Mechanical Physics

While teaching students the finer art of building robots, all standard physics principals are at play!  The concept of friction, resistance, balance, gravity, torque etc are all important.  Here are some websites with explanations or basic experiments to convey these concepts to your students.

Web Resources

• http://www.maximum-velocity.com/fivekeys.htm Basic experiments which can be easily replicated using standard LEGO, VEX IQ or VEX EDR parts to explain friction, gravity and momentum.

Other helpful hints

Below are some simple LEGO based examples of gearing, transmissions and other key mechanical aspect useful in robot design.

Manual Transmission to reverse direction. The manual transmission shown in here is only a prototype. The idea is to be able to use forward and reverse from a single motor for separate tasks. The details of an actual implementation are left up to you. In the setup shown, driving into a wall moves a gear from one gear train to another, perhaps allowing the robot to change direction without changing the direction in which the motor rotates. One problem is how to move forward again. Simply using a rubber band or spring to return to the original gear train, not enough time will have passed to allow the robot to back away from the wall very far. With a bit of ingenuity and mechanical experimentation, it is possible to multi-task motors.

Simple Gearing System Gearing serves two main purposes: transmitting and transforming mechanical energy. For the purposes of a drive train, the gears will change the high speed and low torque of a DC electric motor to the low speed and high torque that is required to move a robot. Experimentation with different gear ratios is important. The gear ratio determines the important tradeoff between speed and torque. This figure illustrates a sample LEGO gear train that achieves a gear ratio of 243:1 through the use of five ganged pairs of 8-tooth to 24-tooth gear combinations (this gear ratio may be overly high for a robot drive). It is suggested that a copy of this gear train be built for evaluation.

Differential Gearing. The differential gear is used to help cars turn corners. The differential gear (placed midway between the two wheels) allows one wheel to turn at a greater speed than the other. Even though the wheels may be turning at different speeds, the action of the differential means that the torque generated by the motor is distributed equally between the half-axles upon which the wheels are mounted. Assuming the robot’s weight is sufficient and distributed properly, the robot should be able to turn with its drive motors at full power without causing either wheel to slip. In terms of robot construction, this means that one wheel could be completely stalled, while the other would continue to revolve. Because slipping of the wheels is avoided, static friction between the surface and the robot is maintained providing a better translation of rotational force to linear force.