View Full Version : robotic arm BS/2 kinematics
01-25-2006, 09:54 PM
Hello i have built a robotic arm. I use the bs/2. Does anyone knows how can i·write··the kinematics equations in the editor, in order to find the angles off the servos for a desired position in space;;i would appreciate any possible example or finished project in order to give me ideas. Thanks.
01-25-2006, 10:30 PM
Just a passing commnet - ALL CAPS is generally view as SHOUTING, and I doubt that was your intention. Unfortunately, some folks are offended when all caps are used for no reason. Personally, I sometimes use a single word or two in CAPS, just for empahsis.
Since analog R/C servos offer no feedback information, you will need to use a servo controller board, which you might well need any way, depending on how articulated this arm is, and what other tasks will be going on concurrently with the operation of the arm. I believe the Parallax Servo Controllers (and perhaps others as well) offer positional feedback, but since I've never used one, I can't say much more than that. The Parallax Servo Controllers can be found here:
01-25-2006, 11:03 PM
Hey, could I see that arm?· Could you post a picture of it?· (sorry I cannot help with your question.)
01-26-2006, 12:07 AM
this is a cross posting- I attempted to help you in the thread you originally started, and you did not respond. I'm removing the other thread in lieu of this one.
Parallax Tech Support
01-26-2006, 02:03 AM
http://forums.parallax.com/images/smilies/turn.gif·What kind of THE KINEMATICS EQUATIONS, i really don't know how to use it on Pbasic, but i use the DENAVIT-HARTENBERG Algortihm, it's really good, but i use it just on paper.... Here 's an arm that i developed a few months ago 4 Goverment Xmas Party.
·if u want more pictures, just ask
Best Regards from Santiago,Chile
01-26-2006, 05:03 AM
thanks to all..i have a few more things to fix on the arm and i will post photos. GoTeN, it would be greate if you could send me a scanned example of the DENAVIT-HARTENBERG Algortihm. thanks.
01-26-2006, 05:28 AM
http://forums.parallax.com/images/smilies/turn.gif·i attach a PDF file with an arm kinematic Denavit-Hartenberg Algorithm. (it's in spanish, i'm sorry, i guess you could translate it with a good software or maybe search on google D-H Algorihm)
·If you need some more information like the matrix and everything, just ask for it.
01-26-2006, 07:09 AM
What is the specific problem you are having? Solving the matricies? Do you have a copy of Matlab?
Parallax Tech Support
01-26-2006, 07:42 AM
Since Denavit-Hartenberg algorithms appear to use matrix math, if you're asking if any of the PBASIC Stamp platforms can do matrix math, the answer is no. I have no experience with the Javelin Stamp, but I suspect the answer on that Stamp platform is no as well. As far as I am aware even the most advanced Parallax platform, the SX/B compiler, has no native matrix math features. Presuming the SX/B compiler supports a macro language (and I don't know that it does) one might be able to design a set of generalized, but limited, matrix math routines (Mat_Add, Mat_Sub, Mat_Mult, Mat_Sum, Mat_Trans, Mat_Sort, Mat_Ident, Mat_Invert, etc). Just remember that many matrix math functions are quite time consuming and memory storage intensive as well.
There MAY be some math co-processors which can handle matrix math, but I've not used any that do, so I have no recommendations there. Here is a web site which offers some freeware macros for Microsoft Excel so that you can use it for matrix math calculations. I'm sorry it's an Italian web site, but I suspect BabelFish or one of the other web page translators might be quite helpful in translating the page if you don't read Italian. Here is that link:
As others have suggested, you might do well to do the matrix math on a PC (by MatLab or whatever means) and then just transmit the resolved parameters to the Basic Stamp for processsing.
Post Edited (Bruce Bates) : 1/25/2006 11:45:21 PM GMT
01-26-2006, 09:41 AM
You're completely right Bruce, but anywahy D-H algorithm its a great exersise.·Then·could get practice with inverse kinematics.
Robotics & Math goes together....·
01-26-2006, 10:27 AM
Is this a real cross-posting? The other post on inverse kinematics in the Robotics forum was from a different user, and was a bit more specific.
Anybody interested in doing higher order math might want to check out an application called Ch, which is a C/C++ interpreter.
It can do quite a bit, is extensible, and freely available for for commercial use (Standard version) or academic use (Professional version).
You don't need to be a student/teacher to freely use the Pro version, if you are using it for personal education.
Here is the url:
01-27-2006, 02:36 AM
Just for interests sake and a laugh, i dug through some of my old notes and found an old program i used on my TRS80 to multiply matrices. Pretty crude and simple, but it worked, and sure beat trying to do it on paper. Anyway, as you can see the math is pretty basic. I scanned the sheet which was a little faded, most of it can be made out fairly easily. You may want to do the " save link target " thing.
Post Edited (kelvin james) : 1/26/2006 6:39:43 PM GMT
01-27-2006, 04:27 AM
thanks all of you. every single answer has helped me. I ll try to consider what you have said and if i cannot come up with a solution i will contuct again..