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Thread: BRAT Based Mech?

  1. BRAT Based Mech?

    Would a Lynxmotion BRAT be capable of becoming a mech? In its stock configuration, it comes with 6 HS-425 servos, but if you buy 6 HS-645's, they offer a price cut, if you already own a BRAT. Since its so lightweight, it doesn't really require powerful servos, so I'm thinking the 645's would enable it to carry all of the extra weight from the gun, camera, etc.

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    Re: BRAT Based Mech?

    The problem I see with such a mech, is that the guns and camera are gonna weigh quite a bit. Don't underestimate just how much payload it really is. On the BRAT, I'd be concerned you won't be able to shift the weight over, and that if you do shift the weight either the ankle servo would be overloaded or that you'd drag the feet badly (i.e. similar issues to Hagetaka...).

    [edit to remove statements about 5990, since manufacturer insists HS-645s would be enough]

    That said... you wouldn't have a terrible amount invested in a HS-645 brat mech if it didn't work... you could try it, but I'm just not sure you could carry that payload.

    Edit to add: If you do go this route... be sure to switch to LiPo to help keep the weight down, you can easily cut your battery payload in half.

    -Fergs
    Last edited by lnxfergy; 10-14-2009 at 12:16 PM.

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    Re: BRAT Based Mech?

    Not even close to the payload required with 645's, I'm afraid. [Doh! Fergs beat me in there - with a better answer]
    I Void Warranties´┐Ż

  4. Re: BRAT Based Mech?

    Oh well. I guess I'll have to look elsewhere.

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    Re: BRAT Based Mech?

    Quote Originally Posted by Adrenalynn View Post
    Not even close to the payload required with 645's, I'm afraid.
    Wow.. and people say I crush dreams...

    -Fergs

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    Re: BRAT Based Mech?

    Quote Originally Posted by Roboman View Post
    Oh well. I guess I'll have to look elsewhere.
    Manny's 4dof legs were pretty impressive. I doubt that he could keep that think walking for 12-15 minutes with the 645s... but with 5990s, I bet it'll be a competitor next year. His weight distribution was done very well, and if he can get his control solution to stop glitching (hmm, checksums and onboard controller), he'd be a heck of a biped to reckon with.

    Connor's mech could be in the similar boat as manny, he just needs to scale his guns back a little and work on the weight distribution (he's using 6DOF for reference, so that's quite a bit more than a BRAT)

    -Fergs

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    Re: BRAT Based Mech?

    Then again... as I sit here avoiding doing work.... If the goal is a cheap mech, a quad is always gonna be less expensive. And here we go with me being a servo whore: you can't beat the bioloid system for cost. An AX-12 is $5 more than an HS-645MG, and for that you get twice the torque, thermal and overload shutdown, and a serially controllable, pose-and-capture-capable servo. Add a bioloid comprehensive frame kit for $99 bucks and you have more brackets and screws than you know what to do with (and way cheaper and lighter than any of the SES parts).

    -Fergs

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    Cool Re: BRAT Based Mech?

    Well said, Fergs. Don't even think about 645's carrying all that mech gear. You'll need 5990's and that's with a stripped down cam, light-weight guns (you won't be able to carry even one fully automatic Defender, ask Connor) and no pan and tilt for aiming. So, you'll have to create stances to aim with the body. And if you're not handicapped enough, you will deal with heat and power issues. For my bet, start with a Bioloid. You'll start off with torquier, more cost-effective servos that can take more power. Even then, Issy, a quad, had some heat issues, so you'll have to rest your servos and be a sitting duck. But I'm hardheaded and just think bipeds are kool!

    -Manny

    Wow, before I finished, there were 6 posts ahead of me!

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    Re: BRAT Based Mech?

    Quote Originally Posted by mannyr7 View Post
    Well said, Fergs. Don't even think about 645's carrying all that mech gear. You'll need 5990's and that's with a stripped down cam, light-weight guns (you won't be able to carry even one fully automatic Defender, ask Connor) and no pan and tilt for aiming. So, you'll have to create stances to aim with the body. And if you're not handicapped enough, you will deal with heat and power issues. For my bet, start with a Bioloid. You'll start off with torquier, more cost-effective servos that can take more power. Even then, Issy, a quad, had some heat issues, so you'll have to rest your servos and be a sitting duck. But I'm hardheaded and just think bipeds are kool!

    -Manny

    Wow, before I finished, there were 6 posts ahead of me!
    All of issy's heat problems were solved when I went to 2dof. His servos never topped 65C on Sunday, and most of them were <50C (at default, thermal shutdown on an AX-12 sets in at about 100C I believe). Building a bioloid biped will be quite a bit tougher, the AX-12s are about half the torque of a 5990.... but I intend to build a bioloid biped for next year, it's just gonna take a bunch of engineering and magic....

    -Fergs

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    Re: BRAT Based Mech?

    I started with 645MGs on my Biped Scout (yeah, I know, it's much heavier then the Brat), and the only time it would stand up on its own strength was when I volted the servos to 7.2V (instead of the max 6.0V).

    645MGs are powerful, but they are only 133 oz/in at 6.0V. Consider the 5990TG servos at 7.2V, it has over 400+ oz/in. Each 5990TG is capable of what takes three 645MGs to do...

    Too much torque is not a problem usually, but too little torque means "gotta buy new servos"...

    Guns, cameras, and other stuff do add up. The biggest contributor IMO are the batteries that need to fuel these additional electronics and electro mechanical devices, which will also add to the pay load...
    ---
    Sleep? You don't need sleep...

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