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6dof (Six-Axis hexapod) with complete 3D motion

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Posted: 2011-07-18 15:09 
Well this project is exactly what it says it is... but im guessing you weren't thinking this?!

This is a 6dof Stewart platform hexapod.
A Stewart platform is a type of parallel robot that incorporates six servos arranged in a prismatic layout.
The servos are mounted in pairs to the base, crossing over to three mounting points on a top (Target) plate.
Devices placed on the Target plate can be moved in the six degrees of freedom in which it is possible for a freely-suspended body to move.






These are the three linear movements x, y, z (lateral, longitudinal and vertical), and the three rotations pitch, roll, & yaw.

Now the interesting part.. :lol:

This six-axis Hexapod is not entirely or solely the only Hexapod to be part of this project.
My plan is to mount a "Puppet hexapod" or "Slave Hexapod" to the Target plate. This Hexapod wont have any servos or electronics with in it 'nor will it be powered! the legs will be jointed using a similar build to this, but not entirely this:

This is to give the legs structure and so they can also move in the correct way when the Target plate moves.
Please ignore the indirect driven tibia. this leg is from an earlier design for a different project, but is the only example i have.

So to tell the story in short, i will be simulating a hexapods body movements
I dont quite plan to show what the Hexapod will look like, and in actual fact its a Octopod! but this will come later.

I recently posted about the programming of such a device but id like to start here by asking, does anyone have experience with a Stewart Platform, running on the Basic Atom Pro28?

anyway there it is, i hope its of interest?!

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Posted: 2011-07-18 15:51 
Birthday present? Happy birthday!

I don't think you'll find too many people driving a Stewart Platform with ah BAP 28!

Looks like it worked out quite nice, all the links (legs?) and such. Is it scaled to a real platform? I.e., have you preserved the geometry?

I'm guessing you could start with a single pair of links?

Have you started to work out some of the leg relationships? Hum, you do have the "triangles" moving in two planes... That might get complicated!

I have my own geometry to work out. My "new" ('84 surplus) Scrobot ER-III JAR (Jointed Arm Revolute) arm turns out to be more then just a simple 5-axis arm. The distal joints are run from timing belts OVER the proximal joints, so the end-effector (gripper) stays in the same aspect (same plane) as the shoulder and elbow joints are moved. Which means, no simple 3 joint IK (ignoring base and grip axis)! And there are two servos that work in tandem to give the wrist rotate and tilt.







Alan KM6VV

Good luck!

Alan KM6VV

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Posted: 2011-07-18 17:19 
Hi Jonny,

Very interesting project! You sure got a nice setup using the LM parts, well done!

But I'm not sure if I understand what you are planning to do. You are talking about hexapod body movements. Do you mean six legged hexapod or a six axis alignment system, or both? :? :lol:

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Posted: 2011-07-18 17:36 
I've seen images of this hexapod system before, but it never dawned on my that the top plate has lateral movement! Very interesting... Not sure what you're doing with it, but it is cool! ;)

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Posted: 2011-07-18 18:12 
innerbreed wrote:

I dont quite plan to show what the Hexapod will look like, and in actual fact its a Octopod! but this will come later.
................
anyway there it is, i hope its of interest?!


Hi Innerbreed,

Didn't even take time to celebrate your birthday, eh? Or is this the result of too much birthday imbibing? It is very much of interest. Your Stewart Platform,especially when enclosed in glass reminds me of missile silo platforms that were designed to isolate a sensitive missile from shockwaves transmitted through the surrounding terrain. Or similarly of secure conference rooms that were raised so they could be inspected underneath as well as isolated so they didn't transmit sound vibrations. You are not up to anything nefarious are you? :shock:

Of course not. Why would we ever think that about the creator of the animatronic alien? :P A Hexapod that is really an Octopod? Either you're going to have one really confused, schizophrenic pod, or you've embarked on some weird gene splicing. :twisted: You haven't be rereading Mary Shelley lately have you? :roll:

Once again you have me totally enthralled :D

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Posted: 2011-07-18 18:16 
RoboTed wrote:
Your Stewart Platform,especially when enclosed in glass reminds me of missile silo platforms that were designed to isolate a sensitive missile from shockwaves transmitted through the surrounding terrain. Or similarly of secure conference rooms that were raised so they could be inspected underneath as well as isolated so they didn't transmit sound vibrations.


