Talk:Inverted pendulum

Equations

The signs on the first equation (= F) for the cart model of the inverted pendulum is wrong from our calculations. The signs should be reverse on the sine an cosine from after the Lagrangian. Someone please confirm.128.63.18.10 (talk) 18:30, 11 June 2008 (UTC)

I agree. I've just wasted two days with this. I'm going to put warnings up. RatnimSnave (talk) 14:49, 6 December 2010 (UTC)

Why is there even an F in this equation? It isn't defined anywhere and the usual Euler-Lagrange equations just have a 0 on the RHS. If it is supposed to be an external force, why not include it in the Lagrangian? With this F=0, the signs work out for me. 128.189.209.122 (talk) 21:40, 8 December 2010 (UTC)

I just looked through the revision history for the article and I can't figure out if the signs are actually correct in the current article or not. Also, are there any references for these equations? It feels like there really should be a citation-needed flag in that section. 140.193.219.234 (talk) 22:40, 10 April 2014 (UTC)

Broken link

Vest link is 404. —Preceding unsigned comment added by 84.255.194.155 (talk) 11:41, 30 November 2010 (UTC)

Aerodynamically unstable

As of 01/17/2011, the article contained the following sentence relating to rocket stability in the Overview section (included here with parts of the surrounding sentences for reference):
"...cart-pendulum system on a see-saw. The inverted pendulum is related to rocket or missile guidance, where thrust is actuated at the bottom of a tall vehicle. The understanding of..."
The sentence falsely implies that a rocket "with thrust actuated at the bottom" (under the center of gravity) is inherently unstable, like an inverted pendulum. While not immediately intuitive, in actuality the position of the application of thrust is irrelevant to rocket stability, but rather the relative position of the center of drag (a.k.a. center of pressure) to the center of gravity; the rocket (or any aircraft for that matter) is stable if the center of drag is behind the center of gravity. This concept is reliably explained at length by a NASA publication.
I have changed the sentence to: "The inverted pendulum is related to rocket or missile guidance, where the center of gravity is behind the center of drag causing aerodynamic instability." This new reference also alludes to the fact that many modern large-scale rockets are in fact aerodynamically unstable (but not because of where on the rocket the trust is actuated). --AeroMech (talk) 06:48, 17 January 2011 (UTC)

References

Broomstick balancing

I'm surprised there was no mention of this here, so am including it.

• It's also mentioned in Bicycle and motorcycle dynamics#Center of mass location: A bike is also an example of an inverted pendulum. Just as a broomstick is easier to balance than a pencil, a tall bike (with a high center of mass) can be easier to balance when ridden than a low one because its lean rate will be slower.
• And the Segway PT apparently uses Silicon Sensing gyros: [...] classic implementation of the ‘inverted pendulum control theory’ – balancing a broomstick on your fingertip is another example of the same thing.

--Trevj (talk) 08:53, 14 September 2011 (UTC)

Significant Editing

I'm doing a wikipedia project for an English class. Our task is to find a wikipedia article that is a stub or start and make significant edits to it. I am an Applied Physics Undergrad and have done a research project on an inverted pendulum robot. I am planning on elaborating on the setups in which the equations of motion are shown. Also, I planning to add a number of examples and variations of an inverted pendulum. Any feedback would be great. Feel free to edit or delete anything I add or change...I'm new to wikipedia. Bradyjs bradyjs (talk) 16:10, 17 April 2012 (UTC)

Great additions to the page. Good torque and moment derivation. Mcginnsc — Preceding unsigned comment added by Mcginnsc (talk • contribs) 16:32, 3 May 2012 (UTC)

The Lead: "An inverted pendulum is a pendulum which has its mass above its pivot point"

An inverted pendulum has a *weight* above its pivot point. In a metronome, it is a moveable weight. Even though it is a small amount, the entire mass of the pendulum is *not* above the pivot. So an inverted pendulum does not have its mass above the pivot point. Not *all* of it! The area below the pivot may be small, but it is part of the pendulum, and part of the mass and is a necessary part or else the pendulum would not function if there is nothing below the pivot.

The ordinary English term <weight> makes more sense than the technical jargon word from the Metric System <mass>; and in normal conversation, people refer to a weight, as in adding a weight to a fishing line, for example. No one would say he is putting a "mass" on his fishing line.

One could say that the preponderance of the mass is above the pivot point. But one could say it in plain English: "An inverted pendulum is a pendulum which has a weight above its pivot point"

Changing this terminology would improve the article. Maybe what I suggest is picky. But the sentence to which I refer in the lead is not correct. -r 69.166.30.216 (talk) 09:51, 15 October 2012 (UTC)

"Center of mass" is probably a better term. It appeases the physicists by not letting "weight" enter into it while still addressing the problem of saying "mass above pivot". 83.70.170.48 (talk) 09:52, 15 October 2012 (UTC)

Thanks. That makes sense to me. Although I still say--- thinking of the metronome--it does indeed have a "weight" that is moveable. Nobody would say " move the mass up or down", but your piano teacher might very well say " move the weight up to 120 beats per minute".

Anyway, I won't alter the article: I am merely suggesting something that someone who is taking care of the article may want to improve. -r 69.166.30.216 (talk) 10:01, 15 October 2012 (UTC)

I agree with the "center of mass" suggestion and do not agree with the assertion that "mass" is a technical jargon word from the Metric System. I'll make the changes. -AndrewDressel (talk) 13:43, 15 October 2012 (UTC)

Examples of inverted pendulums

It is amazing to me that the metronome is not mentioned in this section. It is the most widely known inverted pendulum. Anyone want to tackle that? I would have thought it would be the first thing listed!

And include in the article the fact that metronomes are uneven in their beating. That could be explained.

Thanks.

-r 69.166.30.216 (talk) 10:14, 15 October 2012 (UTC)

The metronome probably wasn't mentioned because it isn't, in fact, an inverted pendulum (the centre of gravity being below the pivot point), though it might look that way at first glance. I deleted it from the list just now. 79.73.145.112 (talk) 22:49, 27 July 2016 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Inverted pendulum/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

I believe the last equation misses a minus sign on the right side since the equation should simplify for that of a normal pendulum if y is zero.

Last edited at 22:35, 7 October 2007 (UTC). Substituted at 19:03, 29 April 2016 (UTC)