Every motor needs to deliver its torque somewhere — to a wheel, a spindle, a conveyor, a pump. The method you choose to connect the motor shaft to the driven load is power transmission, and the three most common mechanical options are belts, chains, and direct drive. Each has a clear sweet spot.

Belt Drives use a flexible loop (flat, V-belt, or toothed/synchronous) running over pulleys. They're cheap, quiet, absorb vibration, and tolerate slight misalignment between shafts. The tradeoff: standard V-belts slip under load, so you lose 3–5% efficiency and can't guarantee exact speed ratios. Toothed (synchronous) belts fix the slip problem — they're what run your car's camshaft timing and your 3D printer's axes. Belt drives excel when shafts are far apart, noise matters, or you want a mechanical "fuse" (the belt breaks before expensive components do).

Chain Drives (roller chain, like a bicycle) give you positive engagement — no slip. They handle higher torque loads than belts of comparable size, and they're durable in dirty environments. Downsides: they're louder, require lubrication, and stretch over time (requiring periodic tensioning). You'll find chain drives in motorcycles, conveyor systems, and agricultural equipment. Standard roller chain is specified by pitch — #40 chain has a 0.5″ pitch, #60 has 0.75″ — and rated power charts in manufacturer catalogs tell you exactly which size to spec.

Direct Drive eliminates the intermediate element entirely: motor shaft connects to load through a coupling or the motor is the load (like a hub motor in an e-bike wheel). You get maximum efficiency (no transmission losses), zero backlash, and the fewest parts to maintain. The catch: the motor must produce the exact speed and torque the load needs, which often means a larger, more expensive motor. Direct drive shines in precision applications — CNC spindles, turntables, and washing machine drums.

Quick sizing example: You need to drive a conveyor at 200 RPM using a 1,750 RPM motor. The speed ratio is 1750 ÷ 200 = 8.75:1. A single-stage belt or chain drive tops out around 6:1 practically, so you'd likely use a two-stage reduction (e.g., 3:1 then ~2.9:1) or pair a belt drive with a gearbox. This is a real constraint that shapes your design.

Rule of thumb for selection:

• Need quiet, cheap, moderate loads → belt
• Need positive drive, high torque, dirty environment → chain
• Need precision, zero backlash, minimal maintenance → direct drive
• Need exact timing (no slip) but belt simplicity → synchronous/toothed belt

In practice, many machines combine methods. A CNC router might use a servo motor with a toothed belt driving the X-axis, a ball screw (direct-coupled) on the Z-axis, and a spindle motor on direct drive. Matching the transmission to each axis's requirements is core mechanical design work.