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A short class with Sarah and her students. The other ways are under More.
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Today, we will start with rolling resistance. Can anyone tell me what rolling resistance is?
Is it the resistance a vehicle faces while rolling on a surface?
Exactly! Rolling resistance is essentially due to the deformation of tires. Now, if we have a machine that weighs 50 tons and a rolling resistance of 28 kg per ton, how do we calculate the total rolling resistance?
I guess we would multiply 50 tons by 28 kg per ton?
Yes! This gives us 1400 kg of rolling resistance. Remember to think of it as an acronym: TRRP - Total Resistance from Rolling Power.
So could we use this method for other weights too?
Absolutely, this formula applies universally!
What about penetration resistance?
Great question! Penetration resistance depends on how deep the tire sinks into the surface.
In summary, rolling resistance affects how much effort is needed to move. We multiply gross weight by rolling resistance value to find it. Next, we will explore penetration resistance.
Moving on from rolling resistance, let's calculate penetration resistance. What factors do we need to consider?
We need to know the penetration depth in centimeters and the weight of the machine in tons.
Correct! For our machine weighing 50 tons, if it sinks 6 cm, and we know it requires 6 kg per ton per centimeter, what is the calculation?
So, we do: 6 kg/ton/cm * 6 cm * 50 tons, right?
Precisely! This gives us 1800 kg for penetration resistance. Remember the acronym: PRD - Penetration Resistance Dynamics.
So, total resistance now includes both rolling and penetration resistance?
Exactly! Total Resistance equals TR + PR. Now let's calculate total resistance.
To recap, rolling and penetration resistance give us total resistance calculations which are crucial for machinery selection.
Let's discuss grade resistance. What happens when a machine goes uphill?
It needs more power to overcome the weight against gravity!
Correct! The steeper the slope, the more resistance it faces. For 1% of grade, we add 10 kg per ton to our calculations. Can anyone tell me about our example machine?
If it's on a 4% grade, it would need an additional effort of 40 kg per ton?
Exactly! So that includes 4% multiplied by 10 kg per ton, which equals 600 kg additional resistance for our 15-ton machine.
And how does this affect our total resistance?
Great question! Total resistance is now the sum of rolling, penetration, and grade resistances. Remember: GR - Grade Resistance!
So, it's essential to minimize grade resistance in haul route selection?
Absolutely! Understanding these resistances helps us choose the right equipment.
Let's recap all that we've learned about total resistance. Can someone summarize the components?
We have rolling resistance, penetration resistance, and grade resistance.
Correct! So how do we arrive at the total resistance?
By adding all three types of resistance together.
Exactly! Now, why is this important for selecting machinery?
To ensure the machine can generate enough power to overcome total resistance!
Precisely! You must know the total resistance to select appropriate equipment effectively.
So, our key takeaways today include understanding the types of resistance and how they contribute to machinery efficiency.
The force resisting the motion of a rolling vehicle.
Resistance due to tire depth affecting movement.
Force needed to move uphill, opposing gravity.
Sum of all resistive forces affecting machine movement.
Total force required to overcome resistance.
To find resistance, don’t delay, just multiply and add away!
Imagine a truck crossing a hill. As it rolls, it struggles uphill, sinking deep where tires feel the weight. Remember, each climb needs more power to compensate!
Remember TRP: Tractive Resistance from Power, where T stands for total, R for rolling, and P for penetration!
GRT for Grade Resistance: G for Grade, R for Resistance, T for Total force needed.
Term
Total Resistance
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Term
Rolling Resistance
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Term
Penetration Resistance
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Term
Grade Resistance
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Term
Tractive Effort
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The opposing force experienced by a vehicle due to tire deformation and the contact with the ground.
The resistance encountered by a vehicle due to the depth of tire penetration into the surface.
The additional resistance a vehicle faces when moving uphill against gravity.
The force required to overcome resistance and move the vehicle forward.
The sum of rolling, penetration, and grade resistances affecting the motion of the vehicle.
This section covers the calculations involved in determining total resistance for vehicles on haul routes, including rolling resistance and grade resistance.
This section explains the process of calculating total resistance for heavy machinery by considering both rolling resistance per ton based on vehicle weight and grade resistance based on slope percentage. Detailed examples illustrate the importance of these calculations in determining the tractive effort required to overcome resistance.
In this section, we explore the calculation of total resistance faced by vehicles, particularly in the context of machinery used at project sites. The gross weight of the machine is initially converted into tons for simplicity, using a conversion factor (1000 kg = 1 ton). Once the gross weight is identified, rolling resistance is calculated by multiplying the gross weight by a given rolling resistance value, expressed in kg per ton. For instance, a machine weighing 50,000 kg (or 50 tons) with a rolling resistance of 28 kg per ton results in a rolling resistance of 1400 kg.
Next, penetration resistance due to the depth a tire sinks into the surface is determined, with the energy needed per centimeter of penetration also given as kg per ton per centimeter. Continuing with the same gross weight example, a 6 cm penetration results in a penetration resistance of 1800 kg. The total resistance is the sum of both resistances, leading to a total of 3200 kg of resistance that the machine must overcome. The section further discusses grade resistance, highlighting how slope steepness impacts the tractive effort required, with every 1% of slope demanding an extra 10 kg per ton. Lastly, the significance of accurately estimating these resistances is emphasized for selecting appropriate machinery capable of overcoming the identified total resistance.