Hello robot enthusiasts,
We are happy to report our prototype leg’s first movements!
We are equally happy to report that it takes roughly 600 pounds of force to crush a Macbook G3.
Now that we’re past the orgy of destruction, let’s talk about the fun stuff… safety! When pressurizing a newly constructed hydraulic system for the first time, one must take extreme care. Our systems are pressurized to ~2300psi. That’s 2300 pounds of force per square inch. These are levels of pressure that most people don’t ever deal with and don’t have intuition for.
There are many inherent dangers to working with fluid at these pressure levels. If a fitting blows, the pressurized fluid can send pieces flying with great energy. Jets of the hydraulic fluid itself can also cause terrible injury… a jet of pressurized hydraulic fluid will cut flesh and inject the wound, giving the double whammy of slicing trauma and poisonous injection. Here’s the kicker: these jets are often so thin that they’re effectively invisible. Google “pinhole leak injury” if you want to know what this looks like, but be warned that it’s pretty gruesome.
To try to avoid these potential problems, we pressurized the system to full pressure and just let it sit for a while with everyone standing far away. This gives oil a chance to accumulate in places where it is leaking. The HPU is then turned off and any leaks are addressed. We found a few slightly loose fitting with this method.
Next, we did a “rag sweep”. This involves tying a loose rag to stick and just sweeping the airspace around every hose. If there are invisible pinhole leaks, they will make their presence known by deflecting the rag. We found no pinhole leaks, which makes the following video very boring (but we feel it should be included so you can see the process).
Our first moves were very slow and cautious – we want to explore our full range of motion and make sure we didn’t have any hose or cable pinching happening. We had the system at roughly full pressure (~2300psi supply, ~250psi return) but very limited (1.5gpm) flow, to guarantee very slow motion.
Here are a few range of motion pics:
And the full range of motion video.
Next we’ll be coordinating multiple joints under computer control. Sweet.