Unmanned vehicles must maneuver through harsh terrains and environments, and serve a multitude of functions or operations. Applications include hauling, transportation, disposing and disarming explosives, and surveillance.
For military and industrial use, this high-speed robotic vehicle needed a compact drive system to manage omnidirectional movement, accommodate a wide range of power levels and complement a distributed motion network.
One particular high-speed vehicle is a ground-based omnidirectional robotic platform for industrial and military use. It can reach speeds of more than 25 mph (40 kph). All wheels steer independently, so that the vehicle can move in any direction. It is also equipped with a manipulator arm with 5‚Â° of freedom and lift capacity of more than 100 lbs (45 kg) at full extension.
The Eagle digital drive provides encoder-only velocity control for the drive wheels, and weighs less than 25 oz.
The vehicle needed a capable and compact drive system that could accommodate a wide range of power levels and complement a distributed motion network.
The initial drive implementation fell short on power for the wheels and could not control velocity well. Thus, the vehicle had limited drive capability on an incline. When coming to a stop, the drive made a final corrective move based on the servos closing any position error present. The vehicle‚â€™s control system was originally based on the CANopen DSP402 protocol.
The compact nature of the vehicle required comparably compact electronics and minimal cabling. The engineering team chose the Eagle digital drive from Elmo Control. It provides encoder-only velocity control for the drive wheels, 60 A continuous at a 46-195 Vdc bus, and weighs less than 25 oz.
The Harmonica digital drives were chosen to handle the platform steering and the lower power manipulator arm joints.
For the manipulator arm control, the design team chose Elmo‚â€™s Falcon digital drives because of the power density available for the higher power arm joints. Encoder-only velocity control is used in conjunction with absolute position feedback from an analog absolute encoder.
Elmo‚â€™s Harmonica digital drives were also chosen for both the platform steering and the lower power manipulator arm joints. The Harmonica drives were selected for their compact size and ability to support up to a 200 Vdc bus. The platform steering uses Hall effect sensors. As with the Falcons, the Harmonicas control the manipulator arm in encoder-only velocity mode.
The Falcon digital drives power the manipulator arm control.
The Eagle and Falcon use D-sub style connectors. The D-sub connectors are rugged and can withstand the shock and vibration encountered while the vehicle travels through rough terrains.
Lastly, the Elmo system supports the CANopen protocol. With CANopen, the drives can be mounted very close to the electrical axis, which reduces overall cabling. The system supports both CAN In and CAN Out terminals and allows daisy-chaining of the CANopen communication lines from drive to drive.
Filed Under: Motion control • motor controls