Lisa Simpson's Perpetual Motion Machine?

[Ed]

Hi Everyone,

This one has been buggin' my feeble brain for some time now...on and off of course ;-)

About five years ago I had an idea (springwheel.gif) that education will tell you can't work, but something about it still interested me.

Then one day I saw a Simpsons episode (refer to my avatar image) which portrayed a PMM...not just any typical PMM (MT1,2,3...) but a familiar curious one. Then, after re-looking at all the MT images (by the way thanks Bill) I came across a few that seemed to follow the same theme (correct me if any of you think I am wrong). Look at the MT image also in this post for reference. I included MT51 because MT52-55 all seem to benefit from the ratchet mechanism.

I wanted to test this out once and for all so I created a simulation (besslerLever.gif, yellow is 1lb effort and cyan is 1lb load) and sure enough it didn't do what I hoped it would.

I assume it has to do with the distance move by effort vs. load, but I believe all these "devices" try or do compensate for that as well.

Can someone please set me straight?

Thanks,

Sym Smith

[Oxygon]

lisa PMM

p.s. - I may have gotten this pic from someone here...

[Jonathan]

I don't understand what you want to be set straight about?

[Ed]

Sorry.

Please look at my springwheel.gif image (this concept should apply to the other devices I mentioned above in one form or another, but let's use my springwheel example for discussion).

1. is a point that the effort is applied to and is 10 units away from the hub
2. is a cam that is 1 unit away from the hub and is where the load is applied (actually the opposite clothes pin)
3. is the short side of a 1:3 lever
4. is the long side of the same lever
5. is a spring that's extended to, say, 1 lb. force
6. is just a joint to let the arm pass the peg while spring is getting extended

So we have:

A) 1 lb. force exerted at rim (10 units from hub) equals 10 lbs. force at cam (1 unit from hub);
B) 10 lbs. of force on short side of 1:3 lever equal 3.333 lbs. of force at long side of lever (10 x 0.3333 = 3.3333)
C) 3.333 lbs. force exerted again at rim equals 33.3333 lbs. of force at cam
D) etc.?

I'm not saying it should work, but it does seem to be a principle behind all these things I mentioned above. Some use springs and some use gravity.

I know the rim moves further than the cam but the cam has more force to be able to apply to the short side of the 1:3 lever, which in turn should makes up for the further movement of the rim...or maybe this is where the problem is?

So I guess this is where I need settin' straight. Just don't dismiss it out of hand because it's levers, others would do the same for us just talking about this subject matter in general. ;-)

[Jonathan]

I'm sorry, but I'm still not clear how it works. Is the cam stationary or attached to the wheel? How can the pegs be on the same (left) side of the wheel as shown? Or, how can the upper mechanism escape from its position to the right of the peg so that once at the bottom it is again to the right of the peg? And which way is it supposed to turn?

[Ed]

My apologies. I should have described that image better. Please take a look at this animation. Hopefully it will clear things up.

[Lightwave]

wow i really like that anim

[Gravmaster2000]

I really like how the animation looks too-love the way the timing
of the pushes is always exactly right at any reasonable speed.
One thought-bessler said shifting weights around was pointless for OU;
that is avoided here, a good sign.
Another thought- How about running it at resonace in the springs?
That would help both the set (less power needed)
and push/release phases.(more power, longer push?)

[Jonathan]

Oh! That makes sense, and I really like the animation too. for some reason I thought the stationary bars that the springs connect to were mounted on the wheel.
This design is hard to analyse rigorously (spring streched along chord of lever arc, etc.), and ultimately I don't think any all mechanical device (A pushes B pushes A, dry mills, etc.) will work. As far as I can tell a force causing the wheel to turn would, through the mechanisms, cause a greater force to be exerted at the periphery of the wheel, but you can see in the animation that this greater force is exerted through a very small angle, whereas the cam presses on the short end of the lever for a large angle (about 5 and 60 degrees respectively?). But, as I said, it is hard to tell if the distances and forces cancel as they usually do.
I could make a model this on Friday if you like?

[Ed]

Thanks. If you could give it a try that would be great. I know you've said many times that you don't think springs (i.e. mech only?) will work, but I think if gravity works then other conservative forces should work as well. I'm attaching an animation of MT53 which should be easier to study than my springwheel idea. Keep in mind that the checkered part of the weighted arm is where the ratchet is.

Thanks again for any help in analyzing and building you all can give.

[Ed]

I just want to recap my original thought...

I'm not that hopeful that any of these type of devices would work, but I have seen enough of them, including Bessler's, and there is something about them that still intrigues me. Why would Bessler include them in MT if they are so easy to dismiss?

So, I can obviously see how a simple lever trades distance for force, but in some of these compound lever designs it is not as easy to see why they would not work, and even seems like they could.

I'd like to know, if they definitely do not work (probable) why and where they break down. Then I can chuck a whole line of thinking and get on with some other ideas! ;-)

Thanks!

[Jonathan]

I tried to build the model today, but I was unable to get the timing right. In order for the lever to hit the pin, the receding side of the cam must be quite steep. This allows the lever to move quickly and hit the pin. But I couldn't get the receding side steep enough, so as it turned it would ride up and then down the cam, never having a fast release, and all the spring's energy going back through the cam.
Bessler included them in MT to show what doesn't work. The idea is that we are supposed to think of all possible deisgns, and then MT eliminates all the ones that don't work, and we are supposed to see the only other possibilty.
Compound lever devices don't work because they are no more than the sum of their parts, and since their parts conserve energy, then the whole thing does too.

[Kirk]

Compound lever devices don't work because they are no more than the sum of their parts, and since their parts conserve energy, then the whole thing does too.

Symmetry is a PITA isn't it?
;)

[Ed]

Ok, Thanks.

I think I got what I needed from this line of thought.