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Interactive Audio Lesson
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Understanding Rolling Resistance
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Let's start with rolling resistance. Can someone tell me why we convert vehicle weight into tons?
Isn't it because rolling resistance is given in kg per ton?
Exactly! For our example, a 50,000 kg vehicle converts to 50 tons. If rolling resistance is 28 kg per ton, what do we get?
We multiply 50 tons by 28, which gives us 1400 kg of rolling resistance.
Great! So, if we need to know the total resistance, we also have to consider grade resistance. Let’s take a look at that next!
Calculating Grade Resistance
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Now, moving on to grade resistance. When machines climb a slope, what do we need to account for?
The slope's steepness and how it affects the force opposing the vehicle!
Exactly! If a slope is 4%, that means for every 100 meters horizontally, the vehicle rises 4 meters. How do we calculate the tractive effort needed for this grade?
We take the percentage and multiply it by 10 kg per ton. So for a 4% slope and 50 tons, it should be 4 times 10 times 50?
That's right! So that’s 600 kg for grade resistance. What’s next?
Total Resistance Calculation
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Excellent! Now let's find the total resistance. How do we combine rolling and grade resistance?
We just add them up! So, 1400 kg plus 600 kg gives us 2000 kg total resistance.
Almost there, but remember there were some earlier numbers in our example. Correct this with rolling resistance being 900 kg for another case.
So that makes the total resistance 1500 kg.
Perfect! And this indicates the minimum tractive effort needed for a project site. What machine should we select based on that?
Understanding Power Requirements
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Now that we know total resistance, how do we utilize that in selecting equipment?
We need to know the maximum rimpull of the machine.
Exactly! If the maximum available rimpull is 7000 kg, how much power do we have left for actual work after overcoming resistance?
If we use 1500 kg to overcome resistance, we have 5500 kg for towing!
Correct! So remembering this power-pull relationship assists in ensuring we choose the right machine for the task. Keep these calculations in mind!
Introduction & Overview
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Quick Overview
Standard
In this section, the calculation of rolling resistance based on vehicle weight and rolling resistance per ton is discussed, followed by an explanation of grade resistance due to incline. It emphasizes understanding tractive forces required to overcome resistance while operating vehicles on slopes.
Detailed
In the study of major resistances affecting vehicle performance, we focus on rolling and grade resistance. Rolling resistance is calculated by converting vehicle weight into tons and applying provided rolling resistance values. For a machine weighing 50 tons and encountering a rolling resistance of 28 kg per ton, the total rolling resistance amounts to 1400 kg. Additionally, when a vehicle operates on a slope, grade resistance arises from the gravitational force opposing its motion. This section illustrates how to quantify this force based on the slope's percentage—4% grade equates to a resistance of 40 kg per ton. Thus, we see the total resistance combining rolling and grade resistance, with their calculations leading to critical insights on necessary tractive efforts and suitable machine power selection.
Audio Book
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Understanding Grade Resistance
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When the machine is climbing up the slope, obviously you need some additional efforts to make it move up the slope because it is pulling against the gravity. So, there is a force opposing the movement of the machine when it is moving up the slope that is causing grade resistance.
Detailed Explanation
Grade resistance refers to the additional force required to move a machine up an incline or slope. This resistance is caused by the weight of the machine acting against gravity, which necessitates more power or effort for the machine to ascend. As the slope becomes steeper, the grade resistance increases, meaning more power is needed to maintain movement.
Examples & Analogies
Imagine trying to ride a bicycle up a hill. You have to pedal harder to overcome the pull of gravity compared to riding on flat ground. Similarly, when heavy machinery climbs a slope, it faces a greater challenge due to grade resistance.
Calculating Grade Resistance
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To overcome this grade resistance, that depends upon the percentage of the slope how steep is your slope? According to the tractive force requirement will vary. For 1% of grade, the amount of tractive effort needed to overcome this 1% of grade is 10 kg per ton.
Detailed Explanation
The grade resistance can be calculated based on the slope percentage of the incline. For every 1% of slope, a machine requires approximately 10 kg of force for each ton of its gross weight to counteract this resistance. This formula helps in estimating the total tractive effort needed based on the slope's steepness and the machine's weight.
