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Thread: Let's Discuss Kinematics, Shall We?

  1. #51
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    Re: Let's Discuss Kinematics, Shall We?

    Quote Originally Posted by gonzo View Post
    Hi guys, it's an interesting topic that you're talking about.
    I'm not an expert in kinematics, but I've learnt it for a year and implement it
    in some of my robots like phoenix hexapod and Katana Industrial arm simulation.

    But I think it's time to talk about a whole new level, maybe DYNAMICS will be a good
    point to start. I've been dreaming about whole body force-interactive robots.
    Imagine adding COMPLIANCE CONTROL to Phoenix hexapod so it reacts when we push or pull
    its legs. That would be wicked cool...
    Well, in theory, you can add sensors to find the load of a servo, but it will take a bit of work. You will have to wire up a current sensing resistor in between botboard/ssc-32/arc32 board and your servo's power line and sense the current by sensing the voltage across it... You then take the voltage across the resistor and pipe that into a differential amp and connect the output of the differential into the A/D ports of the botboard/arc32...

    This can get messy with 18+ servos. Robotis servos are a huge advantage in this department in that each servo has its own micro inside that serves as the serial interface, current/load sensing, temp, encoder, and etc...
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  2. #52
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    Re: Let's Discuss Kinematics, Shall We?

    This is all very interesting stuff guys and love reading it, but sad to say its way above my head to understand, love to implement this 1k into my ed 209 aka the scout 6dof, but i guess im dreaming lol. but carry on guys all good to read.:-), oh btw is flowstone any good for bipeds?? i might be able to understand a gui icon based interface better than code.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  3. #53
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    Re: Let's Discuss Kinematics, Shall We?

    Quote Originally Posted by 4mem8 View Post
    This is all very interesting stuff guys and love reading it, but sad to say its way above my head to understand, love to implement this 1k into my ed 209 aka the scout 6dof, but i guess im dreaming lol. but carry on guys all good to read.:-), oh btw is flowstone any good for bipeds?? i might be able to understand a gui icon based interface better than code.

    Welcome back MIKE!!! I actually have never heard of flowstone. Zenta (Kare) on these forums and the Lynxmotion forums have a successful biped working. It's a very scout-like reverse knee design, which he incorporated kinematics into. Maybe he has an Excel PEP program or something that he can share with you...

    I've abandoned all works in bipeds for now since I'm trying to concentrate on hexapods... Mike, I'm not sure if I've ever recommended this book, but you'll see that I've recommended this book many times:

    [ame="http://www.amazon.com/Theory-Applied-Robotics-Kinematics-Dynamics/dp/1441917497/ref=sr_1_1?ie=UTF8&s=books&qid=1303075806&sr=8-1"]Amazon.com: Theory of Applied Robotics: Kinematics, Dynamics, and Control (2nd Edition) (9781441917492): Reza N. Jazar: Books[/ame]

    This is the only book I needed for coming up with body translations... But I would highly recommend browsing the pages of the book online before you buy, the same texts have different effect on different people...

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  4. #54
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    Re: Let's Discuss Kinematics, Shall We?

    Hi tom, yeah its good to be back after being so long away. Thanks for the recommendations on that book ill have a look ty. Sorry to here that your not into bipeds lol but hexapods are cool to. currently working on my T1 from Terminator lol.will be remote controlled to start with then convert to pc mini itx based system.

    Omg Tom just looked at the book on Amazon lol the equations are way bevond me, lol thats why i never get to program what i build lol .
    Last edited by 4mem8; 04-18-2011 at 01:43 AM.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  5. #55
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    Re: Let's Discuss Kinematics, Shall We?

    4mem8 - I also highly recommend the same book! Your concern about the equations is understandable, but after having studied the book for a few months the equations aren't nearly as bad as they first look. The important part is to walk threw the book slowly, and as you move forward each equation is built on some part of the last. If you jump into the book even in the middle of the second chapter the equations would look like a night mare! Hope that helps!
    -Scott

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    Re: Let's Discuss Kinematics, Shall We?

