2021-12-02 Meeting Minutes - Drivetrain

Goals

• Discuss member commitment for Winter term?
• Discuss plan for manufacturing Drivetrain
• DFM tips/standards we want to agree on?
• Ordering plan (in more detail)
• Due dates
  • When to have final CAD changes in: 
  • When to have final BOM ready: Dec. 13th  
    • Export to Excel from Solidworks → Ethan tutorial Wed.
    • Will decide what we need to order ASAP
  • When to have all drawings done: Jan 4th?
• Bonding update

Manufacturing Breakdown

Chassis

Demtool...

• Chassis plates → laser cut
• Potentially carbon fibre mounting tubes
• Middle connector block
• Lower priority: chassis connector blocks

In-house...

• Quarter mounting blocks
• Rocker top block
• Gimbal stand sheet metal plates and brackets
• Gimbal/antenna plate
• Suspension connectors

Notes...

• Compromise: make lightening pattern not as dense, room to add holes as we go
  • Remember this doesn't have to be 

Suspension

Wheel Hubs

3D Printing Sponsor...

• Wheel hubs

Demtool...

• Motor support piece

In-house...

• Wheel-carbon fibre connector

Differential

Demtool...

In-house...

• Eye joint mounts (x4) -> waterjet, then mill down faces, add PEMs to some
• Diff shaft mount (x1) -> waterjet
• Nylon blocks (x2) -> mill slot, then slice, do holes for heat set inserts, add heat set inserts
• Diff shaft -> cut, do retaining ring groove on lathe, drill and tap end
• Turn buckles -> cut, thread
• 3/8" bar (x1) -> or routed
• Chassis mount

Update & Action Items

........we need to recruit.............

• Karan?
• Elizabeth?

New Tasks

• Everyone: finish manufacturing CAD 
• Create BOM after Ethan spheel
• Start making drawings!

General Notes

• Demtool info...

  • Standard tolerances for machining are +/- 0.005"
  • Inside bend radii should be equal to or larger than the material thickness being
    used
  • The simplified formula dictating the shortest flange length is 4x the material
    thickness from the bend line
  • When designing hole locations on sheet metal, use the above 4x material thickness
    from bend line rule
  • Holes are best drawn at mid-tolerance. This means the mid point between the range of acceptable deviation
  • Holes intended for tapping in up to 1/2” thick steel should be drawn at the exact tap drill size

• Protocase tips! → Note: they have tables outlining compatible tolerances, materials, etc. following up on all of these tips
  • Self-sinching fasteners need to be harder than the material they are being inserted into
    • Generally, 400-series stainless steel are good
    • They have PEM nuts, standoffs, and studs :O
  • The larger the internal radii, the faster the machine can cut
    • Make internal radii as large as the design can allow, or reference Protocase's minimum radius table
  • Chamfers > fillets for external corners/edges
  • In general, don't make tight tolerance where not needed
  • For tapped holes, drilled hole length will equal the desired thread depth + length of tap's taper + some additional thread allowance. Keep in mind.
    • Going for a smaller thread depth decreases costs
  • 6061 aluminum is best if the part needs to be machined. 5052 for sheet and plate metal as it is the strongest of the non-heat-treatable alloys
  • To check out:
    • https://www.protocase.com/resources/tolerances/
    • https://www.protocase.com/products/cnc-machining/cnc-milling/constraints.php

• Other places with resources: Fictiv, Protolabs

• Tips from Mechanical peeps
  • Four decimals for millimeters is pretty much impossible
  • Austin's rule of thumbs (metric):
    • Hole locations → 3 decimals
    • Surfaces/shapes, less critical → 2 decimals
    • For COTS, check if they have recommended ISO fits or housing fits
    • Min. 3 thread engagement, but ideally more → 1.5x bolt diameter for threaded holes
    • If we need a specific hole size on the waterjet, better to undercut and then drill it out
  • Use relief notches to move the bend radius 
    • Specific numbers can be found from Protolabs, Protocase, etc.
  • Specify ISO fits for critical dimensions. Can use ISO calculator and ISO preferred fits for personal reference
  • Student machine shop mills have a bolt radius tool !!! And multiple datums
  • M4/5 for basic mounting, M3 for small, M6/8 for big
  • Flanged socket heads!!!!!
  • Check out PEM nuts requirements on Penn Engineering website
• Preloading is what the clamping force comes from, preload above vibrational rating