Or Space Shuttle Simulators? :wink:

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Posted: 2011-07-18 18:52 
that is gonna look sweet and jim how much would you want for another diy controller the kind you made for zenta


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Posted: 2011-07-18 19:31 
Hexzilla wrote:
that is gonna look sweet and jim how much would you want for another diy controller the kind you made for zenta

You'll have to get in line for one of those beauties. I'd like to have somebody build one for me too. :D I want to use a touch screen based display/keyboard system though. :D

8-Dale

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Posted: 2011-07-18 19:41 
I have endless SES Alan! no ,i built this a few night a go.

ok 'first excuse.... this is a few beers later.

The plan for the Target end effector is to simulate the same out put as would a hexapods body when performing in "body moves mode".

So if you can imagine a Hexapod sitting in the top of the target plate from the centre of the body. and the passive legs "sprawled" out.
The idea is to have the Six-Axis plate 'perform the same movements as would a Hexapod robot would do if in body move mode.
A simulation of those moves.

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Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk
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Posted: 2011-07-18 20:58 
with this system i kind of know how it should all be worked out but again im not sure how it would all look on the screen, as a working code.

'll try to explain:

The inverse kinematics problem is that i know that every Ball joint on the target plate has 3 values (x,y,z) in a 3d coordinate system.
So we have the cartesian coords(3x1 vectors) of the platform in the home position, then a projection of each position once the Target Plate has been told to move. not sure how to explain it.

maybe im thinking in a more complicated way. maybe its simpler than this, im not sure?! its would be nice to think of this as a Delta Robot with 3 Points of movement with in a 3D system but this is 6 points of movement + also introduces another 3 coordinates of "pitch, roll, & yaw" and has become far more complicated.
There are some excellent papers on the web on how to work out the IK on this but i cannot seem to get this into a program.

After the weekend ill try some more.
thanks for your interest. :D

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Jonny Poole,
Freelance Concept Art & Animatronics, 3D Art and 3D Modelling, as well as Physical Modelling, Mechanical design, and illustration.
http://www.innerbreed.co.uk
Create, Innovate, Inspire.


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Posted: 2011-07-18 21:24 
The "classic" examples of the Stewart platform I have seen put the "base ends" in one plane, and the "table ends" in another.



I can't help thinking that would make the calcs easier. I suppose the table ends ARE in a single plane, but I'm not so sure about the base ends!

Have fun!

Alan KM6VV

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Posted: 2011-07-18 22:05 
[quote="Robot Dude"][quote="RoboTed"]Your Stewart Platform,especially when enclosed in glass reminds me of missile silo platforms that were designed to isolate a sensitive missile from shockwaves transmitted through the surrounding terrain. Or similarly of secure conference rooms that were raised so they could be inspected underneath as well as isolated so they didn't transmit sound vibrations.[/quote]

Or Space Shuttle Simulators? :wink:[/quote]
:mrgreen: :mrgreen: :P :P


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Posted: 2011-07-19 02:08 
Robot Dude wrote:
RoboTed wrote:
Your Stewart Platform,especially when enclosed in glass reminds me of missile silo platforms that were designed to isolate a sensitive missile from shockwaves transmitted through the surrounding terrain. Or similarly of secure conference rooms that were raised so they could be inspected underneath as well as isolated so they didn't transmit sound vibrations.


Or Space Shuttle Simulators? :wink:


Space Shuttle...what was that? :?

Okay, Robot Dude, you forced me to look it up. :D You are much closer to the mark than I was as space shuttle and other space vehicle simulators are among its many interesting applications

On the other hand, though quite wide of the mark, I was still absolutely correct: it did remind me of the structures I cited however unlikely or impractical that would have been. :roll: :oops:

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Posted: 2011-07-19 04:36 
Ok, I think I got it now. So you are going to place a "puppet hexapod" on the target plate. Is that an animatronic project? The cool part of this idea is that you can design your "puppet" with very slim legs and make it look very realistic.

Good luck with the math, sounds like a fun challenge.

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Kåre Halvorsen, Zenta
-----------------------------------------
Zenta's blog
http://zentasrobots.com/
Zenta's YouTube channel
http://www.youtube.com/ZentaOlbaid
-----------------------------------------


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Posted: 2011-07-19 10:09 
what so is this gonna be animatronic or not oh and thanks a lot jim for messaging me back about the controlller


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