Problem with Dobot Magician Coordinate frame


#1

Hi,

I am using the API to control my Dobot Magician to draw a straight line with the pen for testing purposes (x = 200 … 300 and y = 80, z = -60). Robot and paper are both on a plain table. I am sending the commands manually as shown in the python example but using the SetPTPCmd method with linear interpolation. The line, however, is not straight along the x-axis of the robot but rotated in the x-y-plane about the robot’s z-axis by approximately 15 degrees, not even intersecting with the robot base. Is there any way to calibrate the robot?

Thanks,
Lukas

Ps. There seems to be a similar problem with the orientation of the x-y-plane with respect to the x- and y-rotations. When drawing a circle, half the circle is drawn in mid-air, seemingly along a slope, even though the z-axis coordinate in the command doesn’t change.


#2

Hi,

I’m observing the issue you mention in the postscript. Currently I’m discussing it with the support for nearly 2 months now and still there is no solution so I’m not happy about it either.

You should have a sheet of paper about A3 size that have top-down image of the bot and 3 pairs of colored dots.Use this sheets instructions and the calibration menu from Dobot Studio to calibrate. Make sure you home the arms before starting the procedure. The calibration is done by positioning the arm to the points by eye so there is degree of error and from my experience so far do not expect too much.
The X axis vector you talk about does not seem to be strictly perpendicular to the bot base. It vary depending on how good the homing is and there seems to be a slight offset on the base rotation but 15 degrees is a bit too high error.

Good luck
Hristo


#3

Hi Hristo,

many thanks for your reply. Unfortunately, my Dobot Studio is not working (issue described in a different topic) so I guess I am left with a not adequately functioning robot arm? Do you know by any chance if there is any equivalent functionality embedded in the Dobot API that I could use for that purpose?

Many thanks,
Lukas


#4

Hi,

I have not explored the API in detail. I played a bit with the Blocky stuff and there is homing function but I don’t think there is calibration functionality in the API but can’t be sure.

Regards.


#5

Use the calibration paper to calibrate the robot as Hristo said, and before you home Dobot, better wait about 20s to make sure all the sensors are well stabilized.