3.3. Rimpull and Drawbar Pull

So, let us convert the vehicle weight into tons, because your rolling resistance is commonly expressed as kg per ton. So, let us convert the weight of the machine into tons you know that the gross weight of the machine is given as 50,000 kg. So, 1000 kg = 1 ton, so divided you will get the gross weight of the machine as 50 tons. Now the rolling resistance you need to calculate for this particular haul route it is given as 28 kg per ton.

This chunk introduces the concept of rolling resistance, which is the force resisting motion when a vehicle rolls on a surface. First, the gross weight of a machine, given in kilograms (50,000 kg), is converted into tons (50 tons). This conversion is necessary because rolling resistance is typically expressed in kg per ton. For this machine, the rolling resistance specified for the haul route is 28 kg per ton, meaning for each ton of weight, an additional force of 28 kg is required to move the vehicle.

Think of rolling resistance like trying to push a heavy shopping cart on a bumpy surface versus a smooth one. The bumps create resistance (like rolling resistance), making it harder to push. If your cart is heavy (like a truck), every additional kilo of weight means you need more effort (force) to push it.

So, you multiply the gross weight of the machine by the rolling resistance value. So, gross weight is 50 tons multiplied by the rolling resistance is 28 kg per ton for that particular haul route. So, now we are going to calculate for your particular vehicle what is the total rolling resistance? That is nothing but 1400 kg, so 1400 kg is your rolling resistance.

In this section, we see how to calculate total rolling resistance using a formula. You multiply the gross weight of the vehicle (50 tons) by the rolling resistance (28 kg per ton) to get the total rolling resistance, which equals 1400 kg. This value tells you the total extra effort needed to move the vehicle solely due to the weight and the specified rolling resistance.

Imagine pushing a sled that weighs 50 kg across snow. If the snow creates a drag (rolling resistance) of 28 kg for every 100 kg, you would need to exert an extra 1400 kg of force to just get it moving. It’s like the heavier the item, the harder it becomes to push across a rough surface.

Now we need to find the penetration resistance. It is given to you in the problem that the tyre is sinking to the depth of 6 centimeters into the surface. So, you know that for each centimeter of penetration the amount of effort needed is 6 kg per ton per centimeter.

Penetration resistance refers to the resistance encountered when a tire sinks into a surface, such as mud or soft soil. In our case, the tire sinks 6 cm into the surface. The resistance is determined by knowing that each centimeter of penetration requires an additional force of 6 kg per ton. Therefore, we multiply the depth of penetration (6 cm) by 6 kg per ton and then by the gross weight of the vehicle (50 tons) to get the total penetration resistance.

Consider a car tire sinking into soft sand at the beach. As the tire sinks deeper, it requires more effort to pull it out. If you're on sandy ground, every inch of sink means you have to push harder (more penetration resistance). Here, each cm of tire penetration adds extra force needed to keep driving.

Now we can find the total resistance, that is nothing but add your rolling resistance and the penetration resistance. It is nothing but your 1400 kg + 1800 kg, so that gives me the answer as 3200 kg is the total resistance.

To find the total resistance a vehicle faces, we simply add the rolling resistance (1400 kg) to the penetration resistance (1800 kg). This results in a total of 3200 kg, representing the total effort required to overcome both types of resistance when moving the vehicle across the specified haul route.

Think of this total resistance like trying to walk on two different terrains - one is rocky (like rolling resistance) and the other is muddy (like penetration resistance). The total effort you need to exert to walk through both terrains is the sum of the effort needed for each terrain.

So, I need tractive effort of at least 3200 kg to overcome this resistance in a project site. So, the total tractive effort needed to overcome this resistance is 3200 kg. So, select the machine accordingly, that is the purpose of estimating all this resistance, so that we can know what is the required power for your machine? Select a machine that can generate enough power to overcome this resistance.

The term 'tractive effort' refers to the force required to move a vehicle and overcome the total resistance (3200 kg). This calculation is essential for selecting the right machine; it must be powerful enough to produce at least this level of tractive effort in order to function effectively on the project site.

Think of a car trying to drive up a steep hill. To ensure it can make it up, you need to know how much power (tractive effort) the car must have capable of overcoming gravity and resistance, just like knowing how much horse power you need when trying to tow a trailer up a hill.

