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96 a Clearpath Network Station, enables longer range comms. Some users have implemented cellular systems, Edwards notes, and the company also recently shipped a Jackal with a tether as the power and comms link. Structure and materials Most of the Jackal’s structure is made from 5052 aluminium alloy, chosen for its suitability for bending and welding as much as for its durability. “Formed metal manufacturing has allowed us to make rugged vehicles which our clients don’t have to worry about breaking in the field,” Edwards says. “It also allows our integration team to easily modify the UGVs when adding new sensors or other hardware. The volumes we manufacture these bots in don’t warrant investing in injection moulding parts.” While aluminium naturally forms an oxide layer on the surface that protects it from further corrosion, all of the Jackal’s aluminium components are powder- coated in the company’s signature black and yellow. Most components are metal, but those that are not are off-the-shelf items such as polymer wheel hubs and rubber tyres. Energy storage and power supply While battery-electric propulsion was the obvious choice for a slow-moving UGV that is often used indoors and carries other components and payloads that need current, there were still choices to be made in terms of the operating voltage and battery capacity. The battery chosen was the HE-2413, a 24 V, 13 Ah lithium-ion pack from All Cells Technologies, which comes with the same company’s battery management system. Clearpath offers an external battery charger that is optimised for lithium-ion batteries. It can replenish the battery in situ while the vehicle is powered off, or away from the vehicle. Edwards explains that 24 V is enough to run the propulsion motors at a reasonable current while providing ample power and remaining safe to work with and maintain. At the same time, it works with many readily available off-the-shelf components such as motors and power conditioning electronics. In addition, 5, 12 and 24 V power outlets are provided to run payloads that are commonly integrated into the Jackal, such as Lidars, cameras and small manipulators. The outlets are supplied by Clearpath-designed regulators located on the Jackal’s MCU (microcontroller) board. While range-extending internal combustion generators have been integrated onto some of Clearpath’s larger vehicles, the Jackal is too small for one, Edwards says. Also, there has been no demand yet from customers for such a solution, although some have mounted larger batteries on the vehicle’s deck. Propulsion and mobility A four-wheel-drive, skid-steer vehicle, the Jackal powers the left pair of wheels with one motor and the right pair with a second; each motor is linked to the wheels it drives by a belt. The motors themselves are Midwest Motion S22- 346F-24V GP52-025 EU-1024 units, each with a 1024-line encoder and a 25:1 reduction gearbox. Managed from the Jackal’s MCU board using closed-loop velocity control scheme, each motor is rated at 6.7 Nm of torque and 160 W of power in continuous operation, but they can achieve much higher torque figures for short periods. Edwards emphasises that because they are somewhat oversized for the Jackal, they don’t need an active cooling system – the natural thermal conductivity of the aluminium chassis is more than sufficient. In the interests of simplicity and ease of maintenance, there is no suspension. What’s more, the Jackal neither has nor needs mechanical brakes, as all slowing and stopping is handled through the motor controllers, turning the motors into generators in what is effectively regenerative braking. However, under emergency-stop conditions, excess power is dissipated as heat through an air-cooled brake resistor. The 8 in pneumatic rubber tyres fitted to the Jackal were originally developed for use on mountain skateboards. April/May 2020 | Unmanned Systems Technology Most Jackals communicate via 802.11 wi-fi, but PX2 wi-fi radio is an option and cellular systems have also been implemented