By: Nate Laverdure
New: 02-28-2016 11:01 AM
Updated: 02-28-2016 11:50 AM
Total downloads: 420 times

As seen on Triple Helix's 2016 robot:
http://www.chiefdelphi.com/forums/sh...hreadid=144877

Triple Helix's changes to FingerTech 2.125" OD mecanums

1. Modify hub to allow 1/2" hex drive

1.1. Fully disassemble wheel to isolate hub.

1.2. Enlarge hub bore to 1/2" ID
-- simple lathe operation

1.3. Broach hub bore to 1/2" hex
-- must stack multiple hubs together because they are too thin for broach
-- use pins or 4-40 screws through the attachment holes to maintain concentricity
-- use hose clamps around OD to maintain concentricity
-- CRITICAL: align points of hex to minimize interference with heads of standoff screws

1.4. Enlarge bore of both side plates
-- Must clear points of drive axle
-- Try to stay concentric with existing hole
-- Bore must exceed .577" if using 1/2" hex
-- Bore must exceed .542" if using thunderhex
-- Recommend using step drill to enlarge up to 5/8"

2. Reassemble mecanum with modifications

2.1. Replace BHCS #4-40 x 1/4" LG with SHCS
-- Hex profile will NOT fit between existing square pattern of BHCS
-- Switching to SHCS allows hex profile to fit in existing square pattern
-- McMaster 91251A106, $8.20/pack of 100, 4 needed per wheel

2.2. Replace roller axles (1/8" pin and E-clips) with SHCS #5-40 x 1-1/2" LG and nylon lock nuts
-- E-clips WILL NOT hold up to FRC use; need better axial shaft retention method
-- If E-clips fail, you'll likely lose the whole roller
-- Although it's an uncomfortable nonstandard size, #5 is chosen because it has a .125 nominal diameter.
-- Screws: McMaster 91251A175, $9.46/pack of 10, 6 needed per wheel
-- Nuts: McMaster 90631A006, $2.76/pack of 100, 6 needed per wheel

Cost breakdown
Mecanum 14.28 (19.76 CAD)
Hub upgrade fasteners .33
Roller upgrade fasteners 5.84
TOTAL 20.45 plus shipping

Resources
http://www.fingertechrobotics.com/pr...mecanum-set-v2
https://www.sparkfun.com/products/11578

Attached Files

• Mecanum assembly CAD screenshot

  mecanum assy cad screenshot.jpg

  download file

  uploaded: 02-28-2016 11:02 AM
  filetype: jpg
  filesize: 56.75kb
  downloads: 196

  
  

• Mecanum hex broaching detail screenshot

  mecanum hex broaching detail screenshot.jpg

  download file

  uploaded: 02-28-2016 11:03 AM
  filetype: jpg
  filesize: 27.58kb
  downloads: 175

  
  

• Mecanum assembly CAD

  FingerTechMecanum_THmodifications.STEP

  download file

  uploaded: 02-28-2016 11:11 AM
  filetype: TEP
  filesize: 2MB
  downloads: 47

  
  

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