Reply With QuoteWe need a sketch to understand your problemOriginally Posted by Taylor
I have studied how gear trains work, but can't find an analogous situation where the forces in the gear train oppose each other. Can someone help me with this problem?
There is a 2:1 gear ratio on a dual rack and pinion gear train connected to opposing pistons, and there is equal force on both pistons (force = 2), in what direction does each piston move and how far?
Force -->|piston1|----------(1:2 gear train)----------|piston2|<-- Force
We need a sketch to understand your problem
Here's a sketch:
pistons.jpg
The device is in an environment with ambient pressure, so the forces are equal on both pistons. The top of the pistons are exposed to the environment and there is a single sealed chamber connecting the pistons and containing the gear train. The opposing pistons are connected to shafts (pinions) attached to a 2:1 gear train. Both gears are on the same axis. One piston pinion is connected to the 1 gear, and the other piston pinion is connected to the 2 gear.
Normally, when the ambient pressure increase, the volume of the piston chamber would decrease. I would like to use a gear system so that when the ambient pressure increases, the volume of the piston chamber increases as well. Is there any way to accomplish my goal of increasing the volume?
Last edited by Taylor; 11-12-2012 at 03:22 AM.
The pistons in your sketch may be arranged in an "opposing" style, but functionally they are not opposing each other. As the pinion turns they will both move toward the center. The one connected to the larger pinion diameter will move twice as fast as the other one.
To be truly "opposing" in function, they would both have to ride on the same side of the pinion, in other words both on top or both on the bottom. Both pistons would create a torque on the pinion. The force of both pinions is the same, but the moment arms of their contact points on the pinion are different. That means the resulting torque would be different. That means the pinion will rotate, and both pistons will move in the same direction, one twice as fast as the other.
I cannot see how that will work. Both pistons are open to ambient pressure yet you have a common shaft with two different ratios. HUH? Am I missing something here?
It will be like a dead clock. Correct only twice a day.
Forum.jpg
Thanks for your responses. jboggs, yes, the diagram is incorrect. I have attached another diagram that shows the pinion in the correct place and an alternate configuration with a gear train.
I think there are only three ways for the device to move. If all the resulting forces are equal on both sides of the gears, there will be no movement. If the force on the left piston (Piston 1) is stronger, both pistons will move to the right and lose volume. If the force on the piston (Piston 2) is stronger, both pistons will move to the left and gain volume.
Both pistons have forces acting upon them from the outside (Force “A” in the diagram). This force is transferred to the opposing piston through the gear train. There is a resulting opposing force one each piston (Force “B” in the diagram).
How do the Forces A and B on each piston add or subtract together to get the net movement “N”? That is, how do I add or subtract the force from one piston to the force of the other piston, taking the gear ratio into consideration, to determine the ultimate movement of the device?
I have calculated this:
Given an ambient pressure force = 2; A1 and A2 both equal 2.
Force A1 is multiplied by 2 (2:1 gear ratio), so B2 = 4.
Force A2 drops by half (1:2 gear ratio), so B1 = 1
N = (A1 – B1) + (A2 – B2)
N = (2 – 1) + (2 – 4)
N = -1, or a force of 1 moving in Piston 2 direction (to the right in the diagram).
Since any movement caused by a force on Piston 1 moves Piston 1 twice the distance of Piston 2, Piston 2 would move half the distance of Piston 1. If Piston 1 moved a distance of 1, then Piston 2 would move ½. Therefore, the cylinder would have a net loss of volume of ½ the movement of Piston 1.
Am I correct?
Last edited by Taylor; 11-13-2012 at 03:58 AM.
Think about this statement.
The positive work done by the process would normally compress the fluid inside the contained volume and that work would increase the internal energy by the same amount.
So instead of the internal energy increasing by work done by the ambient pressure ,it would decrease, thus violating the 1st law of thermodynamics. On that basis it won't work.
Isn't the decrease in work converted into the energy required to expand the volume by the mechanical advantage of the gears?
Higher external pressure results in greater internal volume? No.
So you don't think it's possible under any configuration?
Another approach.
First off, there are 2 possible motions of the cylinders of you design, one in which the entrained gas volume increases ( your hope) and one which decreases the volume.
Case 1:
you postulate that the left piston will move, right a small distance x while the riht cylinder would move a distance 2x , also right, so the volume would increase by xA, where A is the piston area.
Now consider the energy.
The atmosphere would add an amount of energy equal to Fx on the left cylinder and the cylinder on the right would deliver 2Fx to the atmosphere, so you have violated the conservation of energy and it won't work for that scenario.
Case 2
you postulate the reverse ( the actual case)scenario, the right cylinder moving leftward=2x and the left cylinder moving leftward x, then the internal volume decreases Ax , but that isn't what you want.
BTW, the direction should be obvious if you see the moment imbalance on the pinion.
Conclusion is you can only DECREASE the internal volume for this process
We are all assuming that both pistons are in contact with a singular internal volume. Is that the case? Or is the volume inside each piston isolated from the other?
