RC15OmniWheel

This page is a sub-section of the RoboCup 2015 Mechanical page. Specifically, the Omni Wheels allow the robots to move in any direction at anytime.

Background

The omni wheel serves the purpose of allowing the robot to move in any direction at any time. This is important for having highly dynamic robots that can execute their plays as fast as possible.

The 2008 fleet of robots designed by the team utilized a 

The 2011 fleet of robots utilized rollers supported by individual pins which proved to be easier to assemble despite the increased part count. Additionally, the omni wheel had an internal ring gear mounted on the rear to engage the spur gear mounted on the 30W motors. This design proved to be compact, allowing for more internal space on the robot. 

Both the 2008 and 2011 fleet of robots use wheels that are mounted on 1 radial bearing. While this design works, it allows for a lot of out of plane motion of the wheel, which has resulted in significant rubbing and reduced performance. Both designs use simple o-rings as contacts for the ground. The 2011 robots utilized an outsourced aluminum core to seat the o-ring.

Requirements

1. In-house manufacturable (including ease of manufacturability)
2. Provide more grip/contact than previous designs
3. Must be able to mount the internal ring gear for a more compact design
4. Ground clearance of 0.XX inches
5. Must include more rollers for smoother driving performance.

Potential Design Variants

Body/Housing

1. Injection molded design
   1. Pros:
      1. Highly geared towards mass manufacturing. Saves development time
      2. Significantly more freedom with design parameters than a purely machined design
      3. Potentially lighter if designed and analyzed correctly
   2. Cons:
      1. Relatively unknown realm of manufacturing
      2. Generally weaker material than most metals
      3. Development of the mold is time consuming and not easy
2. Typical aluminum machined design
   1. Pros:
      1. Sturdy
   2. Cons:
      1. Manufacture time
      2. CAM setup time
3. Thinned and heat treated steel machined design
   1. Pros:
   2. Cons:

Roller Rubber

1. Round o-rings
   1. Pros:
      1. Simple
      2. The most inexpensive option
      3. Same as what we've done in the past, so it the easiest to re-imple
   2. Cons:
      1. Smallest contact area ("point" contact)
      2. Most effectively seated via a semi-circular groove on the roller - this was an outsourced job in the past
2. Double seal o-rings
   1. Pros:
      1. More contact area = more grip
      2. Relatively cheap
   2. Cons:
      1. Slightly more expensive than round rings
3. Custom rubber rings
   1. Pros:
      1. Easily designed to have high contact area
   2. Cons:
      1. Not a commercial-of-the-shelf product and would require our team to manufacture it (more development time)
      2. Potential inconsistencies with our in-house manfacturing process (the waterjet cutter may leave a slight flap on the edge at the "lead-in/lead-out" locations.

Materials

Item	Material	Fleet Quantity	Stock Material	Cost per part	Total Cost	Vendor	Part Number	Manufacturing Method	Notes
Body	Aluminum 7075	32				McMaster		CNC Mill
Cap	Hardened Steel	32				McMaster		Waterjet
Pin	Stainless Steel	576				McMaster		(Stock component)
Roller Core	Carbon Steel	576				McMaster		Waterjet	Hardened after cut
Roller Rubber	Rubber	576				McMaster		Waterjet

Assembly Structure

Parts List

1. 15 - Rollers (RC-2008-01-00)
   1. 1 - O-Ring (RC-2008-01-01)
   2. 1 - Roller Hub (RC-2008-01-02)
   1. 1 - Wheel Body (RC-2008-02-01)
   2. 1 - Plate (RC-2008-02-02)
   3. 1 - Ring / Axel (RC-2008-02-03)
   4. 3 - 6-32 1/4" Long (RC-2008-07-04)

   Instructions

   1. Place 15 rollers on wire axle.
   2. Bend to circular shape.
   3. Drop in omni body.
   4. Place omni plate on omni body.
   5. Fasten using RC-2008-07-04

   Cost Estimates

   1. Rollers - $0.42 x 15 = $6.30
   2. Body - $4.00
   3. O-rings - $0.03 x 15 = $0.45
   4. Plate -
   5. Fasteners - $0.30 x 3 = $0.90

   Total - $11.65 (missing plate)

   Note - Shipping is included in per unit cost.

   Action Log

   
   Manufacturing

   WaterJetting

   WaterJet proved to have loose tolerances innitially however it can be adjusted to reduce taper utilizing the A-Jet settings. So far the best outcome has been setting the A-Jet tilt to -2.02174 degrees and tool offset of .02175. (Original settings for comparison tilt: 0 degrees and offset: .021).