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close this bookAppropriate Community Technology - A Training Manual (Peace Corps; 1982; 685 pages)
View the documentThe Farallones Institute Rural Center
View the documentCHP International, INC.
View the documentPreface
View the documentAcknowledgments
View the documentIntroduction
Open this folder and view contentsPhase I: Introduction to training
Open this folder and view contentsPhase II: Earthen construction and fuel-saving cookstoves
close this folderPhase III: Pedal/treadle power
View the documentPhase III Calendar
View the documentSession 1. Maternal and child health: part 1
View the documentSession 2. The path of the sun
View the documentSession 3. Introduction to pedal/treadle power
View the documentSession 4. Design considerations for pedal/treadle power
View the documentSession 5. Classical mechanics: principles of pedal/treadle power
View the documentSession 6. Use of appropriate aids to communication
View the documentSession 7. Maternal and child health: part 2
View the documentSession 8. Part one: familiarization with materials and tools
View the documentSession 8. Part two: familiarization with the bicycle
View the documentSession 9. Introduction to design considerations
View the documentSession 10. Presentation of designs
View the documentSession 11. Construction of pedal/treadle-powered devices
View the documentSession 12. Blacksmithing and metalwork
View the documentSession 13. Appropriate technologies for health
View the documentSession 14. Case studies in community health
View the documentSession 15. Preparation for pedal/treadle presentations* *
View the documentSession 16. Heat transfer
View the documentSession 17. The role of the volunteer in development: international development part 1: the green revolution: successes and failures
View the documentSession 18. Presentation of pedal/treadle-power devices
View the documentSession 19. Volunteers in development part one. women in development
View the documentSession 20. Mid-program evaluation part one : program evaluation
Open this folder and view contentsPhase IV: Solar water heaters
Open this folder and view contentsPhase V: Solar agricultural dryers
Open this folder and view contentsPhase VI: Concluding the program: The energy fair
Open this folder and view contentsAppendices
 

Session 5. Classical mechanics: principles of pedal/treadle power

Total time:

2 hours

Objectives:

* To demonstrate and discuss the mechanical principles of torque, momentum, inertia end sprocket ratios
* To discuss the application of these mechanical principles to pedal/treadle-powered devices
* To practice facilitation skills

Resources:

* Meriam, Mechanics
* Attachment III-5-A, "Demonstration of Torque"
* Attachment III-5-B, "Demonstration of Momentum and Inertia"
* Attachment III-5-C, "Demonstration of Sprocket. Ratios"
* Attachment III-5-D, ''Ratio Designs" Worksheet;

Materials:

Newsprint and felt-tip pens; materials listed in attachments.

Trainer Notes

This session will require advance preparation. Part of this preparation should have been made at the end of Session 4 with the selection of three participants to present the demonstrations in this session. Each of the three participants/facilitators should choose one of the three demonstrations and be provided with the corresponding attachment. (See Resources.)

Be certain to allow sufficient time before the session for the facilitators to prepare their demonstrations and provide them with the materials necessary. If the participant feels that he/she can present the principle in a more effective manner, encourage the development of that demonstration. Explain they they have 15 minutes to present the demonstration and 20 minutes for follow-up discussion.

Plan for time at the end of each of the three demonstrations for feedback on the facilitation skills of the individual giving the demonstration. You can encourage this feedback by asking the facilitator what he or she feels was best during the demonstration and where improvements could be made.

Step 1. (40 minutes)
Have the participant/facilitator demonstrate the concept of torque as outlined in Attachment III-5-A.

Trainer Notes

You should fill in any points missed or not covered to your satisfaction during all three of the demonstrations or discussions.

Step 2. (40 minutes) Have the second participant/facilitator demonstrate the effects of momentum and inertia as outlined in Attachment III-5-B.

Step 3. (40 minutes) Have the third participant/facilitator demonstrate the principles of sprocket ratios as outlined in Attachment III-5-C.

Trainer Notes

At the end of this session, distribute Attachment III-5-D, the "Ratio Designs" worksheets, explaining that the worksheets should be completed for the next day's session.

DEMONSTRATION OF TORQUE

Through this demonstration, the participants will gain practical understanding and experience with the effects of torque and its relationship to pedal/treadle power devices.

Total time:

40 minutes

Materials:

2 boards of equal length and nails

Procedures:

Step 1.
(15 minutes/Steps 1-4) Nail 2 boards together in a V-shape.

Step 2.
Have a participant grasp the two boards at the middle and attempt to pull them apart by opening the V. Point out the force required to move the boards.