Theoretically you might set up a dual volume system with a mechanical connection where a large decrease in volume under one piston might cause a very small increase in the volume under the other piston, but realistically I don't see how you could make it work. The seal friction alone would be a killer.
I have created another 2 designs. In both designs, I have two separate pistons connected by a 2:1 gear train. As you can see, in the first design, the pistons balance each other out, so the increase in volume is zero. In the second design, I add a compression spring in the first piston equal to the force of the ambient pressure. This allows the other piston to power an increase in volume equal to the force of the compression spring. (I use positive and negative values in the drawings corresponding to the direction of the force).
The next issue is how do I load the compression spring.
Prelim Designs 3.jpg
Last edited by Taylor; 11-15-2012 at 09:21 AM.
Taylor,
What are you trying to achieve? None of your sketches make practical sense and your development path seems to be a long way from where you started. With gears connecting them as shown, the piston with the highest force will control the other piston. I cannot see where a spring can be useful with it's constant rate against a variable pressure on the piston top. It makes no sense at all.
I suspect you are stuck on a concept that will not work for whatever it is you are ultimately trying to do. You need to stop and regroup and figure out something else that does not use pistons and gears. I think you could benefit from some paid advice from a Mechanical Design Engineer. Check the local Yellow Pages.
However, I have been wrong before.
Ditto to Dave's comments.
I'm curious too. Exactly what are you trying to accomplish here? What is your end goal?
I stated my goal at the top of the thread: to have the volume of a chamber increase as the ambient pressure increases, using only the force of the increasing pressure to power the device. I'm really just testing the concept at this point. I don't see where my logic goes wrong in these diagrams; maybe you do and could let me know.
I don't want to give out the whole idea on a forum because it's a simple concept and potentially lucrative. But, I will be happy to let you know my idea by email if you email me:{email removed -- use PM if you must} . I'm not an engineer or physicist. I took high school physics and have done some research for this project. Most of the basic material I found covers gear ratios and such, but not something this complicated.
I have submitted a project on Freelancer for some paid professional advice, and am waiting for all the responses. Some have said it's impossible, some claim to have made it work. You can check Freelancer if you want. The project's called "Volume expander".
Thanks.
Last edited by PinkertonD; 11-15-2012 at 02:46 PM. Reason: Removed Email address
Taylor,
That was **not** the kind of paid help I was thinking off. You need to sit down and talk with a local Engineer with some prototype development experience, someone you can get a feel for working with.
I understand not divulging too much on the forum and in fact would not even offer email explanations.
If this thing has commercial value then start paying now, otherwise the advice you get will be worth exactly what you are paying for it, nothing. I would be loathe to hand over a project to someone I could not look in the eye and shake hands with. Even that is no total guarantee but in my humble opinion, certainly better than plucking a name from a list online.
If this thing has commercial value, then you will need that Engineer to help develop it to a commercial level. Maybe with great success, (sales) you will need to scale it ten-times or a thousand-times. To have the Engineer in at the design start will server that end well.
Just one old fart's opinion.
"I have submitted a project on Freelancer for some paid professional advice, and am waiting for all the responses. Some have said it's impossible, some claim to have made it work. You can check Freelancer if you want. The project's called "Volume expander".
Mr Taylor,
You have already received substantial professional advice here on your "perpetual motion machine".
And lucky you, it has been for free.
So, if you are still hell bent on yet another source of advice, go to the physics department of a good university that has a doctoral program and ask if one of their doctoral candidates with expertise in Thermodynamics would look at it; they would do it at a fraction of the cost (or possibly for free) that the inventor usually pays for less than professional advice.
[QUOTE=Taylor;4403].... to have the volume of a chamber increase as the ambient pressure increases, using only the force of the increasing pressure to power the device.... QUOTE]
I've looked at this entire thread a couple times and haven't been able to get a grip on what you want to accomplish. These pistons are sealed in bores and going to move up and down right? With what you have drawn up IF/when one moves down the other will move up. So is it the volume above these pistons that you want to become greater or the volume below or towards your gears that you want to increase?
Is there a lid on top of this thing or a cap or is it just open to air or water or whatever? Are you looking for something that let's say... if you sink it in a pool the further down it goes the increased pressure will cause more volume to be created under the pistons? Or above the pistons?
Do the volume of these two bores both above and below the pistons share common air or water or whatever it is that is somehow varying in pressure? Meaning is the space above the pistons shared or connected and the air or whatever below the pistons shared or connected?
Can valves of any type be incorporated into this gadget?
Bob
Bob,
I think Zeke may be closer to this with "perpetual motion." It may sound like one of those things that should work, but the OP is not taking into consideration efficiency losses etc. He/she really needs to sit down with an Engineer and see if what he/she wants is possible and that should not happen on an open forum.
As I keep suggesting, find a local Engineer to work with and it will save a lot of angst. If it is do-able then he/she are on their way, if not, then time to drop it and move on.
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