Modular EV platform · design study

One spine.
Any powertrain.

A rolling chassis built around a single formed channel. Drive units and hydraulics live inside it. Batteries, fuel and a 30 kW turbine generator hang off the sides in swappable bays.

Wheelbase 170 inTrack 73 inTires 35×12.50R17Generator 30 kWTarget 80 mpg

Scroll to take it apart ↓

01 · The spine

Everything that moves the car lives in one channel.

The backbone is a formed U-channel of ¼ in plate running the full length of the car. A motor, reduction gear and differential sit inside it at each axle, along with the inverters.

The hydraulic power unit shares the channel: pump, reservoir, main accumulator, manifold and the per-axle height valves. No batteries go in the channel, so the drivetrain stays serviceable from above.

Channel: 16 in base
Wall height: 12.25 in
Plate: 0.25 in
Drive units: 2 · F + R

02 · Modular bays

Six bays. Pick what goes in them.

Between the wheels, three bays hang on hanger rails each side of the spine. Each one latches on with quick-release pins and plugs into the HV bus with a single connector, so a battery can come out and a fuel cell, tank or generator can go in.

Bay length: 35 in
Section: 21.6 × 13 in

03 · Suspension

Long-travel A-arms, one gas spring per corner.

Each corner runs unequal-length double A-arms. A single hydropneumatic piston replaces the coil-over: its top eye pins into a billet aluminum bracket on the spine, and its bottom clevis rides the lower arm. Nitrogen spheres inside the channel act as the springs, and oil volume sets the height.

The layout borrows from three places: the off-road A-arm geometry of Oshkosh's TAK-4, the hydraulically linked corners AMZ Racing developed for Formula Student, and Citroën's gas-sphere springing.

Oshkosh TAK-4 independent suspension ↗ Oshkosh TAK-4 family brochure (PDF) ↗ AMZ Racing: hydraulic decoupled suspension ↗ AMZ Racing team profile, Formula Student Germany ↗ Hydropneumatic suspension (Citroën and successors) ↗

04 · Adjustable ride height

Pump oil in to stand tall. Let it out to kneel.

Because the spring is gas and the strut is a hydraulic ram, height is just oil volume. Solenoid height valves at each axle meter fluid from the main accumulator into the pistons, or back to the reservoir. The A-arms swing, the wheels stay planted, and the frame rises or drops.

14.5in frame-to-groundNormal

Ride height

Scrolling sweeps the range automatically; drag the slider to hold a height. Figures are measured on the model: 3 in of lift and 4 in of drop from the 14.5 in design height. Oshkosh's gas-spring TAK-4i quotes about 20 in of wheel travel for comparison.

05 · High-performance tuning: suspension

Tune each motion on its own.

A coil spring gives one stiffness for everything. Linking the pistons through hydraulics lets each way the body moves get its own spring and damping. Race teams have used that to run soft over bumps and still stay flat in corners and under braking.

Heave: All four up or down. Soft and progressive, firming up as load builds.
Roll: Lean in corners. Stiff and symmetric left to right.
Pitch: Dive and squat. Held level under braking and power.
Warp: Diagonal twist over rough ground. Left free, with no spring.

AMZ Racing, ETH Zürich · 2017

Their car pilatus linked all four wheels to a central unit with one hydraulic element per motion, running at 120 bar. Warp had no spring at all. They set roll balance by changing lever-arm lengths. The aim was at least 25% lower single-wheel stiffness. In testing, the cross-axle load difference plotted against cornering load held a much tighter band than their 2016 car's. Concept ↗ · Build and test ↗

Creuat with Racing for Holland · Le Mans 2005

Jan Lammers' team ran Creuat's hydropneumatic interconnected suspension. A central device linked front and rear and responded separately to roll, pitch and vertical motion. Roll and pitch rates could be adjusted during the race. Lammers singled out traction and grip over bumps. Racecar ↗

