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  1. #21
    Registered Klox's Avatar
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    There's a company near me that uses the same principal to manufacture flight simulation equipment.....
    I'm going to pay them a visit January.
    I'll see what i can come up with, even if it's only a fact finding mission LOL!

    Klox

    *** KloX ***
    I'm lazy, I'm only "sparking" when the EDM is running....


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    Like that StarWars ride at Disneyland....???



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    Interesting, but those big hydraulic struts would cost a fortune. Precision valves, motors, all kinds of stuff. Hydraulics ain't cheap.

    Electric Muscle:
    However, I read an article in Scientific American about artificial muscle. It seems many types of plastic can be used as 'Electric Muscle'. It might be fun to make a mini hexapod machine using that and a Dremal. The only problem would be it's not really precision so you would have to have some very precision sensors to determine the power you send to them and their positioning.
    Perhaps a mini 1' tall hexapod could be done with a minimum of electronics, and no motors, acme screws, messy hydraulics, etc...
    However, as far as I know no one is selling the 'Electric Muscle' yet. And, you would have to use allot of them because they don't have a great deal of power.

    Air Muscle:
    To get even more weird, I know for a fact you can make 'Air Muscles' for super cheap. They run on compressed air and look pretty cool. Of course, you would have to use allot of them because they don't have a great deal of power.
    Imagesco
    Shadow Robot Co
    Chris's Air Muscle page
    Robot Store UK

    Air Actuators:
    Or, why not just use simple 'Air Actuators'. I don't know much about them but they couldn't be too expensive. Although, again, they don't have allot of power.

    Satellite Dish Actuators:
    The BUDs (Big Ugly Dish - from 4'-15' diameter) have powerful actuators on them. They arn't very fast but they come ready to mount, with an encoder for positioning, have a long throw, and are pretty powerful. You could make a large hexabot! Plug-n-play baby! And, since everyone is moving to cable or the little dish you can sometimes pick up whole systems for nothing.
    I think this would be the best idea for a quick, easy to do, hexapod. Get 6 actuators of the same make and your ready to rock!

    Just throwing some ideas out there!


    Last edited by samualt; 12-21-2003 at 09:15 PM.


  4. #24
    Gold Member chuckknigh's Avatar
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    Satellite dish actuators are an EXCELLENT idea. I wonder if they've shown up at BGMicro, yet? (Mail order electronics surplus, that's located in Dallas)

    I know they have a "windshield wiper" style system available, right now, and the price is right. I'm not sure if it's just an "all or nothing" type of actuator, or if it's controllable.

    As for the air muscles...they're an interesting technology, but they're EXPENSIVE for what they are. They are nothing more than a Chinese finger puzzle, with a balloon inside, and a few pneumatic fittings. That's IT! I had some discussions with their inventors, a few years back, for another project...fascinating and really brilliant idea. They'd managed to increase the pull to several hundred pounds, for a muscle you could hold in the palm of your hand.

    -- Chuck Knight



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    Ok guys,
    I've been reading the replies on Hexapods. Doing some searching. Dang now you got me wanting to build one. I have experience with g-code on a three axis router. Have used DeskNC, and a g-code generator, turbocad and some other. Can write or edit g-code when necessary. Think I can copy and improvise design to build the machine. Here's where I get stuck. On a Hexapod we are working with 6 axis at the same time to make the machine do anything. How do you get from a CAD design to g-code? I know on a three axis machine the g-code generator (either me or software) reads the drawing and assigns x and y coordinates. I have been then going in and editing in the z axis coordinates. If I am understanding the Hexapod there would be imputs from all six axis at the same time to create each movement or function. As an example to move right one inch would take a correct input to all six axis together, each having it's own seperate distance and direction it must travel in order to move straight right 1 inch. Is there a g-code generator that understands to take the CAD drawing and convert it to the six axis of control? Any help would be greatly appreciated. Please just tell me where to go guys (maybe I said that wrong) to find the info I need. Thanks Ron



  6. #26
    Community Moderator ger21's Avatar
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    I think most hexapods you see all use their own custom software. I don't believe there are any standard CAM packages that can generate code for one, but I could be wrong.?

