Uncrewed Systems Technology 049 - April/May 2023

Delivering uncrewed and autonomous engineering jobs directly to your door www.uncrewedengineeringjobs.com Ottonomy Ottobot | Digest Powertrain and control Korupolu explains here that because of the weight of the robot and the cargo payloads to be carried, Ottonomy needed electric motors with a high load capacity, as well as highly precise initial triggering for accurate odometry. That influenced the company to design the Ottobot with a 4WD system. Each wheel is driven by its own dedicated BLDC hub motor, and rotary electromechanical actuators for individual steering to provide nimble swerving, sidestepping and zero-radius turns through crowds of people. “Every motor uses a closed-loop control topology, so we get all the feedback from themotors,” he adds. “Performance is more accurate that way, in that the UGV’s control inputs consistently result in the desired output. On the rare occasion that it doesn’t, it is rapidly corrected.” “So in addition to the in-wheel motors and steering actuators, our in-house synchroniser software on the main computer ensures execution of all the correct commands – particularly electric motor positions and speeds – and we use field-oriented control to ensure smooth, jerk-free motion of the robot.” Although Ottonomy was initially tempted to use similar electric motors and controllers to those in e-scooters – as they are also designed for closed-loop operation – their loops were nonetheless not robust enough for the Ottobots, so the company customised its motors and ESCs in-house. “Key to the motor designs was including encoders for feedback, as well as optimising the top speed for fine steering and acceleration or deceleration control,” Korupolu says. “We use 350 W motors on each wheel, and have a 6 kph autonomous speed cap, although the robot is mechanically capable of a lot more. “The motor controllers [from Roboteq] are rugged and reliable, and they’re programmed such that even in emergency stops, the torque output is smooth enough to prevent excessively harsh braking. We don’t risk hurting anyone, nor do we hurt the drivetrain.” Energy is stored in a pack built around lithium iron phosphate (LFP) cells. Nickel manganese cobalt cells were used in early Ottobots and tests, but the company found itself questioning their charging times and safety. By contrast, the greater customisability of LFP enabled the team to shape and ruggedise the pack to its desired safety standards, and Vijay reports no difficulty in sourcing safety-certified LFP cells from vendors worldwide. “We also use the battery suppliers’ BMS and charging software,” Korupolu adds. “At the moment, charging is manual. A technician either plugs in a connector to the receptacle at the rear, or swaps the entire pack, and charging takes around 75-90 minutes using DC fast charging. We’re also working on integrating wireless charging so the robot can dock itself and leave autonomously to go to a job when recharged.” High Information Maps As might be expected, some mapping information for localisation is key to the Ottobot’s contextual navigation. Delivering uncrewed and autonomous engineering jobs directly to your door An LFP battery pack sits at the bottom, a cell chemistry that meets Ottonomy’s requirements for safety and customisation over NMC