We have converted the cart to a single wheel drive in the rear, so the motor only has to overcome the friction at 1 wheel to make it move. In this case, would we then use the weight of the cart measured at that wheel, or would we still use the entire weight of the cart?
Oh no, that's the wrong way to think about it!
You must NOT overcome the kinetic friction of the wheel to the road..
(that'd mean tyre-slip or burn out behaviour)
[well.. considering it's a rolling contact surface that might be static friction... anyway you need to keep it
]
you must overcome the friction in the bearings and build up momentum without breaking friction between the tyre and the road.. that's what makes the kart move.
that's still all the friction in all four wheels' bearings, and rolling resistance
And in fact.. much easier with a live axle;
since you have twice the tyre-road friction value as your upper limit to move
The total weight will be moved of course, thus it's the total weight you need to know in order to calculate the power or torque or even force you need to get rolling.
For the friction values you can add up the weights just on the rear wheels
(either one wheel as you have now.. or both if you go back to two wheel drive which I'd recommend tbh)
But again that's the upper limit you have, add more and you'll likely break traction which looks cool but isn't fast
just put the biggest kid on the kart, tie a rope to the front and slowly pull on the rope while measuring the force required to move the kart... (scale with peak memory, you'll have that in the physics departement of your school... hopefully a big enough one)
that number will include every bearing, every nut and bolt and even the condition of the road surface.
And it'll be fun for each kid to test his' own value as an experiment.
and you could derive every kid's weight from that knowing the weight of just one kid ...
'sid
