What are different types of wheels good for?

Hi!
Just looking to expand my knowledge here. What characteristics do different wheels have, and what applications are they good for?

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Mecanum wheels are good drivebase wheels if your goal is getting DNPed (designated a “do not pick” by other teams), since though they enable you to move sideways, you lose a lot of traction and controllability. Useful on intakes though, since they apply a force vector at an angle and can center gamepieces if oriented right

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I feel that this is still relevant, though, some parts of it may be considered outdated.

Compliant wheels, otherwise known flex wheels, are flexible, which makes them great for intakes and other mechanisms that require a bit of compliance, but they’ll explode at high RPMs, so they’re not great shooter wheels. For those applications, solid roller wheels like Fairlane wheels tend to be popular.

Omni wheels allow game pieces to move freely along the direction of the roller’s axis, which is useful in combination with vectored intake wheels like mecanum wheels. Larger omni wheels can also be used on standard skid steer drivetrains like the KOP drivetrain to increase maneuverability at the cost of traction in the direction of the wheel’s axis. While special drivetrains can be built to move omnidirectionally using omni and mecanum drive wheels, I wouldn’t recommend them as you then lose the ability to pivot over to defense effectively, making you functionally useless as a third pick.

Regular drive wheels generally come in two types, pre-molded, and treaded. Pre-molded wheels, like HiGrips, VersaWheels, and Colsons save you the trouble of applying tread to a wheel yourself, but have to be replaced entirely when they wear out. Colsons in particular have also been shown to increase the impact of carpet grain direction on odometry, which has resulted in them falling out of favor with many top-tier teams. Treaded wheels use tread riveted or bolted onto the wheel for traction, and this tread can be replaced without replacing the entire wheel. They exhibit much more consistent odometry under different carpet grain directions than Colsons do.

I should probably note two things here:

  1. Some teams have noted that cutting tread patterns into Colsons helps solve this underlying odometry issue, but this also means that the modified wheels will no longer remain COTS under current FRC rules and regulations.
  2. You can mold your own wheels, and some teams like 2767 have done so, but frankly, it’s likely not worth it for the vast majority of teams in my opinion. You can also print wheel tread from TPU though, if you’re interested in that kind of thing.

Pneumatic wheels, like these ones sold by WCP, help with shock absorption in games with rough terrain, like 2016. Not sure how they impact odometry though, although some teams have used different center wheels on their skid steer drives to combat the effect the compression of the wheel has on driver feel.

Regular aluminum treaded wheels can be found sold by both WCP and AndyMark, but I personally prefer WCP’s to Andymark’s just because they’re lighter and frankly look better. You can purchase tread for them from Andymark, WCP, or the Thrifty Bot, or just cut your own to width from McMaster.

Here’s the RAP Design Guide. It has a section on wheels for use in FRC that might help you out. Check page 100 for drive wheels and page 146 for intake wheels.

Here’s the SDS 4 in. billet wheel @heatblast016 referred to, and here’s the precut and drilled tread that you can purchase along with it as well. While I’m still here, I guess I might as well plug the Armabot Tread Tool for WCP’s 4 in. Aluminum Wheels here too.

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Regolith wheels are not good for anything

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With fairlane wheels, teams usually have to 3d print or machine their own hubs to adapt the wheels to FRC hardware, which can be a tricky process (though there are several threads on it on CD). While WCP has similar wheels that come with a hex bore, they’ve been out of stock for quite some time now. You can also use any of the molded wheels mentioned for shooters, though they have less efficient energy transfer.

You can also get treaded wheels from swerve drive specialties, which look really nice and (iirc) have pre-cut tread sold for them, at a slight price premium

There are a lot of wheels that get used in FRC, so I’ll just talk about the classic choices and their use case.

The Colson

The colson is a classic wheel, with some good characteristics. It’s commonly available with a .5" hex bore from VEXPro, and other suppliers without a .5" hex bore (but VEX sells a press-fit insert for the bore).

