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Crab

August 23rd, 2011 Leave a comment Go to comments

My second walking vehicle. Features 8 legs loosely based on the Klann linkage, driven by a single motor.  

Datasheet:

Completion date: 23/08/2011
Power: electric (Power Functions)
Weight: 0.495 kg
Suspension: none
Propulsion: 1 x RC motor geared 3:1
Motors: 1 x RC

My second walker, intended to use legs with spider-like pattern of movement. I have developed a chassis that used the Klann linkage to move legs, and it walked well and fast – however, it jammed every once in a while and the legs were too fragile to support even medium loads. I have then reworked the legs design to a form that loosely follows the principles of the Klann linage, but in a simplified way. The resulting chassis was small, sturdy and worked smoothly. I have been testing it with two separate motors for propulsion, each driving four legs on one side, which could allow the walker to turn like a tank. Unfortunately, the chassis steered poorly, and proved unstable as it was impossible to keep all legs properly synchronized with two independent propulsion motors.

Eventually, I settled for just one motor, but a fast one. I have also equipped the chassis with two long arms that could be fixed in various positions, thus affecting the walker’s centre of gravity and its walking path. Under certain circumstances it could allow to make the walker turn, but much more often its movement was largely chaotic.

This was definitely not a successful walker, but still a funny build. It allowed me to observe how eight synchronized legs work when set at a number of various phases and angles. I think it wasn’t a good MOC, but it was a good lesson that hopefully would allow me to properly realize the Klann linkage in the future.

Photos:

1.jpg dsc05387.jpg dsc05389.jpg dsc05391.jpg dsc05392.jpg dsc05400.jpg dsc05401.jpg dsc05403.jpg

Video:

Categories: Walkers Tags: , ,
  1. Sariel
    February 6th, 2014 at 16:40 | #1

    @technicfan
    So, you put subtractor everywhere on principle?

  2. technicfan
    February 6th, 2014 at 16:33 | #2

    Why don’t use a subtractor, Sariel? I’m sure this would improve steering. but nice MOC!

  3. Sariel
    August 26th, 2011 at 07:43 | #3

    @Spiller
    Yes, basically I simplified the whole thing, that’s why legs don’t have perfectly linear motion and there is a lot of up/down travel.

  4. Jeff
    August 26th, 2011 at 05:04 | #4

    I like the way it sounds as it walks. Kinda creppy looking but watching it made me think of MGS crab battle. ” A knife is useless against those massive claws. They could rip a tank apart.”

  5. August 26th, 2011 at 03:12 | #5

    @Sariel
    Ahh, I messed up : \
    Since the message was gone, I pressed the back button and copy pasted the message without thinking. Apparently that was the OLD message, not the new.

    To sum up the lost words:
    Evaluating my design once more I guess I allowed to wide angles for that one beam, and combined with flexibility in Lego this allowed it to drop down. A friction pin almost solved it, but using rubber-bands gave better results in my prototype:
    http://www.brickshelf.com/cgi-bin/gallery.cgi?i=5162665
    Can’t quite make up a better design in this scale.

    I tried looking at your design on Facebook for inspiration. In your second prototype it looks like you made a variation of Klann linkage, rotating that beam I have trouble with 180 deg. Wouldn’t this affect the path of the legs negatively (since the point of this linkage is to move the leg as horizontal as possible when it touches the ground)?

  6. Sariel
    August 25th, 2011 at 23:25 | #6

    @Spiller
    Mister, there is your comment with my answer right below.

  7. August 25th, 2011 at 23:14 | #7

    (Not quite sure if it posted this message, so trying again. Looks like it might have timed out since I forgot to post it for over 24 hours… -__-)
    The Klann linkage looks very interesting, very linear travel. When I tried a simple 4-legged walker (http://spillerrec.files.wordpress.com/2010/12/dsc02466s.jpg) the stability was terrible. (Experimenting with the center of gravity made it at least stable enough to walk.)

    I just tried doing a mock-up of Klann linkage and it looks very promising. However I couldn’t get it to work without using a rubber-band as the lever right beside the propulsion lever (which is connected together with the lever that goes to the leg) kept falling below the axle, thus ruining the linear travel of the leg.
    Do you know what I’m doing wrong?

  8. tom
    August 25th, 2011 at 13:16 | #8

    nice nothing else i can say . must have been a hard time getting the geometry right i tried something like this once and it pretty much ended in me giving up and starting smething else :p

  9. Mike
    August 24th, 2011 at 20:25 | #9

    😀 😀 WTF?????
    look weird but I bet it was hard to put together… nice.

  10. Mecho12345
    August 24th, 2011 at 05:56 | #10

    lol! cool!

  11. Sariel
    August 24th, 2011 at 00:46 | #11

    @Spiller
    Most likely your geometry is wrong. Getting Klann’s geometry right is hell, just look at this formula: http://www.mechanicalspider.com/enable.html

  12. August 24th, 2011 at 00:42 | #12

    The Klann linkage looks very interesting, very linear travel. When I tried a simple 4-legged walker (http://spillerrec.files.wordpress.com/2010/12/dsc02466s.jpg) the stability was terrible. (Experimenting with the center of gravity made it at least stable enough to walk.)

    I just tried doing a mock-up of Klann linkage and it looks very promising. However I couldn’t get it to work without using a rubber-band as the lever right beside the propulsion lever (which is connected together with the lever that goes to the leg) kept falling below the axle, thus ruining the linear travel of the leg.
    Do you know what I’m doing wrong?

  13. Avalyah
    August 24th, 2011 at 00:27 | #13

    Absolutely amazing, my favourite. Out of all your constructions it was the crab that made my day. The movie is top notch, music with those kind of werid moves… FANTASTIC! Can’t wait till your next walking something 🙂

  14. Lexhoya
    August 23rd, 2011 at 23:12 | #14

    Poor Lucius… at 1:09 it really looks like a crab running for its life while being captured. I like it when you also make other contraptions, other than vehicles.

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