🚀 go-pugleaf

In article <5639co$tv8@pulp.ucs.ualberta.ca>, uncleal0@ix.netcom.com 
says...
>
>artiste@pathcom.com (T. Sloan) wrote:
>>Hi there,
>>
>>       A couple of weeks ago, our prof. by some outworldly motivation,
>>assigned the term design and thesis:
>>
>>* Build a buggy of mass<250g, powered by rubber bands and cabable of 
pushing a
>>mass00g of specified distances of up to 6.5m.
>>
>>How the hell do I do this!!!!! In theory, it should work (according to 
>our prof.), but with a mass of 300g (weight<3N), the lim. static 
>friction to ove
>>This of course required me to put on wheels with a greater mass, and 
>better traction (I used a roller blade wheel, 72mm, 78a hardness). The 
>earlier whe
>
>[snip]
>

A cheap and available high friction improvement would be to simply get a 
fat rubber band like the post man drops off here every day, and wrap that 
around the wheel.  It is a low durometer rubber like Al said to use.

The next problem is one of normal force on the friction surface.  If you 
use four wheels, you might try to push the mass where it is located in 
between the two front and two rear wheels.  By straddling the mass, you 
will get a downward component of torque to apply to the rear wheels, so 
drive those.  By adjusting the way your ram rod comes into contact, you 
could even work out a clever sort of cam arrangement that slightly 
"lifts" the mass you are pushing.  

If you do that, the mass you lift gets transfered onto the wheels of your 
cart.  Get the front wheels way out ahead of the mass, and have the mass 
close to the rear wheels.  Basically, you want the cart to be on the 
verge of flipping over, ie lifting the front wheels off the ground.  That 
way, all of the mass on the cart is on the drive wheels (that is unless 
you go for a four wheel drive version, then don't worry.

But in any case, if you can arrange a lever sort of like;

                 _________
        |    /| |         |
        |   / | |         |
   cart |  /  | | mass    |
        | /   | |         |
        |/    | |_________|

           ^ lever

where as the lever is compressed, it tends to lift the mass off the 
ground, then you can remove some of the sliding friction from the system 
and transfer it to normal force on your traction wheels.  I assume that 
just lifting the mass and setting it on top would be cheating, so this is 
a sneaky way to cheat a little bit!

Make certain the leading edge of the mass isn't going to dig into the 
ground.  And if it isn't specifically precluded, just get out a sheet of 
teflon and slip it under the mass!

Ross Tessien