anyone know of any Machinekit kinematics for hangbots?

[Doug LaRue]

I've got a MaslowCNC and there's discussions on moving off of the 8bit Arduino and PC software to an integrated system.  

Since the Maslow CNC is a CNC machine, but not your typical one, my thoughts went directly to Machinekit. So I thought I'd ask if anyone

knows of any previous work on Machinekit for a hangbot. The Maslow CNC uses 2 geared DC motors with encoders with chains hanging down

and connected together at the router motor.

M1         M2

--\         /--

   \       /

     \   /

       V

     router

knowing there's some code to work with already might help.

Two main features of interest: hangbot kinematics and DC motor encoders.

Thanks.

[ce...@tuta.io]

Aug 10, 2019, 02:09 by doug....@gmail.com:

I have no idea if somebody is using Machinekit for Hangbot. But there are (is) transformation module for CoreXY (which I tested), this - I think - could work on similar principle.  In goes XYZ cartesian, then it is transformed by magic of linear algebra to another space and then you feed it to hardware.

DC motors and encoders should not be problem. With MKSOCFPGA it should be possible to directly feed PWM to H-bridges.

Cern.

[TJoseph Powderly]

Hi,

Linuxcnc calls the kinematic 'bipod'

its pretty simple polar graphing

History goes back to cable driven crane by NIST

and to Hektor the spray painting robot ( interesting anti sway techniques in a proprietary language )

google up   linuxcnc bipod   to see demos and videos

like this   https://github.com/mattvenn/linuxcnc-bipod/blob/master/bipod_stepper.hal

since the machines are so simple, they are typically stepper, but the etch-a-sketch conversion used servos and encodere (iirc )

There's differences between LinuxCNC and MachineKit so it's not going to be plug-n-play

hth

tomp

[Doug LaRue]

Thanks!  There is talk about porting the original code to work on GRBL-ESP32( by Bart Dring ) but it ends up being almost the same as the Arduino in that the system

requires another computer to work with the robot.  An embedded computer like RaspberryPi and BeagleBone Black means the controller is also the computer so it

becomes more of a self contained machine.  I think it's still up in the air as to which way the upgrade will go and I'm just trying to help them along with my little knowledge

of Machinekit's capabilities( still have a delta/Mini Kossel 3D printer running Machinekit/CRAMPS ).

BiPod, great and thanks.  I found the git repo of the museum piece Matthew Venn and while it's not using DC motors and encoders, it's very close as it uses encoders

with stepper motors.

Thanks for the very useful information!

BTW, if you don't know about Maslow CNC, it's a 3 axis bipod router which does full sheet( 8' x 4' ) routing where the router is hung and weighted(with 2 bricks ) and

the kit and router costs < $600.  Another nice feature is that because it's a bipod/hangBot its foot print in the shop is very small compared to a horizontal full sheet CNC.

Doug

[b...@basdebruijn.com]

Hi Doug,

 

As others have said, there seems to be a similar configuration. But if it’s not perfect then it’s relatively simple to create your own kinematics for your setup.

You also mention encoders, since you seem to want to use a beaglebone, you can have a look into the eQEP encoders. There are 3 of them, you seem to need 2. http://www.machinekit.io/docs/drivers/hal_arm335xQEP/

Not sure what this means for your hardware connection, going from whatever voltage the encoders use to the BeagleBone voltage.

 

You can also look into the driver you’re going to use. If it’s a driver which accepts your encoders and can drive your motors, then you could provide the driver with pulse/dir signals. This is not a closed loop back towards the beaglebone, although with the correct settings you won’t loose pulses.

 

Or if you can do some electronics (power to the motors), you could think about driving the motors with 2 PWM outputs and reading the encoders directly back. Nice closed loop setup.

 

Bas

[Doug LaRue]

Hi Bas,

  I was able to find some sample code in the museum piece by Matthew Venn.  The encoders used on the MaslowCNC are built into the motors but

all the parts are there to get started with.  That is if the Maslow developers are interested. I think one of them is but it's a big step up from the current

Arduino and custom Ground Control software(python).  They already have built a custom driver shield for the Arduino so they would probably look

to make a new custom board for whatever is next.

But the information provided here will allow them to better evaluate the task of porting to Machinekit.  Thanks everyone!

Doug