    Sarendt: yeah i tend to agree with you, very much like digital electronics, i build a lot of circuits, look at the whole package and its daunting, break it down into sub sections and digital blocks it becomes easy to construct. check these circuits that i built a 32 channel i.r remote halfway down page, quite daunting but broken down no problem.http://www.robosapienv2-4mem8.page.tl/4mem8-Robot.htm its just that im not good on math lol, so not to sure if i can understand it that well, but i will go ahead and order it and see.
    Last edited by 4mem8; 04-18-2011 at 04:49 AM.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  7. #57
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    Re: Let's Discuss Kinematics, Shall We?

    Just another endorsement for that book~


    After seeing it in this post I went to my University's library and checked it out. It's a great read so far!
    -parallax

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    Re: Let's Discuss Kinematics, Shall We?

    sounds good then parallax, looks like my brain will be scrambled lol after reading it. and probably will be ignoring my wife for a few months lol.mmmmmmmmm now is that good or bad lol.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  9. #59
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    Re: Let's Discuss Kinematics, Shall We?

    I just want to point this out - something that I was stuck with understanding kinematics and legged robots and the software behind it:

    Implementing inverse kinematic DOES NOT make your robot walk... Kinematics can only tell you where the end effector (tips of the leg) need to be given the body is (x,y,z) and going to the next (x,y,z) and etc...

    Here are the "layers" of code you will need to make it walk (at least the layers that my software is structured).

    Navigation - This is the layer which I tie my sensor inputs to feed the gaiting layer which is below. For those of you who are using remotes/radio controlled, you can replace this layer with the controller interface software (such as for the PS2 controller like in many of LM's kits).

    Gaiting/Body Position - This layer is where the walking gaits and the body roll-pitch-yaw is written. A few constants are only needed(such as how big are each step, how many paces, etc.). This layer also sequences the legs, since you have to have at least ONE leg up in order to "cycle" through a walk/rotation/run/etc... For example, this is a sample line of code that I use to call up certain gaits:

    ripplewalk(1.0,0.0,2.0,5)

    This makes the bot do a ripple walking gait, step size of 1 inch on the x axis, 0 inch on the y axis, and 2.0 inch on the z-axis, and it will walk this way for 5 paces.

    Inverse Kinematic - This layer takes the constants from the gaiting/body position and calculates out the position of the end effector (leg tip) in order to accomplish certain body and leg orientation and positioning. (This is where Reza's book comes in handy).

    Angle/Pulse Calculation - This layer is takes the position of the end effector and translates it into angles of each servo for the end effector (leg tip) to be at the position that was calculated above. Once you have to angle, it's a matter of just simple proportion to calculate out the correct PWM for each servo. (This layer uses simple trigonometry and trig identities to solve since the femur, tibia, and the coxa are all known).

    LOWEST - Servo controlling. For most of us, this is just a small piece of code to send a string to the serial port to control our servos through SSC-32. For ARC32 users, this could just be PWM syntax... This layer also takes care of the different "signs" you have to put in, because you may have to add or subtract certain PWM offsets depending on which "side" the leg is attached to (left side of the bot, right side of the bot which has a mirroring effect).
    Last edited by tom_chang79; 04-18-2011 at 03:38 PM. Reason: poor grammar :P
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  10. #60
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    Re: Let's Discuss Kinematics, Shall We?

    @4mem8 - I'm sure you will enjoy your time, maybe you should see if your wife wants to help? Mine asked if she could learn kinematic's with me and help me :*) Also your bot's look really sweet! I am reading through your page now.

    @Tom_Chang79 - that was a great review of the software and motion control! I always thought of IK as the glue between what you wanted and getting there. So it was up to me to decide where the robot was to go (either through remote control or some type of navigation algorithm) and then I feed that to the IK software for that particular robot. Details about speed, gait and ground topography would also be feed into the IK software. This would then produce values that would tell us how much to move the servo's. That seems to be in sink with what your saying, you just said it better.

    Cheers,
    Scott

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