Computational LEGO Technic Design
(Patent is Pending)
Hao Xu1
Ka-Hei Hui1
Chi-Wing Fu1
Hao Zhang2

SIGGRAPH Asia 2019

We introduce a fully automatic method to compute LEGO Technic designs (c & d) that resemble user input sketches, which may be annotated with joint rotations (bottom-left). The designs are built by coherently-connected LEGO Technic bricks (b) that respect the symmetry and structural integrity of the models, as well as the dynamics implied at the specified joints, while aiming for minimalistic layouts.


We introduce a method to automatically compute LEGO Technic models from user input sketches, optionally with motion annotations. The generated models resemble the input sketches with coherently-connected bricks and simple layouts, while respecting the intended symmetry and mechanical properties expressed in the inputs. This complex computational assembly problem involves an immense search space, and a much richer brick set and connection mechanisms than regular LEGO. To address it, we first comprehensively model the brick properties and connection mechanisms, then formulate the construction requirements into an objective function, accounting for faithfulness to input sketch, model simplicity, and structural integrity. Next, we model the problem as a sketch cover, where we iteratively refine a random initial layout to cover the input sketch, while guided by the objective. At last, we provide a working system to analyze the balance, stress, and assemblability of the generated model. To evaluate our method, we compared it with four baselines and professional designs by a LEGO expert, demonstrating the superiority of our automatic designs. Also, we recruited several users to try our system, employed it to create models of varying forms and complexities, and physically built most of them.

Interactive Assembly Visualization of the AIRPLANE

Swipe me!

Paper and Supplementary Material

Hao Xu, Ka-Hei-Hui, Chi-Wing Fu, Hao Zhang
Computational LEGO Technic Design
In SIGGRAPH Asia 2019.
[Paper] [supp] <data & code: to release>


            @article {xu_siga19,
                author = {Hao Xu and Ka Hei Hui and Chi-Wing Fu and Hao Zhang},
                title = {Computational LEGO Technic Design},
                journal = {ACM Trans. on Graphics (SIGGRAPH Asia)},
                volume = 38,
                number = 6,
                year = {2019},
                note = {Article no. 196},


We thank all the anonymous reviewers for their comments and feedback. We also acknowledge help from Ruihui Li for UI development, Shufang Wang and Tianwen Fu for model assembly, Chun Yu Liu for designing the models shown in Figure 21, and Wallace Lira and Johannes Merz for paper proofreading, and thank Nicolas Lespour and Will Gorman for their permission to show their works in Figures 2(b) & (c), respectively. This work is supported in part by grants from the Research Grants Council of the Hong Kong Special Administrative Region (Project no. CUHK 14201918 and 14203416), NSERC grants (No. 611370), and gift funds from Adobe.