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titleUpdated Link Length Arm Calculations

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:


AxisOutput 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)
12.63.257.69.5
2445595119
31012.54050

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)

Image Added


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.

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titleSummary Table - Option A

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

AxisMassBacklashBackdriveableMotor CostGearbox CostTotal CostMotor Operating Range at No LoadMotor Operating Range at Max LoadIntegration Feasibility
11.51kg0.3ºYes$173$251$424Within Continuous Operation Range of MotorMotor Within Continuous Operation Range of MotorHigh
2

No$170$437 + $607


30.83kg0Yes$170$1345 CAD
Within Continuous Operation Range of Motor (for shortened link length arm)Within Short Term Operation Range of Motor, likely can be operated for ~ half of thermal winding time constantHigh
4/5/60.61kg1ºYes$170 ea.$465 ea.$635 ea.Within continuous operation range of motorWithin continuous operation range of motorHigh

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. 

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