Mechanical Caracteristics

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

Prospective

Drive Mechanical Componentstrain

Micro motor

Three possibilities, depending on the power I need:

The base of the robot will be an assembly of two couples (RPM2(RPM15 + wheel).
The motor drives directly the wheel, butthanks fromto the reductor directly on the exterior of the wheel. The shaft drives the rubber band tire of the wheel.

This reduces the number of needed mechanical pieces, as this mount works as a 1:25 reductor.motor.

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

The total width of this assembly can fit in 40mm.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).