Spring 2016 AdBot Motor Driver Trade-Off Studies

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By Don T. (Mission, Systems, and Test)
Dang Le (Project Manger)

Motor Driver Trade-Off Study
The Arduino pins supply less than 0.040 A. The small Pololu motors with 120:1 or 200:1 gear ratio run on 0.120 mA and more. The result is to find motor drivers.

The motor drivers’ specification of interest are tabled. The integrated circuit selected is the L298N. It is feared that the L298N is not powerful enough. It works fine so far. The L6203 has built in diodes despite it can drive only one motor per device. The L298N needs external diode bridges. Get motor drivers with the diodes built in.

Motor Drivers Trade-Off

Motor Trade-Off Study (and Torque Information)
DC motors are commercially available and offer choices. The motors have gears that changes thousands of rpm into hundreds. The motors of interest offer more torque force with decreasing speeds. Several motors are purchased and tested as stores do not claim the torque information or stall current. The requirement calls for a motor with 84 rpm or more. The 6 V motors have a no load speed of 85 rpm. The torque of 5.4 kg-cm meant that the motors stall at 5.4/3.175  (for 2.5 inch diameter wheels) or 1.7 kg of force, which is 3.75 pounds. The mass of the 6061 aluminum chassis is and arms is 1.108 kg. This figure without the motors and other components added is close to the full load specification of the motor. Instead a 12 V motor is used in its place. The design has front and back motors. The front motors have 9.2 kg-cm and the back motors have 5.4 kg-cm. 25 kg-cm of torque is required to lift the front of a 3.75 lb. rover over a 11-cm step of a staircase.