 | | articulation points? —Jason Coronado
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| | | just wanted to ask some fellow mech-ers exactly what constitutes a point of articulation. i am just finishing my second mech and i used at lease seven ball joints for the shoulders, hips, waist, and feet. i also used plate hinges in elbows and (...) (22 years ago, 17-Nov-02, to lugnet.build.mecha)
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| | | | | Re: articulation points? —Eric Sophie
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| | | | Hello, I would define a POA as a point when mobility occurs whereas the rotattion is counted once. That is to say if a Shoulder joint spins forwards and back it counts as one POA and should not be counted as two. Example: In this picture of the (...) (22 years ago, 19-Nov-02, to lugnet.build.mecha)
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| | | | | | Re: articulation points? —Jason Coronado
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| | | | | thanks for taking the time to answer my question. if i calculated correctly (assuming that i count each joint only once per semetrical side , i.e., one shoulder joint, one hip joint, etc.) my model has about 20 poa and 40 dof. this is how i figure (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha)
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| | | | | | | Re: articulation points? —Eric Sophie
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| | | | | | (...) Your welcome, anytime. (...) Sounds right. Good Luck! e (22 years ago, 20-Nov-02, to lugnet.build.mecha)
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| | | | | | Re: articulation points? —Jennifer Clark
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| | | | (...) Pedant's corner: This reminds me of an argument I've had several times, and to be honest have yet to come to a definitive answer. The maximum number of degrees of freedom an object can have in three dimensional space is six; translation in the (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | Re: articulation points? —Eric Sophie
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| | | | | (...) Oh? Hmmm...do tell. (...) Right! I see. In my own way I work around certain "movements" or joints by making two separete joints cover the same envelope or Area or Control. I mean in that, for example. The Arms of my Super Mech-Bot don't have (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | | Re: articulation points? —Jason Coronado
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| | | | | | o.k. so let me get this right: poa doesn't necessarily dictate dof. poa refers to the axes a given object can rotate around, but dof refers to the limitations (or lack thereof) in space a given object can move around in. according to eric, i may use (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | | | Re: articulation points? —Eric Sophie
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| | | | | | (...) It seems so, Jenifer has brought to light that the two don't always correspond, and or there can be differences. It's pretty interesting, although I never really thought about it seriously before, I just build stuff. ;) (...) Well, more so (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | RE: articulation points? —Bram Lambrecht
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| | | | | (...) However, a device is made up of several objects. Each component, if treated separately, has six degrees of freedom. Thus each component of, for example, the human arm (reduced to an upper arm, lower arm, and hand) has 6 DOF, for a total of 18. (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | | Re: articulation points? —Eric Sophie
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| | | | | | | Not to be a goof, but, OMG! Bram is Crazy Smart! I gotta go a take some more vitamins and drink Carrot Juice! Ahhh! I see the concept much the same, I figure if we refer to a POA in a Mecha model as the counting scheme, we won't get alot of run away (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | | Re: articulation points? —Henrik Johansson
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| | | | | | | (...) Very interesting thread. A bit OT (and picky ;) mabye, but about the human arm: If you examine your arm closley you'll find that the rotation of the hand actualy comes from the elbow witch rotates the under arm. The wrist only actes as a dual (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | | | | Re: articulation points? —Jason Coronado
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| | | | | | | | i never really gave it a thought about the hand not having rotation of its own accord, but rather gets it from the elbow. that solves a huge problem i'm having with my mech. you see, i'm having difficulty with my mech holding his weapon because it's (...) (22 years ago, 20-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | | Re: articulation points? —Steve Baker
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| | | | | | (...) >be honest have yet to come to a definitive answer. The (...) Opinion seems to be divided on the meaning of this term. In my field (computer graphics), I'd say that each joint in the mechanism had between zero and six degrees of freedom, but (...) (22 years ago, 21-Nov-02, to lugnet.robotics)
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| | | | | | | | Re: articulation points? —Anders Isaksson
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| | | | | | "Steve Baker" <lego-robotics@crynwr.com> skrev i meddelandet news:3DDC4185.404050...ail.net... (...) Agreed. (...) Not agreed. In mathematics (and statistics is just a part of math), you are not limited to 3D space, and higher spaces need more (...) (22 years ago, 21-Nov-02, to lugnet.robotics)
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| | | | | | Re: articulation points? —Rob Limbaugh
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| | | | | Everything I've ever seen mentioning DOF refers to absolute reference points (a focus, if you will, or origin) that the range is controlled by. In terms of articuation, each DOF corresponds to a joint, which is a fixed focus point that the range (...) (22 years ago, 20-Nov-02, to lugnet.robotics)
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| | | | | | | Re: articulation points? —Eric Sophie
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| | | | | | You present interesting aspects of the term, could it be that the term has many meanings and really if we understood it correctly we would do justice to the proper meaning. Context is everything, yet you raise ideas and examples that indeed (...) (22 years ago, 20-Nov-02, to lugnet.robotics)
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| | | | | | | | Re: articulation points? —Jennifer Clark
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| | | | | | (...) I think you've hit the nail on the head here Eric. To me, the most logical way of looking at a robot arm would be from the point of view of the end effector, i.e. what it can and cannot do. The way the arm moves to get there may be of less (...) (22 years ago, 20-Nov-02, to lugnet.robotics, lugnet.build.mecha, lugnet.technic)
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| | | | | | | | Re: articulation points? —Trevyn Watson
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| | | | | | | (...) Here I go, tossing my 2 cents in to the fray: I would say that any differential drive on a flat surface has 3 DOF: -Assume it drives along the X axis (thats 1) -it can rotate around the Z axis (2 now) -once it rotates it can drive along the y (...) (22 years ago, 18-Nov-02, to lugnet.robotics, lugnet.build.mecha, lugnet.technic)
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| | | | | | | | | Re: articulation points? —Gordon Bentley
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| | | | | | | | (...) Exactly. Another way to look at DOF is that it is the number of things that have to be specified to define a particular configuration of the system. In other words how many RCX outputs does it take to drive. Another thing to keep in mind is (...) (22 years ago, 22-Nov-02, to lugnet.robotics, lugnet.build.mecha, lugnet.technic)
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| | | | | | | | Re: articulation points? —Gordon Bentley
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| | | | | | The main reason it would make sense to quote the total DOF is that is determines the volume the arm needs or is able to work in. For example imagine a snake-bot with a dozen 2 DOF joints. It can reach around objects to position it's effector. So it (...) (22 years ago, 21-Nov-02, to lugnet.robotics, lugnet.build.mecha, lugnet.technic)
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| | | | | | | | Re: articulation points? —Steve Baker
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| | | | | | (...) The trouble with this is that it's not necessarily true. Take 100 Lego turntables and connect them up into a vertical column. By this measure, it has 100 DOF - but as a mechanism, it has no more flexibility than a single turntable (1-DOF). (...) (22 years ago, 21-Nov-02, to lugnet.robotics)
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| | | | | | Re: articulation points? —Geoffrey Hyde
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| | | | All this talk of articulation points reminds me of an actual splined robot. Basically, it was a series of convex circles through which ran a series of wires, with a space in the middle for a spray hose or pressure cleaning equipment to pass through. (...) (22 years ago, 23-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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| | | | | | Re: articulation points? —Mike Fusion
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| | | | A few years back i was showing my platform arm )now defunct) to a friend of mine in engineering,and while talking about degrees of freedom and he said something about half a degree of freedom. I have done some research and have founf nothing on this (...) (22 years ago, 24-Nov-02, to lugnet.build.mecha, lugnet.technic, lugnet.robotics)
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