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    Not totally on topic but while on a robot course for work I discovered these, very alien like flexipicker robots made by ABB. Very cool video on their page.

    IRB parrallel robots

    Attached Thumbnails Attached Thumbnails Hexapod designs?-irb340-1-2-jpg  


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    Has anybody tried using hydraulic hexapod for milling?

    My idea is to get 12 identical hydraulic cylinders where 6 of them are in the pod and the rest are elsewhere producing the hydraulic control for the pod. So there would be six pairs of cylinders connected with pipes. When one cylinder is moved with stepper and screw, the another will follow.



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    Quote Originally Posted by Jonathon
    Not totally on topic but while on a robot course for work I discovered these, very alien like flexipicker robots made by ABB. Very cool video on their page.

    IRB parrallel robots
    Those are kinda creepy...but oh so cool!! Damn things are FAST too!!

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
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    Gold Member chuckknigh's Avatar
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    WOW! I think I want one!

    -- Chuck Knight



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    Quote Originally Posted by Xerxes
    Has anybody tried using hydraulic hexapod for milling?
    My idea is to get 12 identical hydraulic cylinders where 6 of them are in the pod and the rest are elsewhere producing the hydraulic control for the pod. So there would be six pairs of cylinders connected with pipes. When one cylinder is moved with stepper and screw, the another will follow.
    can you use hydraulic cylinders in open loop control with sufficient accuracy ?

    or, in this kind of setup, do you need a continuous position feedback ?

    12 actuators instead of 6 seems to complicate things a lot although I can imagine that hydraulic rams create _lots_ of force.



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    I want one! This is sooo cool!



  7. #87
    Registered Xerxes's Avatar
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    Quote Originally Posted by andy55
    can you use hydraulic cylinders in open loop control with sufficient accuracy ?

    or, in this kind of setup, do you need a continuous position feedback ?

    12 actuators instead of 6 seems to complicate things a lot although I can imagine that hydraulic rams create _lots_ of force.
    It may work just fine in open loop. Oil is hardly compressible and minimizing rubber pipe lengths would probably make stiff enough positioning.

    12 simple hydraulic cylinders would be much easier to do than servo/ballscrew/whatever struts that are seen in most designs. Also joints at end of struts would be simpler to implement (ball joints will do..).



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    There was a flex picker in the technology museum in Stockholm when I visited, but it wasn't working!!!!! I was gutted.

    Notice they use half round ball joints and just pull the pairs together with springs. The video on the website showing lubrication shows what I mean. Basically you can get huge angular movement and only need pretty basic joints

    Graham



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    Wow, this is really an amazing idea. I really like the hexapod setup. If done correctly it will make for a very cheap and fast and accurate machine with 5 axis. Now we need a good and cheap design for the actuators...



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    Now I am curious... What kind of accuracy could we get if we took a cheap ball screw satellite dish actuator like the one from http://www.burractuators.com/hd_series.htm (I'm thinking the 55:1 gear model) fitted them with cheap stepper motors, automotive type ball joints on both ends, and gave it a shot? How bad a system could this be? Even keeping the out-tilt angles reasonable with a 30" base it would have a workspace over 48 x 48 x 17. For some applications 1/16" accuracy and repeatability in this sort of volume would be more than sufficient. I wonder just how cheaply it could be built and still have use?



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    How expensive would those actuators be? I would guess very pricey! If you used the parts you were summing up I would wager you would spend 500+ dollars and have an amazing machine capable of doing true 3d work at amazing accuracy.



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    Quote Originally Posted by TimKoene
    How expensive would those actuators be? I would guess very pricey! If you used the parts you were summing up I would wager you would spend 500+ dollars and have an amazing machine capable of doing true 3d work at amazing accuracy.
    It is very cheap and easy to get salvage actuators from big dishes...of course, getting 3 matched ones might be tough...

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    I'd say buy new ones... less wear in them so better accuracy, but if you can find a bunch of matched used ones, so be it. If I knew where to come up with the controller hardware so it could be run from standard CAM packages, I would throw this much money at the attempt. Heck, it is cheaper than any comparable 48"x48" XYZ router machine!

    Anyone want to handle the electronics side of things if I put together the mechanics?



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    Hi all!

    This is my first post on cnczone...i'm an electronics engineer and interested in building my own router/mill for quite some time now.

    I learned about the HEXAPOD design two days ago browsing the web and i fell in love with it immediately. I was quite pleased to see a thread about building one over here and i really hope this will be start of a new hobby.


    anyway...about the hexapod:

    I've read this thread and saw that many people question the availibilty for the translation from standard x y z(possibly more) coordinates to the correct geometry for the hexapod.

