Unmanned Systems Technology 023 I Milrem Multiscope I Wireless charging I Logistics insight I InterGeo, CUAV London & USA show reports I VideoRay Defender I OS Engines GR400U-FI I Ultrabeam Hydrographic Ultra-2 I IMUs

28 Dossier | Milrem Multiscope are any spikes in demand – to turn, accelerate or climb, or if the vehicle has to pull itself through mud or sand, for example – the extra power comes from the batteries. Other critical considerations include current ratings for the drive motors, cold cranking to start the generator, providing power to run auxiliary loads, and any ‘silent time’ required for stealthy military surveillance missions. To optimise the overall system, the designers try to use the smallest diesel generator possible to produce the average power required, and then rely on the batteries to handle the other demands, Karri says. The THeMIS and the Multiscope use lead-acid batteries at the moment, he explains, because they provide very stable power and are cost-effective. “We are also testing lithium-ion, but because of the hybrid technology, our requirements aren’t so tough that we need the tremendous amount of energy that lithium-ion offers,” he says. “Based on our calculations, the price- performance ratio of lead-acid is better for the applications we are targeting with the Multiscope,” he says. Lead-acid batteries are also safe, easy to handle and replace, and are available almost everywhere. Critical parameters to get right for the battery pack, he says, are the current and power ratings, the temperature range and then the energy density. Lead-acid batteries don’t need very sophisticated – or certified – balancers and control logic. However, it is important to control charging and discharging so that they don’t quickly shorten battery life. Lead-acid batteries don’t like to be deep discharged, but do like to be topped up continuously, so Milrem has written software that produces proper charging and discharging curves at different temperatures, voltage levels and power ratings. “In some applications with our other [military] programmes there is definitely a requirement for very long silent times and electrical drives,” Karri continues. “There, lithium-ion is the only solution that provides enough energy.” Milrem’s electrical engineering team is working on the integration of a lithium-ion battery pack into the THeMIS, which would also make it an option for the Multiscope and which should be available at the end of 2019. Milrem is also keeping an eye on fuel cell technologies as auxiliary power units in other programmes, particularly applications in which long silent times, perhaps up to 15 hours, are needed. “That is doable,” Karri says, “but to have power for traction as well is very difficult because of the size and complexity of fuel cell systems.” Milrem writes all the software for its power management and control electronics but sources the hardware, regulators, rectifiers, inverters and ECUs from outside, as it does with the motors, which are all motor/generator units (MGUs). Supplied by Heinzmann or Vogel & Plotscher, all the MGUs are permanent magnet, synchronous machines. The traction motors provide a regenerative braking capability, either charging the battery or transferring power from one side to the other as the Multiscope vehicle steers, which is done in typical fashion by braking one track and accelerating the other. The generator that charges the battery also serves as a motor to start the diesel engine. As well as regenerative braking, both the Multiscope and the THeMIS have a separate mechanical braking system, with one disc at the rear of each track module. Electrically driven hydraulic pumps control the pressure in the brake system, providing extra power assistance to an electric actuator in the same way that hydraulically boosted brakes reduce the pedal effort in some cars. All the wiring is made to Milrem’s design, Karri explains, and feature flame- proof connectors with high IP ratings that are used widely in the automotive and heavy industry markets. They come from multiple suppliers and OEMs. Military-grade connectors are used in the THeMIS, while less expensive automotive and heavy plant connectors are used in the Multiscope to keep prices down. Even though these components have high IP ratings, they are given additional protection using custom enclosures, again of Milrem’s own design. They are fabricated by local contractors. December/January 2019 | Unmanned Systems Technology This ‘pancake’ type synchronous permanent magnet motor is made by Vogel & Plotsher which, along with Heinzman, supplies the UGV’s electrical machines (Courtesy of Vogel & Plotsher)