Team 2890 uses the **Swerve Drive Specialties MK4i** swerve module. This is the core drivetrain component — each robot has four modules, one per corner.
## Key Features
- **On-axis steering encoder** — zero backlash, module can be disassembled/reassembled without resetting encoder offset
- **Corner bias** — compact 4" × 4" internal frame width (MK4i has same corner bias as MK4n, different from MK4)
- **Full steering ratio:** 150/7:1 (passes through one gear pair, then a 64T belt pulley pair)
- **Mounting hardware:** Updated June 2023 — changed from 8-32 to **10-32 screws**
- **Wheel options:** Standard 4" wheel (can be replaced with 3" for weight savings)
## Drive Ratios
| Ratio | Best For | Notes |
|-------|----------|-------|
| **L1** | Standard full-weight competition robots | Most popular |
| **L2** | Standard full-weight competition robots | Most popular |
**L1 = faster, less torque.** **L3 = more torque, slightly slower.** Swap based on game demands — L1 for high-speed defense, L3 for climbing/pushing.
*(Gear ratio diagram: `mk4i-gear-ratios.png`)*
## Connection to Training
**For students learning swerve:** This module uses a 1/2" hex output shaft. Understanding hex shafts and how they transfer torque is fundamental mechanical knowledge. Students should also understand:
- Why steering ratio matters (fast steering vs. precision)
- What "corner bias" means for turning radius
- How the belt drive multiplies torque from motor to wheel
**Related training modules:**
- [[motor-basics]] — understanding Kv, torque, current relationships
- [[frc-drivetrain-training]] — swerve kinematics and control
- [[2890-codebase-index]] — how the code configures these modules
Chris uses these modules with NEO Vortex motors and SPARK Flex controllers. The full stack is: **MK4i + NEO Vortex + SPARK Flex + YAGSL**. The YAGSL library (Yet Another Gyro Library) handles the swerve math and motor control in code.
