Lenny the big dumb bot.

A couple years ago I bought an old IBM 7575 scara robot at a surplus auction. The mechanicals are really nice but the control was completely absent.  I started a conversion using a Mesa card and Machinekit.  I have no serious plans for this but wanted to learn ROS and maybe more about the FreeCAD robot workbench.

The first part of the conversion went well but then I hit a snag and the project sat idle for almost two years.

I got frustrated when I couldn’t make the machine move in cartesian coordinates without errors.  Machinekit/linuxcnc has two different movement modes. ‘joint mode’ allows you to jog individual motors and this worked perfectly. I could move any joint very fast and smooth without errors.  I could also do the homing sequence.  Once the individual joints are homed, you can then switch into ‘world mode’ and jog in cartesian space or execute gcode. The kinematics are calculated automatically and everything should work.

But for me, not so much.  Jogging gave following errors. I verified and re-verified the configuration and everything was perfect but just didn’t work.  I posted in lots of places but never found any help. I don’t think people use these scara bots very much and, it turns out, mine is a little bit different.

I started out calling this thing ‘Gypsy’ after the robot in Mystery Science Theater 3000 but somewhere along the line it changed it’s name to Lenny after the character in ‘Of Mice and Men’  He’s big, strong, and dumb.

I finally dug into it again a couple weeks ago and had a breakthrough. Next step is to start learning something about ROS.


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