With one of our crew out, I've been working double duty all week, so I don't have all too much to report on this week. One of the things that came up is the need for something a little more robust then the RobotGeek Gripper for our RobotGeek line. The InterbotiX line has the Parallel Gripper, and we actually made some prototypes that use that gripper with RobotGeek servos a while back, but it never really went anywhere. Upon revisiting the project with our slightly newer, slightly stronger servos, we found that it actually works out pretty well. We made a jig for drilling the extra holes needed, and made some new prototypes. Matt came up with some clever ways to mount everything and the gripper seems to do pretty well.
I toyed around a little with the 3D printer over the week, intent on making some new gripper fingers. I started of by printing the original finger file, which turned out decently. I think opening up the rails would make it move smoother, but I also had a sanded-down bottom plate it could attach to, so I forged ahead. I tried a couple of other designs.
A parallel gripper works by connecting the servo motor horn to two swings arms. The swing arms then connect to two finger pieces. The finger pieces are on a plate with parallel rails. As the servo rotate, the swings arms bring the finger plates in or push them out. This means that the maximum movement of the fingers is defined by the servo rotation and the swing arm length. So by changing the size and shape of the fingers, you can change the size of the object you can grip. But since the overall distance the arms move doesn't change, this means that you can only grip objects in a range. So If I can normally grip objects between 0 and 25mm, and I modify my fingers to be 25mm apart, I can only grip things from 25mm to 50mm. Anything below 25mm wide and I won't be able to grab them. For some tasks, this works out.
Matt is experimenting with cutting/modding the existing fingers and has had some luck. He also had the idea to mount 3D attachments to the cut-down fingers, so I printed out some fingers designed for a soda can. I didn't put much thought into the design, so it's kinda ugly. Because the gripper has such a small travel, I don't think this gripper will really work - you'd have to be super accurate or you'd be more likely to spill the can before you could pick it up
Still, there are a lot of grippers you could design that would be actually useful. We've got a couple secret designs in the work. Hopefully next week I'll be able to share some more as well as some improvements to our other 'bots.