Flat-Wire Motors Explained: What They Change in a Direct Drive Wheelbase

A flat-wire motor builds its stator windings from rectangular copper conductors instead of round wire, so more copper fits in each slot. In a direct drive wheelbase, that mainly changes how much heat the motor produces at a given torque and how quickly it gets rid of it. Together, those two factors largely set how long the base can hold strong force feedback before its thermal protection scales it back. That thermal headroom matters most if you run long endurance stints, drive cars with heavy sustained steering loads, use high overall force feedback strength or race in a warm room. The same copper advantage also lets a lighter motor deliver a given torque.

What Is a Flat-Wire Motor?

The stationary part of a direct drive motor is the stator. Its slots hold the copper windings whose magnetic field turns the rotor and, with it, the steering shaft. Traditionally, those slots are wound with round copper wire.

Round wires can never fill a space completely. However tightly the coils are wound, gaps remain between adjacent wires, and every strand carries a thin layer of enamel insulation to prevent short circuits.

A flat-wire motor changes that geometry. Its stator uses rectangular copper conductors, also coated in enamel, that stack against each other like bricks in a wall and fill the available space far more completely. Engineers call this the slot fill factor: the share of a slot's cross-section occupied by copper rather than gaps or insulation. Once insulation is accounted for, conventional round-wire windings typically achieve 50 to 60 percent, while MOZA's flat-wire motor reaches 72.5 percent.

Why Does More Copper Mean Less Heat?

The motor in a direct drive wheelbase is typically a permanent-magnet servomotor, and its torque tracks the current flowing through the windings. When the force feedback calls for more steering weight, the drive electronics deliver more current.

That current, flowing through the windings' electrical resistance, generates heat (Joule heating, written I²R), and heat grows with the square of the current. Holding twice the torque produces heat in the windings roughly four times as fast. And because that heat accumulates over time, the heavy load you hold through a long, fast corner warms the motor far more than brief kerb strikes of the same peak.

Packing more copper into the same slot lowers the winding's resistance for the same number of turns, so producing the same torque wastes less energy as heat.

How Does a Flat-Wire Motor Shed Heat?

A motor must also get rid of the heat it produces, moving it from the copper winding into the stator core, then out through the housing into the air.

Round wires make much less contact with each other and with the slot walls, and the irregular spaces between them are filled with air or impregnating resin. Both conduct heat far worse than copper, so those pockets act as an insulating blanket that slows the transfer into the stator core.

Flat conductors sit flush against one another and make broad contact with the slot walls, creating a shorter, better-connected path from the copper into the core. Under equivalent conditions, MOZA's flat-wire motor dissipates heat 15 to 20 percent better than a conventional round-wire motor, in both theoretical calculations and physical testing.

What Does a Flat-Wire Motor Change in a Direct Drive Wheelbase?

Sustained Torque and Thermal Fade

A direct drive wheelbase typically monitors or estimates the temperature of its motor and electronics, and when that temperature approaches a safety threshold, the control system reduces the current. Less current means less torque, and you feel it as thermal fade. An hour into an endurance race, the same fast corner can start to feel lighter at the wheel, kerb impacts soften, and the front-end grip limit becomes harder to read. A cooler-running motor holds its output longer before the electronics scale the current back: on MOZA's flat-wire bases, lower heat generation combined with better heat dissipation keeps thermal fade minimal, even through extended sessions at strong force feedback.

Heat is what mainly caps a motor's sustained torque (the torque it can hold continuously), so less heat per unit of torque lets a motor of a given size sustain more. Holding strong torque for tens of minutes is one of the key reasons MOZA builds its Ultra Series around flat-wire motors. The Ultra bases are rated accordingly, in sustained torque rather than peak: 16 Nm for the MOZA R16 Ultra, 21 Nm for the MOZA R21 Ultra and 25 Nm for the MOZA R25 Ultra.

Torque Density

Because each slot carries more copper, a flat-wire motor produces a given torque with less size and weight. How much of that advantage goes into a lighter motor rather than extra thermal headroom is a design choice. Compared with a non-flat-wire motor of similar performance, MOZA's flat-wire motor shows a 41.94 percent difference in torque-to-weight density in its favor: similar torque from a lighter design. That lighter motor takes weight out of the finished base, making it easier to install, move and integrate into a wider range of setups. In the MOZA R25 Ultra, that means a sustained 25 Nm from a 9.1 kg base.

What a Flat-Wire Motor Does Not Change

• Force feedback character. The winding type does not set it on its own. The detail and responsiveness you feel come from the whole system: the sim's physics output, the wheelbase's force feedback algorithm and its tuning, the control electronics that turn those commands into current, the motor's magnetic design and the base's mechanics. A flat-wire motor driven by a poorly tuned algorithm simply delivers poorly tuned force feedback for longer. On the MOZA R16 Ultra, that tuning layer is the NexGen Force Feedback Algorithm U1.

• Thermal protection. The motor still heats up when pushed, which is why a flat-wire base like the MOZA R21 Ultra still pairs its motor with real-time temperature monitoring and torque regulation. Nor does the winding reduce the heat generated in the drive electronics. The thermal limit is pushed further out, not removed.

• Where heat never builds up. If your sessions are short and your force feedback strength moderate, the motor may never get near its thermal limit, and you are unlikely to notice the difference.

Why Are Flat-Wire Motors Still Rare in Sim Racing?

Rectangular conductors are established in electric-vehicle and high-speed rail traction motors, valued there for their structural rigidity, power density, efficiency and thermal performance. Their best-known drawback, extra losses that build up at high electrical frequency, mainly affects EV motors in their high-speed range. A wheelbase motor works at low speed, turning a steering wheel rather than a drivetrain. What keeps flat wire uncommon in sim racing hardware is largely what it demands in production.

Flat-wire production requires tight dimensional tolerances on the rectangular conductors, precise positioning during assembly and, in segmented designs, exacting welding at the end windings. The sharp edges of rectangular conductors also put more stress on the enamel insulation than round wire does. Doing this reliably takes precise, automated equipment, and rectangular wire typically costs more than round wire. MOZA's own automated flat-wire motor production line, with processes optimized specifically for sim racing wheelbases, is what makes the technology practical here.

A Question of Consistency Over Time

A flat-wire motor keeps strong force feedback available for longer. What that force feedback feels like still depends on the rest of the wheelbase. When you choose a wheelbase, winding geometry is a clue to how closely the steering weight and detail on your final lap will match what you felt on the first.