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A short class with Sarah and her students. The other ways are under More.
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Let's begin with rolling resistance. Can anyone tell me what rolling resistance means?
Is it the resistance a vehicle faces when moving because of its weight?
Exactly! Now, if a vehicle weighs 50 tons and the rolling resistance is 28 kg per ton, how do we calculate it?
We multiply 50 tons by 28 kg per ton, right?
Correct! This gives us the total rolling resistance of 1400 kg. Great job! Now, remember this acronym: ROLL - Rolling Overcomes Lots of Load!
That’s a good way to remember it!
Now, can someone explain why we convert weight to tons in these calculations?
Because rolling resistance is expressed per ton!
Exactly! We're setting the stage for calculating penetration resistance next.
Now, let's dive into penetration resistance. What happens when tires sink into the ground?
They create more resistance that needs to be overcome, right?
Absolutely! If the tire sinks 6 cm with a resistance of 6 kg per ton per cm, how do we calculate the penetration resistance?
We calculate it by multiplying 6 cm by 6 kg per ton by the gross weight in tons?
Exactly! This results in 1800 kg of penetration resistance. Who remembers the total resistance calculation?
You add the total rolling resistance and penetration resistance!
That's right! And what is our total again?
3200 kg!
Perfect! Remember the mnemonic: DEPTH - Depth Equals Penetration's Total Hardship!
Let's turn our attention to grade resistance. What do we mean by 'grade'?
Isn’t it just the slope of the ground we're working on?
Good! So how does a steep slope influence our tractive effort?
We need more tractive effort to go uphill because of gravity!
Correct! For example, how much tractive effort is needed for a 4% slope?
You multiply the percentage by 10 kg per ton and then the gross weight.
Exactly! So if we have a total machine weight of 50 tons for a 4% slope, what’s our grade resistance?
It's 600 kg!
Nicely done! Remember: SLOPE - Steep Lands Overtake Power Exertion!
We need to make sure our machines can handle the calculated total resistance. How do we verify this?
By checking the power ratings the manufacturer gives us.
Right! What are the factors affecting the usable power on-site?
Altitude and temperature conditions can change the efficiency of the machinery.
Well done! Remember the acronym: POWER - Project Operations Will Evolve with Resistance!
That helps a lot!
Finally, if our machine has 7000 kg of maximum rimpull and we've calculated a 1500 kg resistance, how much usable power is left?
5500 kg for towing!
Excellent summary of our session!
Converting vehicle weight to tons for rolling resistance calculations.
The process of calculating both rolling and penetration resistance for any vehicle.
Understanding how different slope percentages influence the tractive effort needed.
The connection between the manufacturer's power ratings and the machine's ability to operate under specific conditions.
For rolling resistance we say, weight and grip lead the way!
Imagine a truck struggling up a hill — the steeper it gets, the harder it spills, rolling down it's a thrill, but up it needs a power drill!
RAMP - Rolling And Moving Power: how to think about tractive efforts on slopes.
REPOWER - Resistance Equals Power On Weight and Resistance.
Term
What is rolling resistance?
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How do you calculate penetration resistance?
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What does grade resistance depend on?
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The force resisting a vehicle's motion due to its weight, expressed in kg per ton.
The additional force required when a vehicle's tire sinks into the surface, typically dependent on depth.
The additional effort required to overcome gravity when a vehicle moves up a slope.
The force that a machine must exert to move itself forward, overcoming all forms of resistance.
The designated path over which vehicles move, which can affect total resistance based on its characteristics.
This section covers the calculation of penetration resistance in vehicles, including rolling resistance and grade resistance.
The section outlines methods for calculating rolling resistance based on vehicle weight and specific resistance values. It also discusses grade resistance and how it impacts total resistance when a vehicle travels up or down a slope, allowing for a better understanding of the overall resistance that a machine must overcome at a project site.
The calculation of penetration resistance is crucial in understanding the total resistance a vehicle must overcome in a worksite, particularly for off-road machinery. This section begins with the conversion of vehicle weight into tons, which is essential since rolling resistance is commonly expressed as kg per ton.
Rolling Resistance Calculation: The gross weight of a machine is typically given, in this case, as 50,000 kg, equivalent to 50 tons. The rolling resistance for the specific haul route being analyzed is given as 28 kg per ton. By multiplying the gross weight by the rolling resistance (50 tons * 28 kg/ton), the total rolling resistance is calculated to be 1400 kg.
Penetration Resistance Calculation: The section continues with penetration resistance, which occurs when tires sink into the ground. The problem specifies a penetration depth of 6 centimeters, with a resistance of 6 kg per ton per centimeter of depth. Thus, multiplying the depth by the resistance and the gross weight (6 cm * 6 kg/ton * 50 tons) yields a penetration resistance of 1800 kg.
Total Resistance: The total resistance, the sum of rolling and penetration resistance, is calculated as 3200 kg (1400 kg + 1800 kg). This total is crucial to determine the required tractive effort needed to move the machinery across the project site, emphasizing the importance of selecting appropriately powerful machines for overcoming these resistances.
Grade Resistance: The section also discusses grade resistance, which arises when a vehicle must move up a slope, requiring additional effort to pull against gravity. It highlights how the grade slope percentage directly influences the additional tractive effort needed. The relationship for grade resistance is simplified where 1% of grade resistance requires 10 kg/ton.
Final Power Requirements: Finally, considerations about the available power ratings of machines are discussed, explaining that these must be compared against resistances to ascertain usable power at project sites.