Science Buddies: "Ask an Expert"

Hey ive got a project to do
the design brief giving was

Energy Conservation Demonstration Rig

Design a demonstration rig that can be used as a teaching aid for engineering classes to investigate the principle of conservation of energy in mechanical engineering systems. The design should be:
• Limited to 500mm x 500mm and a height of 400mm.
• Easy to assemble and disassemble.
• Easy to clean.
• Safe and robust.
• Hygienic and made from non-toxic materials.
• Simple to operate and use.
• Cost less than £300.
• Allow the main operating parameters to be measured and tested easily.


This is what i have came up with


now im going to have to make my own water wheel, but my main problem is i don't know if the low rpm from the water wheel will be enough to turn a generator to produce measurable electricity, and im not to sure how to calculate this.
im looking to buy a motor and use it as a generator and wasn't sure if one of these would do
http://www.maplin.co.uk/general-purpose-motors-11966

any help would be great
cheers

Hello colinglancy,

You are right that most small motors will also function as generators, and you are right that they are built to turn at very high speeds.

One option to get higher rotational speed would be to use gears or pulleys. The downside of this is that some of your energy gets lost in the mechanics.

Another option is to use a type of water wheel that spins fast. Consider a Pelton Wheel for this benefit.

Many small motors used to power hobby devices use dc motors with brushes to contact the rotor. The brushes cause a lot of friction, and thus they will dissipate a lot of your power. A brushless dc motor has no such friction, and it has only the rotary bearing friction. Fortunately, you can also get one cheap or for free.

Brushless dc motors are used in almost all small computer fans. Scavenge one from any old computer, or cajole one from a computer repair shop. A little modification is required to convert such a fan to a generator. See this url for conversion directions.
http://www.instructables.com/id/Upcycle ... &offset=40.

I hope these comments help. Get back to us on the details if you go ahead.

Good luck, WW

em also doing da same project
i think water sprinkled would travel fast to run da shaft