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WHEEL RESEARCH
Considerations:
- OTS : no custom hubs, cheaper, faster for prototyping
- Timeline/prototyping
- Accuracy to what can be used on an actual Mars mission
- Weight
- Price point
- Customizability/design uniqueness
- What has been successful for other teams
- Size (less than 16”, greater than 10”) for 6 wheel drivetrain
- maintenance
- coefficient of friction
- maximum load
- width/tire thickness
- Internal diameter (ID)
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Consideration/Topic | Entirely 3D Printed Wheels | beach tires with 3D printed treads | Solid Tread, flat free wheels |
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general/description |
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Timeline/prototyping |
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Educational aspect |
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Accuracy to what can be used on an actual Mars mission |
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Size options | entirely customizable (between 10" -15") |
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Weight | unsure, but would likely be heavier as it is made of solid material | WheelEEZ: 11.8" : 1.3 kg (2.9 lbs) McMaster-Carr 10": couldn't find | n/a |
Price point | n/a | 11.8": $89.00 10": $85.58 | $75-160 13": $124.43 |
Customizability/design uniqueness |
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maintenance |
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Coefficient of friction | 0.38 (for hole wheel design)* 0.45 (for spike wheel design)* | WheelEEZ: 0.2-0.25 (website did not have specific values, against steel) McMaster-Carr: n/a | n/a |
Maximum load | n/a | WheelEEZ: 55kg McMaster-Carr: 1.2kg | 0.3kg |
Other teams |
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OTS Options/purchase options | filament here Thermoplastic Polyurethane TPU (AGH Space Systems, ITU) Polyethylene terephthalate glycol PETG (ITU) black SemiFlex clear generic TPE90A white NinjaFlex (very soft, therefore harder to print) | WheelEEZ McMaster-Carr | McMaster-Carr |
Example photos | Monash: ITU: | WheelEEZ wheel: Cornell: hub: Custom hub (cornell): |
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Material type | Description | Coefficient of Friction μ | Benefits | Drawbacks | Other Notes |
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Air Tires | beach tires |
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Rubber | ATV sand tires |
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cast with molds | 0.9 (on asphalt) |
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Metal | Aluminum (curiosity rover) | 1.10-1.35 (on aluminum) |
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Titanium nickel alloy (webbed material used for bike tires created by The SMART Tire company) |
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| https://www.syfy.com/syfywire/nasa-space-tires-never-go-flat-coming-to-your-bicycle | ||
3D Printed (use thermoplastic elastomers) | white NinjaFlex (very soft, therefore harder to print) | 0.69 (for smooth wheel design)* |
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| *referenced this report which used small scale wheels https://www.sciencedirect.com/science/article/pii/S2212827117300793 (μ measured on aluminum)
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clear generic TPE90A | 0.45 (for spike wheel design)* | ||||
black SemiFlex | 0.38 (for hole wheel design)* |
Tread Adhesives (for prototyping/removable)
- can be used for glass, metals, plastics
- water resistant, flexible
- can be removed with exacto knife and acetone (for excess remaining)
- any cuts made by exacto knife on wheel can be fixed with soldering iron
- equipment: caulking gun
- can be removed with heat and force: heat gun and scraping
- good long term option, used for outdoors (bike tire repairs)
- acetone can be used to remove any excess remaining
- note: acetone supposedly beads up on/does not affect polyurethane
- equipment: brush for application
- does suggest scuffing up the area first for better adhesion
~$9 for 8oz container
mcmaster carr:
plastic cement
https://www.mcmaster.com/adhesives/for-use-on~polyurethane-rubber/cement-for-plastic/
- stanford used zip ties to attach the treads to their wheels
- would only use for prototyping
Tread Styles
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Symmetric
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- thick groove patterns, wear down evenly over time
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- move in a single direction, most common type of tire tread
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- highest level of traction, control
- designed to roll in only one direction
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Michigan Mars Rover Team
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- highest SAR Score
- scored well in 2019 competition
- greatest diameter along center of wheel
- angled ridges/small paddles
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- 4th place for SAR
- video shows strong traction on snow
- contact about material type?
