need a general opinion from all you experts...

[archiver]

Posted by Anton Abaya at 1/18/2001 1:31 AM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NASA, Mathsoft, Solidworks.



given the assumption that there is enough torque, can a robot with a 4 wheel drive train, using the 8" wheelchair wheels, pull a goal up a bridge? or will the wheels slip?

will mere adding of traction on wheels make the difference ?

also, what is the ideal weight of a robot that needs to pull an 80lbs goal? i imagine 70+ ?

-anton

[archiver]

Posted by Tom S. at 1/18/2001 6:47 AM EST


Student on team #177, The Bobcats, from South Windsor High School and International Fuel Cells & ONSI.


In Reply to: need a general opinion from all you experts...
Posted by Anton Abaya on 1/18/2001 1:31 AM EST:



Anton-
Based on tests that we have run on past robots, a two wheel drive robot, with a not-so-good gear ratio (geared for speed) can pull both a full and empty goal up the ramp without much of a problem. This is definitely a strain on the bot, so 4wd would be better... but we made it up...

this is also assuming that there is weight over the drive wheels, we had to keep our basket from last year extended. The wheels did slip, a little.

Good luck

Tom

: given the assumption that there is enough torque, can a robot with a 4 wheel drive train, using the 8" wheelchair wheels, pull a goal up a bridge? or will the wheels slip?

: will mere adding of traction on wheels make the difference ?

: also, what is the ideal weight of a robot that needs to pull an 80lbs goal? i imagine 70+ ?

: -anton

[archiver]

Posted by Gary Stearns at 1/18/2001 1:41 PM EST


Coach on team #236, Techno Ticks, from Lyme Old lyme High School and Millstone Nuclear Power Station.


In Reply to: need a general opinion from all you experts...
Posted by Anton Abaya on 1/18/2001 1:31 AM EST:



: given the assumption that there is enough torque, can a robot with a 4 wheel drive train, using the 8" wheelchair wheels, pull a goal up a bridge? or will the wheels slip?

: will mere adding of traction on wheels make the difference ?

: also, what is the ideal weight of a robot that needs to pull an 80lbs goal? i imagine 70+ ?

: -anton

Well Mr Bill (not his real name) sez "Even if we are light lets add the weight for traction" and we haven't been light yet!! :{)

[archiver]

Posted by Joe Johnson at 1/18/2001 9:27 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: need a general opinion from all you experts...
Posted by Anton Abaya on 1/18/2001 1:31 AM EST:



2 wheel drive vs 4 wheel drive

this is a complex issue as we have already discussed on
this web site.

There are a lot of factors.

Basically, it comes down to keeping weight on the drive
wheels. When you are pulling a load up hill there are
two things working to take weight off the front wheels.

First the fact that the line between the center of
gravity and the center of the earth passes closer to
the rear wheels. This means that the rear wheels get
more of the weight and the front wheels get less.

Second, assuming a pivoting hitch for pulling, the
pulling force from hitch tends to rotate the robot
about the contact point of the rear wheels (making the
robot pop a wheelie). This tendency to pop a wheeling
takes even more weight off the front wheels.

So...

Can a 2WD machine pull a goal up the hill?

Yes, but it will have a better time if the drive wheels
are in the back and if the hitch point is high enough
to put "enough" extra weight on the drive wheels
without being too high so that the robot flips itself
over.

Finally, the grip to the ground plays a key role as
well. Make sure you have drive wheels that have good
friction properties with the carpet.

Good luck,

Joe J.

P.S. One more thing, a 2WD robot may have some trouble
if it "over balances" on the bridge and has to back up
over the ramp. Now it will have to push the goal up
hill with its drive wheels on the high side of the
ramp. This is a very different condition. A lot of
these types of robots will have go all the way over the
bidged and turn around to head back up the hill with
their drive wheels low and lovely. JJ