Page Comparison

Rough Calculations:

Relevant Pictures:

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 18 Sep 2021 , 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:
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.

Motor: https://us.nanotec.com/products/2152-db59l024035r-a

• Continuous rated torque of 0.47 Nm
• $173 CAD with no discount (although we should contact this company and ask for sponsorship before buying
• rated speed of 3500 RPM
• Weighs 0.72kg
• Currently in stock 16 Sep 2021 

Gearbox: https://us.nanotec.com/products/9903-gp56-n2-35-sr

• 35 ratio → ~16 Nm of torque on output when operating at motors continuous torque rating which exceeds our requirement at a 12.5x SF
• Weighs 0.78kg
• Easily configurable with selected gearbox (according to manufacturer website, although would need to confirm that no additional costs are required to mate components)
• Currently in stock 16 Sep 2021 
• Maximum backlash of 19 arcmin according to manufacturer (0.3º)
• $251 CAD with no discount (although we should contact this company and ask for sponsorship before buying

Overall Pros

• Fulfills and exceeds our torque requirement
• Relatively low cost option, even without any discounts ($424 CAD)
• Potentially we could buy an encoder which mates to the motor on the back of the encoder for easy integration, although this is not necessary
• Very low backlash
• All parts are currently in stock, need to confirm lead times though

Overall Cons

• Exceeds our mass requirement (total mass combination mass of ~ 1.51kg), however this will not be on-joint mass (mass will be mounted to turntable) so it will not affect the performance requirements of other motors
• Somewhat bulky. If we use an inline option, the length of the configuration will be approximately 150mm. We would likely need to attach this to a belt drive off axis with respect to A1, as if we mount it directly underneath the turntable we will lose a considerable amount of chassis clearance
• Joint will be backdriveable, although we should not see too many loads that will move this arm
• Will operate at approximate 100RPM after gear ratio. Further speed control is required via PWM to reduce the motor's speed for a reasonable teleop range. 

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.