Adding Homing to the SCARA

After much thought I just super-glued the micro switches onto the SCARA arms:

I have had big problems in the past with interference from stepper motor phase cables. So it was a relief that the RC filters worked (like magic). But I also twisted cables as that also helps.

• I have been thinking about this problem and I think the answer is the "old" RS-232 current loop concept. Not the actual RS-232 current loop, but a pull-up resistor (between 1k and 10k) and a dedicated twisted pair signal and ground connection.

The standard GRBL build assumes you have a Z axis for the Homing procedure. I do not so I downloaded GRBL V1.1 and recompiled it for X and Y axis only.

After carefully aligning the arms with "jog", I ran the homing routine and recorded the stopped position (X=214.75 and Y=-124.25 degrees). With the stop position I can go to zero home after a Homing procedure.

After increasing the step size from 1/16 to 1/4 the "SCARA" steps are obvious (note the image is about 50mm across and 1/4 step is less than 0.4 mm so big steps are oscillations from overshoot):

Somewhat annoyed that after Homing the machine position (not the work position) is not zero. This could be a problem for some G code commands (G28/30 for example). After some research I found that I need to enable:

  #define HOMING_FORCE_SET_ORIGIN

in "config.h".

Setting the machine position to zero is acceptable. I can then set G28/G30 to the work home position.

A minor point is the the nuts and bolts come loose pretty easily. I don't want to over torque them. When I am finished playing with the setup I may glue the nuts and bolts.

Well this project is pretty complete now. Many things learned for the next version.

I made up a quick webpage to present a video of the SCARA: http://amaze.surge.sh/

AlanX