Subject:
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Re: Almost 300! And another Mindstorms Challenge! And more!
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 22 Jul 2006 14:20:53 GMT
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Viewed:
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3744 times
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In lugnet.robotics, steve <sjbaker1@airmail.net> wrote:
> bobcrean wrote:
> > I read the entire thread, and the rules and ask the question: Why must it
> > ROLL at all? If friction is the name of the game, and if the wheels (tires)
> > are the parts that have the "stickiest" qualities, then why not maximize the
> > surface area of those. To do that, you lay them on there side and inch the
> > robot along, barely lifting half of them alternatively, inching them
> > forward.
>
> So you have (in essence) a walking robot - but you wouldn't want to
> halve your traction by having only half of your feet on the ground at
> any one time - you'd want to have a robot with LOTS of feet and pick
> up just some tiny fraction of them at any one time. Something with a
> hundred little feet which only lifted one of them at a time would have
> almost twice as much surface on the ground as a biped.
>
> However, surface area on the ground isn't everything. The pressure
> exerted onto the ground matters too. With more area but the same weight
> of robot, you have less pressure at each point. Whether this is a
> terrible thing or not depends on the nature of the surfaces in contact.
>
> For some surfaces, it's almost irrelevent what the surface area is - the
> amount of friction depends only on the weight of the object and the
> coefficient of friction. For other surfaces, both the weight and the
> surface area matter. That's one of the things that makes this tricky.
>
> > In this arrangement, "speed" becomes irrelevant, in that you are not relying
> > on the torqe of the motors to do anything but lift the "pads", scooch them
> > forward and put them down and drag them backwards.
>
> That's not true. There are two parts to walking - one is the trivial
> act of lifting an unloaded foot and moving it forwards - but the power
> is required in pushing down on that foot such that it propels the body
> of the creature forwards.
>
> So - no - you are completely incorrect. The torque of the motors still
> matters a lot.
>
> > Wouldn't this approach "walk away" with the prize vs. any rolling robot
> > using the same wheels?
>
> Not necessarily.
I see a high amount of torque required on the Lego motors also. In general, and
if done poorly, all you have is a bot with a stalled motor for one minute
running at full power. Clutch gears could help, but it would have to be done in
such a way as to not severely hamper the pulling force. This can be heavy wear
and tear on Lego hardware and be expensive!
Dave H.
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