Hexapod designs?

[chuckknigh]

Well, while surfing last night, I found a site that mentioned HEXAPOD designed 5 axis routers. Shortly afterwards I had managed to find a slew of information about these things.

Benefits are said to include no sliding parts, and simplified construction, but with the down side of increased processor power being required.

So, has anyone ever built one of these hexapod systems? They look ingenious. Supposedly they offer 5 or 6 degrees of freedom, and the equivalent to a 5 axis router system, but with the stability of a fixed spindle.

It's an interesting way to think "outside the box."

I've tried to include a picture from one of the sites, but unfortunately it's too big. Here's a URL.

http://www.hexel.com/hexabot.htm

-- Chuck Knight

[jlinhart]

These are also known as stewart platforms (I guess 'Hexapod' is trademarked by someone). Here's a link to a guy that built one.

Stewart Platform

Does anyone know of off-the-shelf or open source software that would be able to run a system like this?

jason

[chuckknigh]

It appears that he is using an X10 control system to translate his designs into control signals. Crude, but obviously it works, from looking at his site. I'm guessing he wrote his own control software.

Other than that, the hexapod/Stewart platform design looks pretty straightforward and simple to build. Of course the Devil is in the details...and this design looks to have a lot of details.

-- Chuck Knight

[ToyMaker]

I one time designed and built a hexapod ...

but it was a six-legged mobile robot .

Guess that doesn't count here though

robotic regards,

Tom

[paulried]

I saw one of these last year that the IMTS show in Chicago but it was a whole lot bigger and the cutting tool was mounted from the pod and the table was fixed. It was from one of the Japanese machine companies but I can't remember which. It was fascinating to watch run and was very fast. I believe it was a cool 1/2 million!!

[chuckknigh]

That's where homebuilding comes in!

Heck, if I had to buy a gantry style CNC router, instead of building one, it'd cost me several thousand dollars! We're homebuilders, on this forum...we don't pay retail.

-----------------------

So...back to my original question. Anyone ever played with one of these things? Built one? Modelled one? Thought about one? Seen software that could run one?

Surely I can't be the only one interested in this kind of thing.

-- Chuck Knight

[chuckknigh]

The guy whose site is listed above...he's reported some amazing results with his. The accuracy of his is less than it could be, and he mounted his spindle on the Stewart Platform.

He reported, in his sweet zone (his most accurate, centered zone) that he was getting accuracy down to .002". He claimed overall accuracy was down to .005" all across his active area, and that was without antibacklash nuts, precision threads, etc. In fact, it was with allthread and X10 control boxes providing the interface.

He's rebuilding (version 2) with ballscrews and proper parts...I can only imagine what the accuracy of that thing will be.

Improved accuracy was supposed to be one of the benefits of this design...that errors don't add up across multiple planes, and the parallel, triangulated construction provided increased stiffness, further increasing accuracy.

This might be worth playing with!

-- Chuck Knight

[EvanRobert]

Originally posted by jlinhart These are also known as stewart platforms (I guess 'Hexapod' is trademarked by someone). Here's a link to a guy that built one. Stewart Platform Does anyone know of off-the-shelf or open source software that would be able to run a system like this? jason

I did a quick search and found a site that might have the information. Check out:

http://www.i-way.co.uk/~storrs/lme/L...odMachine.html

Good luck. I'd like to see more of the Stewart Platform.

Evan

[Fish]

This sounds lilke a project that I would love to get involved in. Maybe a joint project to overcome the large R&D side? Anyone interested?

I have a disc from Okuma showing their product line-up. It shows a Hexapod milling machine in it, with a small description. I have never seen any other information from them on it.

A few years ago, there was a company marketing three different sizes of Hexapods with tool changing. I haven't heard anything since. They did claim accuracy that was within the expected range of your average machining centre. Their design used six ball screws, mounted in pairs to a single milling head platform. Each pair had one in tension and one in compression for increased rigidity. I will take a look through all my old stuff to see if I still have any brochures. If you want, I can send you the info on the Okuma version from their CD.

Adam

[chuckknigh]

I'm not sure there would be a large R&D side to the project. The mechanicals look relatively straightforward, and there is documentation of at least 1 homebuilt unit already, linked at the top of this thread.

And, on a related matter, a linear actuator is a relatively simple thing to build...even considering accuracy and backlash. Since imprecision is not cumulative, like on a gantry machine, the individual members could conceivably be less accurate, and consequently cheaper. (And, easier to homebuild, for someone without a complete metal shop in his garage) For reference, the guy whose site is linked above, got .002" resolution using allthread and hardware store angle iron, on his prototype unit. He's rebuilding it for much higher accuracy, but .002" is pretty darned good!

My concern is control...turning standardized coding into control sequences for one of these machines. Surely, since there are machines available commercially, *someone* has come up with a software library dealing their control. If not, this thing was designed in the slide-rule days...how hard could its control algorithms be to understand? :-)

The only real problem area for a homebuilder would probably be the ball joint. The ball joint requires a rather significant degree of freedom, and no backlash. One common solution I've seen on the attempted homebuilt units, is to use a universal joint. It would provide the level of precision necessary, but has all the grace and elegance of a baseball bat. Surely there is a better solution available. What we would need is the ball joint equivalent to Cranky's rollerblade bearings on gas pipe solution as linear bearings...it's the only really precision part we would need, and with 6 struts requiring one for each end, that's 12 ball joints for a single machine.

I just accessed McMaster-Carr's site, and they're not horribly expensive, but in this type of endeavor, cheaper is almost always better. These may be cheap enough, though I wonder about their accuracy?

http://www.mcmaster.com/catalog/109/html/1043.html

-- Chuck Knight

[ToyMaker]

Panavise, who build electronics holding fixtures, uses a ball joint style mechanism in their vise bases that looks like it could be reproduced in a home-shop. And it has that "elegant simplicity" you referred to.

robotic regards,

Tom

[anoel]

Surely to goodness a simple ball joint from an autoparts store. would suffice. Don't know which ones would work but all cars have them in the steering linkage. So, I'm sure it could be cheap.