Sunday, July 3, 2011

Working on the Gripper

It was 118 degrees outside so I just stayed in doors and worked on my droids gripper arm.
My L16 Linear Actuator came in and I had planned on using it in my CPU arm. In the photo its positioned where it should be in the tube. As you can see the L16 is about 1 inch too long. Sure I could cut out the breadpans to accommodate.
However I noticed it seems to be about the right length for the gripper arm's tube.
The L16 fits inside Tom D. Waterset gripper tube like a glove. This is a pretty good pairing up. Even the hole around the black nylon tip is the exact size!  The next step was to use the existing hole  you see and drill it wider. Then tap it for a 1/4-20 thread.
The thin aluminum I just tapped isn't going to be enough to maneuver this later with a servo. So I took a low profile 1/4-20 nut and sanded it down so I could slip it in between the tube and the L16 .
Hopefully this is going to be strong enough to muscle the arm up and down hundreds of times without failing.
This is going to be very tricky to pull this off. It has to be screwed in just the right amount. If you go too far you start eating into the plastic of the L16. 
Upon further tweaking of this build. I decided I had to push the L16 further into the tube and remove more aluminum material I marked with black. I used a dremel to cut remove the material.
Then I marked a squarish area I'll need to file away until the front of the L16 can slip through it.
Now it sits flush when its fully retracted. Otherwise you don't want it to go inside the tube and snap off the gripper.
I cut this small tube off to act as a shim to make a tighter fit for the gripper to attach to. Its not my idea method, I'd rather drill and tap something but I'm not in the mood to take the L16 apart  yet.
Now its ready for some test fits in the breadpan. This next tass is going to be difficult to do when you mount these for your first time. You have to make sure it don't hit the skins when it goes up and down on its right. At the same time on the left you have to make sure on the other side it don't hit the hinge on the door. Which is usually fine when the door is open. When it closes check to make sure the hinge don't hit the tube and closes properly. So you gotta find the sweat spot in the middle of that and have your hole on the breadpan drilled in just the right spot to clear the left, right and up and down or this arm won't work right.
I added a short threaded rod during test fitting that I'll use to mark where I'll need to drill a hole in the breadpan. Since I pushed the L16 into the tube deeper the end of the tube is hitting the back of the breadpan. So I marked the area I need to remove and its off to the Dremel. Its pretty hot outside cutting this stuff. So far we broke a ten year record of 116 to 118 outside! Ouch.
Now its shorter and ready to install. I'm not sure if this would fit inside without removing some of the back it barely fits in after I shortened it.
This is how I mounted the gripper arm in my breadpan with the servo. Now its time to install it and hope it works. Without the gripper on the tube worked electronically clearing where it needed to. 
In this photo I'm using a tube to hold up the arm. The reason is I have to take the photo and can't operate the transmitter at the same time. The other reason is it didn't work:(

It took 6 hours of work to get to this spot. The bottom line is the servo couldn't handle the weight. I had to remove the gripper and now it barely works rising up. I don't know why it worked fine in the tests before this. So this is version 1.0 of my development of getting the gripper to work. 

The next phase will involve upgrading the servo to something more heavy duty. I might also take apart the L16 and change how it attaches to the gripper. The ultimate thing is to have the gripper open and close. I have a couple of ideas on how to do that. I need to do that because as you can see in the video. The door won't close unless the gripper claw is also closed. Its very tight in the box but over all I'm happy I have gotten this far in my astromech build.

I'm going to order a shorter version of the L16. This one is servo operated instead of using a Styrene 10 motor controller for it like I'm using now. That comes with an advantage of being able to limit its travel via coding. Another thing is I can shove it further into the tube and have more meat for the servo to screw into the tube so its not so flimsy. I might get a slight thicker tube and start over. Its basically a simple aluminum tube with a nylon plug is all.

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