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

batteries, feed to the motors and translate into torque at the wheels to get the performance they want. “We’ve done quite an in-depth study on different terrains, calculating and physically verifying rolling coefficients, then translating that into how much torque and power we need to climb up to 60% gradients in different terrains – on highways, grass, wet mud, sand, gravel and so on,” he says. “What that translates into is a target of 75 kW continuous power rating per wheel and a 150 kW peak, then with the ratios in our reduction hubs we will be up to 6000 Nm of torque per wheel.” That, he says, covers the extremes of what the vehicle is likely to be asked to do in service, ranging from the most demanding end of the spectrum represented by a fully laden vehicle climbing 10-25% gradients in sandy conditions, to an airport fire tender that simply has to cross flat ground quickly at the other end. “Fire tenders don’t need anywhere near that much torque, so you can fit just two driven axles or look at reducing the cost to the customer by changing to a less powerful motor.” Regan notes that it is important to avoid closing off technical options so that they can retain versatility. “Wherever we have been able to offer different motor power ratings or reduction gear ratios, for example – something that doesn’t really add any cost but adds versatility – we’ve done that kind of thing all round the vehicle,” he says. “It means working with a supplier who can provide a substitute part with exactly the same form and fit but with a different function, such as a motor with a different type of winding or a reduction hub with a different number of teeth on the output. We want to make it an easy tick-box option.” At the moment, the development vehicle is fitted with relatively low- powered motors and a 48 V primary electrical system, owing to the longer lead time for the higher performance parts that production examples will have. “We wanted to get the vehicle performing, doing tests and trials to verify our calculations, which is what this interim system has allowed us to do,” Williams explains. “And we are now looking to integrate an 800 V system with high-power motors and associated driveline components.” Regan adds, “We have a drivetrain in there that provides us with a fraction of our final torque for the production model, but it tests the steering, the suspension, the manoeuvrability and the braking systems. Getting a lower-spec driveline in there early has provided us with some valuable early learnings, and we are now waiting for components for that 800 V system to arrive.” Motors and reduction hubs The Dana motors in the development vehicle are radial flux machines that provide 1500 Nm per wheel, or a quarter of the 6000 Nm that the production vehicle will have. The Lancereal hubs through which these motors drive are two-stage planetary reduction gearboxes with a 29:1 overall reduction that gives a top speed of about 30 mph, Williams says. With torque at 1500 Nm, that translates into about 15-20 kW from each wheel motor. In the production vehicle, the motors will be new; the reduction hubs might be as well, pending the results of an experiment that Williams has in mind. “I quite like the fail-fast approach, trying something to see if it works before committing a huge amount of time to a particular task,” Williams says. “Depending on how our timeline is looking, we could use the existing hubs with a more powerful motor and accept that we won’t achieve our desired top speed – we were hoping for 62 mph – but we would get all the power and torque we need in the configuration that the vehicle is in now.” He notes that one of the biggest challenges with the hubs is input speed, as many that are available are restricted to around 5000 rpm, and EMotive wants to run at higher speeds than that, probably between 8000 and 10,000 at the input. However, the motors being Some key suppliers Steel fabrication: Atom Fabs Steel fabrication: Luffman Engineering Inverters: Curtis Instruments Motors: Dana Fusing, relays and power management: ETA Energy Technology Dampers: Koni Reduction hubs: Lancereal Battery packs: Webasto Empty at the moment, this large front compartment could hold a second Webasto battery pack, a range-extending diesel or an alternative-fuel IC engine or a fuel cell generator (Author’s photo) 24 Autumn 2022 | E-Mobility Engineering