    Wouldn't it be possibly to solve these rather basic triangle equations with a microcontroller, possibly one for every actuator to keep the program straight forward.

    ANother solution could be to have an old computer buffer the input and convert it all together.

    As of yet i don't realy know exaclty what kinda signals normally go into the actuators controller but i quess these are simple bit trains acting as clicks with every click being one microstep...is that true?????

    in the end i'm just trying to say that i too really want one and i'd like to contribute....possibly in the form of programming a microcontroller.
    I guess that 'll be about the only thing i can help with cuz i haven't got a clue to what technology is available for slides, actuators etc....



  15. #95
    Community Moderator ger21's Avatar
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    I saw a site somwhere that had software that took standard 3 axis g-code, and converted it to 6 axis gcode to run a Hexapod. I think it was a university project, but don't recall. This would be relatively easy to do for 3 axis work. 5 axis work would be much more difficult.

    Gerry

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  16. #96
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    why would you want to convert the G code? It shouldn't be machine specific...right?



  17. #97
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    Quote Originally Posted by mattijs
    why would you want to convert the G code?
    Because it would be a lot easier to write a converter than to write a program that could create g-code for a hexapod.

    Gerry

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    http://www.thecncwoodworker.com/2010.html

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  18. #98
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    My understanding is that the g-code says things like go 6.2 inches in the x direction. This code then needs to be translated into the "language" of the machine that tells the motors how many microsteps to go. A hexapod needs to move all of it's actuators to accomplish even a one dimensional translation.

    Someone mentioned that there is some code available from NIST that does this (using Linux I think). The electronics and software to build the machine driver is beyond my skills I admit, but the machine side of things is doable.



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    Cool Pentapod

    Hi,

    maybe somebody is interested in the latest design from Germany, the Pentapod (Hexapod=six actuators, Pentapod=five actuators).

    You can find a video with a Pentapod, directly milling of molds from sand here,
    and another one showing the Pentapod cutting steel here.

    BTW.: I'm in no way involved with the manufacturer Metrom.

    Regards,
    Fritz



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    Hi Guys,
    This is a very interesting thread, there are some unbelievably cool videos and pics. When I saw the Prsco (http://www.prsco.com/index.html) R series Rotopod working I couldn't stop laughing in amazement of how ingenious the design is.

    I thought I'd put my spin in about 5a machines vs. n-pods. One thing I have noticed about hexapods/rotopods is that they have 3 great translation axis, maybe 1 great rotary axis depending on design and 1 not so great rotary axis. XYZ and a 360 rotary C-axis equivalent are fine (like the R series above) but the A/B-axis equivalent doesn't have a great range of movement. We are designing a 5a at the moment ('we' being a consortium of nerds with a little spare cash lol) to reduce the tooling required for the stuff we want to do. For example if you want to face all of the sides of a 100mm high box it is better to do it with a short face mill parallel to the face being machined rather than a long end mill cutting on the side. You can also do drafted sides without ball nosing down the face or having to buy/make a tapered cutter. Its all about shorter cutters and reduced inventory of tooling. We can do what we want only if we have 360 degrees of movement on both of our 2 rotary axis. The n-pod designs are obviously more rigid but do not seem to (I could be wrong, I haven't spent more than a couple of hours researching) have a practical amount of rotary axis equivalent movement. Its what I see anyhow.

    On the subject of controller translators for a hexa-ma-pod (Simpsons reference lol) I think it is as hard (definitely not simple) as creating translation and rotation matrices that would output the lengths of the 3 sides and one angle of each of the 3 triangles (since the other angle is inferred) that form a hexa-ma-pod. There is also another angle which needs to be defined which is the angle of the plane from vertical/horizontal that the triangle lies within. Sounding a bit more difficult than a couple of scaling factors. Hmmm. For the R-series Rotapod the only side of the triangle that changes length is the 'bottom' side which lies on the circular track. I would assume this would be easier to code for (and less processor hungry) than a hexa-ma-pod that has two variable and one fixed side of each of the 3 triangles. I believe this would be a more rigid design than two variable sides. Once you have the required lengths you equate that to pulses generated by the controller to the drives. The translator would be part of the controller software which would generate required pulses to each of the 6 actuators (not axis) which define the lengths of the side(s), the internal angles of the 3 triangles and also the angles of the planes in which the 3 triangle lie. The R-Series rotapod has another variable which is the relationship of each of the three triangles to each other.

    From what I can gather the three points under the table define the desired xyz and two rotary axis position. Once you know where you want these three points in space you construct triangles back to your 6 pivot points on the machine.

    Please be kind lol. This is all based on 10 minutes of assumption lol.

    Cheers
    Derek



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