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Hi all,
You will find here:
http://www.philohome.com/traction/traction.htm
the results of a few experiments on pulling power of different Lego® wheels
and tracks.
Enjoy!
Philo
www.philohome.com
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Thank you for posting that! A useful resource. I have thought about having 2
narrow tires at an angle so that they almost meet at the ground. My thought is
that they might increase traction by sort of pinching the carpet pile. Thanks
again.
Best regards,
Paul
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I think that carpet hair would have to be fairly long to get that pinching
effect - but then it might work...
Not easy to set up though !
Philo
In lugnet.robotics, Paul Krieg writes:
> Thank you for posting that! A useful resource. I have thought about having 2
> narrow tires at an angle so that they almost meet at the ground. My thought is
> that they might increase traction by sort of pinching the carpet pile. Thanks
> again.
> Best regards,
> Paul
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"Philippe Hurbain" <philohome@free.fr> wrote in message
news:HEq6un.1xC2@lugnet.com...
>
> You will find here:
> http://www.philohome.com/traction/traction.htm
> the results of a few experiments on pulling power of different Lego® • wheels
> and tracks.
Fascinating! I wonder if the tracks of both types would perform better if
they had a series of idlers placed along the bottom of them to keep more of
the track in good contact with the ground, in the same way as real
excavators, tanks etc do? From my entirely subjective point of view, I think
this might serve to increase traction. Of course it may just be the
equivalent of adding more wheels as stated in your experiment, in which case
you gain little or nothing.
Jennifer
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Hello Jennifer,
I tried with one idler in the middle of RIS tracks. The result was not
significantly different with or without it - so it seems indeed equivalent
to adding more wheels, dividing weight between them. In real life, tracks
are useful in mud or soft ground where contact area is important to prevent
vehicle from burying itself... here we are on hard, even surface !
Philo
>
> Fascinating! I wonder if the tracks of both types would perform better if
> they had a series of idlers placed along the bottom of them to keep more of
> the track in good contact with the ground, in the same way as real
> excavators, tanks etc do? From my entirely subjective point of view, I think
> this might serve to increase traction. Of course it may just be the
> equivalent of adding more wheels as stated in your experiment, in which case
> you gain little or nothing.
>
> Jennifer
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"Philippe Hurbain" <philohome@free.fr> wrote in message news:HEq6un.1xC2@lugnet.com...
> Hi all,
>
> You will find here:
> http://www.philohome.com/traction/traction.htm
> the results of a few experiments on pulling power of different Lego® wheels
> and tracks.
very interesting
and usful
maybe you could add the bar with the traction on sand :)
br
pixel
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Hi Paul,
>
> very interesting
> and usful
>
> maybe you could add the bar with the traction on sand :)
Sure, if you clean my Lego after the test ;o))
More seriously, the true problem here is to get a consistant test: a piece
of wood is not affected by previous runs, sand is !
Cheers,
Philo
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"Philippe Hurbain" <philohome@free.fr> wrote in message news:HErz5u.1uKs@lugnet.com...
> Hi Paul,
> > maybe you could add the bar with the traction on sand :)
>
> Sure, if you clean my Lego after the test ;o))
philo
send me all your bricks
i'll keep them very clean i promisse :))
> More seriously, the true problem here is to get a consistant test: a piece
> of wood is not affected by previous runs, sand is !
yeah of course!!!
but i thought about the box with sand
which will be lined up after every trial
if the sand wouldn't be lined up the long jumpers couldn't jump
br
pixel
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In lugnet.robotics, Philippe Hurbain writes:
> Hi all,
>
> You will find here:
> http://www.philohome.com/traction/traction.htm
> the results of a few experiments on pulling power of different Lego® wheels
> and tracks.
Oh, very useful! Thanks for the work!
I thought about doing this myself but never got around to.
And spinning speed is important! Power Pullers use high speed to actually toss
the ground behind them to get more force. Don't see how you could use that in
Sumo though .)
Best regards,
/Tobbe
http://www.lotek.nu
(remove SPAM when e-mailing)
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In lugnet.robotics, Philippe Hurbain wrote:
> Hi all,
>
> You will find here:
> http://www.philohome.com/traction/traction.htm
> the results of a few experiments on pulling power of different Lego® wheels
> and tracks.
>
> Enjoy!
