
#1
Feb1313, 09:48 PM

P: 2

Hey guys,
I am trying to figure out which motor to order for a side project of mine. I am trying to push a 1000 pound cart up a 10 degree incline. The cart has four elastomer wheels, and may possible encounter carpeted surfaces. I'm not quite sure what to expect in regards to a coefficient of friction yet on a carpeted surface, but I wanted to check my math a bit to understand if I am approaching this problem correctly: Coefficient of Friction = Cf Required Force = Fr Weight = Fw Force Normal to Slope = Fn = = Cf*Fw*Cos(10) Force Parallel to Slope = Fw*Sin(10) So Fr = [Cf*Fw*cos10] + [Fw*Sin(10)]? Thanks for any help in advance! I just wanted to double check if I am doing my statics correctly. 



#2
Feb1713, 06:22 AM

P: 2,861

The motor power depends on how fast you want to go up the slope eg power = force * velocity. The static force gives you the minimium torque required.
This equation.. Force Parallel to Slope = Fw*Sin(10) is correct but I'm not so sure about the friction term. I think what you have used.. Cf*Fw*Cos(10) .. is the friction between wheels and ground. For the driving wheels that force is actually acting up the slope not down it. I think you also need to find the rolling resistance instead. I'm not sure if that's typically the same. Edit: I checked and they are very different. If the wheel doesn't slip no power is dissipated overcoming friction between tyre and ground. You need to use the rolling coefficient instead. 



#3
Feb1713, 02:35 PM

P: 2

Thanks for the response. The coefficient of friction method seemed like it was returning really high values.
Is the COF based on a surface to surface contact and the rolling resistance is based on a point to surface contact? It seems like that would results in some more reasonable values. 


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