Pros:

  • Low maintenance - service for this wheel is most commonly “remove and replace”
  • Good traction - provides relatively good traction on the field carpet, and stands up to defense.
  • Good mobility - allows for a robot to turn relatively easily.
  • Sizes - available in many sizes (both width and diameter), allowing for different mechanism characteristics and gearing.

Cons:

  • Wears quickly - colsons used in traction applications
  • Expensive - especially for a part which wears quickly, colsons are relatively expensive.
  • Heavy - colsons are relatively heavy wheels
  • Not extremely compliant - the tread is typically not very “compliant”, and given the aluminum hub it doesn’t really deflect very much when encountering a game piece.

The bottom line: colsons provide an excellent choice on drive trains, and commonly used as a 4x1.5 size for west coast style drivetrains. They provide good traction with few tradeoffs. Some teams also use colsons for their flywheels for powered shooters, with success. Colsons have been used by teams for years, at the highest level of play in FRC.

The “traction wheel” (aluminum hubs + tread)


(aluminum hub pictured)

The traction wheel is also a classic drive train or light mechanism choice, with excellent drive characteristics. It is available in many sizes, and from multiple suppliers (commonly VEXPro, WCP and AndyMark).

Pros:

  • Great traction - provides excellent traction on field surface, and stands up well to defense.
  • Good mobility - allows for robot to turn relatively easily.
  • Sizes - available in many sizes.
  • Weight - most hubs have a large amount of open space, and therefore are relatively lightweight.
  • Re-usability - hubs can be reused from year to year, provided new traction material is applied.

Cons:

  • High maintenance - the tread can wear quickly, and replacing tread can be a hassle. Tread if not secured can also come off during a competition, rendering the robot effectively traction less.
  • Expensive - hubs alone typically cost in the 15-20 dollar range, per wheel. Although they can be easily reused, tread also starts to add to the cost. Initial investment for an 8wd would be close to the $300 range, which is rather expensive for especially newer teams.
  • Not extremely compliant - the tread is typically not very “compliant”, and given the aluminum hub it doesn’t really deflect very much when encountering a game piece.

The bottom line: traction wheels are great in drivetrains, but their cost, traction surface and lack of compliance makes them a hard choice for most manipulators. They are a first-rate choice for many teams for drive trains, and have been season tested for years by many teams at the highest level of play.

The mecanum wheel

The mecanum wheel allows for drivetrains to strafe (that is, move directly left-right and right-left), but provide very low traction on field surface and make teams incredibly susceptible to defense. Their vectoring characteristics make them a great choice for intakes for some game pieces. They are commonly available from AndyMark and VEXPro, with a 3d-printed version available here on chief as well.

Pros:

  • Vectoring surface - these wheels allow intakes that move a game piece across the robot, allowing for teams to design a single cutout in their bumpers / robot, and have game pieces travel to that location.
  • Strafing - if used in a drivetrain, this wheel allows robots to strafe directly to the left and right, without turning the robot.

Cons:

  • No traction - these wheels effectively provide zero traction on the field surface, and leave robots out to heavy defense.
  • Heavy - many mecanums are very heavy, as they depend on several shafts inside the mecanum.
  • Cost - unless you are 3d printing your mecanums (which is hard to do for a drivetrain), they are very expensive, around $30 / wheel.

The bottom line: not a popular choice for drivetrains, just based upon their lack of traction. They are great for intakes for some game pieces (2016/2020 had great game pieces for this), but intakes with them can be expensive and hard to set up.

The omni wheel

The omni wheel is similar to a mecanum, allowing for robots to move directly sideways. However, since it is lower profile and has a slightly different geometry, it is sometimes placed in drivetrains with other traction wheels (usually 2 in the front or rear corners, commonly referred to as “4x2”, “6x2” or sometimes “2x2”). They are commonly available from VEXPro and AndyMark.