>
> Philo
> www.philohome.com
Hello Philo,
This is an extremely interesting and informative analysis. Did you notice
any effects caused by the location of the scale attachment point? It seems
to me that any attachment point below the axle centerline creates a lever
arm with the front axle as the fulcrum. This would make the vehicle try to
behave like a wheelbarrow, with the pulling force transferring weight from
the rear wheels to the front wheels. The reverse effect would occur if the
attachment point was above the rear axle. As the vehicle pulled, it would
tend to lift the front wheels off the ground, transferring all of the
vehicle weight to the rear wheels (see set 8457 - Power Puller in action).
As your "More Weight" graphs show, more weight produces more traction, but
that 'benefit' is offset by a corresponding decrease in the coefficient of
friction. The result appears to be that as weight is transferred from the
rear wheels to the front wheels because of the attachment point of the
vehicle, the rear axle traction decreases at a faster rate than the front
axle traction increases. This causes a net decrease in the total traction
of the vehicle. If the attachment point is at the same height as the axles,
the effect should be zero, and it would increase as the attachment point
gets farther from the axle height. This would mean that larger diameter
wheels would suffer more from this effect in your test than would small
diameter wheels.
It also seems like you could extrapolate a maximum weight for a wheel set,
beyond which adding additional weight would not add a significant amount of
additional traction.
Finally, your "More Speed" graph implies that as long as the tires can spin,
lowering the gear ratio (increasing torque and lowering wheel speed)
actually reduces the total vehicle traction!
Thanks for some great and informative work!
Jim
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James Ryan wrote:
> This is an extremely interesting and informative analysis.
Yep.
I've been looking at the theoretical basis for how rubber tyres work
in full-sized cars - and it's an insanely complicated process.
However, one thing one learns early on is that the normal rules of
friction that we were taught in school were only ever approximations - and
they are very poor approximations for flexible, rolling things made from
long chain polymers with complicated sculpted surfaces.
In short - theory is useless - you need this kind of practical experiment.
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://www.sjbaker.org
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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Subject:
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Biped robot
|
Newsgroups:
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lugnet.robotics
|
Date:
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Wed, 8 Oct 2003 02:40:16 GMT
|
Original-From:
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Luiz Antonio <celibertojr@ANTISPAMuol.com.br>
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Viewed:
|
3527 times
|
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I am start to build a biped robot, its easy in teory but in pratic is
not..hehe
See the pictures:
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=535998
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=535999
Tks
Luiz Antonio
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Hi Jim,
| |
This is an extremely interesting and informative analysis.
|
Thanks ;o)
| |
Did you notice
any effects caused by the location of the scale attachment point? (snip)
|
Definitely YES. That’s why as I changed wheels I modified the test vehicule to
try to keep attachment point in line with wheel center. It is also important to
keep the retaining rope horizontal, to avoid the creation of a lifting or
pressing effect - this also has a great impact on measurements.
I also had problems in some cases with uneven pulling (probably a kind of
mechanical relaxation oscillation between full grip (high static coefficient)
and slipping (lower friction coefficient). Horizontal shift was sometimes
annoying too, with one side pulling more than the other.
As I said in my page, comparison results should be taken with a grain of salt
(who said a spoonful? well... he may be right!!!)
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As your “More Weight” graphs show, more weight produces more traction, but
that ‘benefit’ is offset by a corresponding decrease in the coefficient of
friction. (snip)
|
I don’t agree: as you can see from this curve, friction coefficient is quite
constant over measured range...
I must say that I was somewhat surprised to get a result that fits so well the
theoretical behaviour - though as Steve Baker pointed out, the theory behind
polymer friction is itself quite involved !
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It also seems like you could extrapolate a maximum weight for a wheel set,
beyond which adding additional weight would not add a significant amount of
additional traction.
|
Well, I think that the real limit lies in material strength: I actually broke an
old style z24 gear while performing this test!
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Finally, your “More Speed” graph implies that as long as the tires can spin,
lowering the gear ratio (increasing torque and lowering wheel speed)
actually reduces the total vehicle traction!
|
I don’t think so : traction remains the same whatever wheels rotation speed is
(provided that they rotate).
You simply have to gear down enough to make sure to avoid motors stall. Gearing
down more just slows down your vehicle when not pulling, but will not provide
more (or less) traction.
Philo
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