    Gerry

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    foamcutter:
    This site has some kind of software for Hexpods, downloadable. Their machine looks like an upside down hexapod.
    LME Hexapod Machine

    Here is some more code for you:
    Sandia Hexapod - Software Utilities

    Try this page also. He seems very nice. I bet if you asked him he could help you:
    Stewert Platform Notebook

    Or, just search Yahoo:
    Yahoo - Keywords: Hexapod Software


    Also, I would look up all the hexapod pages on the net and email every person involved. You might be suprised how much they help!

    Last edited by samualt; 01-01-2004 at 01:53 AM.


  8. #28
    Gold Member chuckknigh's Avatar
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    And, as I understand it, EMC (free controller package that runs under LINUX) has some limited support for hexapods.

    That's my main concern...I'd LOVE to build one, but controlling it without predesigned software could be a real chore. I've never played with EMC, before...it's supposed to be an industrial type package.

    -- Chuck Knight



  9. #29
    Gold Member chuckknigh's Avatar
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    On a Hexapod we are working with 6 axis at the same time to make the machine do anything. How do you get from a CAD design to g-code?
    In exactly the same way as for any other machine.

    Regardless of how many axes the machine has, or what is required to move it, g-code merely describes the *movement* desired...X axis should move +1.00 inches. That's it!

    It's up to the controller software, to translate that into the instructions needed to move the machine.

    If I am understanding the Hexapod there would be inputs from all six axis at the same time to create each movement or function.
    Essentially correct, though I think there are some movements that could require less than 6 movements simultaneously.

    This is a simple matter of doing some math (remember translations in geometry and algebra?) and creating some instructions from the resulting coordinates.

    Once the equations are described, it's a fairly simple process to change it into the necessary pulses...the programming isn't inherently hard. The difficult part, until recently, was having enough computing horsepower to do it, in real time.

    Is there a g-code generator that understands to take the CAD drawing and convert it to the six axis of control?
    Nope...g-code just describes the movements. EMC translates them into the control sequences...

    http://www.linuxcnc.org is the EMC home page, if memory serves. If I understand the process, correctly, it's just a matter of setup...telling it you have a hexabot, that sort of thing.

    Take a look at http://www.hexel.com/rotobot.htm and see if you can figure out the math for this one. It makes my head hurt! They already have full software available, too, but they sell it *with* the machine, and the whole shebang costs US$85K. Yes, eighty-five-thousand dollars...

    -- Chuck Knight



  10. #30
    Community Moderator ger21's Avatar
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    In exactly the same way as for any other machine.

    Regardless of how many axes the machine has, or what is required to move it, g-code merely describes the *movement* desired...X axis should move +1.00 inches. That's it!

    It's up to the controller software, to translate that into the instructions needed to move the machine.
    Not exactly. On a standard 3-axis machine, the X-axis (1 motor) only moves 1". On a hexapod, all 6 would have to move vs just the 1. If you look at the Sandia link above, their software translates what seems to be 3-axis g-code into the proprietary code that their custom controller runs on. I don't know how EMC handles the hexapod, but I'm guessing that for TurboCNC or Mach2, you'd use 6 linear axis'. Since the majority of CAM software writes g-code for 3, 4 or 5 axis machines, you could convert this code into what would essentially be just another g-code file, but it wouldn't really be readable like a standard g-code file is. Follow me? I bet if you ignored the 4th and 5th axis to start with, the math wouldn't be that difficult to translate x-y-z moves into the 6 linear moves required. It is, just a bunch of triangles, right?

    Gerry



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    Ok,
    As I read your replies I get the idea that there may be actually two ways to control.
    1. standard 3 axis g-code x,y,z would be fed to a controller software that would translate it into impulses to the six motors to make it move. This way your CAD drawing is just converted into g-code same as a standard 3 axis router. The controller software takes the g-code and translates it to the seperate pulses to each motor.

    2. The mathmatical equasions are figured out to make each arm move the specified distance per rotation of each motor and these factors are used to create six axis g-code. ie: CAD design would be converted to g-code using the factors giving you six axis of g-code.
    With my limited knowledge I'm thinking plan #1 would be the way to go if possible. Any thoughts?

