Ramp Efficiency

Challenge:  To design a motorized winch and adjustable ramp that can measure the efficiency of that winch as it lifts a load up the ramp.

Parameters: Your winch must be a small DC motor with pulleys or gears (to improve Mechanical Advantage), connected to an ammeter and voltmeter so that electrical power can be measured and monitored.  Your ramp must be at least 50 cm long and must be able to change from 5° to 30°.  Your loads must slide up the ramp or roll up the ramp, and must be of known masses.  From video or stopwatch analysis, you must be able to calculate the lifting power (example formula below).

Scoring:  You will be scored on how well you are able to support your answer to the original question with data you collect from your device.  The efficiency of your ramp is output lifting power divided by input electrical power. 

Efficiency = 100% • (m•g•v•sinø) / (I•V)

m mass of the load (kg)

g gravitational field strength (9.8 N/kg)

v linear speed along the ramp (m/s) (or ∆d/∆t)

ø angle of the ramp

I current drawn by the winch (A)

V voltage used by the winch (V)

Physics:  The ramp surface is not perfectly smooth or flat, so it is important that your winch has a large mechanical advantage (pulleys or reducing gear).  In order to maintain a constant velocity, forces acting against the motion of your load must be exactly balanced by the forward tension force in your string.  A Free-Body-Diagram is extremely useful for your analysis.  A NiChrome wire (variable resistor) is an excellent way to control the speed of your winch.

Extensions: To analyze your setup scientifically, you should control all variables except the one you are testing (eg. angle of ramp).  However, there are many variables that affect your system.  (all the letters above!)  The speed at which the motor turns can affect its efficiency dramatically at very low or very high rpm.  How can you ensure the motor is not struggling to turn?

Help/Hints: You can time the load between a start line and stop line, but you should have the load already in motion so it is moving almost at a constant velocity.

Quiz Topics: simple machines, work, power, efficiency, simple circuitry

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