FRC Swerve Modules Compared: MK4/MK4i, MAXSwerve, WCP & Thrifty

Choosing a swerve module is one of the biggest early decisions a build season throws at you. It shapes your motor purchases, your gear-ratio math, your maintenance routine, and how much floor-to-frame clearance you have for intakes and bumpers. The good news in 2026 is that you no longer have to design a module from scratch — several vendors sell mature, well-documented commercial-off-the-shelf (COTS) swerve modules that thousands of teams run every season.

The catch is that they are not interchangeable. An SDS MK4i, a REV MAXSwerve, a WCP Swerve X2, and a Thrifty Swerve each make different trade-offs around motor support, wheel size, gear-ratio spread, and serviceability. This guide breaks down the major families, gives you a verified spec-by-spec comparison, and walks through how to actually pick the right one for your robot and your team's resources. If you are new to how these things drive, start with our swerve drive explained primer and come back here for the hardware.

What a COTS swerve module actually is

A swerve module is a self-contained drive corner. Each one has two motors: a drive motor that spins the wheel and a steering motor (sometimes called the azimuth or turning motor) that rotates the whole wheel assembly around a vertical axis. Because each corner can point and drive independently, a four-module robot can translate in any direction, rotate in place, and combine the two — that is the whole appeal.

A "COTS" module means the vendor has done the hard engineering: the gears, bearings, belt or gear reductions, wheel, and steering encoder mount are all designed to fit together and to accept standard FRC motors. You buy four (occasionally three), bolt them into your frame, wire up eight motors and four absolute encoders, and spend your engineering time on software and the rest of the robot instead of on gear meshes. The differences between families come down to which motors they accept, how the steering is driven, what wheel they use, and how the drive reduction is configured — which is exactly what determines your speed, pushing power, and packaging.

The main COTS swerve families in 2026

Swerve Drive Specialties: MK4, MK4i, MK4n

Swerve Drive Specialties (swervedrivespecialties.com) is the most widely run family in FRC, and the "MK4" line is effectively the default reference point everyone else gets compared to. All of the current MK4-series modules accept the same four brushless drive motors — REV NEO (V1.1), NEO Vortex, VEX Falcon 500, and WCP Kraken X60 — and none of them accept a CIM, which is too large in diameter to fit.

• MK4 is the original geared-steering module. Its steering ratio is 12.8:1, and it offers four drive gear ratios (L1 through L4), giving it the fastest top-end option in the family. The drive motor mounts up high, alongside the wheel.
• MK4i flips the drive motor down low ("i" for inverted), which lowers the center of mass and tucks the motor inside the frame for protection. It uses a 150/7:1 steering ratio (about 21.4:1) driven through a gear pair and a belt. Its three drive ratios are L1 = 8.14:1, L2 = 6.75:1, and L3 = 6.12:1, and an optional 16T drive pinion adapter raises free speed by roughly 14%. A NEO-equipped MK4i weighs about 6.0 lb (6.3 lb with a Falcon 500).
• MK4n is the narrow variant. Its narrow side is only 4 inches wide inside the frame member, freeing up room for wide intakes while keeping the same frame-to-floor height as the MK4 and MK4i. It uses an 18.75:1 steering ratio and 16T drive/steering pinions, and its drive ratios (L1+, L2, L3+) match an MK4i fitted with the 16T pinion kit. It supports both a 0.25" magnet encoder and a 0.5" hex encoder, and requires mirrored "A"/"B" module layouts.

Buying tip: For most standard full-weight robots, MK4i in L1 or L2 is the safe, boring, correct default. L3 is aggressive and really meant for lightweight robots that won't brown out chasing that top speed. Don't buy the fastest ratio just because it exists.

REV MAXSwerve

REV's MAXSwerve (revrobotics.com) took a different design path and is the most popular alternative to SDS. The defining choice is the 3-inch wheel — smaller than the 4-inch wheels most competitors use — which keeps each module compact and lets you push your wheelbase to the corners of your footprint. The drive motor can be a NEO, a NEO Vortex (with a replacement shaft), or a Falcon 500 (with a replacement shaft).

The steering side is what really sets MAXSwerve apart: instead of a large motor, it drives azimuth with a small NEO 550 through an UltraPlanetary gearbox at roughly 46.42:1 (exactly 9424:203). The base kit ships with three drive speed options; the optional Gear Ratio Upgrade Kit adds two motor pinions and four spur gears for five more high-speed ratios, bringing the total to eight configurations. If you are already invested in REV's control system, MAXSwerve slots cleanly into the rest of the REV Robotics ecosystem.

