Hi Stretch Community,
We have been working towards supporting research works that use Stretch in a simulation environment and groups trying to achieve close-to-real dynamics of the real robot. Therefore, we have gathered information on accurate Mass parameters, Forces/torques, and velocity parameters for the Lift, Arm, Base, and Wrist Yaw joints.
Masses and Inertial Values
We now have an accurate itemized breakdown of all the masses and inertial values specific to each link mentioned in our URDF files. This data is now publicly available. You can refer to this forum post: Stretch - URDF Mass Parameters
Forces and Torques
All the force data were measured using a force gauge in a fixed position except the Wrist-Yaw joint.
Mobile Base:
The maximum forces mentioned below are the peak forces the robot’s base can exert due to the drive wheels above which the wheels would start slipping. Therefore, these forces are the maximum tractive forces measured specifically to two different surface conditions (Hard Concrete, Low pile carpet). The below-mentioned forces are not to be confused with the actual maximum capable driving force of the base.
The maximum force (N) that can be applied when moving the robot forward and back:
The maximum forward and backward (same) tractive forces are:
- Hard Concrete Surface: 95.2 N
- Low Pile Carpet Surface: 82.2 N
The maximum torque (N.m) that can be applied when rotating the robot clockwise, and counter-clockwise:
The maximum CW and CCW (same) torque calculated based on the Wheel separation (0.32m) and above total tractive forces are:
- Hard Concrete Surface: 7.6 N.m
- Low Pile Carpet Surface: 6.6 N.m
Lift and Arm
The maximum forces that can be applied to lift & Arm before it would stop are measured based on the default guarded contact thresholds the robot ships with. Guarded contacts is a safety feature that comes enabled by default, and it limits the amount of force that can be applied to the Lift and Arm joints before it stops.
The maximum force (N) that can be applied when moving the Lift joint upward and downward:
- Moving Upward: 38.1 N
- Moving Downward: 55.8 N
The maximum force (N) that can be applied by the extending arm, and retracting arm:
- Extending: 56.3 N
- Retracting: 39.5 N
Wrist Yaw
The maximum torque that is capable by the wrist yaw joint is quoted from the Dynamixel servo motor specification multiplied by the gear ratio used.
The maximum torque (N*m) that can be applied when rotating the Wrist Yaw clockwise, and counter-clockwise:
- The maximum torque of the wrist yaw joint in CW and CCW (same) is 4.56 N.m.
Velocities
Mobile Base
- Maximum Linear Velocity: 0.3 m/s
- Maximum Rotational Velocity: 109 deg/s
Lift and Arm
- Maximum Linear velocity of Lift: 0.15 m/s
- Maximum Linear velocity of Arm: 0.4 m/s
Wrist Yaw
- Maximum rotational velocity of Wrist Yaw: 171 deg/s
Feel free to contact us with any questions or additional data that you may need for your work.
Best,
Mohamed Fazil