Subject:
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Re: Wheels, Tyres and Tractions
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 5 Oct 2003 17:37:30 GMT
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Viewed:
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2881 times
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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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Message has 2 Replies:
 | | Re: Wheels, Tyres and Tractions
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| (...) 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 (...) (21 years ago, 5-Oct-03, to lugnet.robotics)
| | | Re: Wheels, Tyres and Tractions
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| Hi Jim, (...) Thanks ;o) (...) 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 (...) (21 years ago, 6-Oct-03, to lugnet.robotics, FTX)
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