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Thread: SMALdog

  1. #1
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    SMALdog

    Thought I would post a few details about my new quadruped, SMALdog (Sorta Maybe Almost Littledog). (I was originally calling him "Littler Dog" for lack of a better name). He's a bioloid robot inspired by Boston Dynamic's Little Dog. I started assembling on yesterday, and was able to find enough time last night to get the IK worked out, and today got a default gait going pretty decently.

    SMALdog is using 12 AX-12 servos, a variety of bioloid brackets, SES tubes for the lower legs, and a simple sheet metal frame to tie everything together. His ArbotiX robocontroller is doing a full IK solution for each leg.

    Here's a quick video of the default gait:


    The default gait I've got right now is just a simple ripple gait, but he's already doing almost 20cm/s in a straight line, and 30 degrees/second turning in place -- better than Issy's highly-tuned gait performed at CNRG. (Needless to say, this bot may very well replace Issy as my fire fighter, he's smaller too, only 8" long).

    Now onto the fun part - developing a geometrically stable non-periodic gait engine to maximize his speed. Future plans for this bot also include adding an IMU for stabilization, springs in the tibias, and adding sensory to the legs (my eventual goal is to be able to actually run with this bot...).

    -Fergs
    Last edited by lnxfergy; 12-09-2009 at 05:21 PM. Reason: Robot finally has a deserving name!

  2. #2

    Re: Littler Dog

    Wow... Excellent choice of axis!

  3. #3

    Re: Littler Dog

    Wow yet again! I love to quality of IK solution being run on the uC thats great to really show the abilities of modern robotics and how far it has come to the consumer level! I love the representation, done wonderfully!

  4. #4
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    Re: Littler Dog

    Looks realy good!

  5. #5
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    Re: Littler Dog

    Quote Originally Posted by MikeG View Post
    Wow... Excellent choice of axis!
    I concur, Mike. The hips are really quite innovative, imho. And the performance has to speak for itself!
    I Void Warranties´┐Ż

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    Re: Littler Dog

    Great work as always fergs...I really like the symmetry between the front and back of the bot...I'm also really impressed with you IK work you do. Can't wait to see more.

    How do those hip twist servos work? Are they really helpful?

    DB

  7. #7
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    Re: Littler Dog

    Turning without them would be tough on the servos. And balanced gaits would be impossible.
    I Void Warranties´┐Ż

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    Re: Littler Dog

    Wow!

    Thats awesome work on both the IK/programming and the design. Seems like the COG are relative low too. Placing the hip at top like you did was a really good idea! I'm wondering, does your Littler dog even shift the cog while walking? It seems like the gait are fast enough for avoiding the body to tip over when lifting a leg. May I ask how many cycles of IK calculations you are doing per sec?

    Excellent and very inspiring work as always, congratz! Looking forward to see more of this project.

    -Zenta
    Last edited by Zenta; 11-28-2009 at 12:18 AM.

  9. #9
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    Re: Littler Dog

    Quote Originally Posted by Zenta View Post
    Wow!

    Thats awesome work on both the IK/programming and the design. Seems like the COG are relative low too. Placing the hip at top like you did was a really good idea! I'm wondering, does your Littler dog even shift the cog while walking? It seems like the gait are fast enough for avoiding the body to tip over when lifting a leg. May I ask how many cycles of IK calculations you are doing per sec?

    Excellent and very inspiring work as always, congratz! Looking forward to see more of this project.

    -Zenta
    He's not shifting his COG yet. Frankly, he's still running the simplest ripple gait conceivable (he is, after all, only 2 days old). His stride is currently limited by the fact that he falls over when I increase the stride much more. I've got a geometrically driven gait in the works, but it's not quite ready -- that gait will shift the COG in order to maximize stride length.

    He's currently doing 2 IK calculations for each leg forward motion (one to put it in the up and centered position, and 1 to put it on the ground at the front of a stride), and then of course 6 cycles per leg while on the ground, giving us 8 calcs per full cycle. He's then doing 30Hz linear interpolation between points. The interpolation for each cycle is currently 65ms, so a stride length of 100mm, gives us forward velocity of about 20cm/s (2 full cycles/sec). Certainly, the number of IK calcs could go way up (but I haven't tested what the max rate is... something I probably should do. It's all fairly un-optimized though).

    This project has definately slid to the top of my interest list, so there will certainly be quite a few updates coming down the line.

    -Fergs

  10. #10
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    Re: Littler Dog

    Ok, thanks for the information.
    Quote Originally Posted by lnxfergy View Post
    He's then doing 30Hz linear interpolation between points. The interpolation for each cycle is currently 65ms, so a stride length of 100mm, gives us forward velocity of about 20cm/s (2 full cycles/sec). Certainly, the number of IK calcs could go way up (but I haven't tested what the max rate is... something I probably should do. It's all fairly un-optimized though).
    I'm not sure if I get the 30 Hz interpolation part. Do you update each servo every 33mS with the value from the interpolation calculation?

    Are you going to share your ArbotiX code one time?

    -Zenta

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