Author Topic: A rolling cylinder and piezos (Read 9747 times)

Rapadura · « **on:** March 04, 2010, 04:06:11 AM »

Imagine the two ramps that are in the image below.

Imagine that the rolling surfaces of the two ramps are covered with piezos, made of a very sensitive piezolelectric material (don't know if quartz would be the best choice, it have to be a material that gives the best outputs with very small deformations).

The two ramps have the same initial height from where a cylinder (or sphere) begins to roll.

Does anyone here agree that the deformation of the piezos is proportional only to the weight of the cylinder (or sphere) and not to the speed with which the rolling cylinder passes over the piezos?

And if the deformation of the piezos is equal, regardless of the speed of the cylinder, the amount of electricity generated by each piezo is equal, don't matter if that piezo is on ramp 1 where the cylinder passes with greater speed, or if that piezo is on ramp 2, where the cylinder passes with lower speed.

Is this reasoning correct?

Rapadura · « **Reply #1 on:** March 04, 2010, 04:07:01 AM »

Sorry, forgot the image. Here it is:

Rapadura · « **Reply #2 on:** March 04, 2010, 05:10:12 AM »

I hope someone can answer my question about the equal deformation of the piezos.

Because if it's right, we can put much more piezos on ramp 2 than we can put on ramp 1. Then, rolling on ramp 2 will generate more electricity than rolling on ramp1. And the initial height is the same.

Rapadura · « **Reply #3 on:** March 04, 2010, 02:09:51 PM »

Sorry, I didn't realized that, after the ramp ends, the cylinder keeps on rolling. And in ramp 1 it keeps on rolling for a greater distance after reaching the end than in ramp 2. So, in both ramps, the final point where the cylinder finally stops is in the same horizontal distance from the starting point. So, we can put the same amount of piezos in both cases. Never mind. Forget it.

Rapadura · « **Reply #4 on:** March 05, 2010, 06:08:16 PM »

Just asking...

gyulasun · « **Reply #5 on:** March 05, 2010, 07:37:09 PM »

@Rapadura

Your question can only be answered by practical tests.

-figure out how much voltage a piezo can give for the press of a ball of a given weight and this voltage should be fed into capacitors to store them (key factor here is the inherent efficiency of the piezo and the loss due to the forward voltage drops of the diodes bridge)
-figure out how the ball will return to the starting point, waiting for the next lift up of the 20cm height
-figure out how to lift the ball up to the 20cm height (probably you wish to use an electromagnet that is fed from the capacitors charge provided by the piezos, the electromagnet preferably made to work as a gun to fire the ball up to 20cm)
-figure out a simple circuit that senses when the electromagnet should be fired, the energy for this circuit should also come from the energy stored in the capacitors

So?

rgds, Gyula

Rapadura · « **Reply #6 on:** March 05, 2010, 08:14:55 PM »

In the unlikely event of the piezos can generate enough electricity to lift the ball a little more than 20 centimeters (say, about 22 centimeters), the elevator used to lift the ball could simply lean to one side and dump the ball on another ramp, equal to the first ramp, which will take the ball toward a point on the side of the beginning of the first ramp, where another elevator will do the same thing. Closed loop.

Rapadura · « **Reply #7 on:** March 05, 2010, 08:29:00 PM »

If the angle is just 0.5 degree (half degree), instead of 1 degree, the ball will travel 22.9 meters.

DreamThinkBuild · « **Reply #8 on:** March 06, 2010, 12:10:50 AM »

Hi Rapadura,

You may not even need to lift the ball. From the High road-Low road example it might be better to keep the ball on a constant slope. If you keep the ball in a oscillating energy well it wouldn't take as much power to push the ball in the opposite direction. A small pulse coil can keep the whole system oscillating. With no pulse coil friction from the ball and pivot will eventually wear away at any gains. The challenge then becomes generating enough energy to run the pulse coil. Attached is a picture of the basic idea.

Rapadura · « **Reply #9 on:** March 06, 2010, 03:24:03 AM »

@DreamThinkBuild

I think it's a good idea! I guess this thing can oscillate for a quite good time before completely stopping, no?

If the rolling surface is covered with piezos, the weight of ball will constantly deform the piezos, and that will create electricity...

We just need to know if, after the system stops completely, the stored electricity in a bank of capacitors is enough to push the ball until one of the two ends of the device (left end or right end), in order to make it oscillate for as long as in the first attempt.

DreamThinkBuild · « **Reply #10 on:** March 06, 2010, 06:03:34 AM »

Quote

I think it's a good idea! I guess this thing can oscillate for a quite good time before completely stopping, no?

Friction of the fulcrum, springs and ball will stop it eventually. Simulations show it run for 3 or 4 cycles with all friction on, sometimes more when the spring settings are lower but more chaotic. The springs could possibly be replaced with magnets but would interfere with the steel ball, unless a heavy acrylic ball is used instead.

Quote

If the rolling surface is covered with piezos, the weight of ball will constantly deform the piezos, and that will create electricity...

In the sim it's a heavy steel ball so it should work at activating the piezos as long as the surface remains flat.

Quote

We just need to know if, after the system stops completely, the stored electricity in a bank of capacitors is enough to push the ball until one of the two ends of the device (left end or right end), in order to make it oscillate for as long as in the first attempt.

That is the real challenge. I've attached a small video of it, this is with air friction turned off. This simulates what it would look like if you could pulse a small coil/magnet near/attached to the end of the beam to keep it in oscillation.

I can't post the 340k video because the max attachment size is 300k.

DreamThinkBuild · « **Reply #11 on:** March 06, 2010, 06:08:57 AM »

Sorry for the double post. Here is the video(flash format .flv) in a 2 part .rar file.

Is there no way to re-edit to add attachments?

onthecuttingedge2005 · « **Reply #12 on:** March 06, 2010, 10:49:48 AM »

Quote from: Rapadura on March 04, 2010, 04:07:01 AM

Sorry, forgot the image. Here it is:

do you see the incline? the incline only has as much kinetic energy as the highest point over time, a longer incline means that the object will roll slower over time, it doesn't contain anymore kinetic energy than the very height of incline.

a height of 1 meter with a falling incline of 1 foot has the same kinetic energy as a height of 1 meter with an incline of 1 mile. the difference is the rate of fall over time. the rate of fall is divided up.

if an object falls at 1 Newton straight down from 3 meters up it will have the same kinetic equivalent of an object falling at an incline of 1 mile who's height started at 1 meter up.

a lot of people are fooled by this illusion of distance over time.

Rapadura · « **Reply #13 on:** March 07, 2010, 02:08:00 AM »

But Jerry, when we are talking about piezos, we just need something rolling over the piezos, at any speed, to deform the piezos and generate electricity. Speed will not be important, we just need the "something" to deform a large amount of piezos. The larger the amount of piezos that are deformed, more electricity we can store in a capacitors bank. That's why I think it could be interesting to make the "something" travels the greater possible distance.

Rapadura · « **Reply #14 on:** March 07, 2010, 02:09:18 AM »

@DreamThinkBuild

Nice videos. But, the ball escapes from the device at the end? How could we prevent that?

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