Wheel Construction

general/description

• self explanatory, design entire wheel 

• design various attachable 3D printed tread patterns to the beach tires 

• most basic option

• used as is

Timeline/prototyping

• may take many weeks to create from designing, sourcing filament, printing, prototyping to final product

• can reliably test far faster - begin testing with just the beach tires and can add treads later 

• would need to alter hub to accommodate motor 

Educational aspect

• improve design skills

• opportunity to analyze various tread styles for the terrain

• analyze possible spoke styles/internal support for weight of rover as well deformability

• create/implement custom hubs

• opportunity to analyze various tread styles for the terrain

• figure out a way to firmly attach treads to wheel

  • Stanford - zip ties (prototyping)

  • Cornell (2020)-adhesives -cyanoacrylates, epoxy?

• altering hub

Accuracy to what can be used on an actual Mars mission

• airless tires would be more accurate to what is possible on Mars missions

n/a

• airless tires

• foam filled

Size options

entirely customizable

(between 10" -15")

Wheeleez:

• diameter: 9.4"      width: 

• diameter: 11.8"  width: 7.3"

• diameter: 16.5"    width:

McMaster Carr

• 8"

• diameter 10"  width: 1 5/8"

• 10"

• 12"

• 13"

• 15"

• 16"

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

• entirely custom allowing for custom wheel hubs and any spoke/tread design we may want

• would have the ability to expand on this for future years

• tire is OTS but treads would/could be custom made and this would also allow us to prepare for a more advanced wheel design for a future rover

• possibility of a custom hub (hub that comes with wheels is completely removable

• n/a

maintenance

• cannot be fully sure until prototyped

• design could be less resistant to catching sand, wearing down etc. 

• unlikely, but sand could enter hubs/bearings - should choose a reliable design (Wheeleez has multiple parts such that the entire hub can be easily taken apart and cleaned/repaired/replaced)

• cuts can be repaired using a soldering iron

• possibility for 3D printing different interchangeable attachable treads to have better treads prepared for competition/less worn down/new treads

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

• Monash

• Ryerson Rams

• ITU

• Stanford

• Cornell

n/a

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

https://www.mcmaster.com/22245T33/

https://www.mcmaster.com/rubber-tread-wheels/

Example photos

Monash:

Open

ITU:

Open

WheelEEZ

wheel:

Open

Cornell:

Open

Open

Open

hub:

Custom hub (cornell):

Open

Air Tires

beach tires 

• can purchase commercially

• cost is under $100

• have to design within constraints of COTS wheel hubs

• similarly to Stanford, nylon chains and grips can be added to the surface of the wheels for more traction

• 8-12" diameter for a 6 wheel design (from old research

• can adapt

• Can adapt to a 6” diameter hub motor

• Width exceeding 4” (by experience, can analyze for more detail, too narrow tires can significantly increase ground pressure)

• Any 2 tires in design must be able to handle entire rover load without rupturing

Rubber

ATV sand tires

• tried and tested to be efficient in sand dunes 

• would have to emulate the design ourselves/cannot buy commercially because regular ATV sand tires are too big

• can change pressure within tires, when tires are deflated to 10-20 psi, better for sandy terrain

cast with molds

0.9 (on asphalt)

• customizable 

• can use with custom hubs

• prototyping time that could  be spent working elsewhere

• need to learn how to use molds and casting 

• refer to Ryerson Rams design

Metal

Aluminum (curiosity rover)

1.10-1.35 (on aluminum)

• more similar to current tech used on Mars (air tires cannot be used due to Mars' atmosphere)

• depending on thickness of wheel/design, similarly to Curiosity Rover, the aluminum wheels could experience some damage 

Titanium nickel alloy (webbed material used for bike tires created by The SMART Tire company)

• has been approved by NASA

• would be more suitable for real Mars conditions

• difficult and expensive to imitate 

• deformations can occur if shape memory alloys are not used

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)*

• customizability 

• compliant wheel internal design (with soft thermoplastics)

• Can rapidly prototype various wheel designs 

• custom hubs can be used which is easier for mounting motors on wheels

• With custom hub design as well, possibility of swapping tires

• FEA justified

• printing/prototyping time that could  be spent working elsewhere

• less reliable than commercially designed tires

*referenced this report which used small scale wheels https://www.sciencedirect.com/science/article/pii/S2212827117300793

(μ measured on aluminum)

• another material option is elastomer latex, but that is not commercially available

clear generic TPE90A

0.45 (for spike wheel design)*

black SemiFlex

0.38 (for hole wheel design)*

Humvee Airless Tire

• in prototype stage for (U.S.) Army Research Lab by Resilient Technologies

• made of polymers 

• benefit: would be more accurate to tech that can actually work on Mars

• drawback: have to ensure that nothing can get stuck within spokes

Michelin UPTIS airless tire

• demo clips of it rolling over a nail and continuing 

• no need to check air pressure

• cast a design like this or 3d print (with soft thermoplastics) a design like this?

• benefit: would be more accurate to tech that can actually work on Mars

• drawback: have to ensure that nothing can get stuck within spokes

Loopwheel

• a bike tire design, but the "spokes" are interesting bc they have been designed to readjust and therefore change the shape of the tires for rougher terrain

Sand tires

• specialized ATV/UTV 

• rear tires: paddle like ridging to dig into sand

• front tires: completely smooth, few ridges for steering purposes, ridges raised along the center allow for bite to make more immediate turns-might not be good to implement these bc the rover won't be going as fast (don't need to glide).

SMART Tires

• bicycle tire design

• still in prototyping phase-final product is planned to be encased in rubber & polyurethane 

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 (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

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.

Silicone Sealant/glue

• 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

~$20 for 11oz container

APAO Based hot melts

• non crystalline adhesives that stay flexible and tacky

• good adhesion

• long open times

• can be used for woodworking, automotive assembly

• remove with rubbing alcohol, hot gun, scraper

• equipment: hot melt gun (glorified glue gun)

• https://www.hotmelt.com/products/high-performance-product-assembly-apao-hot-melt-300-second-open-time

• requires a quote?

rubber cement

• 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