Hi All,

I tried posting this once, it looks like it didn't go through. Sorry if this is double posted, this is my first post on this forum!

I graduated from college a few years ago having studied Mechanical and Electrical engineering with a focus in controls. I currently work for a large industrial automation company as a project engineer for motion control (servo) systems. I have too many hobbies already (I have a full machine shop in my basement), but I have wanted to purchase and rebuild an industrial 6 axis robot for some time now. My original intention was to look for a unit which came complete with a controller and teach pendant, however I caught on early that finding one of these used was either rare or prohibitively expensive.

Not to be discouraged, I decided that with my background in motion control, PLC programming, and access to industrial servo motors/drives, I would be ok buying just the robot itself and interfacing to the existing motors or replacing them entirely. In doing so I realized that I would be writing the control software and would need to teach myself the kinematics. I purchased “Introduction to Robotics: Mechanics and Controls” by John Craig and began studying it along with any college course material I could find that followed along with the book. My goal was to learn the material well enough that I could derive the forward and inverse kinematic equations and program these into a PLC to control the robot.

Unfortunately after a year or so of working at this, I got busy and lost the kick to keep working through the book. It felt like I was very much on my own and was struggling with a few of the concepts. I passed on a number of opportunities to purchase a robot like I was looking for in the <$1000 range, and kind of put the project away on the shelf.

For whatever reason I got the itch to pick it up again now and see if I can’t actually make this happen. I don’t know why I never got involved with the forums before but I’m hoping someone can answer a few broad questions below to get me pointed in the right direction:


  1. Is anyone aware of people trying to do anything along the lines of what I want to do? If so, where can I find information or examples?
  2. Which forums would be good to get involved with? I’ll be wanting to discuss the math of robot kinematics, interfacing to existing hardware, and just the project in general. I really get motivated by sharing the projects that I do, so I think getting involved with an online community would be the best way to keep me on track.
  3. My understanding of kinematics for these robots is that there is not guaranteed to be a closed-form solution to the forward/inverse kinematics of a serial robot, but in the special case of a robot with a spherical wrist, there are solutions possible. Is this correct or is it a fool’s errand to try to derive these?
  4. During all my research, I found very few examples of someone truly working out all the kinematics (the only one I remember was a graduate thesis on the kinematics of a Universal Robots UR5). Does anyone know of an example where someone worked out the kinematics for a 6 axis serial robot with a spherical wrist?
  5. Does anyone know a good place to look for buying a robot? There is an industrial surplus company not far from me at all that often has used robots come through. They are often in the $2000-7500 range, but sometimes, smaller units come in without controllers and sit until they sell for a few hundred. I’d prefer to find something in better shape than I see there, but I’m hoping to keep the actuator purchase around $1000.



I feel confident that if I were to derive the forward and inverse kinematic equations AND I were to find a robot in good enough shape to be run, I have the knowledge and resources to interface to/replace the motors and write motion control code in a PLC to actually use it.

Thanks for taking the time to read this. I am very interested in your thoughts!