    Thanks for the sites to go see and input. I can see I'm going to be doing a lot of emailing, asking questions, and asking for help. Thanks guys, if you have any other ideas please let me know and I will keep you posted. Thanks Ron



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    Any 3- to 6-axis CAM package will do, for example TurboCAD/CAM.

    OK, now you ask yourself “is this guy correct or cracked?” Well, g-code does NOT control your CNC machine. It’s the software that interprets the g-code and converts it into electrical pulses that controls the machine. So, it’s the software that interprets the g-code that will see the command to move “right 1 inch” and properly move the pods legs so that the point of contact between the material and tool moves 1 inch in a horizontal plane. Think about Mach2. It interprets the g-code and moves the CNC machine for you. The “trick” is to think of g-code as describing “what” you want the machine to do while the software figures out “how” to do it.

    OK, so the next question is “what software to use?” I don’t believe Mach2 can control a pod. I’m not aware of any general package that does. If you were to buy a pod, the s/w that comes with it will properly interpret the g-code. For the DIY CNCer, I think we’ll have to write our own s/w. If done correctly, it should be able to handle a wide variation of pods built using similar design principles.

    I’m a software engineer and have worked on hardware control systems (nothing to do with CNC, but the principles are the same). I’m willing to donate some of my time working on the controller s/w (g-code interpreter) if someone is willing to build the h/w.

    --bb99

    There are 10 types of people in this world; those that understand binary and those that don't.


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    bb99,
    Thanks for the offer to create the interpit code. I spent most of newyears looking up pods on the net. There seems to be a couple places that talk about controller code. One is NIST who developed the EMC code using linux as a base. Another is LME Hexapod Machine, the Sandia site listed earlier in this thread, and the The Stewart Platform Notebook also listed earlier. I emailed each asking questions, haven't heard back yet but didn't expect a reply for a couple days because of the holiday.

    By h/w I assume you are talking about the motor controllers (drivers). Are you thinking of something using a PIC chip? I saw a guy on ebay selling some controllers that he sells as a kit with PIC's either pre-programed or not. I will look again at them, try to get the specs and get an auction number for you to look up. I myself have a little knowledge about them, very little actually, but just enough to think maybe it would work. I can assemble electronics, have some basic knowledge but don't know how to design. Let me know what you think. Or would something like gecko drives or any of the numerous other ones out there work? I guess what I'm asking is do you think off the shelf drivers would work or do we need a custom driver? Ron

    Last edited by foamcutter; 01-02-2004 at 10:23 PM.


  14. #34
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    foamcutter,

    I’m purely a s/w guy. In part that’s why I’ve decided to build a CNC machine (I want to learn more about the h/w side). With my ignorance about h/w firmly in place, I’ll make a guess and say any 6-axis linear motion system will do. The pod is not linear motion, rather its rotary motion (at least the design presented at the beginning of this thread). However, that is not an issue since most of the motion control systems described here have no intrinsic linear knowledge. All they do is say “spin the motor’s shaft clockwise/counterclockwise X number of steps”. For linear motion, that translates into Y number of linear inches moved. While for rotary motion, that will give you Y number of degrees of motion for a leg. The trick is to have the s/w produce the correct movements on the legs to produce the desired movement. As long as the motion control h/w can handle moving up to all 6 axes simultaneously, I don’t see any reason not to use off-the-shelf h/w.

    It’s all in the math!

    --bb99

    There are 10 types of people in this world; those that understand binary and those that don't.


  15. #35
    Gold Member chuckknigh's Avatar
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    Precisely...the g-code says to move the X axis 1 inch, and the controller software interprets that, and outputs the step and direction pulses over the pin/s specified in the setup, for however many steps that requires.

    It's all a matter of setup.

    Once the hexapod motions are understood (that's where the math comes in) then writing a program to interpret the g-code, and output the pulses, is not that difficult.

    But, like I said a while back, EMC has *some* support for hexapods, already. Why reinvent the wheel? It even has source code available...maybe a new "module" at most?

    http://www.linuxcnc.org

    -- Chuck Knight



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    I agree that EMC is the most promising platform for the home CNCer. My point is that the motion control h/w can and should be off-the-shelf. The issues that first need to be addressed revolve around the pod itself. For example, since the pod is symmetrical, limit and home switches can be associated with each leg rather then with the base. This would allow full 360 rotation of the pod table without any of the legs inadvertently tripping a limit switch.

