Mechanical

Asimov 1 form factor, load capability, joint layout, motion limits, actuation, and mechanical design.

Explore the Design Interactively

Design update in progress

The interactive model does not yet include the latest part design. It will be replaced when the updated mechanical model is ready.

The public Asimov 1 repository provides the mechanical design files.

Structural Architecture

Asimov 1 is organized into the head, torso, pelvis, left and right arms, and left and right legs. These modules form the load-bearing frame and define the primary mechanical interfaces between body assemblies.

Form Factor

Characteristic	Specification
Height	1.2 m (3.94 ft)
Mass	35 kg (77 lb)
Powered degrees of freedom	25
Legs	6 DOF per leg
Arms	5 DOF per arm
Body	1 waist-yaw DOF
Head	2 neck DOF: yaw and pitch
Structural materials	7075 aluminum and MJF PA12 nylon

Load Capability

Activity	Rated load	Peak load
Squat	5 kg	Not specified
Bicep curl	5 kg per arm	15 kg per arm
Front raise	5 kg per arm	15 kg per arm
Lateral raise	6 kg per arm	18 kg per arm

Rated loads describe sustained operation for the published activity. Peak loads are short-duration limits rather than continuous operating targets.

Powered Joint Layout

Region	Joint axes	Powered joints
Each leg	Hip pitch, hip roll, hip yaw, knee, ankle pitch, ankle roll	6
Each arm	Shoulder pitch, shoulder roll, shoulder yaw, elbow, wrist yaw	5
Waist	Yaw	1
Neck	Yaw, pitch	2
Total		25

For locomotion, the two neck joints are locked to use a 23-DOF body model.

Joint Direction and Limits

The signed values below use the robot model coordinate convention. Mirrored left and right joints can use opposite signs for the same physical movement.

The frame convention is blue for z, red for x, and green for y.

Actuator ID Mapping

Interactive joint-limit visualization coming soon

An interactive visualization will be added so you can move every joint and test its limits. Until then, use the signed limits in the tables below.

Legs

Joint	Left range (rad)	Left axis	Right range (rad)	Right axis
Hip pitch	-2.09 to 1.00	`0 1 0`	-1.00 to 2.09	`0 -1 0`
Hip roll	-0.79 to 0.79	`1 0 0`	-0.79 to 0.79	`1 0 0`
Hip yaw	-0.79 to 0.79	`0 0 -1`	-0.79 to 0.79	`0 0 -1`
Knee	0.00 to 1.50	`0 1 0`	-1.50 to 0.00	`0 -1 0`
Ankle pitch	-0.35 to 0.35	`0 1 0`	-0.35 to 0.35	`0 -1 0`
Ankle roll	-0.10 to 0.10	`-1 0 0`	-0.10 to 0.10	`-1 0 0`

Arms

Joint	Left range (rad)	Left axis	Right range (rad)	Right axis
Shoulder pitch	-3.14 to 0.87	`0 1 0`	-0.87 to 3.14	`0 -1 0`
Shoulder roll	-1.57 to 0.00	`-1 0 0`	0.00 to 1.57	`-1 0 0`
Shoulder yaw	-1.57 to 1.57	`0 0 -1`	-1.57 to 1.57	`0 0 -1`
Elbow	0.00 to 2.44	`0 -1 0`	-2.44 to 0.00	`0 1 0`
Wrist yaw	-3.14 to 3.14	`0.766 0 -0.64`	-3.14 to 3.14	`0.766 0 -0.64`

Waist and Neck

Joint	Range (rad)	Axis
Waist yaw	-1.57 to 1.57	`0 0 1`
Neck yaw	-1.57 to 1.57	`0 0 1`
Neck pitch	-0.79 to 0.79	`0 1 0`

Actuation and Mechanical Power

Joint roles	Actuator family	Rated torque	Peak torque
Hip pitch and waist yaw	`EC-A6416-P2-25`	40 Nm	120 Nm
Hip roll and shoulder pitch	`EC-A5013-H17-100`	30 Nm	90 Nm
Hip yaw and shoulder yaw	`EC-A3814-H14-107`	20 Nm	60 Nm
Knee and shoulder roll	`EC-A4315-P2-36`	25 Nm	75 Nm
Elbow, wrist yaw, and neck	`EC-A4310-P2-36`	12 Nm	36 Nm

Rated torque is the continuous actuator output under normal thermal conditions. Peak torque is available only for short events.

Full Actuator Specifications

The table below maps every physical actuator ID to its joint role and model parameters. The parallel ankles use physical actuators A and B, so their joint-space pitch and roll limits are defined by the ankle mechanism rather than by one actuator alone.

