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The purpose of this document is to log the progress, track issues, contemplate the design for future members who work on this.


 

Current State of Affairs

  • The 3D printed prototype has been made and tested. tldr; adaptive grip works, now going to figure out the allen key thing and move into a high fidelity design (metal)
  • There is a preliminary higher fidelity cad model, but it needs some work before manufacturing
  • Napkin math has been performed to get a rough estimate of the required force (120 N squeezing force)

The goal is to finish the CAD of the metal pieces and sort out the pin joints

Motor to be used will be a Polulu motor, or a similar 12V gear-motor for testing purposes.

Task List

  • Figure out the pin joints
  • try to eliminate any folded sheet metal parts
  • look into fattening the front plate (most adaptive grippers in this category have a much larger distance between the front pins and the base plate)
  • Investigate if the tip lengths should be shortened (tip lengths may interfere with each other when adaptively gripping smaller items
  • Improve the tip design - Milled
  • Consolidate mounting options for rubber pads
  • Figure out the Allen key attachment
  • More precise calculations for the output speed/torque of the jaws as a function of input speed/torque and relative position

  • Adaptive spring placement


 

Current State of Affairs

  • The CAD has been created and reviewed by two mentors
  • The slides prepared before the meeting were hugely advantageous.
    • Helped organize thoughts before the meeting
    • Allowed the meeting to efficiently flow through all the topics without stalling
    • Structured meeting
    • one downside is it takes time to make good slides. The time is worth it
  • The design is sound except for a few minor changes to further optimize the design primarily for manufacture
  • There will be no Allen key attachment - our mentor Cory suggested the tooling bit is the simplest solution and should be used.
  • Effort is now focused on fixing the cad CAD and preparing for manufacture
  • Effort is also focused on creating a complete BOM

Constrains & Criteria

Constrains and criteria were outlined in the slides to help define the task, but the constrains and criteria were backwards. for clarity these are defined here. Constrains must be met for a design to be considered. Criteria are used to compare different designs. A design matrix can be used in the future to help compare different concepts and designs against each other.

Below is a list of everything mentioned in both design reviews. Some of the items on the list will not be performed they are crossed out.

Task List

  • L-Bracket for motor mount, milled component for motor mount
    This is final design type of issue, for now 3d printed is fine, milled is better because it can hold tighter tolerances
  • Take out chamfers of the front and back milled components
    Cost little to nothing, some chamfers are essential
  • Make the nut carriage simpler to manufacture
    costs 100 on fictiv, similar to the other brackets
  • Ream holes on laser cut pieces
  • Add anti-seize to BOM for pin joints
  • Add 3/16 id shims to bom
  • specify spot welds instead of weld fillet (help retail temper on the sheet metal parts)
  • Misumi shaftmight not be able to get the steps required, or will require a post op -see if this can be machined in house first
    a tight tolerance step at the minor diameter of the lead screw is required to interface with the f-loc gear, might bot beable to post op machine that out of an existing screw
  • Adhesive backed rubber
  • Try different rubbers - sorbethane
  • add loctite 660 to bom - mcmaster
  • redo the spring location - interface is fine but location is wack
  • spring calculations and iteration
  • make drawings for all of the components


 

Rubber bands will be used. The reasoning for choosing rubber bands for the compliant portion is that they can extend way more than springs. They can also stack much easier than springs, in case the force of a single rubber band is in sufficient. another reason to choosing rubber bands over springs is that the rubber bands worked very well in the preliminary prototype. Again, this this current design is still a prototype, if the rubber bands are insufficient, springs can be used in the final design - want to dive into the prototype as soon as possible. A few possible disadvantages to using rubber bands compared to springs is their lower chemical resistance to oils, may have to end up replacing these springs more often than springs. - good corrosion resistance though. another disadvantage may be that rubber bands to not follow hooke's law. That being said, rubber band are still easier and cheaper to work with than springs.

 

Demtool package sent out today with all of the sheet metal parts and the carriage nut

Things to be done still: hardware bom this includes stuff from mcmaster, KHK and one part from misumi. The front and end bracket also need to be machined and the lead screw needs to be modified once it arrives.

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