Contact and Coil | Nearly In Control



OWI-535 Robot Arm with USB Controller from C# and .NET

I got the OWI-535 “Robot Arm Edge” 5-Axis robot arm and USB Controller add-on for Christmas:

The robot arm comes as a kit that you assemble yourself, and my 3 year old and I had lots of fun putting it together (it helped to have some tiny fingers around, honestly). It comes with a manual controller that allows you to rotate all 4 joints, plus the gripper. It’s fun to play around with, but let’s be honest, everyone wants to hook it up to their computer.

Unfortunately the software that comes with the USB controller works on Windows 7, but “32-bit only”. That was a little annoying, but hey, I didn’t really want to stick with their canned software anyway. I figured I would see if I could get it to work from C#. I was surprised to find a great site by Dr. Andrew Davison in Thailand who wrote some Java code as part of his site for his book Killer Game Programming in Java (chapter NUI-6 Controlling a Robot Arm, which doesn’t appear in the book). Surprisingly he went as far as to do the inverse kinematic equations so you can give the arm a set of X,Y,Z co-ordinates (in mm) in “world frame” and it will calculate all the join angles to get to that location, and then used timed moves to get the arm into that position.

His Java library uses libusb-win32, and that library has a .NET equivalent called LibUsbDotNet. The API’s don’t appear to be the same, but thankfully I managed to find a thread on SourceForge about controlling the OWI-535 using LibUsbDotNet. So, over the course of a couple of nights, after the kids went to bed, I ported Dr. Davison’s Java code over to C# (quite easy actually) and replaced the libusb-win32 calls with LibUsbDotNet API calls. It worked!

Here is the .NET solution that I wrote called TestOwi535. I used Visual C# 2010 Express Edition to write it, so that’s free. Also, you must download and install LibUsbDotNet first and run the USB InfWizard first to generate a .inf file (you have to do this with the robot arm plugged in and turned on), and then use that .inf file to install LibUsbDotNet as the driver (technically you’re installing libusb-win32 as the driver and LibUsbDotNet is just the C# wrapper).

If you right click on the C# project in the solution explorer, you’ll find 3 options for startup object: MainClass is the original code I found in the SourceForge thread, but it’s just proof of concept code and only moves one joint in one direction for a second. The ArmCommunicator class is an interactive console application that allows you to move all joints (and control the gripper and light) by typing in keyboard commands. Finally the RobotArm class is the full inverse kinematics thing. In the last case, make sure you start with the arm at the zero position (base pointing away from the battery compartment, and all joints in-line straight up in the air, gripper pointing directly up, and gripper open). It will do a move to the table, to the front right of the arm, close the gripper, and then move back to zero and open the gripper.

Unfortunately that’s where you start to see the obvious deficiency of the arm: it has no position feedback. That means even though it tracks its position in the code, the physical position eventually drifts away from the internal position tracking, and the arm eventually doesn’t know where it is (it’s just using timed moves). One of the biggest areas where you could improve it is to change the joint rates so that it knows that the joints move faster when going down than when going up.

Still, it’s a neat little toy for the price. I’m going to start hunting around for a way to add joint position feedback, as that would really improve the performance. I also want to rewrite a new module from the ground up that allows concurrent joint moves (this one only moves one joint at a time). Ideally you want to control this thing in “gripper frame” instead of “world frame”.

Happy hacking!

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  • Jeremy Sluyters · February 5, 2012 at 9:49 am

    Sounds like the perfect Christmas present!

  • Andy Watt · April 11, 2012 at 2:11 pm

    Nicely done! I plan to get my arm to wave at me to tell me I have new mail at work. My desktop is often covered by VNC windows so I need something to actually raise my attention. 🙂

    Thanks for doing the leg work, especially with the Java port – I found that lib too and had considered doing the work: very pleased to find a well-rounded C# environment off the peg!

    Feels good to have uninstalled the horrible flash environment.

    Thanks again


  • Younes Najif · April 13, 2012 at 11:44 am

    Hello Mr. Scott, i have the same robotic arm but with different vendor and product ids, i tried your C# program but there was no response from the arm, even though i changed the vendor and product ids in your program so it can recognize it. can you please guide me on what to do to make it work.
    this is my email: [email protected]

  • abdelrazzaq · November 20, 2013 at 10:34 am

    Hi… can i have a copy of the c# code please.. i just cannot find the solution explorer 🙁

    [email protected]


  • Idham · March 14, 2014 at 3:46 pm


    Thank you very much for this article, that helped very much, just one question, can I implement this with a windows phone application to control the arm ?

    Thanks again,


  • Pete Baron · December 25, 2015 at 7:06 am

    Awesome article Scott, very nice of you to do all the leg-work so I can start to really play with my new Christmas present right away 🙂 I’m hoping to integrate some motion control with visual position feedback (a webcam positioned behind and above the arm) using the OpenCV library for all the heavy lifting.

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