8.3. Gravity Resistance

Generally, what is the power needed by the machine to overcome the resisting forces in the project site and keep the machine moving, that is what is a required power.

Required power is the total power necessary for a construction machine to operate effectively at a project site. It includes the power required to counteract all the resisting forces the machine faces, such as the weight of the load and the resistance of the ground over which it operates.

Think of required power like the effort needed for a person to push a car. If the car is on a flat road, less effort is needed than if it's on a hill or muddy ground. In both scenarios, the person pushing (the machine) needs power to overcome the hill (resisting forces).

What are all the different types of resistances the machine is going to encounter? That is what we are going to see, one is rolling resistance, other one is a grade resistance.

Machines face different types of resistance when they operate. Rolling resistance occurs when the wheels or tracks of the machinery roll over the surface, resisting movement. Grade resistance, on the other hand, refers to the challenges presented by slopes, requiring additional power when moving up or down.

Imagine riding a bicycle. Riding on a flat road is easier (lower resistance) than riding up a steep hill (higher grade resistance). Similar to how the bike can struggle depending on the surface and slope, machines also experience different types of resistance, affecting the needed power.

Rolling resistance is nothing but what is the resistance offered by the hauled route to the wheel which is rolling over the particular surface.

Rolling resistance is the force that opposes the motion of a wheel as it rolls over a surface. This force is affected by the type and condition of the surface – for example, hard surfaces like concrete provide less resistance compared to soft or uneven terrains, such as dirt or gravel, which can create more drag.

Imagine pushing a grocery cart on different surfaces. It is much easier to push it on a smooth floor (like concrete) than on a rough gravel path where the wheels face more resistance. In the same way, construction machinery needs more power to move over soft or unmaintained surfaces due to higher rolling resistance.

Your rolling resistance is going to depend upon so many factors; one is on your mounting. If it is going to be a wheel mounting, it depends upon the dimension of your tread, it depends upon inflation pressure in your tyre.

The rolling resistance varies not only with the type of road but also with the machine's design. For instance, a wheel-mounted machine's rolling resistance can change depending on tire size and tread pattern, as well as the tire's inflation pressure. Wider tires typically distribute weight better on softer surfaces, reducing resistance.

Consider a car; if it has wider tires, it spreads its weight over a larger area, causing it to sink less in the sand when driving on the beach. Thinner tires may dig in more, making it harder to move. Similarly, the machinery selects tire types based on their operating environments to minimize rolling resistance.

Rolling resistance is expressed in kilograms of tractive effort or pounds of resistance, these are just different types of units.

Rolling resistance can be quantified in terms of tractive effort, which is the force required to keep the machine moving at a certain speed on a level surface. This measurement helps engineers determine how much power is necessary for the equipment to perform its tasks efficiently.

Imagine trying to push a friend on a sled across a flat surface. If you know how heavy the sled is, you can estimate how hard you need to push to get it moving. This is somewhat similar to how rolling resistance tells us how much force is needed to operate machines on different surfaces.

--