ID	Physical role	Model	Motion range (rad)	Velocity limit (rad/s)	Kt	Armature	Rated torque (Nm)	Peak torque (Nm)	Static friction	Dynamic friction
1	`left_hip_pitch_joint`	`EC-A6416-P2-25`	-2.09 to 1.00	12.57	2.75	0.095625	40.0	120.0	0.70	0.050
2	`left_hip_roll_joint`	`EC-A5013-H17-100`	-0.79 to 0.79	3.98	7.15	0.11	30.0	90.0	0.20	0.020
3	`left_hip_yaw_joint`	`EC-A3814-H14-107`	-0.79 to 0.79	5.45	5.70	0.038	20.0	60.0	0.70	0.050
4	`left_knee_joint`	`EC-A4315-P2-36`	0.00 to 1.50	12.25	2.53	0.0339552	25.0	75.0	0.70	0.020
5	`left_ankle_A`	`EC-A4310-P2-36`	See ankle mechanism	9.32	1.81	0.0565056	40.0	145.4	0.40	0.015
6	`left_ankle_B`	`EC-A4310-P2-36`	See ankle mechanism	9.32	1.81	0.0565056	17.0	57.6	0.40	0.015
7	`right_hip_pitch_joint`	`EC-A6416-P2-25`	-1.00 to 2.09	12.57	2.75	0.095625	40.0	120.0	0.70	0.050
8	`right_hip_roll_joint`	`EC-A5013-H17-100`	-0.79 to 0.79	3.98	7.15	0.11	30.0	90.0	0.20	0.020
9	`right_hip_yaw_joint`	`EC-A3814-H14-107`	-0.79 to 0.79	5.45	5.70	0.038	20.0	60.0	0.70	0.050
10	`right_knee_joint`	`EC-A4315-P2-36`	-1.50 to 0.00	12.25	2.53	0.0339552	25.0	75.0	0.70	0.020
11	`right_ankle_A`	`EC-A4310-P2-36`	See ankle mechanism	9.32	1.81	0.0565056	40.0	145.4	0.40	0.015
12	`right_ankle_B`	`EC-A4310-P2-36`	See ankle mechanism	9.32	1.81	0.0565056	17.0	57.6	0.40	0.015
13	`left_shoulder_pitch_joint`	`EC-A5013-H17-100`	-3.14 to 0.87	3.98	7.15	0.11	30.0	90.0	0.20	0.020
14	`left_shoulder_roll_joint`	`EC-A4315-P2-36`	-1.57 to 0.00	12.25	2.53	0.0339552	25.0	75.0	0.70	0.020
15	`left_shoulder_yaw_joint`	`EC-A3814-H14-107`	-1.57 to 1.57	5.45	5.70	0.038	20.0	60.0	0.70	0.050
16	`left_elbow_joint`	`EC-A4310-P2-36`	0.00 to 2.44	9.32	1.81	0.0282528	12.0	36.0	0.40	0.015
17	`left_wrist_yaw_joint`	`EC-A4310-P2-36`	-3.14 to 3.14	9.32	1.81	0.0282528	12.0	36.0	0.40	0.015
18	`right_shoulder_pitch_joint`	`EC-A5013-H17-100`	-0.87 to 3.14	3.98	7.15	0.11	30.0	90.0	0.20	0.020
19	`right_shoulder_roll_joint`	`EC-A4315-P2-36`	0.00 to 1.57	12.25	2.53	0.0339552	25.0	75.0	0.70	0.020
20	`right_shoulder_yaw_joint`	`EC-A3814-H14-107`	-1.57 to 1.57	5.45	5.70	0.038	20.0	60.0	0.70	0.050
21	`right_elbow_joint`	`EC-A4310-P2-36`	-2.44 to 0.00	9.32	1.81	0.0282528	12.0	36.0	0.40	0.015
22	`right_wrist_yaw_joint`	`EC-A4310-P2-36`	-3.14 to 3.14	9.32	1.81	0.0282528	12.0	36.0	0.40	0.015
23	`waist_yaw_joint`	`EC-A6416-P2-25`	-1.57 to 1.57	12.57	2.75	0.095625	40.0	120.0	0.70	0.050
24	`neck_yaw_joint`	`EC-A4310-P2-36`	-1.57 to 1.57	9.32	1.81	0.0282528	12.0	36.0	0.40	0.015
25	`neck_pitch_joint`	`EC-A4310-P2-36`	-0.79 to 0.79	9.32	1.81	0.0282528	12.0	36.0	0.40	0.015

Parameter Definitions

Kt is the actuator torque constant: torque (Nm) = Kt * current (A).

Armature represents reflected rotor inertia in joint space and contributes corresponding damping. For a geared actuator, armature = JG^2, where J is rotor inertia and G is the actuator-to-output angular-velocity ratio.

Rated torque is the continuous output the actuator can sustain under normal thermal conditions.

Peak torque is the short-duration maximum used for events such as impacts, push-off, or fast recovery.

Static friction is the torque required to start the joint moving from rest.

Dynamic friction is the lower resisting torque after the joint is moving.

Parallel Ankle

Asimov 1 uses a parallel RSU ankle (Revolute-Spherical-Universal) rather than a serial single-DOF mechanism. Two revolute actuators work through parallel linkages to produce ankle pitch and roll.

In simulation, ankle pitch and roll are modeled as directly actuated ideal joints. On the physical robot, the two actuators move endpoints on a straight bar, so a kinematic mapping converts actuator A/B positions into pitch/roll coordinates for Sim2Real deployment.

Fixed flat feet

Asimov 1 no longer uses passive toe joints. The current design uses fixed flat feet.

The mapping uses:

theta_p: ankle pitch angle in joint space

theta_r: ankle roll angle in joint space

theta_A, theta_B: actuator A and B rotation angles

r_A, r_B: effective linkage radii for actuators A and B

r: common radius when r_A = r_B = r

d: ankle pivot to bar midpoint-line distance

c: distance between the two bar endpoints

The simplified model assumes small angles, rigid symmetric geometry, constant effective radii, and no compliance, backlash, or slip. Positive y points away from the ground, and the right-leg convention is used for the derivation.

Mapping equations from actuator space to pitch/roll space:

theta_p = (r_A * theta_A - r_B * theta_B) / (2 * d)
theta_p = (theta_A - theta_B) * (r / (2 * d))

theta_r = -(r_A * theta_A + r_B * theta_B) / c
theta_r = -(theta_A + theta_B) * (r / c)

float right_pitch = (right_A - right_B) / (2.0f * K_PITCH);
float right_roll  = -(right_A + right_B) / (2.0f * K_ROLL);

float left_pitch  = (left_A - left_B) / (2.0f * K_PITCH);
float left_roll   = -(left_A + left_B) / (2.0f * K_ROLL);

See the public ankle mechanism derivation for the complete derivation.