Eye-To-Eye Part 5: Mechanical Engineering

Now that the servos are working at the touch of a mouse, all I have to do is make the gimbal, put it in a box, hook up the servos, and away I go. But mechanical engineering has never been my strong point. In fact, my first stab at it is not looking good.

What it looks like

Here’s a brief video of the movement. I’m using the command line to issue very predictable commands. Unlike software, when stuff goes wrong, things actually break in real life (this is experience talking, I broke a servo this way lol), so I needed a very controlled method of moving stuff so that I don’t repeat my missteps.

The Eye Movement – Not Quite Sauron Yet

Problems

There were many problems, all related to either hooking up the parts, or manufacturing the parts. I’ll start with my process for manufacturing.

Centering

The first problem is how to drill a straight hole through a ping pong ball. I have a drill press for my dremel, and I thought it would be relatively simple to put the ball in the hole of the base (pictured below), hold it in place, and just drill through. I kind of expected the ping pong ball to fall apart, but was pleasantly surprised when that didn’t happen. However, what DID happen is that the drill press is not centered – it has some “wobble” so when you press down from the top, it ever-so-slightly curves downwards, but enough to offset the center of the ping pong ball. But, I thought, so what if the ball is not perfectly center? The jury is still out whether this is causing me issues.

Linkage

By far, the biggest problem is linking the servos with the gimbal. I realized that the up-down motion can be hooked up to a rigid link (i.e. piece of a coat hanger hooked into a servo horn), but that I could not use a rigid link for the left-right motion. This is because as the gimbal moves on the y-axis (that is, up or down), it pulls and pushes the rod for the left-right motion. This means that I need a soft link on the x-axis, one that could have some leeway due to the y-axis motion, but also with the requirement that it is rigid enough to push the ball left and right in any y position.

And this is where I’m currently stuck. As you can see from the video, the gimbal is not moving properly at all, and I am all but ready to declare this attempt a failure and go back to the drawing board.

During the second trial, I’ll probably get a smaller diameter PVC pipe (this one is way too big) and I will construct the whole thing out of wood instead of an old cell phone box to make it a bit more rigid. Also, looking at the Eye-See-You design, it looks like the motor for the left-right motion is raised in the axis of the x-rod. This might be a key to getting that smooth left-right motion.

Since I’m a novice at construction, I figure it’s going to take me quite a few tries to get this to work correctly, so it’s a good thing I bought 12 ping pong balls 🙂

Here’s the entire gallery of pics:

As a side note, I realized that I would give up normally at this point and place the half-completed project in a box never to look at it again. But the fact that I’m writing this publicly gives me a sense of accountability and motivation to actually finish the project, so I look forward to writing part 6 of this series, hopefully with more positive results.

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