Progress on the Robot Arm!
First joint of the Open Source Robot Arm
Thanks to the Hong Kong Parcel Post, I got my metal-gear servomotors last week, and then thanks to work commitments, they had to sit taunting me on my workbench the whole week. Luckily, I had a chance to do some assembly work this weekend, and got a couple of the major subassemblies put together. As you could see from the earlier post, I had the base assembled, and it was short work to put the base rotation servomotor in place.
You have to make sure that when you assemble the deck, you put the servo in so that it is at the center of its rotation when the arm is facing forward. Once that was done it was short work to get the deck put on. I went ahead and clipped the little screws that hold the servo horn on short, so they won’t rub on the acrylic frame and scratch it. I also added a trio of modified furniture casters to provide a bearing surface for the rotating platform. The oomlaut guys used M8 screws with acorn nuts, but that would also scratch up my beautiful red acrylic, so I chose to go another way. If you look at the flickr set, you can see how I did it. I had to trim them a bit to allow for the small M3 nuts on the bottom of the platform to have sufficient clearance.
You can see that the first joint of the arm is supported by two servos- note that in order to make the parts fit without undue stress on the lasercut plastic, I put one servo inside and one outside the mounts. I also had to make sure that the motors were both turned to the same degree of rotation before mounting them. The way I mounted them, the first joint can swing from fully to the back of the platform all the way to fully front. This should be perfect, and maximize the reach of the arm.
Assembling the second joint turned out to be much more problematic, and necessitated several tear-downs and re-assemblies. As far as I can tell from the (albeit sparse) pictures on the oomlaut website, it appears that the motors are mounted on the outside of the arm assembly, but as far as I can tell, this will not fit without really bending the lasercut frame. I don’t want to do this as I do not want to break the plastic, but I am at a loss about what to do. I am planning on sleeping on it, and ordering a couple of the motors that the oomlaut guys suggest and see if they fit better. According to the specs posted on the motor source website, they are exactly the same size as the ones that I have now, so I am kind of puzzled.
Next up- second arms joint, gripper (which is its own puzzle, to be sure) and the control mechanism. (Yes, I am still hacking around with my old Playstation2 controller!)
