Sixi Robot Gripper Design Adventures

I thought that the hard part would be making the Six robot arm. Turns out making a two finger gripper is also pretty challenging! I would love to see students take on this challenge to make their own gripper. There’s so many ways to tackle the challenge.

Gripper requirements

The gripper must:

  • Attach to the ISO 9409-50-1-M6 hand
  • Have two fingers
  • Weigh under 1kg
  • Be able to pick up at least 1kg and turn it arbitrarily without dropping it
  • Not crush soft objects like grapes, eggs, or empty cans
  • Have a minimum stroke (movement distance) of 30mm.
  • Run at 12v (max 2a) for motor power.
  • Run at 5v (max 500ma) for logic.
  • Have replaceable fingers that can be customized to different tasks

It would be nice if

  • The gripper would use ModBus (RS485) to communicate with the Sixi robot.
  • The gripping strength could be controlled by the robot.
  • The robot could tell the state of the gripper: position, activity right now, etc.

More to follow as this adventure unfolds! Wish us luck.

Discuss this post in the forums.


How to draw a rectangle in Gcode

So you’ve played with the Makelangelo‘s generated Gcode and now you want to experiment on your own. Cool! Here’s a simple rectangle to get you started.

Now let’s give some values to these parameters:


My method is to lift the pen, drive to a corner, put the pen down, and then trace the rectangle. That means going to five points because we have to come back to the start.

G0 Z90; # pen up
G0 X-10 Y20;  # p1 
G0 Z40; # pen down 
G0 X30 Y20;  # p2
G0 X30 Y-40;  # p3 
G0 X-10 Y-40;  # p4 
G0 X-10 Y20;  # p1 again
G0 Z90; # pen up

And voila! I’ve deliberately done this with the origin away from the center so the numbers are more obvious. I hope you see that in a cartesian system the origin could be anywhere. For example, if it were below and to the left of P4 all the X and Y values would be positive.


Sixi Calibration Tool

The Sixi Calibration Tool helps anyone using a Sixi robot make sure that the robot’s mental and physical states match.

They have to match or else.

If they do not match then the move you expect is not the move you will get. This could very quickly lead to an accident.

Ok, what do we do about it?

There has to be a way to synchronize the mental model and the physical model. The calibration tool is made to fit in one place and attach to the arm in only one way. This forces all the robot joints to move to known angles. Those angles are measured in the mental model in Robot Overlord and then copied to the physical model in the robot’s brain.

Sixi robot joint angles at calibration

JointAngle (degrees)
0 (x)0.0
1 (y)-41.3
2 (z)74.5
3 (u)0.0
4 (v)-33.5
5 (w)0.0