2. Checking for Traction ©2009 Dr. B. C. Paul Note – These slides contain material from slides dating back to 2000 as well as information and screen shots from the Caterpillar Performance Handbook

3. When Tires Spin l The fact that an engine and drive train can develop power does not guarantee it can be transferred to the wheels (if you’ve even driven after a freezing rain you probably know this) l Maximum force that can be transferred is Weight on Drive Wheels*Coef of Friction * Cos (slope of ground)

4. The Traction Calculation l Coef of friction depends on road material primarily Generally get from table l Cos(slope) term is usually almost 1 for 10% grade cos(slope) = 0.995 Common practice to take as unity l Weight is weight on Drive Wheels (in lbs) - important distinction for two wheel drives

5. Cat Handbook Gives the Weight Distribution 53.1% when empty

6. Getting Coef of Friction from Table 0.2 would be common For loose sand (like On the sand dunes)

7. Checking Our Force Available l A two wheel rear drive truck will have the minimum force relative to its weight when it is empty (you folks that put weight in the back of your pick-ups after snow or ice already know this) l 303,025 lbs*0.531*0.2 = 32,181 lbs (from program) (Weight Prop to Rear (Coef of Friction Sand) from Cat Handbook)

8. Now We Need to Know How Much Force We Need l Of course our Resistance to Travel is measured in % equivalent grade which is not the same unit. l The traction available is in Rimpull units or force available at the tire and road interface We need to get our equivalent grade converted to Rimpull

9. Review of Resistance l Grade Resistance Good old physics problem where break forces into components 2000 * sin (pheta)

10. Simplifying Grade Resistance l Tan (θ) = Rise / Run (slope units) l At Slopes less than about 20% Tan (θ) = Sin(θ) l Adjusting for Percentage Grade instead of rise over run 20 lbs/ton * % Grade = Grade Res. l We just took the Trig out of Grade Resistance Calculations and got a way to convert % grade to rimpull

11. Lets Check Out Those Sand Dunes l 1.5% slope of grade resistance and 10% rolling resistance Equivalent grade is 11.5% At 20 lbs/ton * 11.5 = 230 lbs/ton l Empty Weight of Truck (Cat 789) is 303,025 lbs or 151.51 tons l Rimpull needed to go through the sand 151.51 * 230 = 34,874 lbs of Rimpull

12. Todays Word is _ _ _ _ _ _ _ l We need 34,478 lbs of rimpull to go through the sand l We can develop 32,181 lbs of rimpull before the tires spin l Anyone for a fleet of 175 cat trucks stuck inconspicuously in the desert sands on a secret route where they are not suppose to be?

13. Limitations of FPC l FPC does not check good old tire spinning and traction At any rate that lovely fleet of Cat 789 trucks we carefully planned out just went to you know where in a hand basket l With a Fresh dose of Paranoia I’m going to check out my Cat 775 and 777 before going any further (Note that the order of some calculations does not have to be the same)

14. Checking The Cat 775 l 102,490 lbs l X.541 to rear l X.2 Coef Frict l 11,089 lbs rimpull available l 102,490 lbs l / 2,000 lbs/ton l 230 lbs/ton resistance l 11,789 lbs rimpull needed Holly Weasel Crap we just lost another one

15. Checking the 777 l 160,734 lbs l X 0.5825 to rear l X 0.2 Coef frict l 18,756 lbs rimpull available l 160,734 lbs l / 2000 lbs/ton l X 230 lbs/ton l 18,484 lbs rimpull needed Well at least we did not loose them all

16. Plans for the Rest of the Demonstration l Idea was to compare different truck fleets l Get them all to work l Then compare cost l At this point only 1 truck and 1 loader can even work We can, however vary loading pattern And we can vary the exact truck to loader ratio