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RoverX
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- additional rubber (??) strips added, horizontal lines
- 10th place SAR
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- 8th place SAR
- horizontal ridges
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- paddle like ridging to dig into sand
- generally smoother than traditional (car) tires
- printing time may be very long
- bc they stick out more, they could be harder to attach/could fall off
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off set paddle tires
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- reduced weight
- maintains turning ability
- printing time may be very long
- bc they stick out more, they could be harder to attach/could fall off
note:
-teams that just used balloon tires as they are: Manipal, Rudra
Tread Styles to use:
Current treads:
notes: possibly have treads stick out slightly less/more paddle like (triangular profile vs square)
Rough sketch of hub design
Interesting Tire Shapes (treads and spokes?)
Tire Shape Name | Photos | Extra notes |
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Humvee Airless Tire |
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Michelin UPTIS airless tire |
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Loopwheel |
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Sand tires |
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SMART Tires |
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Wheel designs from other teams:
Team Name | Year and Info | Pictures |
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IMPULS: | 2021: 300 mm wheels, wheels have not changed from 2019 design (as far as I can see). Their spokes and frame seem to be custom made (machined and acrylic?) | |
Ryerson Rams: | Previously (before 2019) used rigid wheels, too much force into suspension, not enough traction |
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(stated in video) 2019: Prototyped highly deformable wheels, flexible 3d printing, casting rubber tires - final design seems to be casted rubber tires. | |
2021: 3D printed PETG hubs and casted polyurethane treads for flexibility, shock absorption, traction | |
Stanford |
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2019: included nylon chains, inflated wheels | ||
2020: Wheels are still inflated, more traction(not explained in SAR) but it seems a (rubber?) textured piece has been attached to the outer surface of the wheel |
Small clip in SAR shows one wheel with a different surface? (side note they mentioned a “Grass hopper suspension”, distributes weight away from lowest handing wheel to glide/avoid obstacles/handle rocky terrain) | ||
PCz: | 2021: 3d printed 14 inch wheels for shock absorption and traction. Their design has similarities with the Curiosity rover’s treads: | |
Monash (9th place): | 2019: beach tires | |
2021: 3D printed wheels, individually driven- frame and treads are all 3d printed. |
Research from NASA's rovers:
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Main conclusion (for now): many high level teams switched from inflated tires to 3D printed tires for their customizability and (seemingly) to emulate more of NASA's designs.
PROTOTYPING INFORMATION
Tread Adhesives (for prototyping/removable)
Adhesive name | Description | Cost | Image |
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Silicone Sealant/glue |
| ~$20 for 11oz container | |
APAO Based hot melts |
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rubber cement |
| ~$9 for 8oz container mcmaster carr: plastic cement https://www.mcmaster.com/adhesives/for-use-on~polyurethane-rubber/cement-for-plastic/ | |
other testing option |
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Tread Styles
Style Name | Photo | Notes |
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Symmetric |
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Asymmetric |
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Directional (also called unidirectional) |
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Michigan Mars Rover Team |
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PCz - zig zag pattern |
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RoverX |
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Anveshak |
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ATV sand tires |
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off set paddle tires |
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note: some teams that just used balloon tires as they are: Manipal, Rudra
POSSIBLE PROTOTYPING MATERIALS:
Rubber sheets from Mcmaster-Carr:
width: 1/2"-1"
Black sheets, (dimensions for prices: 6"x6", 12"x12", 12"x24"), hardness level likely 60A (treads are usually 70A for a regular tire)
features: used for outdoors, high tension applications, high wear
cut to length option also available, but far more expensive.
black sheets, also used for outdoors, oil and abrasion resistant, shock absorbing. Same dimensions as above.
Tread Styles to use:
Current treads:
notes: possibly have treads stick out slightly less/more paddle like (triangular profile vs square)
Rough sketch of hub design