Mechanical Design

The Mechanical Design group turns an idea into a physical robot. Members decide the robot's shape and size, design the frame, legs, arms, grippers and drive trains, choose materials, motors and gearboxes, and then make and assemble the parts in the PolyU Industrial Centre.

Every other group depends on this work. A mechanism that jams, a frame that flexes or a robot that tips over cannot be fixed in software, so mechanical members check loads, stiffness and stability before anything is made, and design robots that can be repaired quickly at a competition.

Mentor: Hu Jiahao
Student representatives: To be announced after the 2026 placement
Tools: SolidWorks or Fusion 360, basic FEA, 3D printers, laser cutters, CNC machines
Works on: Robocon 2027 mechanisms, the robot dog legs and frame, drone frames and payload mounts

What the group works on

CAD and drawings

Part and assembly models, engineering drawings and design reviews before any part is made.

Mechanisms

Linkages, gearboxes, lifts, grippers and suction tools for handling game objects and payloads.

Drive trains and legs

Omni, mecanum and swerve drives for ground robots; leg joints and linkages for quadrupeds.

Structural checks

Hand calculations and simple FEA for loads, stiffness and safety factors; weight budgets.

Fabrication

3D printing, laser cutting and CNC machining, with Industrial Centre engineers supervising.

Integration and repair

Mounting points for electronics and sensors, cable routing, spare parts and fast access for repair.

Engineering foundations

A few of the equations members use in this group. Training sessions build up to them step by step.

Bending stress in a beam

\[\sigma = \frac{M\,y}{I}\]

Checks that a chassis rail or arm will not yield under load. M is the bending moment, y the distance from the neutral axis and I the second moment of area.

Safety factor

\[n = \frac{\sigma_y}{\sigma_{\max}}\]

Yield strength over the largest working stress. Robot parts that take impacts are usually designed with a clear margin above 1.

Motor torque through a gearbox

\[\tau_{\text{motor}} = \frac{F\,r}{N\,\eta}\]

Torque the motor must give to push force F at radius r through a gear ratio N with efficiency η.

Two-link leg kinematics

\[\begin{aligned} x &= l_1\cos\theta_1 + l_2\cos(\theta_1+\theta_2) \\ y &= l_1\sin\theta_1 + l_2\sin(\theta_1+\theta_2) \end{aligned}\]

Foot position of a robot dog leg from its hip and knee angles: the starting point for leg design and gait control.

Mecanum wheel kinematics

\[\begin{bmatrix}\omega_1\\ \omega_2\\ \omega_3\\ \omega_4\end{bmatrix} = \frac{1}{r}\begin{bmatrix}1 & -1 & -(l_x+l_y)\\ 1 & 1 & l_x+l_y\\ 1 & 1 & -(l_x+l_y)\\ 1 & -1 & l_x+l_y\end{bmatrix}\begin{bmatrix}v_x\\ v_y\\ \omega_z\end{bmatrix}\]

Wheel speeds needed for a chosen sideways, forward and turning motion of an omnidirectional competition robot.

Tipping limit

\[a_{\max} = g\,\frac{d}{h}\]

A robot with its centre of mass at height h and distance d from the edge of its wheelbase tips over above this acceleration. Lifting mechanisms raise h.

What we expect from members

Expectations grow with the member tier. Tiers are reviewed regularly, so members can move up as their skills grow.

Tier 3 · General

Interest in how machines work. Learns basic CAD and workshop safety in introductory sessions.

Tier 2 · Training

Can model parts and assemblies in CAD and produce drawings; has completed Industrial Centre safety training for the machines used; takes part in design reviews.

Tier 1 · Advanced

Leads the mechanical design of a subsystem or a whole robot, does load and stability checks, runs design reviews and mentors Tier 2 members.

Before you join: Statics and mechanics of materials, a CAD tutorial (SolidWorks or Fusion 360) and any hands-on building experience are good starting points. No member is expected to know everything at the start.

Photos