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Thread: First steps for Legavos

  1. First steps for Legavos

    I've been wanting to build a mech for a long time, but, well, it's a complex thing. My last attempt (http://forums.trossenrobotics.com/sh...uple-questions) ended up with a bunch of parts and some technical knowledge, but no actual mech. So after a year of building micro (~10cm) tracked FPV vehicles, I thought I'd turn my attention to walking robots again.

    So, I decided to strip things down to the basics, and let me present to you the light-class mech: Legavos

    Click image for larger version. 

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    Today it took it's first steps under remote control:



    Mechanics:

    Specs as of video above:
    - AUW: 524g
    - Max Operating AUW: 1kg (at 1/4 servo stall torque)
    - Footprint: 20cm x 20cm
    - Theoretical max speed: 24cm/sec (not shown in video above. This is probably not achievable, but I'm hoping for >15cm/sec)
    - Step height: 2cm

    With the current mechanics the payload could be doubled (to 2kg) at the cost of halving the speed, but I'm not sure the chassis is stiff enough for that. The chassis is mostly 3D printed, and needs just a handful of 5x11x4 bearings and m3x15 bolts to assemble. Parts be downloaded from https://gitlab.com/sdfgeoff/legavos/.../generated/stl

    The design is based on Gertlex' Twitch, but adapted for quadrupedal form. (This is a statically stable quadruped, so I'm hoping it doesn't fall under the gimmick clause. I didn't see anything in the rules precluding static stability from quadrupedal mechs.)
    Target plates will be mounted on the (yet to be designed) turret


    Electrics
    - Servos: 3x standard MG996R servos
    - Brain: ESP32 running micropython. Internal loop rate of 50Hz
    - Battery: 2S lipo

    This is a very cheap bot. The servo's were bought for about $5 from china a couple years back. They are really horrid (+-5 degrees backlash), but with this type of mechanics, it doesn't matter so much.


    Development plans:
    1. Mech: Design turret slew system
    2. Soft: Fix the internal event system so it doesn't consume 30% of the CPU time looking for where to route events.
    3. Soft: Fix walk cycle transitions (rapid changes in commanded velocities result in feet dragging or sudden jerks)
    4. Elec: Mount up the camera/video system
    5. Soft: Add support for camera feed to control software
    6. Elec: Add in battery voltage monitoring
    7. Mech: Armament.
    8. Mech: Design gun tilt system
    9. Mech: Possibly find a way to mount batteries on the bottom of the mech to lower CG
    10. Soft: Switch from wifi-based networking to something else


    At the moment my main concern is armament. I can't get any cheap/lightweight AEG's where I live (no amazon here). I do have a couple thoughts about alternatives, but getting something reliable will probably be rather hard.



    Unfortunately the probability of me ever being able to go to the US to actually take part in an event is really low, but I've designing for it just in case the opportunity ever arises.
    Last edited by sdfgeoff; 03-26-2020 at 09:16 PM.

  2. #2

    Re: First steps for Legavos

    Cool! The first walker I built was a three-servo variant, too!

    (You could also post a description on https://forum.mechwarfare.org/c/builds/6 and you'll get a forum "Builder" badge for it :-)

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