Step 3.
Repeat the experiment by having another participant grasp the ends of the boards.

Step 4.
Compare the force required to move the boards when they are grasped at different distances from the juncture.

Note

The conclusion will be that it takes much less force to pull boards apart at the end mark, i.e., equal forces exert more effect on the juncture when they are at a greater distance from it.

Encourage the participants to express the relationship between applied force and the distance at which it is exerted, using the boards as an example. Such a relationship describes torque and may be expressed in the following formula:

torque = force applied x distance of applied force to the point of juncture

Step 5. (20 minutes)
Facilitate a discussion of the methods that might be used to minimize the effects of torque.

Step 6. (5 minutes)
Encourage feedback on your facilitation skills.

DEMONSTRATION OF MOMENTUM AND INPRTIA

This demonstration will enable the participants to experience the effects, parameters and relationships of momentum and inertia to pedal/treadle power.

Total time:

40 minutes

Materials:

Wheel or disk, axle, 4 weights (total weight approximately equals that of the wheel or disk)

Procedures:

Step 1. (15 minutes/Steps 1-5)
Mount the wheel or disk on a shaft so that it can be easily rotated.

Step 2.
Have a participant rotate the wheel at an approximate set speed, taking note of the force required to start it rotating and the time it takes to coast to a stop after the force is withdrawn. Then, have a participant again rotate the wheel up to speed and then try to stop it quickly, noting the force required to stop the motion.

Step 3.
Distribute four weights equally around the outside of the wheel and repeat the procedure.

Step 4.
Ask the participant to note the effects of the added weights.

Note

The conclusion will be that it takes more effort to start the wheel rotating with the added weight but that the wheel rotates freely for a longer time.

Step 5.
Encourage a discussion of the relationships between parameters of momentum (which are the initial weight of the wheel and its added weights), the wheel's rotational velocity and its radius.

Step 6.
(20 minutes) Facilitate a discussion of the application of the principles of momentum and inertia to pedal/ treadle design.

Step 7.
(5 minutes) Encourage feedback on your facilitation skills.

DEMONSTRATION OF SPROCKET RATIONS

This demonstration allows the participants to experience the effects, parameters and relationship of sprocket ratio to pedal/ treadle power.

Total time:

40 minutes

Materials:

Multiple speed bicycle

Procedures:

Step 1. (15 minutes/Steps 1-4)
Put the bicycle in low gear and lift the rear wheel off the ground. Ask the participants to observe how many times the rear wheel rotates for each revolution of the pedal crank.

Step 2.
Change the gear ratio to a higher gear and repeat Step 1.

Note

In the above two steps, ask the participants to observe the relative difference in force necessary to turn the pedal crank.

Step 3.
Have the participants develop the formula which defines the relationship between sprocket sizes and rotation speed.

Note

This relationship is defined as:

Step 4.
Facilitate a discussion of the potential mechanical advantage when sprockets are oriented in the proper fashion.

Note

The conclusion will be that transferring energy from a small to a large sprocket results in a velocity loss but in a mechanical advantage or gain.

Step 5. (20 minutes)
Facilitate a discussion of the application of the principles of sprocket ratios to pedal/treadle power.

Step 6. (5 minutes)
Encourage feedback on your facilitation skills.

RATIO DESIGNS WORKSHEET

1. Given the mobile dyne pod designed to power a food grinder that operates at 100 revolutions per minute, size the sprocket that will be connected to the grinder shaft:

Available sprockets:

35 teeth
42 teeth
48 teeth
18 teeth
22 teeth
30 teeth


RATIO DESIGNS WORKSHEET 1

2. Given the stationary dynapod, size the two sprockets in question to provide the required 400 revolutions per minute output in low gear on the bicycle.

1st gear: 1.4/1
2nd gear: 1/1
3rd gear: 111.4


RATIO DESIGNS WORKSHEET 2

3. Design a mobile dyne pod unit that will provide the driven output shaft speed of approximately 1,200 revolutions per minute necessary to power a bench grinder. The bicycle used will have a front sprocket of 48 teeth and a rear hub sprocket of 18 teeth.

Available sprockets:

35 teeth
42 teeth
48 teeth
18 teeth
22 teeth
30 teeth


RATIO DESIGNS WORKSHEET 3

4. Design a system which will deliver power in a linear mode for a water pump designed to operate at 15 cycles per minute. Pedaling speed of 60 revolutions per minute will be used with a belt/pulley combination. The pump has a driving rod throw of 8".

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