What Are Flex Wheels?
Flex wheels are soft wheels that are designed to be compliant, and are useful for a variety of applications, such as:
- Picking up hard plastic game objects
- Picking up objects that have an irregular shape (e.g., cubes, discs, etc.)
- Driving over field obstacles where regular drive wheels may have difficulty
Flex Wheels were originally designed for the VEXpro product line, which primarily uses 1/2" hex or 1-1/8" round bore for most applications. However, V5 uses 1/8" and 1/4" square shafts. In order to use Flex Wheels on a V5 robot, you will also need to use some specific adapters that allow Flex Wheels to be driven by V5 shafts.
This guide will identify which parts are needed to make each size of Flex Wheel work on either the V5 ¼” High Strength Square Shaft or the ⅛” Square Shaft, both of which are standard in V5.
Flex Wheel Sizes
There are four different sizes of Flex Wheel that are legal for use on VRC robots. The two smaller sizes have a hex bore, while the two larger ones have a round bore.
| Diameter of Wheel | Width of Wheel | Bore |
|---|---|---|
| 1.625” | 0.500” | ½” Hex (undersized) |
| 2” | 0.500” | ½” Hex (undersized) |
| 3” | 1.000” | 1.125” Round (undersized) |
| 4” | 1.000” | 1.125” Round (undersized) |
Because the Flex Wheel material is flexible, the bores are intentionally undersized so that they do not slip on their intended shaft. Because of this, when you look at a Flex Wheel the bore will be significantly smaller than its matching adapter.
Flex Wheel Durometers
Each size of Flex Wheel is offered in three different durometers. Durometers identify the relative hardness of materials, and indicate the flexibility of the resulting Flex Wheel; the ‘A’ refers to the particular scale of measurement used for flexible mold rubbers. Higher-number durometers (e.g., 60A) are more rigid, while lower numbers (e.g., 30A) are very flexible.
Choosing a Flex Wheel durometer based on your specific use case can be helpful for several reasons:
- Allows you to vary how much the wheel flexes when intaking an object. For example, a softer wheel may be better suited for picking up harder objects while a harder wheel may be better suited for picking up softer objects.
- If an intake is wide enough to intake multiple game objects at once, you can use different durometers to affect the grip on one side of the intake to help prevent objects from jamming.
- In a drive application, your choice of durometer flex wheels is like adjusting a suspension on a car. Softer wheels will dampen impacts better and can easily climb objects in their path, but might make the robot bouncy as it drives on flat ground. Harder wheels will have a “smoother” drive, but may have more trouble climbing over objects.
| Durometer | Similar to a… |
|---|---|
| 30A | Soft Rubber Band |
| 45A | Pencil Eraser |
| 60A | Car Tire |
1.625” And 2” Flex Wheel Assembly
The two smallest Flex Wheels, 1.625” and 2”, require two accessory parts in order to be compatible with a V5 ¼” High Strength Square Shaft.
An additional two inserts can be used to make these wheels compatible with a V5 ⅛” Square Shaft.
See the diagrams below to help understand which parts are necessary to use the 1.625” and 2” Flex Wheels on your robot.
3” And 4” Flex Wheel Assembly
The two larger sizes of Flex Wheels, 3” and 4”, require four accessory parts in order to be compatible with a V5 ¼” High Strength Square Shaft.
An additional two inserts can be used to make these wheels compatible with a ⅛” Square Shaft.
See the diagrams below to help understand which parts are necessary to use the 3” and 4” Flex Wheels on your robot.
Optionally, VersaHubs can be retained to Flex Wheels using standard V5 hardware (note that this does not replace the use of the adapters described in this article, but can provide some additional stability if needed). Long screws can be used as through-bolts with nuts on the other side, or ¼” standoffs can be pressed into the bolt circles inside of the 3” and 4” Flex wheels to allow shorter screws to capture the Plastic VersaHubs on both sides of the wheel.
Summary Table
This table summarizes the parts needed to build a single Flex Wheel Assembly to use on a V5 Robot.
| Flex Wheel Size | V5 Shaft Size | VersaHex Adapter | VersaHub | High Strength Shaft Insert 276-3881 |
|---|---|---|---|---|
| 1.625” or 2” | ¼” High Strength | 2x Required | Not Required | Not Required |
| ⅛” Square | 2x Required | Not Required | 2x Required | |
| 3” or 4” | ¼” High Strength | 2x Required | 2x Required | Not Required |
| ⅛” Square | 2x Required | 2x Required | 2x Required |
Part Substitutes
There are a few parts that are functionally identical to those in the images above, which can be used interchangeably to make Flex Wheel Assemblies. The following parts can be substituted for each other, and all are legal for use on VRC robots.
VersaHubs
The following parts are functionally identical:
- 217-8079 - 1/2” Hex Bore Plastic VersaHub v2
- 217-2592 - 1/2” Hex Bore Aluminum VersaHub
VersaHex Adaptors
The following parts are functionally identical:
- 217-8004 - Plastic 1/2" VersaHex Adapters v2 (1/4" Square Bore) (48-pack)
- 217-7946 - 1/2" VersaHex Adapters v2 (1/4" Square Bore, 1/8" Long) (8 Pack)
- 217-7947 - 1/2" VersaHex Adapters v2 (1/4" Square Bore, 1/4" Long) (8 Pack)
Cleaning Flex Wheels
After prolonged use, teams may find they need to clean their Flex Wheels. VEX recommends using deionized water on a clean rag to wipe the surface of the wheels. Do not use Isopropyl Alcohol to clean Flex Wheels, as it may damage the compound used to manufacture the wheels.