Examples & Analogies
Think of it like pulling a sled up a hill. If the hill is gentle (1% slope), it's easier to pull, requiring less force. If the hill is steep, you need to exert significantly more force to keep moving up, just as machinery does on inclines.
Grade Resistance Calculation Example
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For 4% gradient, the grade resistance calculated is 4 x 10 x (gross weight of the machine in tons). If the machine weighs 15 tons, this results in 600 kg as the tractive effort needed.
Detailed Explanation
To calculate the grade resistance for a specific slope percentage, multiply the percentage by 10 kg (the resistance per ton) and then by the machine's weight in tons. For example, for a 4% grade and a 15-ton machine, you would do 4 x 10 x 15 = 600 kg to find the total tractive effort required to overcome the grade resistance.
Examples & Analogies
Imagine a heavy vehicle going up a ramp to load cargo. The steeper the ramp, the more strength the vehicle must exert to climb it. In this case, because of the ramp's steepness, the vehicle must exert an additional effort equating to 600 kg to successfully navigate the incline.
Grade Assistance
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When your machine is moving down the slope, the amount of power needed gets reduced because it can easily move down by the gravity, so this is called grade assistance.
Detailed Explanation
Grade assistance refers to the reduction in power required when a machine is descending a slope. Unlike climbing, the machine benefits from gravity, which helps it move downwards more easily. This assistance decreases the total working power needed from the machine when carrying out tasks on a downward slope.
Examples & Analogies
Think about going down a slide at the playground; you naturally go faster and require less effort as gravity pulls you down. Similarly, machines utilize gravity to aid their descent, thus reducing their power requirements.
Selecting the Right Haul Route
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When selecting the haul route, if there is an option to use a downslope, it is always preferable to use down slopes, because your power required gets reduced.
Detailed Explanation
Choosing the appropriate path or haul route for machinery is crucial. If a route includes a slope that goes downwards, this will reduce the power needed for the vehicle to move. Therefore, optimal route planning can significantly save operational costs and enhance efficiency by minimizing the resistance faced by the equipment.
Examples & Analogies
Picture a delivery truck navigating a series of hills. If the route includes a downhill stretch, the driver can save fuel because the vehicle uses less power to coast down compared to struggling up the next hill. Similarly, choosing to work on downgrades saves energy and costs for heavy machinery.
Definitions & Key Concepts
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Key Concepts
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Rolling Resistance: The resistance encountered due to a vehicle's weight and the surface.
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Grade Resistance: The additional resistance faced when moving up a slope, depending on its steepness.
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Tractive Effort: The force required to counteract both rolling and grade resistance.
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Rimpull: The usable pulling power of a vehicle, calculated after deducting resistance forces.
Examples & Real-Life Applications
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Examples
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For a machine with a gross weight of 50 tons on a road with a rolling resistance of 28 kg per ton, the total rolling resistance would be calculated as 50 tons * 28 kg/ton = 1400 kg.
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When calculating grade resistance for a 4% slope, apply the formula for tractive effort needed: 4% * 10 kg/ton * 50 tons = 600 kg.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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To climb a hill, your power must rise, for every slope, see ‘Resistance’ in size.
📖 Fascinating Stories
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Once upon a time, a truck wanted to climb a steep hill. He had to prepare carefully, measuring his load and the hill's height to ensure he had enough power to overcome the challenges ahead.
🧠 Other Memory Gems
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Remember R-G-T: Resistance, Grade, Tractive, to conquer your vehicle’s uphill grape!
🎯 Super Acronyms
RAGE
- Rolling
- Assist Grade Equivalence to remember essential resistances in machines.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Rolling Resistance
Definition:
The force opposing the motion of a vehicle due to its weight and surface interaction.
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Term: Grade Resistance
Definition:
The force opposing a vehicle's movement when ascending a slope, influenced by the slope percentage.
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Term: Tractive Effort
Definition:
The force exerted by a machine to overcome resistance and move loads.
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Term: Rimpull
Definition:
The usable tractive force generated at the point of contact between the tire and the ground.
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Term: Coefficient of Traction
Definition:
The ratio indicating the amount of grip between the wheel and the travel surface.