E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

considered are of the axial flux type, whose ‘pancake’ proportions suit them well to in-wheel applications. Also, they are optimised for 15,000-16,000 rpm, although they can be limited to the desired speed by the inverters. “We can achieve the power and torque requirements from a lower speed, which then simplifies our mechanical design for the epicyclic hub,” Williams says. EMotive is currently working with Lancereal on the specification for a new design of hub, should that prove necessary. As the motors are mounted in the wheel hubs, which are carried by the suspension’s upper and lower control arms (the wishbones), they have to handle the vehicle’s weight with a full payload and all the torque reaction loads up to the full 6000 Nm plus some safety margin, both when the motors are driving and when they are used for regenerative braking. What’s more, the back-up friction brakes are integral with the hub, adding to the loads that the wishbones must transmit, so they have to be very beefy components. “We intend to perform extensive reliability and durability trials on the platform, so we will look to build a number of prototypes to iron out any faults that appear,” Williams explains. The team has also been testing brake resistors, devices that consist of resistive heaters that are used to dissipate excess electrical energy from regenerative braking when the battery pack is fully charged and unable to accept any more. “We also needed to make sure the service brakes stop the vehicle effectively if we can’t get any regenerative braking, so we have been testing them as well,” Williams notes. “There will be a lot of later-stage learnings,” Regan adds. “Much of our suspension testing so far has been at no load, and we haven’t had the Scarab loaded up to 12 t yet. We have fabricated wishbones at the moment, whereas later on we will have to do production-intent prototyping, which will be with cast wishbones, so there is still a long way to go in terms of learnings.” Much of that knowledge will come in the next stage of development, Williams notes. “Whereas here it is big and bulky, we will go through a mass- reduction exercise using a combination of physical testing and finite element analysis. “We will start lightening the chassis so we can drive our kerb weight down, increase the payload and so on. When it comes to castings, yes we gain: we reduce mass and increase strength, and it’s cheaper to manufacture in volume, so it is definitely in our development plan. However, we are focusing more on the functionality of the vehicle right now, and the productionisation stage will follow that,” he says. “We have kept ourselves on the straight and narrow through various iterations of finite element analysis [FEA] on the chassis, especially when we have been making modifications to the initial design,” Regan adds. In the centre of each axle module is a pair of Curtis Instruments inverters that turn the 48 V DC current into AC for the motors. The shielded orange cables are 800 V-ready (Author’s photo) Autumn 2022 | E-Mobility Engineering 25 Dossier | EMotive Scarab off-road truck