Is Electromagnetic Suspension the Future? It’s Almost Here
My greatest disappointment—the tech I covered in a Technologue column that I most fervently hoped for that never happened—is the Bose electromagnetic suspension, first demonstrated on a leaping Lexus back in 2004. Imagine my delight, then, when I discovered a completely different type of electromagnetic suspension, courtesy of Massachusetts-based Indigo Technologies. Instead of employing God’s own doorbell clacker to move the suspension, this one leverages the individual wheel-hub-mounted electric traction motors to smooth the ride.
Like Amar Bose’s baby, this drive/suspension design sprang from the fertile mind and research team of an MIT professor, in this case Ian Hunter. Suspension savviness may run in Hunter’s blood, as he’s a nephew of legendary Kiwi F1 engineer/team owner/grand prix winner Bruce McLaren. Hunter devised a method of using an electric motor to simultaneously generate both rotational energy and linear motion, with each being controllable separately.
Electric motors generally consist of a rotating “rotor” and a typically stationary “stator.” Electromagnetic fields generated in the stator winding induce rotation in a magnetized rotor. But what if, Hunter wondered, instead of one fixed stator, you split it in two, pinning each half to a mechanical device that translates the difference in the two halves’ rotation into linear motion? Here’s how it works:
Let’s say you need 10 lb-ft of motor torque. Evenly splitting the electrical energy applied to each half of the stator—say 5 lb-ft’s worth to each—results in 10 lb-ft and no linear motion. But if, instead, you send 3 lb-ft’s worth to one and 7 lb-ft’s worth to the other, the rotor still gets 10 lb-ft, but the overpowered half of the stator wants to rotate in the opposite direction of the rotor, while the underpowered one turns with the rotor. This counter-rotational motion is what causes this linear actuator to move. Making it exert a force requires more energy input, while the net side-to-side difference continues to power the rotor.
Indigo has developed a steerable strut-type corner and an unsteered control arm corner, each with a coil-over shock unit, a disc brake, and a Robotic Wheel motor and linear actuator sized to fit within an 18-inch wheel. As presented, the concept features an axial-flux motor with a disc-shaped rotor sandwiched between two stator discs. The motors can generate 30 hp/184 lb-ft of rotational force and 500-plus pounds of linear force across the 7.5-inch total range of suspension travel. Energy can be recovered from both the linear and rotational motion.
For now the ride control is purely reactive, taking input from accelerometers on each corner, but it’s said to deliver a magic carpet ride—quite a feat in a light vehicle bearing so much unsprung weight. The Robotic Wheels can counteract 1 g’s worth of body roll, but they won’t get the Indigo Flow electric microvan airborne.
The Flow EV targets gig-economy drivers in the Uber, Lyft, and Amazon Flex spaces. Light, small Robotic Wheels packaged at the corners free up maximum interior space: The Flow van offers 110 cubic feet, the longer and taller Flow Plus, 130. By sizing them to accommodate either three passengers or one to two shifts’ worth of Amazon Flex parcels, they can be small and light enough (Indigo targets a curb weight of around 2,000 pounds and a payload rating of around 800 pounds) to deliver 250 miles of range from a 40-kWh battery. That’s 200-plus mpg-e, or roughly 2 cents/mile in energy costs. During the break between three-hour Amazon Flex delivery shifts, Level 2 charging provides enough energy to drive another shift.
A central driver’s seat and a single large sliding door on each side allows the driver to exit safely in tight quarters on whichever side isn’t facing traffic, and the roomy cargo area greatly simplifies access to the Amazon Flex parcels.
Indigo tells us that four Robotic Wheels should cost no more than the electric powertrain and suspension of an AWD electric vehicle. This, plus the diminutive size of the van and battery, means Indigo aims for a $25,000 purchase price, with production expected to start in early 2024. But the company is also working with fintech insurer OV Loop to develop a holistic insurance/rental plan that could make the Indigo Flow available to gig workers for 50 cents per mile with no down payment.
That would represent one giant leap for carkind—even if the car itself can’t leap.
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