Pros:

  • Incredible turning characteristics - if placed in corners, this can save some bad design, or allow teams to make otherwise very flat drivetrains.
  • Good game piece manipulation - allows for game pieces to be coming in at an angle, but still move them forward. Great in a mecanum intake, as the middle wheel.
  • Re-usability - can be reused from season to season with relatively low wear.

Cons:

  • No traction - again, with roller surface, these wheels have effectively no traction
  • Relatively weighty - about as heavy as a colson for some wheels, omnis can be weighty.
  • Expensive - again, about $20-$30 for each wheel.

The bottom line: omnis are frequently used in drivetrains, with other traction wheels on the robot. This allows for these robots to turn a little better, or other positive drivetrain characteristics.

The compliant wheel

image

Compliant wheels are very squishy, and allow for great control of game pieces - particularly those that are rigid in nature (2015/2018/2019). They are not a good choice for drive trains, as they deform too much. They are typically available from AndyMark and Banebots.

Pros:

  • Very flexible - at certain durometers, these wheels flex a lot. This really helps pickup rigid items.
  • Price - they are relatively cheap
  • Weight - they are very light, and have little material

Cons:

  • Not a drive wheel - in FRC, robots are simply too heavy to use these as a drive wheel.
  • Deformation - at high speeds, these wheels tend to expand a lot, which can create some deformation problems or different intake characteristics than expected.

The bottom line: compliant wheels are great in manipulators, especially for a firm or rigid game piece.

The Hi-Grip wheels

image

The hi-grip wheels are commonly available from AndyMark, and are familiar to most teams as “the kitbot wheels”. They are relatively high performance, and have been battle tested drivetrain wheels at even the highest level of play.

Pros:

  • Good traction - these wheels provide good traction on the field surface.
  • Inexpensive - these wheels are relatively cheap.
  • Many sizes - these wheels are offered in several sizes, from 4-8 inches.
  • Weight - for their size, these wheels are relatively lightweight.

Cons:

  • Plastic hubs are weak - these wheels can sometimes crack under pressure, so have spares ready.
  • Wear and tear - these wheels tend to wear down quickly, and should be replaced every couple of events.
  • Relatively thin - they are only available in one thickness, and are relatively thin. This makes them more susceptible to defense.

The bottom line: if you’ve been a rookie, or used the KOP drivetrain, you’ve used these wheels. They are high performance, inexpensive, and get the job done without frills. They are an excellent choice for most drivetrains, and are more than serviceable even at high levels of play.

The pneumatic wheel

image

This is an air-filled wheel with good traction, and can take a beating. The extra air cushion that these wheels offer makes them great for rough terrain (2016), and they have excellent traction. They are commonly available from VEXPro and AndyMark.

Pros:

  • Lots of traction - these wheels are sticky, and hard to play defense against.
  • Can take a beating - they can send over rough terrain without issue, and bounce along for a drivetrain.
  • Serviceability - service for these wheels is typically “ensure they’re inflated right”, and you’re off to the races.

Cons:

  • Expensive - this 8" variety is $65/wheel from AndyMark.
  • Too much traction - poorly designed drivetrains, or drivetrains without some considerations suffer from a lack of turning when using these wheels.

The bottom line: while good for rough terrain, these wheels are quite the price tradeoff in a year which does not depend on your ability to cross terrain like that faced in 2016. They don’t make a great choice in intakes due to their size, and for shooters they aren’t well recommended due to the fact that they are an air filled tire.

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Excuse me? Paired with a plastic floor over carpet, they’re among the best wheels for frying electronics and zapping unsuspecting teammates.

Other than that, I have to agree.

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I would a con for Hi-Grips their tread pattern when used in shooters, they like eating foam balls for lunch

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I wouldn’t go that far, appreciable wear on balls was more or less about the same based on what we saw. However hi-grips are nasty if a ball jams.

Point being: The subsystem as a whole often determines how good/bad similar parts are, not the parts themselves.

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I like the way you think…

Yeah, in short, also in my opinion, don’t mold your own. Brings back bad memories. We didn’t have a good go at it.

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