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    Killer Dozers

       

    ...an (almost) alternate model for 8275 bulldozer. "Almost" because in addition to the 8275 set you need one more battery box and RC handset to control the second Killer Dozer.

    Each player control a dozer, the purpose of the game is to tip over the opponent. With the RC handset you control your dozer to go straight forward, to turn in place backwards, and to lift/lower the blade to raise your opponent. Each dozer is set on a different channel, and of course it is forbidden to switch your remote on your opponent channel!

    And of course you can build and control up to four Killer Dozers for more fun... if you have the parts!

     

    Front right view. The front bumper is used to provide a grip point rather than to protect the dozer.

    ...and back right view. The aim is to tip over the opponent, so the battery box is placed high on purpose.

    Detail of the ratchet mechanism. Killer Dozer is powered by a Power Functions XL motor. While going forward, the ratchet slips over the gear under it so both tracks are moving. When going backwards, the ratchet prevent that gear to turn, so the white clutch gear placed on one side slips. Only one track is moving and the Killer Dozer turns on the blocked track.

    Detail of the lifting mechanism. A Power Functions medium motor turns a lever that lead the blade to raise/lower cyclically.

    Bottom view. Movement from the XL motor is transmitted to the right regular 24 tooth gear and to the left clutch gear. The left axle goes through the middle 20 tooth gear that can be blocked by the ratchet.

    Movie, showing the Killer Dozers fighting (3Mb, AVI, DivX 5 codec)

     

    Here is the LDraw/MLCad file of the Killer Dozer.

    and here high quality printable building instructions (7.8MB)
    MPD file ready for LPub4 rendering is here (unofficial parts are not embedded in this file).
    This one is scaled for LDGlite rendering, you have to scale assembly and parts size down for LDView rendering.



    and here is the BOM image.

     

    Mai 2008 update: improvements

    After some time playing with Killer dozers, I noticed that the angle gears that transmit motion at the output of the XL motor grind and slip more and more. If you have other parts than those included in Bulldozer kit, I suggest you replace them with knob wheels.

    As these gears are larger you will also have to replace the gear used for the ratchet with a 16t gear.

    And, last but not least, direction of the tread links does matter! If they are oriented in the wrong direction there is more friction and the killer dozer doesn't perform well. Viewed from top, the tread links must be oriented as the green one shown below. And yes, the treads in my LDraw model are backwards, but it's too much work to correct...

     

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