Buying tip: The 3-inch wheel is a genuine trade-off, not just a smaller number. It buys you a wider effective wheelbase and tidy packaging, but it also means less ground clearance and a wheel that wears faster relative to its diameter. Plan tread replacement into your season if you run MAXSwerve hard.

WCP Swerve X and Swerve X2

West Coast Products (wcproducts.com) makes the Swerve X line. The original Swerve X accepts Kraken X60, 775pro, and 550-class motors and runs a 4" OD x 1.5" wide wheel, with standard and "flipped" (low-mounted motor) configurations.

Swerve X2 is the current generation, redesigned around the Kraken X60 to cut complexity and add traction. It moves to a wider 4" OD x 2" wide wheel, uses a 12.1:1 rotation (steering) ratio that stays constant across motor configs on the 10T pinions, and offers a consistent spread of drive ratios via X1–X4 ratio sets (roughly 13 to 22 ft/s of free speed depending on the set and motor). Ratio kits ship with steel gears that can be swapped for aluminum to shave weight, and the module comes in several mounting flavors (standard, inverted, thin, compact). If you run Krakens and want a module tuned around them, X2 is built for exactly that.

TheThriftyBot Thrifty Swerve

Thrifty Swerve, from TheThriftyBot (thethriftybot.com), is the value-focused entry and has become a serious option for cost-conscious teams. The standard module runs a 4-inch aluminum billet wheel and accepts a Kraken X60, NEO, or NEO Vortex on both the drive and steering axes, and it works with motors mounted inverted or non-inverted. There is also a Thrifty Swerve Narrow module that pairs one 60mm-class motor with a smaller 44mm-class motor (a Pulsar 775 or Kraken X44 on steering) to save space in one direction.

Buying tip: Thrifty Swerve is the strongest argument for a rookie or budget team that still wants real swerve. Price out a full set of four including motors and encoders before you commit — the module cost is only part of the picture, and motor choice usually dominates the total.

AndyMark and where to buy

AndyMark (andymark.com) is a primary distributor rather than a module designer of its own — it stocks SDS MK4/MK4i modules, gear-ratio kits, and the surrounding hardware, and is often where teams actually place the order. When you are comparing prices and lead times, check both the designer's store and AndyMark, because availability during build season swings hard.

Side-by-side comparison

Buying tip: Motor compatibility is the first filter, not the last. If your electrical team is standardized on Spark MAX or Spark Flex controllers, that steers you toward NEO/NEO Vortex modules; if you are on TalonFX/Kraken, WCP X2 and the Kraken-friendly modules make more sense. Decide the motor ecosystem first and let it narrow the module list.

How to choose the best FRC swerve module for your team

There is no single "best FRC swerve module" — there is the best one for your motors, your budget, your machining access, and your game strategy. Work through these five lenses in order.

1. Start with your motor ecosystem

Your module choice and your motor choice are the same decision. Kraken X60 and Falcon 500 run on CTRE TalonFX controllers and a CAN/Phoenix software stack; NEO and NEO Vortex run on REV Spark MAX/Spark Flex and REV's libraries. Buying a module that "supports" a motor you don't own means also buying eight new controllers and rewriting your drive code. The SDS MK4-series is the most motor-agnostic (all four brushless options fit), MAXSwerve leans REV, and Swerve X2 is purpose-built for Kraken. Pick the controller/motor stack your team can actually support in software before you pick the aluminum.

2. Gear ratio: speed versus torque

The drive ratio sets your trade-off between top speed and pushing power (and how hard your motors work to get there). A faster ratio like SDS L3 gives a higher free speed but pulls more current to accelerate and is easier to brown out — it suits light robots. A slower ratio like L1 accelerates crisply, pushes harder in defense, and is gentler on your battery. Most full-weight robots live at L1 or L2. Don't guess: run your weight, motor, and ratio through a drivetrain calculator and check that your predicted current draw is sane. If the ratio math feels fuzzy, our gear ratios explained guide covers the fundamentals.

3. Cost and availability

Four modules plus eight motors plus four absolute encoders adds up fast, and build-season stock is volatile. Thrifty Swerve is the clear budget leader; SDS and WCP sit higher but have deep community support and spare-parts availability. Order early — a module you can't get in week 2 is not on your robot in week 6. Buy at least one full set of spare gears and a spare wheel per module family you commit to.

