Bumper/Sensor Assembly

The evolution of bumper sensing.

Objective: to sense touch on the right or left-hand bumper using two switches

First concept: Build a parallelogram structure with a beam off each side of the robot bumper, and position a switch behind each. See first picture below. A force anywhere on the beam will be reflected to the switch, since the beam can only move parallel to the bumper.

Here we started with one idea for a bumper/sensor assembly:

Testing the bumper shows it takes too much force to activate the switches. Objects like a can are pushed aside without creating enough force to close the switch. A lever can be positioned over the switch so that a smaller force on the end of the lever will create a bigger force at the switch (this is called mechanical advantage: a smaller force moving over a bigger distance creates a bigger force moving over a smaller distance at the switch.) If a beam of 7 units length rotates about one end and the switch is positioned at the three unit point and the force is applied at the 7 unit point, only 3/7 as much force should be needed to close the switch. See figures below for the improved bumper.

Below is an alternative assembly with more accessible parts:

A third step in evolving this design was suggested by Charles Winton:

The small piece shown connecting the 2 3-hole beams in the center are not really needed, thus saving three parts and allowing more options for the center beams.

Now here’s something for you to try: Assignment

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