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Thread: Is there any good information out there on how to generate gaits?

  1. Is there any good information out there on how to generate gaits?

    I've been working on my AX12-based quad. I first tried using Nuke and an ArbotiX to get it working, unfortunately failing because the Nuke generator didn't work for me properly (not those guys' fault at all, of course, I suspect I had dodgy cables or something that didn't interact well with Python's serial code),

    So, I went back and worked out how to do reverse kinematics from scratch. Now I can place my quad's feet where I want them. However, since I am working from scratch, I'm a little at a loss how to construct a good gait. I have my bot walking; the way I do it is like this (given values dx and dy specifying how many millimeters I want the robot to move to the right and forward each cycle) -

    Move robot to its neutral position; each leg moves to a known x,y,z coordinate.

    For each leg in turn
    - move the leg to (x+dx), (y+dy), (z-(hard-coded 'leg off the floor' value))
    - lower the leg back down to the floor

    Once all four legs have been moved, return to the neutral position.

    This is rather jerky, though, and I know there's a better way; I'm just not sure how to figure out what it is. Googling quadroped gaits turns up a lot of academic research papers, but not much that really helps me in understanding the basics here.

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    Re: Is there any good information out there on how to generate gaits?

    I think this is a very hard question to answer because you already answered the hardest part yourself. (putting the feet where you want them in 3D space.)

    Things to work on:

    1) try to get your feet to move in a streight line when the robot is walking, and that feet placement is coordinated so that all feet on the ground move the same distance in the same direction

    2) try to keep your robot's COG withing the triangle created by the three feet on the ground, or on the same plane as the two feet on the ground to keep your robot stable.

    Finally,

    NUKE is a really good solution. Try to figureo out why it didn't work for you. In the least watch quadruped robots on Youtube to see how they do it.

    Good Luck

    DB

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    Re: Is there any good information out there on how to generate gaits?

    Quote Originally Posted by jotheberlock View Post
    Googling quadroped gaits turns up a lot of academic research papers, but not much that really helps me in understanding the basics here.
    You can look into Nuke's and ArbotiX source code to see very practical solution of how this is done. Mike's code is relatively easy to understand.
    You can also search for discussion of gaits, Nuke and ArbotiX on this forum to complement that look at the code.

    I also agree that going back to ArbotiX and figuring out what did not work is an easier way of going about it. That way you would also help this community by using/improving an existing solution (ArbotiX) rather than creating your own custom one.

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    Re: Is there any good information out there on how to generate gaits?

    Quote Originally Posted by darkback2 View Post
    I think this is a very hard question to answer because you already answered the hardest part yourself. (putting the feet where you want them in 3D space.)

    Things to work on:

    1) try to get your feet to move in a streight line when the robot is walking, and that feet placement is coordinated so that all feet on the ground move the same distance in the same direction

    2) try to keep your robot's COG withing the triangle created by the three feet on the ground, or on the same plane as the two feet on the ground to keep your robot stable.

    Finally,

    NUKE is a really good solution. Try to figureo out why it didn't work for you. In the least watch quadruped robots on Youtube to see how they do it.

    Good Luck

    DB
    DB Essentially said what I was going to say. Personaly I'd recomend figuring out NUKE, since it will take many hours to come up with something close to as good.

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    Re: Is there any good information out there on how to generate gaits?

    You can take a look at this write up of the phoenix hexapod. Xan has shared a lot of great info on his gait sequence engine. For another example you can take a look at Gold Rush's source code. Or dig into nuke's source code. All three work essentially the same way.

  6. Re: Is there any good information out there on how to generate gaits?

    Quote Originally Posted by Upgrayd View Post
    You can take a look at this write up of the phoenix hexapod. Xan has shared a lot of great info on his gait sequence engine. For another example you can take a look at Gold Rush's source code. Or dig into nuke's source code. All three work essentially the same way.
    This is very useful, thank you!

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    Re: Is there any good information out there on how to generate gaits?

    Quote Originally Posted by jotheberlock View Post
    I've been working on my AX12-based quad. I first tried using Nuke and an ArbotiX to get it working, unfortunately failing because the Nuke generator didn't work for me properly
    Could you elaborate on what failed? While we've had some minor issues, we've generally been able to walk people through getting NUKE working. I don't recall a thread related to your problem....

    -Fergs

  8. Re: Is there any good information out there on how to generate gaits?

    Quote Originally Posted by lnxfergy View Post
    Could you elaborate on what failed? While we've had some minor issues, we've generally been able to walk people through getting NUKE working. I don't recall a thread related to your problem....

    -Fergs
    I mentioned it in passing in another thread. Basically, the problem was that I'd have my robot hooked up, PyPose installed on the arbotix, all that - but when I went through the sign-checking stage, sometimes (but not all the time) either a leg simply wouldn't move at all, or it would move /after/ I pressed yes or no on the 'did the leg do this' question. Also, sometimes the leg would move very slowly. Strange stuff. This happened on both Linux (Kubuntu 10.4) and Windows 7, incidentally.

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