What’s the Difference Between a Complete Motor, a Lower End, and a BHA?

What’s the Difference Between a Lower End, a Complete Motor, and a BHA?

In drilling conversations, you’ll hear terms like “lower end,” “complete motor,” and “BHA” thrown around as if they’re interchangeable. But while they all work together in the well, they’re different tools with different purposes.

At Commander Downhole Technologies, we specialize in lower ends—including our proven NightHawk series—and we also support customers with motor parts, custom builds, and rental tool packages. That means we’re often helping customers understand exactly where a lower end fits in the bigger drilling picture.

1. Lower Ends – The Commander Specialty

A lower end is the bottom portion of a drilling motor. It doesn’t generate power on its own—instead, it takes the torque from the power section (the rotor and stator) and delivers it to the drill bit. It also handles heavy loads, side forces, and directional steering.

Lower ends include components like:

• Transmission type (Knuckle, CV, Hybrid Flexshaft, or Straight Flexshaft)

• Bearings

• Bend housings

• Flow diverters

Commander’s NightHawk series is a field-proven lower end design with a long track record—dating back through previous owners like Tercel and Rubicon—that’s still in demand worldwide. We build and service NightHawk lower ends, and we supply parts for current and legacy models, even when OEM parts are no longer available.

When to choose a lower end:

• You already have a working power section.

• You need to replace or upgrade just the lower end portion of a motor.

• You’re maintaining legacy equipment still in service.

2. Complete Motors – How Lower Ends Fit In

A complete motor combines two main assemblies:

• Power section – creates torque from drilling fluid flow

• Lower end – delivers that torque to the bit

Commander doesn’t build complete motors—we focus on lower ends and parts. But our lower ends are designed to integrate with compatible power sections, giving customers the flexibility to build a complete motor that meets their needs.

3. BHAs – The Full Downhole Package

The Bottom Hole Assembly (BHA) is everything between the drill pipe and the bit. A complete motor is only one part of a BHA.

A BHA may include:

• Drill bit

• Complete motor (power section + lower end)

• Measurement While Drilling (MWD) or Logging While Drilling (LWD) tools

• Stabilizers, jars, and other subs

• Non-magnetic components for directional control

While Commander doesn’t build full BHAs, we supply critical components like lower ends, motor parts, and rental tools—including stabilizers, jars, and other subs—so customers can assemble the exact BHA they need.

How They All Connect

Component	Fits Into →	Purpose
Lower End	Complete Motor	Transfers torque from power section to bit
Complete Motor	BHA	Generates and delivers torque within the tool string
BHA	Drill String	The full assembly that drills the well

Why It Matters

Understanding the differences helps you:

• Save money by replacing only the component you need.

• Reduce downtime by sourcing compatible parts quickly.

• Maximize performance by matching the right lower end to your power section and drilling conditions.

Commander Downhole Technologies provides NightHawk lower ends, legacy motor parts for Rubicon, Tercel, and G2 models, and a wide selection of rental tools and subs to keep your operation moving. Whether you’re maintaining proven equipment or building out a custom drilling package, we have the parts, inventory, and expertise to help.

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