Official Luthiers Forum!

Thanks Kevin,

I had the photo on my computer for reference but could not find the manufacturer.

Nelson I either got that photo from CNCZone, or Bruce Chaffins from the CNCBrain!

He designed one very similar that could easily be home built, which is exactly what I intend to do when I build my machine.

I actually need to build two machines or buy one and build one. I need a machine dedicated to carve my gunstocks on, and would be able to do guitar necks and bodies as well. But I also need a huge light weight superfast 5 axis machine for carving foam, or I need a used robot with a fairly heavy playload capacity and long reach. I am leaning toward the bot cause I can find them for around $1500

I think that is probably a no brainer.

Mike

That is an interesting video, Kevin!
The name "hot wheels" comes to mind.

Nelson,
I saw the Nexen rollers first hand several years ago at an engineering show. They are actually very nice and my thought was that these could be good for a cnc diy build. They are definitely better than a standard rack & pinion.

_________________
Jim Watts
http://jameswattsguitars.com

I just need one more machine...and it needs to be a 'real' 5-axis (so no using an articulated arm)...but I WANT a robot arm! Where and what are you looking at for $1500? Most of the Fanucs I see for sale are in the 7-10K range, but I know there are places where you can score one cheaper. I found out yesterday that I'm going to have to retro a controller (and derive the kinematics!) on a Hitachi 6-axis with about a 6-foot reach over the next few months.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob,

This is a Fanuc s500 for $1500 is what my friend told me the guy wanted. It has a 15kg limit to the load, so that may be a problem if you are mounting a large spindle on it. He is supposed to have several, but I don't know how many at this price. I don't need the controller since, I am supposed to have the new software for the CNCBrain before the end of Jan for testing. He told me this week in a ph call that it is that close and because I have been so patient, and mostly silent, I get to test it. It does now have reverse kinematics as well as being what Bruce calls a physics engine.

I will email you the link for the bot. I don't really want to spread that info too far till I get one in house! I am interested in one for foam carving. Other than money for the purchase and the retrofit of the CNCBrain, I will have to put up a new building extension to house the thing. It has a reach of nearly 9 ft!

Mike

Are you using it for one very fixed app, Mike? The reason I ask is that if you plan on programming it in any sort of motion except for point-to-point joint interpolated motion you'll need to know the constants for the inverse kinematics of the robot.

Deriving those experimentally is a serious undertaking (both technically and time-wise), and you can't do any sort of interpolated motion (linear) or offline programming without them.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob that is one of the reasons I want the new CNCBrain software asasp. Bruce told me that the Brain could actually map everything, store it along with all the axis extents, ( I think that is the right word) the max speed for each axis with max load.

Now whether or not that results in having a working machine, I know not!

Btw the $1500 includes the machine, controller, all electronics and a teach pendant. Might not even have to have the Brain. The guy said it would also take gcode so maybe all the bad stuff is already done. It is 6 axis, with a 9ft reach and 15kg load capacity. He only has 4 of them so I have to decide quickly. You want the email?

Mike

The problem isn't something software can solve. It would be like software saying it could plug into a servo and tell you the pitch of the ballscrew attached to it. Deriving the constants for the inverse kinematics cannot be done by software and is quite difficult.

Go to where the robots are and check one out under power. Make sure the control and the teach pendant work well and that all axes jog properly. Calling the used robot market a minefield would be generous. You might be able to retrieve the offsets for the axes from the controller somehow, which would make retrofitting a controller possible, though with Fanuc's history of locking stuff up I'd say odds are low.

I'll have to drive or fly to wherever it's held to check out any robots I'd consider purchasing, so unless he's in Toronto and sells a lot of them then I'm probably not in the market

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Can you guys explain the robot kinematics for us that don't speak robot?
I'm guessing this has SOMETHING to do with the limitations of where a given axis can be at a given time relative to all the other axes at a given time.
Thanks
Nelson

The kinematics are the series of constants and functions that define the limits of motion of the robot. The inverse kinematics of a robot is a function that translates a set of X,Y,Z coordinates and an orientation (yaw, pitch, roll) into the actual positions of all the robots joints required to reach that position. So it answers the 'if I want my hand here, where's my arm have to be?' question.

The length of every joint in the robot, as well as the offsets from one joint to another, are required to make the equations work. All errors accumulate. All of these must be determined experimentally, unless they can be pulled from the memory of the original controller somehow. And you still need to understand how to use the values if they can be acquired.

http://en.wikipedia.org/wiki/Robot_kinematics
http://www.soton.ac.uk/~rmc1/robotics/arkinematics.htm

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services