This semiconductor gas sensor detects the presence of combustible gas and smoke at concentrations from 300 to 10,000 ppm. The sensor's simple analog voltage interface requires only one analog input pin from your microcontroller.
This set of wheelchair motors makes great heavy duty robot motors. One left motor and one right motor. They are right angle gear drives have been modified to include encoders. They are 24VDC and the operating speed is 120 RPM.