    As you said, it’s all in the setup. But, that can’t be defined until the geometry of the pod has been worked out.

    --bb99

    There are 10 types of people in this world; those that understand binary and those that don't.


  17. #37
    Gold Member chuckknigh's Avatar
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    Default Hardware / Software specifications

    What level of detail do you need, from the hardware side of the project?

    The basic geometry is simple...it's a standard octahedron, with some variable length struts. We have 2 possible configurations. (imagine triangles) One has 2 variable length legs per triangle, and a fixed base...this is a traditional hexabot. The other has a fixed leg length, and a variable base length...this is the rotobot.

    With a traditional hexabot, "home" is fairly simple to define, as a return of all legs to some standardized length...the home switch could be within each leg assembly. I don't know if that's how they do it in industry, but it makes sense to me...

    With a rotobot, it becomes a little more complicated...each leg has to return to a predefined position, probably equidistant, at 60 degrees apart. Same disclaimer as above.

    Do you need any other information? I'd think anything machine specific, like the exact leg length, would be a variable...something to set up in a configuration file.

    Seriously, think about it, and let us know the specifics of what you need... I've included a picture of a traditionally designed hexapod.

    -- Chuck Knight

    Attached Thumbnails Attached Thumbnails Hexapod designs?-imagefej-jpg  
    Last edited by chuckknigh; 01-05-2004 at 01:44 AM.


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    Gold Member chuckknigh's Avatar
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    Something just occured to me. This is going to be hard to explain...forgive my ramblings.

    Most of us have no real use for 5 or 6 DOF machines. The majority of our work is done in either 2 1/2 or 3D space.

    So, it might be possible to simplify the design of the hexapod to a tetrapod.

    Thinking about it, it's a fairly simple matter to take something like a tetrahedron and distort it within 3D...it wouldn't give control over such things as yaw, but how many of us would use that?

    It might be a simpler initial project, and would require only 3 stepper controllers (instead of 6), if I have it figured right...the only thing I can't figure out is how to hold the cutter rigidly at the vertex of the tetrahedron. Maybe something like making each arm a parallelogram linkage, so that the end of the strut is always aligned as vertical? I know that'd work for something with a fixed strut length.

    Am I missing something? I WELCOME input...

    Let's see..basic regular Platonic solids are tetrahedron (4 sides), hexahedron (6 sides, cube), octahedron (8 sides), dodecahedron (12 sides), and icosahedron (15 sides). The hexahedron is not inherently stable...the 2 lowest order units, that are inherently stable, are the tetrahedron and the octahedron.

    I might have to play with some models, to see what kind of movements I can get out of these things. If a tetrahedron based model would work, that'd be a MUCH simpler homebuilt project...not to mention a heck of a lot cheaper!

    I'm virtually positive a "hexaglide" tetrahedron would work just fine...not sure if a tetrahedron with a fixed base (traditional design, like the picture above) could be done with ease in a home shop, though...and that's my goal.

    -- Chuck Knight



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    I I’ve been thinking of something like the rotobot but that isn’t a requirement. I’ll begin to play with the math and let you know what I come up with.

    --bb99

    There are 10 types of people in this world; those that understand binary and those that don't.


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    Gold Member chuckknigh's Avatar
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    OK, this is the geometry I'm playing with, now. I'm tentatively calling it a tetrabot, after its base solid, the tetrahedron.

    Compare it to the hexabot, above -- same triangular base, and the "tip" should be able to move by varying the lengths of the struts. The hard part will be keeping the router bit "vertical" but I think I've already solved that problem by using a parallelogram linkage.

    I'll build a model, soon, and test out what is, at the moment, purely theoretical. It works in my mind's eye, though... ;-)

    Hmmm...now that I've mentioned it publically, I wonder if I could still get a patent on it? Wouldn't mind being the patent holder for something simple, like this...

    -- Chuck Knight

    Attached Thumbnails Attached Thumbnails Hexapod designs?-tetraqual-gif  
    Last edited by chuckknigh; 01-05-2004 at 10:23 PM.


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