ReconRobotics Inc., Edina, Minn., decided to upgrade its 1.2-lb throwable reconnaissance microrobot to include paddlelike wheels specifically designed for climbing. But to do so, the company had to boost the power of the wheel-driving servomotors. “The robot had to be able to lift its own weight,” explains ReconRobotics Product Management Engineer Casey Carlson. “The original ThrowBot was designed to navigate relatively uncluttered urban environments and could surmount some household objects such as power cords. But we wanted the robot to be able to routinely climb obstacles such as door thresholds and other obstructions commonly found within and around urban dwellings. We also wanted to keep the same size and shape for the main body of the robot, which houses all of the functional aspects of the robot including motors.”
Resembling a small dumbbell, the new ThrowBot TXT comprises a pair of 4.5-in.- diameter wheels linked by a 1.5-in.-diameter, 6-in.-long crossbar. It is tough enough to survive a 30-ft drop onto concrete. SWAT teams and military personnel typically throw the small robots into hostile areas to get remote video and audio of potentially deadly situations. A human operator pilots the robot with a wireless joystick.
Each wheel is driven independently by a 10-mm-diameter, high-power-density dc motor from MICROMO, a member of the Faulhaber Group, in Clearwater, Fla. The 1016 coreless dc micromotors in the ThrowBot TXT are specified to be run at a maximum voltage of 6 V, but the engineers at ReconRobotics needed extra power, which called for feeding the motor at 10 V. “We needed the motor to output about 65% more power than what the motor was originally rated for,” says Carlson.
The standard version of the motor comes with gold brushes. To tolerate the overdriving, MICROMO swapped in silver brushes and added a capacitor ring that minimizes damage to the brushes from arcing. The team also modified the motor windings to optimize output for a particular performance point the ReconRobotics team required. MICROMO also terminates the gearmotors by soldering custom cable assembles to the terminals, as well as mounting a pinion on the front shaft. Finally, MICROMO set up mean-time-to-failure testing to validate the new motor.
ReconRobotics also modified the clutching mechanism between the wheels and motor-drive system on the new ThrowBot TXT. The clutch decouples the wheels from the drive in hard landings so the instantaneous acceleration does not damage the gearmotor. The clutch is designed to disengage just above the maximum torque of the motor. Thus, there is no energy wasted transferring motor torque to the wheels. When higher torque is applied during impact, however, the clutch disengages, preventing the landing shock from reaching the motor and gearhead.
MICROMO delivers an assembly consisting of motor, gearhead, and cabling. As a result, the modules arrive at Recon already tested and operational. “The more plug and play we can get, the better,” says Carlson.
Though the ThrowBot TXT is relatively new to market, Recon says the response from customers has been quite positive, which Carlson attributes in part to the performance of the motors. “They give us the performance and lifetime we need and MICROMO is willing to lend its expertise and adapt the motor to our needs.”