Design notes

Some Design notes information.

Base design info

 Drive Motor Sizing

To calculate the required torque, power, current and battery pack required by a wheeled mobile robot, there are several principles that must be understood.

• Concept of vectors
• 2D Force balance
• Power
• Current and Voltage.

Check out the Drive Motor Sizing Tutorial

Design inputs 

• Total mass: 10 lb
• Number of drive motors: 2 [#]
• Radius of drive wheel: .04mm
• Robot Velocity:  .2 m/sec
• Maximum incline: 20 [deg]
• Supply voltage: 12  [V]
• Desired acceleration: .2 m/sec
• Desired operating time: 120 minutes
• Total efficiency: 65 [%]

Output (for each drive motor)

• Angular Velocity: 47.771 rpm / 5 rad/s
• Torque*: 70.257 ozf-in
• Total Power: 2.4810 W
• Maximum current: .20675 A
• Battery Pack 0.8 Ah 

Motor

131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder

12V brushed DC motor with a 131.25:1 metal gearbox and an integrated quadrature encoder that provides a resolution of 64 counts per revolution of the motor shaft, which corresponds to 8400 counts per revolution of the gearbox’s output shaft.

Dimensions

• Size:  37D x 69L mm
• Weight: 8.1 oz
• Shaft diameter: 6 mm

General specifications

• Gear ratio: 131:1
• Free-run speed @ 12V: 80 rpm
• Free-run current @ 12V: 300 mA
• Stall current @ 12V: 5000 mA
• Stall torque @ 12V: 250 oz·in

Wheels

Pololu Wheel 80x10mm Pair - Black

The wheels have silicone tires and measure 80 mm (3.15″) in diameter.

Equation

Speed = (RPM (diameter * PI) / 60)

Speed = ( 80 rpm ( 80mm * pi / 60)

Top Speed = 335.1 mm/sec / .3351 m/sec/ 1.1 ft/s / 13.195 / in/sec