Formula 1 FRIC · 2014

Front-to-rear interconnected hydraulics, used by most of the grid, used braking load at the front to hold the rear down. That kept ride height and rake steady, so teams could run softer springs and a more aggressive underbody. The FIA pushed it out in mid-2014 over cost and concern that it worked as movable aerodynamics. F1.com ↗ · Autosport ↗

Williams active · 1992–93

Hydraulic actuators held ride height within a few millimetres of the optimum, so the aero made steady downforce. The FW15C won 10 races in 1993. The FIA banned the technology after that season. Motor Sport ↗

What this means for CalhounCar: the corner pistons already plumb back to accumulators and height valves in the spine. Tying them into a central unit, one element per motion, gives the same knobs: gas precharge sets spring rate, valve orifices set damping, lever ratio sets roll balance, and oil volume sets ride height. This is a proposed tuning path. The current model shows independent corners.

06 · High-performance tuning: traction

Grip is the limit. The record cars tune for it.

Formula Student electric teams have traded the EV 0–100 km/h record for over a decade. Most of their gains came from control software and mass. Raw power mattered less.

0.956 sAMZ Racing mythen, ETH Zurich · 2023 · in 12.3 m
1.461 sGreenTeam, Uni Stuttgart · 2022
1.513 sAMZ Racing grimsel · 2016
1.779 sGreenTeam, Uni Stuttgart · 2015
2.13 sDUT Racing, TU Delft · 2013

Slip control in the inverter. Each motor gets a torque request and a speed window set from a target tire slip. A wheel that leaves the window drops to speed control. AMZ runs this with field-oriented control on an FPGA, and fuses optical and IMU ground speed at 500 Hz.
A motor per wheel. grimsel used four 37 kW hub motors weighing 3.4 kg each, for 1,630 Nm at the wheels. Traction control and torque vectoring act on each wheel.
Low mass. The cars use carbon monocoques. mythen weighs about 140 kg.
Downforce at zero speed. Wings don't work at low speed, so mythen uses a suction system to hold the car to the track at the start.
Tune between runs. AMZ and Delft both re-tuned slip targets between record attempts.

On Calhoun, the two spine drive units can split torque front to rear and hold slip at each axle the same way. Left-right vectoring would need hub motors or an active differential. A performance mode can kneel on the hydraulics to lower the centre of mass.

ETH Zurich: 0 to 100 in 0.956 seconds ↗ How AMZ designed the motor controller (MathWorks) ↗ AMZ Racing: world record ↗ grimsel's 1.513 s record (Electrek) ↗ GreenTeam Stuttgart, 1.461 s (Bosch) ↗ TU Delft's 2013 record (IEEE Spectrum) ↗

07 · Onboard generator

A 30 kW microturbine in a bay.

The turbine bay carries a recuperated microturbine sized to Capstone's 30 kW vehicle engine, the same class that powered the CMT-380 and Langford's turbine S-Max. One shaft spins the compressor, turbine and generator together, so there's no gearbox, no oil sump and no coolant for the engine itself.

The fuel tank bay sits right ahead of it. A power controller rectifies the turbine's output and feeds it into the spine's HV bus.

Output: 30 kW
Engine core: 33×22.5×29 in
Bay envelope: 26 w × 31 h in
Fuels: Diesel · bio

The 30 kW turbine is taller than a standard bay, so its bay stands about 18 in above the frame. A 10–15 kW turbine around 13 in in diameter would fit a standard bay.

08 · Turbine-electric drive

80 mpg, by never driving the wheels with fuel.

This is a series hybrid. The turbine never connects to the wheels. It runs only at its single most efficient speed to charge the packs, and both axles are driven by the electric motors in the spine. Braking energy goes back into the packs.

80 mpg is a design target, not a measured figure. The closest real precedent is Langford Performance Engineering's C30-turbine Ford S-Max plug-in, reported at up to 80 mpg in early testing. The Engineer ↗ · Green Car Reports ↗ · CMT-380 ↗

09 · Configure

Your platform.

Same spine, same corners. Set the bays and the stance.

Ride height · 14.5 in

Wheelbase: 170 in
Track: 73 in
Tires: 35 in
Bays: 6 swappable

One spine.Any powertrain.