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A short class with Sarah and her students. The other ways are under More.
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To start, let’s convert vehicle weight into tons since rolling resistance is frequently expressed in kg per ton. Can anyone tell me how we do that?
We divide the weight in kg by 1000, because 1000 kg equals 1 ton.
Exactly! For example, if our machine weighs 50,000 kg, how many tons does it weigh?
That would be 50 tons.
Correct! Now, the rolling resistance is given as 28 kg per ton. Can anyone help me calculate the total rolling resistance for our 50 tons machine?
We multiply 50 tons by 28 kg per ton to get 1400 kg.
Great job! So the total rolling resistance is 1400 kg.
What does that mean for the machine? How do we move it?
It means that the machine needs 1400 kg of tractive effort to overcome that resistance!
Now let’s add another layer—penetration resistance. If the tire sinks 6 cm into the surface, how do we figure out the penetration resistance?
We multiply the depth of penetration by the effort required per centimeter and then by the total weight.
Very well! Given that it requires 6 kg per ton per centimeter for penetration, how do we calculate that?
We can multiply 6 kg by 6 cm and then by 50 tons, resulting in 1800 kg.
Exactly! Let’s find the total resistance. Can someone add the rolling and penetration resistance for us?
That would be 1400 kg plus 1800 kg, equaling 3200 kg total resistance.
Correct! Now, we know the machine needs at least 3200 kg of tractive effort to overcome this resistance.
When machinery ascends a slope, what do we call the opposing force?
That’s called grade resistance!
Exactly! And what happens when the machine is moving down a slope?
That’s grade assistance, which reduces the power needed!
Perfect! Let’s say we have a 5% slope. How would we quantify the grade resistance required?
For each 1% of grade, we need 10 kg per ton. So it would be 5 times that for a 5% slope, or 50 kg per ton.
Right! Can someone calculate the needed tractive effort if our machine is 50 tons?
That would be 50 times 50 kg, which equals 2500 kg!
Awesome! So, how do we apply this when planning our haul route?
We should avoid steep slopes if we can, to reduce required power and costs.
Effective tractive force on wheels; important for calculating propulsion.
Equivalent force for tracked vehicles; crucial for load hauling.
Resistance from vehicle weight; needs to be calculated for efficiency.
Effort to pull a tire sunk into a surface; affects total power.
Force needed to overcome gravity on slopes; essential in route planning.
Reduced power when moving downhill; important for power management.
Impacts usable power; based on the surface conditions.
A machine with a gross weight of 50 tons and a rolling resistance of 28 kg/ton has a total rolling resistance of 1400 kg.
On a 4% slope, using the guideline of 10 kg/ton for grade resistance, a 15-ton machine would require an additional 600 kg of tractive effort.
If the usable power from a tractor is 7000 kg and 1500 kg is used for resistance, 5500 kg is available to tow a load.
Rimpull and drawbar pull, help machines move with power full.
Imagine a heavy tractor on a hill; it needs extra push, even when still - that’s grade resistance, you see, pulling uphill takes more energy.
R R G A: Rolling Resistance, Grade Resistance, Grade Assistance.
RPG: Rimpull - Penetration - Grade; a guide to remember key forces.
Term
What is Rimpull?
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Term
What is Drawbar Pull?
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Term
What does Rolling Resistance refer to?
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Term
Define Grade Resistance.
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The tractive force developed at the point of contact between the tire and the ground, mainly for wheeled machinery.
The equivalent concept of rimpull for tracked or crawler-mounted machines.
The force opposing the motion of a vehicle caused by the weight of the vehicle.
The effort required to move a tire that sinks into a surface, calculated by the depth of penetration.
The additional force required to move a vehicle up a slope against gravity.
The decrease in power needed for a vehicle moving down a slope due to gravitational assistance.
The measure of grip between the tire (or track) and the surface which affects usable power.
The actual power that can be used for work after overcoming resistance.
This section discusses the concepts of rimpull and drawbar pull, highlighting how they relate to vehicle resistance and the requirements for selecting machinery based on resistance calculations.
The section explains how to convert vehicle weight into tons for calculating rolling resistance, penetration resistance, and total resistance. It then explores the concepts of grade resistance and grade assistance, providing guidelines for determining the required tractive effort for machines working on slopes. Additionally, it elaborates on the usable power from machines, emphasizing the importance of traactile resistance and the influences of project conditions on power generation.
This section centers on understanding the dynamics of rimpull and drawbar pull in relation to machinery performance on varying terrains. It begins with conversions of vehicle weight from kilograms to tons, essential for calculating resistance values used in heavy machinery. The rolling resistance is defined as the force opposing motion due to the weight of the vehicle, which in the example provided, totals at 1400 kg when a gross weight of 50 tons and a rolling resistance of 28 kg per ton are applied.
Further, the section delves into penetration resistance, characterized by tires sinking into a surface. Calculating performance requires understanding how penetration into the surface increases the required tractive effort due to resistance ( 1800 kg for a 6 cm penetration into the surface). The overall resistance encountered by the machine is quantified by summing rolling and penetration resistances, leading to a total resistance of 3200 kg.
The teacher then introduces grade resistance, a crucial factor when machines ascend slopes, requiring additional effort due to gravity. The grade assistance concept is also presented, which reduces the necessary power when descending slopes. A clear guideline is given: for a slope of 1% grade, an estimated 10 kg per ton of tractive effort is required, applicable mainly for slopes under 10%.
The section emphasizes the significance of selecting haul routes effectively to minimize resistance and elevate power generation efficiency for machinery. Finally, the available power rating from manufacturers is discussed, highlighting factors such as operational conditions affecting real-world power generation. It is concluded that usable power must emerge post-calculating resistance efforts, with rimpull for wheeled machinery and drawbar pull for tracked machinery defining how much force is effectively exerted at the ground contact point.