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Originally Posted by EricH
Why do you need gas springs or other means of balancing an arm other than its power source?
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I'm not quite sure what you mean here, but I was trying to stay away from the "strap the biggest motor you can and a bit of reduction" method.
See here.
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As for your second question: Your motor does not backdrive? So why are you worrying about keeping the arm in a specific place? For that matter, why are you looking at things other than the motor to keep the arm up? Motors that backdrive (may) need these things, but motors that do not backdrive almost certainly do not.
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My mistake, It was supposed to say a motor that does backdrive. Fixed.
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For the first question... You're actually asking two. Where you want "neutral" to be is game dependent--ask again sometime in January. But the math behind sizing/placement at neutral...
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That itself answered the question. I was asking if it should just be balanced at 90 degrees or something game relevant (like higher then 90 in logomotion)
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You're actually pretty close. You would use an equation something like, (weight of arm side 1)*(horizontal distance from pivot point to arm CG)=(weight of arm side 2)*(horizontal distance from pivot point to arm CG)+(vertical force component from balancer)*(horizontal distance from pivot point to balancer attach point).
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Pesky CG, I knew I left something out. This formula would give you an arm that balances at 90 degrees though, no? What about something angular?
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This would actually fall into the Statics category of problems, which many engineers study early in their college careers--the basic method of balancing out forces is to set up an X-equation, X-unknown system of equations where the sum of all the forces and moments in a given direction or about a given axis of rotation is zero. Then you can solve for your unknowns.
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I'll have to look more into that
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Just to bring something up... I have yet to see one of 330's single-joint arms use any sort of balancer that wasn't the drive motors. Neutral for some was all the way down; for others it was wherever the arm was left--one at least needed a little bit of power to maintain a position. Typical drive, 1-2 FP motors, stock gearbox, heavy reduction afterwards (exception: 2x Globe motors mounted on the arm itself--2004). No braking capability.
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The bit I bolded there is what I'm specifically interested in, would that not be a gas spring? or did they just use two window motors together? Our arm in '11 used two window motors, and well, I can just say it wasn't fun. Then again we were probably doing everything wrong. Thanks for the help!