Protoleg’s first movements

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.

10 thoughts on “Protoleg’s first movements”

  1. IT STOMPS! 😀

    That said, I’m surprised it took 600 lb. What’s the surface area of the end of the leg? It didn’t look like that much to me.

  2. To someone like me who has no clue what the realization of this kind of design project demands, these videos were informative. Now I can blab about the cool thing going on in my maker space with a bit more apparent, if not actual knowledge…

    1. I second that. Seeing the testing process puts the scope of this project in perspective.

      How will the oscillation that was mentioned during the yaw tests be handled? How do you control that when you’ve got this huge steel leg swinging around?

      1. The oscillation in yaw seems to be a recurring problem, going back to Gimpy (and even in evidence on some excavators). Yaw is unique in that it’s not continuously loaded by gravity, unlike the other joints – that means that slop in the pin connections, or oscillations in pump flow have large, visible effects on movement.

        Our initial strategy is to put flow restriction orifices in the valve, to make the joint more resilient to pulsations in hydraulic flow. We’re also going to try to shim the joints to take out backlash, and if necessary investigate some specific types of valves that help deal with overrunning problems.

  3. Now that Stompy has tasted Apple blood, she will want more…

    I can imagine a scene where the new donut shaped Apple headquarters is in the distance and Stompy is making her way to the just completed building (scheduled in about two years from now). Apple employees are all running around screaming.

    Now that would make a great video! Perhaps Microsoft would be interested in picking up the tab.

  4. The pressure test and the function test for the leg looked great. I am very impressed at your progress and it seems that you have the learning curve under control. One very small thing i would like to add would be to control the hoses a little better. When you get full flow to the cylinders, the hoses are going to slap when pressure is applied and released. This is already happening with very limited flow. This is also going to loosen the fittings. There is a product called torque seal (check google images) that would be an easy and quick way to tell if the fittings have loosened up or not.
    Keep at it. I am very excited to see the progress.

  5. AWESOME !!

    In 20 years, when we look back at the demise of apple and ponder the causes…those of us on the inside, will know.
    it all started with a little know hexapod called STOMPY.

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