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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 explain how we calculate it for a vehicle?
Isn't it based on the weight of the vehicle?
Exactly! We first convert the weight into tons. For a vehicle weighing 50,000 kg, that equals 50 tons. If the rolling resistance is 28 kg per ton, what do we get?
We would multiply 50 tons by 28 kg per ton. That gives us 1400 kg!
Great job! 1400 kg is indeed the rolling resistance. Remember, the acronym 'W-R' can help us recall 'Weight to Resistance.'
So rolling resistance is a significant factor to consider when choosing a machine?
Absolutely! Rolling resistance affects how much power we need. Let's summarize: Always convert vehicle weight to tons first and then calculate rolling resistance.
Now, let's discuss grade resistance. Can anyone define what it is?
Is it the force opposing a machine when it climbs a slope?
Exactly right! When climbing, machines face additional resistance due to gravity. The steeper the slope, the more effort we need. How can we express grade percentage?
For example, a 5% grade means that for every 100 meters horizontally, the machine rises 5 meters vertically.
Well said! And if the gradient is -5%, that indicates a downhill slope. Why would we prefer to operate downhill, do you think?
Because it reduces the power needed, right?
Exactly! Summarizing: Greater slope means more power needs, so prefer downhill routes to minimize resistance.
Let’s calculate total resistance. How do we combine rolling and grade resistance?
By adding them together, right?
Correct! If we have rolling resistance of 1400 kg and grade resistance calculated as 1800 kg, what is our total resistance?
That would be 3200 kg!
That's right! To determine the necessary tractive effort, we need at least 3200 kg to overcome both resistances. Remember the acronym 'T-E' for 'Tractive Effort.'
And this is critical for selecting the right machine for a project, right?
Absolutely! Always calculate total resistance to ensure the chosen machinery can achieve the required power.
A force that opposes motion when a vehicle rolls over a surface, determined by weight.
The force that opposes motion when moving uphill, directly linked to slope steepness.
The sum of rolling and grade resistance, critical for determining machinery power needs.
To move up high and not fall back, add your grade to the rolling track.
Imagine a truck climbing a steep hill, struggling against gravity. To decide on the right size, you calculate the load and the slope to ensure the truck can handle the climb.
Remember 'R-G-R-T' for 'Rolling-Grading-Resistance-Tractive'.
Use ‘H.R.U’ for ‘Haul Route Understanding’ to guide route choices for minimal resistance.
Term
What is rolling resistance?
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Term
What affects grade resistance?
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Tractive effort needed?
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The resistance faced by a vehicle when rolling over a surface, calculated based on its weight.
The additional resistance encountered when moving a machine up a slope due to gravitational forces.
The amount of force or power required to move a machine, particularly when overcoming resistance.
The steepness or incline of a slope expressed as a percentage.
A measure of the grip between the wheel or track and the surface.
This section discusses grade resistance and its importance in determining the tractive effort required for machinery operating on slopes.
The section explains how to calculate rolling and grade resistance encountered by machinery on a slope. It details concepts such as rolling resistance necessary to overcome friction and grade resistance caused by gravity, and emphasizes the importance of selecting haul routes effectively to minimize these resistances.
In this section, we explore the calculations surrounding grade resistance, which is crucial for machinery performance on slopes. Starting from basic weight conversions, the section shows how to compute rolling resistance based on a machine's weight and specified resistance per ton. It elaborates on the factors affecting grade resistance, including the slope's percentage and the additional effort needed to overcome gravitational forces acting on the machine when climbing inclines. Additionally, it distinguishes between grade resistance, which increases power needs, and grade assistance, which reduces it when moving downhill. Furthermore, the section describes how to calculate the total resistance encountered by machinery, guiding users to estimate the adequate power requirements based on known resistance values, and highlight the significance of effective haul route selection.