Technology Update

While we still are very much in the planning phase, the picture is getting clearer, and I am ready to share the concepts.

Specification Overview

• Traction motor: A YASA-type axial-flux PMSM with an output target of 180–200 kW
• Battery: 66 kWh nominal capacity, assembled from six NMC modules of 11 kWh each
• Charging: 7 kW AC; 70 kW DC via CCS
• Driveline: Direct coupling of the motor to the existing propshaft. The intention is to dispense with a fixed gearbox at this location. If required, the differential’s final-drive ratio will be revised.
• Chassis and brakes: No suspension or brake modifications are currently planned, on the basis of the intended overall vehicle mass being only slightly increased.

The YASA Motor

Conventional traction motors are radial-flux machines: The rotor spins inside a cylindrical stator and the magnetic flux crosses the air gap radially. An axial-flux machine inverts this geometry. The stator and rotor are discs, arranged coaxially, and the flux traverses the air gap parallel to the axis of rotation. The consequence is a machine of markedly different proportions – a short, large-diameter ”pancake“ rather than a long cylinder – and, because torque is the product of tangential force and radius, a machine in which the large diameter works directly in favour of torque production. Also, the magnetic field is more dense in areas where the force matters most.
YASA (Yokeless And Segmented Armature) refines the axial-flux principle in two respects that matter to this conversion:

The yokeless stator

In a conventional stator, the copper windings are carried on a continuous iron ring, or yoke, which closes the magnetic circuit. YASA’s topology removes this yoke: the stator consists of discrete, magnetically separated tooth segments, each carrying its own concentrated winding, sandwiched between two rotor discs. The magnetic flux path becomes shorter and more direct, and the iron mass of the stator can be reduced. YASA states reductions of up to 80% in stator iron. The machine still contains iron, in the form of the segmented stator cores and the rotor back-iron; what is eliminated is the continuous yoke that would otherwise close the flux path. The shorter flux path reduces iron losses, and the segmented construction allows for short end-windings and a high copper fill factor, both of which improve efficiency.

The double-rotor arrangement

The arrangement of having a segmented stator sit between two permanent-magnet rotor discs, creating two active air gaps means that both faces of the stator contribute torque.

This symmetric double-rotor arrangement balances net axial forces, however, and this is a primary challenge of the design: Substantial local magnetic forces and mechanical stresses remain, and the bearing arrangement, housing stiffness and assembly tolerances must keep both air gaps small and even.

YASA states that this topology delivers up to four times the torque density of other EV motors. The P400R engine produces 370 Nm of peak torque and 160 kW of peak power at 700 V; the larger 750R produces 790 Nm of peak torque and 200 kW of peak power at 700 V (falling to 100 kW at 400 V) over a speed range of 0–3,250 rpm.

A note on Rare Earths

Current YASA axial-flux motors use permanent magnets that require rare-earth materials.

This is a material-supply constraint of the current permanent-magnet implementation rather than an inherent property of the axial-flux geometry. The supply of neodymium is geographically concentrated (China), and heavy rare earths such as Dysprosium and Terbium, which are added to some NdFeB magnets to avoid de-magnetisation at high temperatures, are subject to both price volatility and export-control risk.
The situation is, however, in motion: In August 2026, YASA secured UK Government funding under the DRIVE35 programme for Project Resilience, a research and demonstration programme pursuing two parallel pathways: A heavy-rare-earth-free permanent-magnet machine that dispenses with dysprosium and terbium and is intended to maintain high power density, and a fully rare-earth-free axial-flux design for applications with different performance and cost requirements, both built on the common YASA stator platform.

For this conversion, the motor will be an existing permanent-magnet design, and the rare-earth dependency is accepted as a known constraint of the current state of the art.

Direct Drive to the Propshaft

We really want to avoid any structural changes of the Mk2’s chassis to not risk road legality issues with the car’s conversion in Germany. This requires us to keep the engine in front and use the original propshaft. We will also try to avoid additional fixed gearing between motor an propshaft for efficiency and packaging reasons. If needed, we can change the rear axle’s gear ratio..
The ratio of the reduction gearing in the differential is one of the principal remaining design variables. The feasibility of a single-speed drivetrain depends on the relationship between the motor’s maximum speed, the tyre rolling circumference, the final-drive ratio and the desired road speed.
The axial-flux architecture is an attractive packaging candidate for this arrangement: The motor’s short axial length and its high torque at low speed make it well suited to a propshaft-mounted, single-speed installation. Installation clearances and coupling geometry remain to be confirmed. The original powertrain’s torque at the propshaft — engine torque multiplied through the gearbox — provides the appropriate comparison point for the new installation; the coupling arrangement and the propshaft’s universal joints will require verification.

Battery layout: Six NMC modules

The traction battery comprises six modules of 11 kWh each, for a nominal 66 kWh, with four modules installed forward and two modules aft. The design intent is that the finished vehicle’s mass should differ from the donor’s only marginally, and the mass distribution will be improved.

Why NMC

The selection of Nickel-Manganese-Cobalt oxide (NMC) modules, rather than the Lithium-Iron-Phosphate (LFP) chemistry that increasingly appears in mass-market electric vehicles, is a consequential engineering decision.
The essential trade is between energy density and a set of competing advantages. NMC generally offers higher gravimetric and volumetric energy density, while LFP offers competing advantages in thermal stability, cycle life and cost.

For a conversion in which the available volume is fixed by the vehicle’s structure, the higher energy density of NMC permits a larger installed capacity within those constraints.

The mass-neutrality objective of this project contributes as well to the decision.

Charging

The charging architecture is conventional. AC charging at 7 kW permits a nominal full charge of the 66 kWh pack in approximately 9.4 hours, before charging losses; practical charging time will depend on the installation.

DC will charge at 70kW or more. The 10-to-80-per cent charging time can only be estimated as it needs assumptions on the pack’s thermal management and the battery management system’s calibration.

Retaining suspension and brakes

No modifications to the suspension or the brakes are currently planned. The rationale is the mass-neutrality target: The donor vehicle’s kerb weight, approximately 1,500 kg for the 3.4 and 3.8-litre cars, is to be preserved, give or take, by the removal of the engine, gearbox, exhaust system and fuel tank, and their replacement with an electric motor, battery pack, power electronics and the associated cabling and cooling. A detailed mass calculation is to follow, but the design target is no more than 100kg extra weight.

We are keeping in mind that due to energy recuperation of a BEV, the duty cycle imposed on the friction brakes is significantly reduced.

If the final specification and calculations suggest brakes and suspension changes, I am prepared to carry these out as well.