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Thread: My 4DoF Quad Mech: Numa

  1. #1
    Join Date
    Jun 2011
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    My 4DoF Quad Mech: Numa

    Howdy folks,

    Some of you know me from the Trossen Chat. I've been part of for years. I'm an RL buddy of cire

    I'm working on my own quadruped, eventually for Mech Warfare. This quad is named Numa. Numa was the second of the ancient Roman kings... and so I can use royalty as an excuse to make a purple bot (e.g. I will eventually dye the brackets purple). And yes, I'm aware of the fat-guy video for Ozone's song, Dragostea Din Tei. I don't mind if you choose to associate the name with that

    Hardware specs of Numa:
    -4DOF per leg
    -16 AX-12a servos in the legs
    -Axon MCU
    -Tristate buffer allows Axon to control the dynamixel servos. (Has purple LED to indicate that servos have power!)
    -Can use either Xbee 1.25 mW communication, or serial port communication (Using the Parallax SIP xbee adapter on the robot side)
    -11.1 V LiPo battery for servos, 9V NiMh battery for Axon. TBD how I will power camera and guns.
    -Using dremel, power switches for Axon power, LiPo power, and DC power supply power are integrated into standard Dynamixel brackets

    Obviously I'm shooting for a very similar robot to Immortal, but figuring it out with my own hardware configuration.

    Software approach:
    -Axon runs my own code created with the modules/etc. from Webbotlib
    -Webbot's GaitDesigner format is used for gaits
    -I generate my gaits in this format using Mathematica to do the IK calculations. Using its visualization tools is awesome for verifying what my code actually does.
    -I will be using VB.Net (Unless I learn a new GUI making tool in the near future) to make my own user interface. Input will quite probably use one of these for awesome points.
    -I may eventually have the IK be calculated on the axon, but for now I'm still familiarizing myself with the best ways to do this.

    -Beginning of May: Started ordering parts.
    -Mid May: Made tristate buffer and was finally able to control servos
    -June 12: Finally got the bugs out of my Mathematica code and correctly have my robot walking forwards/backwards
    -June 17: successful remote control of walking with xbee link.

    Stuff to do/determine
    -Give the feet more traction
    -How I will move camera/etc. (e.g. I'd save weight by using hobby servos for pan/tilt)
    -Optimize the gaits for speed and balance
    -Make compensating for changes in center of mass easier
    -How to tie the gaits together to do more complicated walking
    -Design custom body to nicely integrate all of the parts
    -Order the usual Trendnet wireless camera


    And now some pictures!:
    This pic is a few weeks old, but the body is essentially the same. Switches and accessories have been swapped/added in the mean time.

    Animation of top down view of forward walking via Mathematica

    Animation of leg movements via Mathematica

    The servos' battery and its power connector. I like epoxy.

    Combo mutant mount: Axon switch, serial connection interface, and xbee on a parallax adapter.

    Axon and tristate buffer are mounted together on a spring-loaded hinged plastic container. The container was the box for a ring.

    Another pic of same:

    9V battery holder is masking tape + velcro. Real chassis will be nice to have.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Join Date
    Jun 2011
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    Re: My 4D)F Quad: Numa

    And youtube vid.
    [ame=""]YouTube - ‪Sloppy Walking‬‏[/ame]

    The transition between poses is what makes it look so choppy. I might move to a more upright gait. I simultaneously need better traction on the wood floor (apartment below me must hate me if they can hear the stomping), and looser traction on the carpet (it fails to go to it's standing up pose). Wheels parallel to the leg direction might be the way to go for that. Obviously balance isn't managed well, currently.

    (edit: ok that was confusing, but I fixed the link)

    Update: Fixed the turning gait so it's much cleaner. I also bolted these to the back two feet, and that fixes a lot of the balance problems.
    Last edited by Gertlex; 06-18-2011 at 08:51 PM.

  3. Re: My 4D)F Quad: Numa


    :P welcome to mechwarfare

    I have to say awfully good start! Love that walking .gif!

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  5. #4
    Join Date
    Jul 2008
    South Sphincter Idaho
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    Re: My 4D)F Quad: Numa

    Looking good. Keep up the good work..
    Team Maggot---Mechs. "Bheka" (retired), "Maggot Mk.3(A)"
    " Keep your stick on the ice ".... Red Green

  6. #5
    Join Date
    Jun 2011
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    Re: My 4D)F Quad: Numa

    New youtube vid up. This one has (obvious) corrections to the gaits so that turning is much smoother... other than that nothing new to see there.

