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Re: pic: Omni Design Trial
Since you brought up cost of UHMW, I checked McMaster. A 48" square sheet of 1.25" UHMW (item 8619K97, the smallest size that would let you get 28"x38") is $348.38. A 36"x24" piece (item 8619K95) is $164.58.
Just something to marinate on. |
Re: pic: Omni Design Trial
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Re: pic: Omni Design Trial
No, it's not the end of the story....because I have a mecanum wheel sitting here, and you don't :)
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But if you constrain the wheel so it cannot move sideways, it still produces the sideways force vector, but the sideways velocity vector is zero. Quote:
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Also, consider the case of omnis vs. mecanum, with all motors turning in such a way that none of the rollers are rolling relative to the wheel bodies. In the case of the mecanum, the robot goes straight along the axis of the wheels. The omni sits and spins in a circle. So, the omni is most efficient when it is not going anywhere! |
Re: pic: Omni Design Trial
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Re: pic: Omni Design Trial
Wait, so when you are rolling forward and there is a sideways force, where is that force coming from? It is the motors. You don't get the applied force for free.
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Re: pic: Omni Design Trial
Nevermind, beat to it.
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Re: pic: Omni Design Trial
Hey, if my kid says so, it's gotta be true! he designed the mecanum drivetrain for the promobot
http://www.chiefdelphi.com/forums/sh...ad.php?t=59027 edit--he deleted his testimony! oops |
Re: pic: Omni Design Trial
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At least that's my understanding of physics. I could be wrong. edit--think about walking...where's the force? where's the work getting done? where's the velocity? |
Re: pic: Omni Design Trial
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The difference between mecanum and omni-wheel based holonomic is that on an omni system the wheels actually do move sideways when driving forward, while on a mecanum setup they don't. |
Re: pic: Omni Design Trial
Getting back to the model and your questions/concerns about the motor mounts, could you add a closer picture from a better angle of that area? Perhaps you could hide/blank the omni wheel and wheel shroud...
...and by the way, that's a really cool looking chassis design! |
Re: pic: Omni Design Trial
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You cannot transfer velocity to the ground. You can impart a force on the ground and the reaction to that force will make your robot move, but the Earth is a bit heavier than your robot and you're probably not having a significant effect at making it go faster or slower. If the rollers are not turning, as you suggest, then the wheel is not trying to move sideways. If the wheel is not trying to move sideways (as it cannot possibly discern your intention or what the rest of the wheels are doing) it will not, under any circumstances, strafe. A roller that's not turning cannot magically impart a force sideways. |
Re: pic: Omni Design Trial
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It works both ways. I'll paint half of each of the rollers and make a movie.... |
Re: pic: Omni Design Trial
Again beat to it. Dang you, Nr. Forbes!!!!!
I do like this chassis, it looks very open, nice to work on. |
Re: pic: Omni Design Trial
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Re: pic: Omni Design Trial
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A wheel turning forward is going along the straightaway of the race track...a wheel strafing is going around a curve...usually we try to go as fast as we can on the straightaway, and we have to slow down for the curves. So, a mecanum drive is naturally suited to this game, while an omni drive is not, because it is wasting a lot of motor movement spinning the rollers on the wheels. The rollers don't care at all. But you might care if you're trying to decide which drivetrain to use, and you are still considering both omni and mecanum holonomic drives. |
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