[P K Pillai (OP)]

I need inputs to assemble an engine that converts resonance to rotation, for powering my cycle rickshaw - about 300 kg/cm at 50 rpm. The vibrating element could be a thin spring steel strip, about 2 mtrs long x a few cms wide, electrically actuated.

[CliffordK]

There have been people trying shock absorbers that generate electricity.

http://www.extremetech.com/extreme/90102-shock-absorber-generates-electricity-when-it-hits-a-bump

[syhprum]

I am a little puzzled just what you are trying to do you talk of a vibrating spring electrically actuated, if you have a supply of electrical power the best way to use it for propulsion is with a conventional electrical motor.
if you are trying to recover energy from the spring set vibrating by the bumps over which the vehicle travels then see CliffordK's link   

[P K Pillai (OP)]

Rightly so !
Resonance optimises input energy.So a resonant assembly might be more energy efficient than an electric motor.

[RD]

involve more muscles ? ...

Or possibly regenerative braking ... http://en.wikipedia.org/wiki/Regenerative_brake [e.g. to charge a battery ]

[peppercorn]

Erm...

http://articles.timesofindia.indiatimes.com/2011-07-17/mumbai/29783935_1_p-k-pillai-idea-hasleen-kaur
"Ziyad Madon, TNN Jul 17, 2011"

-really?

[syhprum]

Electric motors commonly achieve efficiencies of 90% it is futile to add weighty gadgets to try and produce greater efficiency a resonant device would only capture energy over a narrow range of bump spacing's you need a more broadband arrangement.
An electrical shock absorber will tend to capture energy more at high frequencies you need a hydraulic arrangement that is inherently broadband compressing gas into a reservoir or charging a battery or spinning a flywheel  , there has been much research done in this area for use on F1 cars presumably some has been published. 

[P K Pillai (OP)]

Thanks, all.
My idea was to attach a small solenoid or cam operated geared micromotor close to one (fixed) end of the strip. A variable frequency oscillator could drive this assembly into resonance.
But maybe a motor is the best option.

[evan_au]

To drive the vehicle along the road, a standard electric motor is best.

However, what you are describing sounds like a shock absorber, which normally has two components:

• A spring to temporarily store the energy of the impact
  
• A piston to stop the spring from oscillating excessively, by dissipating the stored energy as heat

I guess you could replace the piston by a coil of wire and a powerful permanent magnet. Any mechanical shocks could then generate a pulse of electricity, which could be used to charge a battery. The battery could then power other functions in the vehicle.

By varying the impedance of the charging circuit, you could vary the "damping" of the suspension for different numbers of passengers, achieving a "critically damped" suspension.

The main challenge is that a 300kg vehicle hitting a bump will generate a large pulse of electricity which would require a large coil, high power electronics and a large battery to absorb the peak power. But the pulse would last only a very short time. This sounds like a high complexity for something that could recycle a fairly small amount of power.

See: http://en.wikipedia.org/wiki/Shock_absorber#Description