Alternative Flex Wheel Mounting Methods
The methods of assembly shown above are the intended and best solutions for mounting Flex Wheels on V5 robots. However, we understand that they may not be feasible for all teams for a variety of reasons. If you have Flex Wheels, and are missing one or more of the adaptors shown above, there are still ways you can make Flex Wheels work on your VRC or non-competition robot.
It is important to note that these alternatives may or may not perform as well as the methods shown above, and that some of these alternatives will perform better than others. The alternative methods all use parts that were not initially designed to work together, but work if you are in a pinch.
Alternatives for 1.625” and 2” Flex Wheel
The following alternatives for 1.625” and 2” Flex Wheels are listed in order of ease of assembly.
Alternative 1: 276-3891 Clamping Shaft Collar (⅛” Shaft) or 276-6102 High Strength Clamping Shaft Collar
The Clamping Shaft Collars can be pressed into the hex bore of the 1.625” and 2” Flex Wheels as a slight interference fit to make these wheels compatible with a ⅛” Shaft or ¼” Shaft.
Assembly Steps:
- Step 1: Line up the shaft collar and the Flex Wheel. It may be easier to place the shaft collar on a solid surface while holding the Flex Wheel above.
- Step 2: Push the Flex Wheel over the shaft collar. It may be easiest to push the Flex Wheel down at an angle and then rock it over the shaft collar to get the shaft collar into the bore.
Alternative 2: 276-2551 12T HS Gear (¼” HS Shaft)
The 12T HS Gear is also a good interference fit into the hex bore on the 1.625” and 2” Flex Wheels. This option makes the Flex Wheels fit on a ¼” HS Shaft.
Note: Because this part is metal, it may begin to tear the Flex Wheel over time. Use this method with caution so as to not destroy your wheels.
Assembly Steps:
- Step 1: Line up the 12T pinion and the Flex Wheel. It may be easier to place the pinion on a solid surface while holding the Flex Wheel above.
- Step 2: Push the Flex Wheel over the 12T pinion. It may be easiest to push the Flex Wheel down at an angle and then rock it over the pinion to get the pinion in the bore.
Alternative 3: Lockbars and Standoffs (⅛” Shaft)
A hub for the 1.625” or 2” Flex Wheels can be created using either the Metal Lock Bar (275-1065) or the Plastic Lock Bar (276-2016-002) with 1” #8-32 screws, ½” #8-32 Standoffs, ½” Long Spacers, and your preferred #8-32 Nuts.
Assembly Steps:
- Step 1: Thread two ½” standoffs onto 1” screws as shown below.
- Step 2: Slide the Flex Wheel over the standoffs as shown below.
- Step 3: Insert the 0.375” OD 0.5” long spacer into the hex bore of the wheel.
- Step 4: Attach the second lock bar and tighten nuts onto screws.
Alternative 4: Hub from 276-1499 Intake Roller (⅛” shaft)
The inner Plastic Hub from a 276-1499 Intake Roller can be used inside of Flex Wheels as well. Simply cut the rubber overmold away from the part, and insert the plastic hub into the 1.625” or 2” Flex Wheel similarly to the steps in Alternatives 1 & 2.
Assembly Steps:
- Step 1: Slice on the line shown on the Intake Roller and remove the inner plastic hub from the overmold.
- Step 2: Line up the plastic hub and the Flex Wheel. It may be easier to place the plastic hub on a solid surface while holding the Flex Wheel above.
- Step 3: Push the Flex Wheel over the plastic hub. It may be easiest to push the Flex Wheel down at an angle and then rock it over the hub to get the hub into the bore.
Alternatives for 3” and 4” Flex Wheels
The following alternatives for 3” and 4” Flex Wheels are listed in order of ease of assembly.
Alternative 1: 2 16T Sprockets, 6P (276-8328) (¼” HS Shaft)
Two 16T 6P Sprockets can be inserted into the bore of the Flex Wheel. A 0.25” long (0.375” OD) nylon spacer can be used to improve functionality by keeping the sprockets evenly spaced inside of the wheel.
- Step 1: Fully insert the first sprocket by squishing the Flex Wheel into an oval shape
- Step 2: Rotate the sprocket in the bore of the Flex Wheel. Insert a shaft (not pictured) and a high strength shaft adapter if needed.
- Step 3: Put the 0.25” long (0.375” OD) nylon spacer and the second sprocket, along with a high strength shaft adapter if needed, onto the shaft.
- Step 4: Push the sprocket assembly into the Flex Wheel. As the second sprocket goes into the Flex Wheel bore it may be easiest to work your way around the sprocket teeth progressively in a circle, pushing them into the bore in sections by applying pressure to the sprocket.
Alternative 2: 60T High Strength Gear (¼” HS Shaft)
A 60t gear has a bolt pattern that is close to the bolt pattern on the Flex Wheel. The patterns don’t line up perfectly to the eye, but the softer Flex Wheels are flexible enough that they can stretch to make the hole pattern line up.
- Step 1: Align two holes of the gear and the Flex Wheel
- Step 2: Insert two 1.75” bolts into holes of the gear and Flex Wheel.
- Step 3: Screw on nuts
Alternative 3: Custom Polycarbonate Plates and Lock Bars (⅛” Shaft)
All VRC teams have an allowance of 0.065” polycarbonate, which can be used to make a plate that mounts to the side of a Flex Wheel and holds a lock bar.
- Step 1: Cut custom polycarbonate plates. The important features are holes on a 1.875” bolt circle to mount to the Flex Wheel, 2 holes to mount the lock bar insert and a clearance hole in the center of the plate for the shaft.
- Step 2: Attach the plates
- Step 3: Attach the lock bars
- Step 4: Screw on nuts