Quote:
Originally Posted by comphappy
What you said is very WRONG check your equations before correcting me!!!
m*a=u*m*g
becomes
a=u*g
therefore mass does not matter, now if you are useing downdraft gas then the "mass" part of Fn will not equal the mass of the robot. But that is not what I was talking about. Watch your equations. |
Frictional force (static) = Ffs
Max frictional force = μ*N, N = the normal force. So far so good, right?
N = m*g, where m = the mass of the object (robot) and g = either 9.8 m/s^2 or 32 f/s^2 depending on your system of measurement. Am I not correct?
For the condition where nothing is slipping or about to slip, Ffs <= μ*N. When the object is about to slip, Ffs = μ*N. When the object slips, you get into Ffk, or the force of kinetic friction. I'm still correct in this, right?
By your equations, you are assuming that the wheel is about to slip. That is, F=m*a (the standard force equation) == μ*N. But wait! Where, oh where, does Ffs come in? It is the force exerted by the static friction, so it is m*a also, I'm assuming. Please correct me if I am wrong here.
Now, on to business.
Ffs = m*a = μ*m*g, assuming a flat plane. I think this is quite reasonable considering the application and that you're about to slip your wheels.
So, m cancels. a = μ*g. You are correct. The mass does not matter.
HOWEVER: you add a fan using your available mass (which doesn't matter) which adds additional force going downwards, correct? mu is constant due to the rules, so we can set that aside. That leaves g and a. a = g. g is a component of the normal force, under N = m*g. The normal force is equal and opposite to the weight m*Ag , such that W (weight) + N = 0. So far so good, right?
When you add the force Ffan going downwards (or upwards), you now have W + N + Ffan = 0. Ffan would be added to either W or N if the fan were pushing down, and you have W+Ffan = -N or N + Ffan = -W.
Your full new equation, therefore, would read:
m*a = μ*m*g + Ffan. (Frictional Force = Normal force times mu plus Fan force) Correct me if I am wrong here.
Fan force is dependent on area and speed, is it not? There is not a mass component there, because it is already accounted for. So you can no longer divide out mass. (basic algebra)
As for your other comment, YOU also need to watch your equations. Unless you can point out what is wrong with my response to your example of a 500 lb and a 10 lb robot, that stands. I could also run it in metric if I wanted to.