Mechanical Caracteristics

• Target max speed: 1m/s
• Target size: 42mm x 42mm x 42mm (cardboard model on the right)
• Target weight: ~60g

Drive train

Micro motor

The base of the robot will be an assembly of two couples (RPM15 + wheel).
The motor drives directly the wheel, thanks to the reductor directly on the motor.

Estimated weight (without the assembly plate and hardware): 10g

The total width of this assembly can fit in 42mm.

 

Torque and Speed

Some tests with the pager motors showed a lack of torque.
Let's check our needs in torque and speed:

Torque

Assume the following parameters:

• Total weight = 0.210 [kg] (150g ball on top of a 60g robot - even if we don't plan to have this configuration)
• Wheel diameter = 0.025 [m] (assume gm10w)
• Acceleration max = 0.5 [m.s^-2] (theoretical)
• Speed max = 1 [m.s^-1] (theoretical)

The necessary torque is the torque needed to compensate the force F = w * a at a distance D/2 when the robot is at a full stop:

Torque = 0.210 * 0.5 * 0.025/2 = 1.3125 [milli-Newton.meters]
Double check with the dimensions: kg*m/s/s*m = N*m OK !

WolframAlpha tells us it equivalent to 13.4 g.cm, our GM15 motor appears to be powerful enough at 3V, and don't forget we use 2 motors to move, so the needed torque is half this number, or 6.7 g*cm \o/ (or 200% security margin).