BLACK OAR STUDIO · ENGINE ROOM 05
Walking Robot Traber
A quadruped with twelve joints, designed in the Engine Room. Inverse kinematics places every foot exactly. The foot stays planted during the stance phase, then swings forward on a cycloid. The page calculates the support polygon, stability margin and joint torques live.
0.30m/s
Walk · Cycle 1.20 s · Real time
Drag to rotate · after a click the mouse wheel zooms · click a leg to select it
Stable · Margin – mm
The 3D model needs WebGL, which is not available in this browser. The charts on the right still run.
Run
Camera
Leg FL
Stance phase- Gait
- –
- Speed
- –
- Stability margin
- –
- Foot force
- –
- Hip torque
- –
- Knee torque
- –
- Duty factor
- –
- Stride length
- –
- Abduction
- Hip
- Knee
- Hip
- Knee
Data sheet
- Design
- Quadruped, with abduction, hip and knee on each leg, 12 actuators in total
- Mass
- 26 kg (model assumption, centre of mass at the middle of the body)
- Body
- 620 × 220 × 120 mm
- Hip spacing
- 480 mm lengthwise, 200 mm crosswise
- Leg
- Thigh 220 mm, shank 220 mm, abduction offset 80 mm
- Knee drive
- Motor at the hip, toothed belt 1 : 1 to the knee
- Foot
- Rubber ball Ø 44 mm
- Walk
- Duty factor 0.80, foot sequence RL – FL – RR – FR, always three feet on the ground
- Trot
- Duty factor 0.55, diagonal pairs FL + RR and FR + RL
- Pace
- Duty factor 0.55, same-side pairs FL + RL and FR + RR
- Stride length
- 280 mm at most, beyond that the step frequency rises
Traber is a freely designed robot, not a real product.
How the model calculates
- Inverse kinematics, solved in closed form: abduction from the transverse plane q₁ = atan2(y, z) − atan2(−h, d), knee from the law of cosines cos q₃ = (D² − l₁² − l₂²) / (2·l₁·l₂), hip from the triangle. The forward calculation hits the target point to within 0.1 mm.
- In the stance phase the foot stays fixed in space and the body moves over it. No foot slips.
- In the swing phase the foot follows a cycloid, with the lift arc above the higher of the two touchdown points. The target is where the hip will be at the middle of the next stance phase (Raibert rule).
- Stability: convex hull of the planted feet, with the margin equal to the shortest distance from the centre of mass to the edge. In the walk the body shifts the centre of mass into the support triangle before each lift. Trot and pace stand statically on a line and balance only dynamically. The model shows this as a negative margin.
- Torques are quasi-static: the weight is distributed over the planted feet according to the position of the centre of mass (with four feet, the solution with the smallest norm). Torque equals joint axis · (lever × force). Accelerations, leg masses and friction are not included.
