Hexapod Info
Posted by
daveland@n...
on 2000-05-03 12:39:11 UTC
Hi
Most people who saw the hexapod asked the following questions?
1) Why did you take the hexapod to NAMES?
The hexapod in the NAMES PHOTOS is a six axis milling platform that is used
to debug and demonstarate the EMC software that NIST has developed. We took
the hexapod to NAMES to illustrate the strong technical foundation of EMC.
We feel that gathering a strong user base is important to the future of EMC.
To this end the six axis capability is rarley found in low end let alone free
software. We wanted to demonstrate that EMC is not a "Toy".
2) What can it do?
The hexapod at names can only move in cartesian (X,Y,Z) coordinates. This is
due to current EMC software limitations at the g-code interpreter level. So
it mimics a 3 axis mill with the tool moving (the triangular platform) and the
work fixed (resting on the floor). The platform is suspended by cables and is
quite rigid in the x,y and Theta plane. The rigidity is poor in the +z direction
(up against gravity). So cutting is limited to low force applications. They
have sucessfully cut blue strofoam with a dremel tool. At NAMES we just let
the table move and amaze people since it looks like it is floating in air when
hung from the thin cables.
3) How does it work?
Well that is a bit tough, but I will try and describe it. The
easiest motion to identify is +z and -Z they are intuitively produced by running
all 6 motors at the same rate up or down. This yields +z and -Z motion. Note
that a constant feed rate on the motors though will not produce a constant +z
or -Z velocity. This is due to the changing angle of the cables as the platform
rises or falls. So you need math to convert the cable length into z axis position.
EMC has a customized driver for the hexapod style machine that computes cable
length from the desired Z axis ( or x,y,z cartesian coord) position given in
the gcode. It uses this "inverse kinematics" to determine the actual moves the
cables (joints) must make to get to a desired xyz position. You tell it the
XYZ and it computes cable lengths for the 6 axes.
So the lowest levels of the EMC hexapod software run in the "joint domain"
which equates to cable length in the hexapod case. The machine just runs from
one set of cable lengths to another set as movement is commanded. This is similar
to the 3 axis mill except that there X=X and Y=Y and Z=Z.
Is this a "special" version of emc?
3) not really. The march 15th release with a somewhat specialized .ini file.
If you want to try running it in a
stand alone mode with no hardware, contact me off list and I can set you up.
dave
Most people who saw the hexapod asked the following questions?
1) Why did you take the hexapod to NAMES?
The hexapod in the NAMES PHOTOS is a six axis milling platform that is used
to debug and demonstarate the EMC software that NIST has developed. We took
the hexapod to NAMES to illustrate the strong technical foundation of EMC.
We feel that gathering a strong user base is important to the future of EMC.
To this end the six axis capability is rarley found in low end let alone free
software. We wanted to demonstrate that EMC is not a "Toy".
2) What can it do?
The hexapod at names can only move in cartesian (X,Y,Z) coordinates. This is
due to current EMC software limitations at the g-code interpreter level. So
it mimics a 3 axis mill with the tool moving (the triangular platform) and the
work fixed (resting on the floor). The platform is suspended by cables and is
quite rigid in the x,y and Theta plane. The rigidity is poor in the +z direction
(up against gravity). So cutting is limited to low force applications. They
have sucessfully cut blue strofoam with a dremel tool. At NAMES we just let
the table move and amaze people since it looks like it is floating in air when
hung from the thin cables.
3) How does it work?
Well that is a bit tough, but I will try and describe it. The
easiest motion to identify is +z and -Z they are intuitively produced by running
all 6 motors at the same rate up or down. This yields +z and -Z motion. Note
that a constant feed rate on the motors though will not produce a constant +z
or -Z velocity. This is due to the changing angle of the cables as the platform
rises or falls. So you need math to convert the cable length into z axis position.
EMC has a customized driver for the hexapod style machine that computes cable
length from the desired Z axis ( or x,y,z cartesian coord) position given in
the gcode. It uses this "inverse kinematics" to determine the actual moves the
cables (joints) must make to get to a desired xyz position. You tell it the
XYZ and it computes cable lengths for the 6 axes.
So the lowest levels of the EMC hexapod software run in the "joint domain"
which equates to cable length in the hexapod case. The machine just runs from
one set of cable lengths to another set as movement is commanded. This is similar
to the 3 axis mill except that there X=X and Y=Y and Z=Z.
Is this a "special" version of emc?
3) not really. The march 15th release with a somewhat specialized .ini file.
If you want to try running it in a
stand alone mode with no hardware, contact me off list and I can set you up.
dave