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Thread: It's ALIVE!

  1. It's ALIVE!

    My first robot walks for the first time today! It's pretty rudimentary still, but I'm pretty happy with the movement considering its my first attempt.

    At the moment, the legs are a bit ungainly. The distals are a bit too long. I'd originally intended each limb to have 4 dof, but decided the power costs and programming complexity weren't worth the extra dof. I've redesigned them and am waiting for Shapeways to finish printing them. The new ones will be shorter and have receptacles to which I will attach rubber feet.

    I still have to attach a battery for improved autonomy, and I hope to ditch the ArbotiX in favor of an Edison.


  2. #2

    Re: It's ALIVE!

    Those legs look pretty cool when it's scrunched together, though :-)
    Are you using Nuke or your own code?

  3. Re: It's ALIVE!

    Quote Originally Posted by jwatte View Post
    Those legs look pretty cool when it's scrunched together, though :-)
    Thanks! The redesign will be similar, just not as long. And, as you can see in the video, the pointy tips have poor traction.

    Quote Originally Posted by jwatte View Post
    Are you using Nuke or your own code?
    I'm calling into the ax library on the ArbotiX to interface with the servos, but the rest is home brewed ... reinventing the wheel, but I want to learn.

  4. #4

    Re: It's ALIVE!

    as you can see in the video, the pointy tips have poor traction
    Are you doing IK? If not, the slipping may be simply because the feet don't move exactly straigt compared to the body/ground.

    reinventing the wheel, but I want to learn
    I wrote my own IK/walking too. Not a bad way to go :-)

  5. #5
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    Re: It's ALIVE!

    Nice work! Looks beautiful when it lower the body and the legs folds like a half sphere. The rather long tibias might be a problem in some cases though, like the need of expanding the initial leg positions.

    Keep up the good work!
    Kåre Halvorsen aka Zenta
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  6. Re: It's ALIVE!

    Quote Originally Posted by jwatte View Post
    Are you doing IK?
    Yes, I am. I have to say I'm pretty impressed with the Arbotix. It's computing the IK on 6 limbs at 20 Hz, and the only reason it isn't going at 30 Hz is that the ax12a bus seems to saturate even though I'm sync writing. 20 Hz is still not as smooth as I'd like. Does anyone have a suggestion as to how I might reduce latency on the Dynamixel bus? Or is the solution to go with more advanced servos?

    Quote Originally Posted by Zenta View Post
    Nice work! Looks beautiful when it lower the body and the legs folds like a half sphere. The rather long tibias might be a problem in some cases though, like the need of expanding the initial leg positions.

    Keep up the good work!
    Thanks, Zenta. You are correct about the length of the tibia. I'd originally intended there to be 4 servos per limb, and the longer tibias made more sense. But I got concerned about the power requirements for 24 servos, as well as update frequency. After actually seeing the thing in operation, it's become apparent that shorter limbs would make for more stability, not to mention less strain on the servos.

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    Re: It's ALIVE!

    Quote Originally Posted by tigakub View Post
    I'd originally intended there to be 4 servos per limb, and the longer tibias made more sense. But I got concerned about the power requirements for 24 servos, as well as update frequency. After actually seeing the thing in operation, it's become apparent that shorter limbs would make for more stability, not to mention less strain on the servos.
    You can run 24 easily. I had a 4dof version of the phantomX a couple of years ago and it wasn't an issue.


    https://www.youtube.com/watch?v=Ywg8VOPoiH4

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    Re: It's ALIVE!

    The darwin-op/nimbro-op/hr-os1/5 frameworks easily push goal positions to 20+ servos at 125Hz at 1Mbps with sync-write and no servo feedback using an embedded-PC for IK and packet building and FTDI+STM32 (cm-730 or arbotix-pro) for pushing the packets to the bus. If there is not a long timeout or latency somewhere in the arbotix ax12 library or your code, then it is possible that the arbotix is just too slow to handle everything running at its measly 16MHz.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  9. Re: It's ALIVE!

    Oops. Looks like I might have toasted my ArbotiX. Doh. I was trying to do a bit of simple profiling to see how much time was spent calculating the IK solution, and I guess it didn't like the way I was doing things cuz when I plugged it back in ... nothing. Guess it's over to the ArbotiX forum to see if Kyle or someone else at Trodden has any opinions.

    Before it went out, I was able to bump the update frequency to 30 Hz, so I guess the difficulties I was having before was due to something else, not saturation of the bus as ticain and Kevin suggest.

  10. Re: It's ALIVE!

    UPDATE. Got my new ArbotiX, new tibias, and completely rewrote the sketch. Now the the IK and gait control are done 100% on the ArbotiX. I did a bit of profiling, and even with floating point matrix math, the IK goal transformations, and IK/FK calculations are taking about 25 ms (+/- 3ms). Slow, but good enough for pretty smooth interpolation.

    Click image for larger version. 

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    https://youtu.be/qOTtPviXGuU

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