2022 Arm Actuator Selection Options
Joint Requirements
Rough Calculations:
Relevant Pictures:
| Axis | Permissible Mass for Motor + Gearbox (kg) | Output Ideal RPM | Output No Load Torque, no SF (Nm) | Output No Load Torque, 1.25x SF (Nm) | Output Max Load Torque, no SF (Nm) | Output Max Load Torque, 1.25x SF (Nm) |
|---|---|---|---|---|---|---|
| 1 | 1.1 | 5-7 | 3.8 | 4.7 | 10 | 12.5 |
| 2 | 1.5 | 3-4 | 61 | 76 | 126 | 158 |
| 3 | 1.3 | 6-7 | 18 | 22.5 | 55.5 | 69.3 |
| 4 | 0.8 | 30 | 1 | 1.25 | 14.1 | 17.6 |
| 5 | 0.7 | 30 | 1 | 1.25 | 14.1 | 17.6 |
| 6 | 0.7 | 30 | 1 | 1.25 | 14.1 | 17.6 |
Note: Permissible mass ratings based off of mass of equivalent actuation components in current arm prototype design. RPM range is based of of teleoperation testing of the prototype arm.
After some investigation, it was realized that the arm can likely be shorter than it how the prototype was designed, as the arm would sit on the chassis of the drivetrain with an approximate 0.35m height above the ground. The proposed new linkage lengths are shown below. If our initial hand calculations used to determine the torques in the table above are accurate (to be validated with testing on , then we can use these updated requirements for axis 1, 2 and 3:
| Axis | Output No Load Torque, no SF (Nm) | Output No Load Torque, 1.25x SF (Nm) | Output Max Load Torque, no SF (Nm) | Output Max Load Torque, 1.25x SF (Nm) |
|---|---|---|---|---|
| 1 | 2.6 | 3.25 | 7.6 | 9.5 |
| 2 | 44 | 55 | 95 | 119 |
| 3 | 10 | 12.5 | 40 | 50 |
Updated link lengths do not have any significant changes to the original calcs of axis 4, 5 and 6.
Calculation PDFS:
shortarmcalcs.pdf
Updated Linkage Sketch: (NEED TO ADJUST LINKS FOR BETTER END EFFECTOR LOCATION)
README:
I think these methodology behind these requirements (for both long and short links) were unclear, so just wanted to clarify how I came across these numbers. I reviewed all the mass properties of OTS components for the prototype in SW, and made sure that all material selections were correct. On our prototype arm, I separated the arm into fixed/rigid links and measured the mass and center of mass location of each link. I then used this updated mass/com information to make a point load diagram of the arm and calculated worst case loading scenarios.
For the shortened link calculations, I changed the lengths of linkages to reflect the image above and used the same methodology - measured masses and COM locations of rigid links and used that information to create a point load model of the arm.
Potential Options
This section will review some potential actuation combos that we can use. These were not solutions recommended by sponsors, but options generated by the mechanical team. The following factors listed below are the critical success factors for potential actuation combination options.
- Low total cost
- Low total mass profile
- Reliability throughout range of operating conditions
- Low Backlash
- Technical Feasibility