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Thread: Dog gears for modular attachments

  1. #1
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    Default Dog gears for modular attachments

    I've judged a number of teams this year who are using "dog gears" to create consistent attachment points for hooking up modular motorized attachments to their robots.
    It looks like this technique is being popularized in a video from Builderdude35.
    Is this the hot trend for FLL robot building this season? I've seen variations on this technique in previous seasons, but not this widespread.
    Last edited by timdavid; 12-13-2015 at 09:48 AM.

  2. #2
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    Default Re: Dog gears for modular attachments

    My son had chosen dog gears to make it easier to change attachments this year (He is the main mechanical builder for the robot as the other kids don't have as much interest). He did see the video from Builderdude35 and that was a part of decision. The big part, he says, is due to last year seeing a big problem with swapping out attachments and trying to get something easier for this year. He also used feedback from other team members to modify attachments to have minimal pin connections so that the attachments could just lay on top of the robot, except the dog gears required pin connections to keep it tight.

    He also notes that dog gears are not totally ideal as there is some play in them and sometimes they don't seat well together, especially under time constraints of the robot runs, so there were several mission failures due to that. At the very least, he has learned there are trade-offs with any of the ways of attaching equipment to the robot.

  3. #3
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    Default Re: Dog gears for modular attachments

    I have also seen several teams using this attachment method due at least in part to Builderdudes' video on the subject. It is interesting to see how different teams adapt the idea in different ways and to different degrees to their particular needs.

    Builderdude got the idea from LEGO Vinir's videos of their Nature's Fury run and they were certainly not the pioneers of the concept either (there is a video of an Ocean Odyssey run where a similar principle is used.)

    Really the "dog gear" (LEGO Vinir called it a clutch system) concept is just one variation on the wider concept of drop on or push on geared attachments. There are several versions using tooth gear connections and I saw one team with a rather effective worm gear version (their attachments all had tooth gears which dropped onto a worm gear connected to a medium motor.)
    Team members and coaches in North Carolina, direct your rules questions to referee@nc-fll.com

  4. #4
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    Default Re: Dog gears for modular attachments

    The team this year decided to modularize their attachments with a power take off, too. However, they've never heard of dog gears, or Builderdude35, so they went with the 4 tooth high torque gears for minimal slippage. They also designed it to be a one-axis shift in power direction (whatever the engineering term for that is) so that the motor points straight ahead, but the attachments shift the power perpendicular to that.

    One of their more complicated attachments uses two gears on the attachment, and pulls power in two directions of rotation, gaining a paired, opposite motion for it (one arm up, one down; and vice-versa.

    It's great watching them learn this stuff!

  5. #5
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    Default Re: Dog gears for modular attachments

    Our team saw the system used by Lego Vinir and used it last year and it worked well. They built it in this year, but found they used very few motorized attachments this year--actually only one arm each for two missions, so they went back to just permanently mounting those on the medium motors. They accomplish the majority of tasks just using the push/pull of the robot. They usually strive for the least complicated ways to solve missions and pride themselves on using as few motorized attachments as possible.
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  6. #6
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    Default Re: Dog gears for modular attachments

    My older boys are also using the "wide dog gears", to power their "extra skin" (a tall robot chassis that drives over the Demo/building). Originally they tried using four point "cross" as a gear, but that was causing problems, so I suggested that there are other types of gears, they tried several different types and settled on those.
    Legolympians - 2009-2015 (retired - joined FRC team 5422 Stormgears)
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  7. #7
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    Default Re: Dog gears for modular attachments

    My team has idolized Cassapeia, with their video of 842 punkte. They wanted the big square frame, and their attachments fit on top as a big square frame. Their solution to the whole PTO problem was standard Lego gears, the fat ones, but the gear on the actual attachment is mounted on a block that slides on an axle for adjustment.

    I'm loving their progression on this, they're starting to really explore the ideas of building instead of solving everything with overly precise movements of the drive motors.

  8. #8
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    Default Re: Dog gears for modular attachments

    This is what "dog gears" looked like back in the RCX days.
    Attached Images Attached Images

  9. #9
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    Default Re: Dog gears for modular attachments

    Quote Originally Posted by Dean Hystad View Post
    This is what "dog gears" looked like back in the RCX days.
    That's about a century ago in "dog years"...two whole generations of Mindstorms controllers.

    Is that from the classic "Building LEGO Robots for FIRST LEGO League"?

  10. #10
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    Default Re: Dog gears for modular attachments

    Quote Originally Posted by Dean Hystad View Post
    This is what "dog gears" looked like back in the RCX days.
    Some teams still use that connection. It worked well for the Droids for World Class.
    Team members and coaches in North Carolina, direct your rules questions to referee@nc-fll.com

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