Joint Requirements
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Rough Calculations:
Relevant Pictures:
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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:
Updated link lengths do not have any significant changes to the original calcs of axis 4, 5 and 6. Calculation PDFS: 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
Option A (24V Motors)
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Motor: https://us.nanotec.com/products/2152-db59l024035r-a
Gearbox: https://us.nanotec.com/products/9903-gp56-n2-35-sr
Overall Pros
Overall Cons
Notes on Other Options: We can also use the 45mm maxon + harmonic drive option here. however, I figured that might be expensive and not really worth investing in. Second Note: Why not use the maxon gear heads and maxon motors here? Well, this option is cheaper. The additional mass does not influence other joint requirements. And, it has significantly low backlash! We can stick with maxon if need be though. |
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Approximate Actual Team Cost (applied a preemptive 25% discount on maxon gearheads as motor was discounted by 25%): 3500 CAD URC Cost (just assumed actual harmonic gearbox cost was 1800 CAD, need to confirm true cost with electromate): 4520 CAD
Note: Integration is high for maxon motor/gearhead or the nanotech motor/gearhead as these components are configurable combinations on supplier website. Additionally, according to actuator sponsor the selected maxon motor and harmonic gear for A3 easily mate to eachother. |
Decision Matrix - Excel Sheet
View file name Arm Actuator Options Master Spreadsheet v3.xlsx height 250