly without gearing or via a gear reduction). However, I have always been wanting to build something with a proper drivetrain since acquiring those motors. This would make it much easier to incorporate e.g. a differential and independent suspension on the driven axle. Because the 42160 Audi set offered brand new non-planetary hubs that use heavy-duty CV joints, they made for a good starting point for this MOC.

Initially I was inspired by the 42160 set's BuWizz motorization which placed two BuWizz motors with their outer outputs connected to form the main driveshaft. However, because I was worried the vertical orientation of the motors in that design would add unnecessary height to the model, I still went with placing the motors horizontally in a transverse position with the inner outputs forming the driveshaft. Although the inner outputs have higher speed and lower torque than the outer ones, connecting the two motors via their outer outputs would result in an unnecessarily wide chassis. Even in the final setup, the motors still protrude from the sides of the body slightly, which interferes with the finished bodywork. Another challenge with the motors' placement is reinforcing the chassis, as their transverse placement makes it difficult to reinforce the chassis longitudinally where the motors sit. While there is longitudinal reinforcement above the motors, the front chassis and rear axle sections are only connected to the bottom of the motors by the friction of pins. I was initially concerned that this would be a weak spot in the chassis, but once the bodywork was installed it was not an issue. The compact design of the rear axle also allowed me to easily include an inline 4-cylinder piston engine (in clear engine blocks this time to allow for better visibility of the pistons), which is another advantage of having a proper drivetrain vs connecting the motors straight to the wheels.

The rear suspension design is similar to that of the 42160 set, with the hubs' steerability restricted by liftarms on both sides. The front suspension has the same geometry as the rear suspension, but because the front axle is not driven, there was no need for specialized hubs, I decided to use the older steerable hubs on the front axle as the integrated towballs for the steering links proved to be a more robust setup. The full independent suspension had decent travel and was quite soft, which is good for a model like this. I also added three sets of Power Functions LEDs to the model (one for the headlights and two for the taillights), although it is mostly for show as I kept them off during driving to allow the RC buggy motors to have enough power. Managing the wires was also a challenge for a model this size, as there are seven electronic components (including the BuWizz) despite having around just over 800 pieces. Finally, as for the bodywork, I went with dark blue as I have a good amount of dark blue Technic pieces from the 42083 Bugatti and 42154 Ford GT sets. Although there are some details done using System pieces, I kept them to a minimum to ensure the robustness of the model.

Performance-wise, this model exceeded my expectations. I was initially concerned that the gears in the drivetrain and piston engine would add some friction, but that was not an issue. I filmed the video at the skate park like my Red Beryl T (my previous MOC), and honestly it performed even better. It had enough momentum to go up the slopes at the skate park much more than my Red Beryl T, and I think the lighter weight of this model helped with that. The wheel diameter is also bigger (I used the tires from the 42160 set), and the final gear reduction is slightly less (7:3 vs 3:1). It was quite fun to drive it around, although I did have issues with the BuWizz cutting power (especially during heavy acceleration or on Fast/Ludicrous modes) and sometimes I ended up driving it too far up a slope where it started getting stuck. Despite the issues, it was still a very agile vehicle and had plenty of speed for some fun driving.

Overall, despite being a simple sub-1000 pieces build, this model ended up being a fun one packed with functions. The RC buggy motors provided plenty of speed and the drivetrain handled that speed well. The 4-cylinder engine and PF LED lighting, although mostly for show, allowed me to squeeze in as much functionality as I can in a small build. I still see potential to further develop things, such as taking the drivetrain setup and extending it to an AWD design.

Video:

Photos:

LEGO Technic Race Buggy - 1

 

LEGO Technic Race Buggy - 2

 

LEGO Technic Race Buggy - 3

 

LEGO Technic Race Buggy - 4

 

LEGO Technic Race Buggy - 5

 

LEGO Technic Race Buggy - 6

 

LEGO Technic Race Buggy - 7

 

LEGO Technic Race Buggy - 8

 

Edited by JLiu15

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Cool build, I like the looks! What's the intended use of such buggies in real life? Fast, but light off-roading, like bumpy dirts roads? I mean they're probably not designed for heavy terrain due to the less ground clearance I guess.

I wonder about one thing regarding the drivetrain. Have you tried using planetary hubs and Audi diffs instead? I wonder which of the two is faster. I experimented with such a setup lately (actually no diff, just 1:1 transfer with 12T gears), it has good speed (cannot tell how it compares to yours), but it also has plenty enough torque to climb such bumps that yours starts to struggle with. I have not tried the Audi hub though, and wonder if that would be faster, though was suspecting that it would not have enough torque for heavier terrain.

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