4. Maintenance and serviceability

Swerve modules take abuse. Ask how easily you can swap a wheel, replace tread, and get at the steering belt or gears without pulling the whole corner off the robot. Belt-driven steering (like the MK4i) is quiet and compliant but adds a belt to inspect and tension; geared steering has fewer wear items but can be louder. Smaller wheels wear through tread faster for a given distance. Whatever you pick, standardize on one module type across all four corners so every spare part and every rebuild procedure is identical.

5. Ground clearance and packaging

Wheel diameter drives ground clearance and how the module packs into your frame. A 3-inch MAXSwerve sits lower and packs tighter but clears less debris; a 4-inch module gives more clearance and a larger contact patch. The MK4n's 4-inch-wide profile is specifically about freeing horizontal space for a wide intake. Sketch your intake, bumpers, and electronics around the module footprint before ordering — packaging surprises are expensive in week 3. Wheel choice also affects grip; see wheels and traction for how tread and diameter change on-field behavior.

Build and programming implications

Whatever module you choose, the software shape is similar: four drive motors, four steering motors, and four absolute encoders reporting each module's heading. You will configure the drive and steering gear ratios in code so the robot converts wheel rotations and module angles into real-world meters and radians — get those constants wrong and your odometry and autonomous paths drift. The steering ratio (12.8:1, 150/7:1, ~46.42:1, 12.1:1, etc.) and wheel diameter from the tables above are exactly the numbers your constants file needs.

Mechanically, plan for mirrored modules where required (the MK4n needs "A"/"B" layouts), consistent encoder mounting, and a repeatable module-zeroing procedure at the start of every match day. Because each corner is identical, a clean build pays off fourfold — one good module assembly jig and one wiring pinout, repeated. Once the hardware reports trustworthy angles and distances, accurate odometry and pose estimation becomes the difference between an auto that scores and one that misses.

Frequently asked questions

Is MAXSwerve or MK4i better?

Neither is universally better — they optimize for different things. MK4i uses a 4-inch wheel and a full-size steering motor for more ground clearance and a larger contact patch, and it accepts any of the four major brushless motors. MAXSwerve uses a 3-inch wheel and a compact NEO 550 azimuth for tighter packaging and a wider effective wheelbase, and it fits most naturally in a REV-based control system. Choose MK4i for clearance and motor flexibility, MAXSwerve for compactness and REV integration.

What is the best FRC swerve module for a rookie team?

For most rookies, the honest answer is whichever module has the strongest support network near you plus a budget you can sustain — Thrifty Swerve for cost, or SDS MK4i for the deepest pool of community documentation and mentors who have run it. Standardize on one type, buy spares, and keep the ratio conservative (L1/L2 class). Reliability and repairability matter far more than top speed in a rookie season.

Can I mix different swerve modules on one robot?

You should not. Mixing module families means mismatched wheel diameters, gear ratios, and steering behavior, which makes the drivetrain nearly impossible to characterize and control cleanly. Run four identical modules so your kinematics, spare parts, and rebuild procedures are all uniform.

Do swerve modules include motors and encoders?

Usually not by default. Modules are typically sold as the mechanical assembly, and you add the drive motor, steering motor, and an absolute steering encoder separately (some vendors offer bundles). Budget the full corner — module plus two motors plus an encoder — times four when you compare prices.

Which motors work with SDS MK4-series modules?

The MK4, MK4i, and MK4n all accept the REV NEO (V1.1), NEO Vortex, VEX Falcon 500, and WCP Kraken X60. CIM motors do not fit because of their larger diameter. This broad compatibility is a big reason the MK4 line is the most widely used family in FRC.

How do I pick a drive gear ratio?

Match the ratio to your robot's weight and your motor. Heavier, full-weight robots generally want a torque-biased ratio (SDS L1 or L2 class) for crisp acceleration and defense; light robots can run a faster ratio like L3. Always verify your choice against a drivetrain calculator so predicted current draw stays within safe limits rather than picking the fastest number on the chart.

Swerve is a big commitment of money and build time, but the COTS landscape in 2026 means you can pick a proven module and spend your energy on strategy and software instead of gear meshes. Nail down your motor ecosystem first, choose a conservative ratio, buy spares, and standardize all four corners — then let the driving do the talking. For more build-season deep dives, browse the full set of guides.