    -I changed to the smaller sparkfun Xbee explorer.
    -Modeling the bot in Solidworks... chassis plates are the main focus for now... The turret gets in the way of things...
    -I figured out how I'll do the math for omnidirectional walking... Next I plan to implement this in mathematica, get it cleaned up nicely, then do the code again in C.
    -Ordered servos for turret + spares, as well as Lipo battery monitor... Need to determine how much walking time I have with the current setup.
    Last edited by Gertlex; 10-08-2011 at 10:23 PM. Reason: Fixing youtube link?

  7. #6
    Join Date
    Jun 2011
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    Re: My 4D)F Quad: Numa

    Recent progress took two forms:
    -Got battery monitor, and Numa walked ran for 13 mins without the blue LED beginning to flash... Voltage after the fact was 11.7V, iirc... Looks like I should be fine even with more weight once Numa is finished...
    -Redid the layout of the 1.25"x1.75" perf-board TriState Buffer. Now it can control either 3 pin or 4 pin servos by closing either of two connections with a jumper pin. I did the design in Inkscape. This allows me to copy/paste all needed documentation into the document for reference. Design and what the screen looks like with this approach are attached.

    On the circuit, blue lines are ground wiring, red is 11.1 V battery Vcc, pink is 5 V regulated via Axon, and dashed lines are connections under the board... Short grey lines are solder connections between holes. The 3 header pins at a right angle in the center of the board are where the jumper is placed.

    I'll pick up my Trendnet camera this weekend (shipped it to my parents place while NM was on fire.. but it was $40!). Still need to get around to finishing a first iteration (aka allow myself to not have a perfect design), of the so-called chassis plates. Taking the bot apart to tighten screws isn't fun...
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Gertlex; 07-12-2011 at 11:10 PM.

  8. Re: My 4D)F Quad: Numa

    Nice work keep it coming

  9. #8
    Join Date
    Sep 2009
    Baumholder, GE
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    Re: My 4D)F Quad: Numa

    Nice work

  10. #9
    Join Date
    Jun 2011
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    Re: My 4D)F Quad: Numa

    Some updates!

    I continued working on designing that board. I don't know what to call it, but it does a lot of things :P
    -Connect 5 chains of Dynamixels (3 or 4 pin)
    -Communicate with 3 pin servos (Buffer IC + Hex Inverter IC)
    OR (mode selectable with a jumper)
    -Communicate with 4 pin servos (Max485 IC)
    -Lipo battery monitor connection
    -5V regulated for Trendnet camera
    -LED indicators for LiPo and 5V (to ICs)

    I then built it, of course. Checking numbers, it uses $19 in parts. I guess I see how "simple" boards get "expensive" easily. Updated design and pics of top and bottom attached. The purple surface mount LEDs are on the bottom of the board because I plan to bolt the board to the underside of Numa. The "top" of the board, with all the wires and connectors will be hidden inside the bot, but the LEDs on the bottom will still be easily viewable (also lighting up the ground under Numa = FTW)

    The board images are attached at the end. I'm pretty happy with how densely I packed all of those features in there.

    I also got the Trendnet camera. I attached it temporarily with zip ties and a bioloid bracket (the cooling slits on the underside are perfect for a zip tie!)

    I've got the Trendnet camera working with a Ad-Hoc network, so I should be good for competition where a router is provided...

    Bot pics with the camera mounted:

    I've also got the chassis plates designed. An initial version will be drilled/cut by my gf since she has access to a machine shop :P. The final version(s) will be carbon fiber. I've got the carbon fiber already, and based on its density of 1.54 g/cm^3, the two chassis plates will weigh less than 50 g combined.

    Below is a top down view of my work in CAD so far. The top and bottom plates are duplicated on the right... The holes on the edges of the top plate are for easy mounting of bioloid brackets.

    I'm hoping to be able to switch to the new Axon Mote, which is much smaller and would easily fit inside the chassis plates (I've got mounting holes for it, even). It remains to be determined whether I can use the built-in zigbee radio in a similar manner to how I'm using xbees currently.

    And one last note: aesthetics!
    I've settled on having external wires (e.g. camera power cable) being sheathed in flexible mesh, with shrinkwrap tubing over the ends of the mesh... see the last attached file.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Gertlex; 07-27-2011 at 10:07 PM. Reason: Replaced faulty circuit :D

  11. #10
    Join Date
    Dec 2007
    Portland, OR
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    Re: My 4D)F Quad: Numa

    Really digging the home-brew look of it so far. Nice work!
    Andrew Dresner
    Principal Engineer
    Interbotix GIthub
    Interbotix Labs Google+

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