Now so far, we have discussed about the rolling resistance, let us look into the other part of the resistance in your project site that is your grade resistance. Most often you can see that equipment has to climb up a slope. So, 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.

Grade resistance is the additional effort needed when a vehicle is moving up a slope. This is because the vehicle has to work against the force of gravity. The steeper the slope, the more tractive effort is required to move the vehicle forward. It’s important to consider this when planning any transport on hilly terrain.

Imagine trying to ride a bicycle uphill. You feel the extra effort required to push yourself up the slope, compared to riding on a flat road. That extra effort required to go uphill is similar to grade resistance, which makes your ride harder and requires more power.

So, similar to this, we should also know about what is grade assistance? So, we discussed about what is grade resistance, there is something called as grade assistance that means what? When your machine is moving down the slope, you can see that the amount of power needed gets reduced because it can easily move down by the gravity.

Grade assistance refers to the reduction in the amount of power needed when a machine moves down a slope instead of up. The gravitational pull helps to push the vehicle down, thereby requiring less tractive force compared to moving uphill. This can greatly lower fuel consumption and preserve power.

Riding your bike downhill feels much easier than going uphill, right? Just like how gravity helps you glide down, machines benefit from grade assistance when descending slopes, requiring less effort and, hence, less power.

So, grade resistance is nothing but by simple elementary I mean a mechanics people have worked out this the relations. Say for example, for 1% of grade so the amount of tractive effort needed to overcome this 1% of grade it is 10 kg per ton.

To calculate grade resistance, a guideline is given that for every 1% increase in slope, an additional effort of 10 kg is required for each ton of weight. This rule helps in estimating the total effort needed based on the gradient of the slope. The steeper the slope, the greater the resistance that must be overcome.

Consider hiking up a hill: the incline makes you exert more energy. If we use percentages to measure steepness, it's like saying for every 1% of incline, you need to push harder. So for a 5% incline, you'd need to exert a cumulative effort that reflects this increased push against gravity.

So, you can convert a rolling resistance also into equivalent gradient. The rolling resistance which you have expressed in kg per ton, that you can converted into gradient percentage equivalent gradient.

Rolling resistance can be expressed as an equivalent gradient, making it easier to compare with grade resistance. By knowing that 1% grade equals 10 kg per ton, rolling resistance expressed in kg per ton can be converted into a percentage. This allows for clearer understanding alongside grade resistance, facilitating better calculations.

Think of solving problems with multiple unknowns. Converting rolling resistance into gradient makes it simpler, just like converting all your measurements into the same unit, ensuring easier comparisons and calculations when planning your project.

Now we are going to look into the estimation of the available power.

The available power of a machine is determined by the manufacturer and can be rated for standard conditions. However, in practical scenarios, conditions such as altitude and temperature can impact the machine's performance, which means that the actual usable power could be less than what is rated. Understanding this distinction is important in order to choose the right machine for the job.

Imagine a sports car capable of going 0-60 miles per hour in a flat area. Now, take it to a mountain: its performance won't be the same because of altitude and other environmental factors that slow it down. Similarly, knowing how much usable power you truly have in your working environment is crucial.

So, now let us see what is the usable power? So, out of the available power prescribed by the manufacturer, how much amount of power becomes usable to you?

Usable power refers to the portion of a machine's power that can be utilized after accounting for the resistance encountered onsite. To find the usable power, you take the total power and subtract the power used to overcome resistance. This usable power is vital for carrying out tasks like towing or hauling material effectively.

Picture a delivery truck that has a certain horsepower rating. But when it is loaded heavily with packages and struggles to move, the effective power it can apply to drive is less than its rated horsepower. Thus, knowing the usable power is essential for the truck to effectively complete its deliveries.

The usable power you can express in terms of rimpull or drawbar pull. So, depending upon the mounting of your machine. So, if it is going to be wheel or tyre mounted machine, we call it as rimpull. The usable tractive force developed at the point of contact between the tyre and the ground is called as a rimpull.

Rimpull (for wheeled machines) and drawbar pull (for tracked machines) are terms used to describe the usable force available at the point of contact with the ground. Rimpull refers to the force generated at the tires, while drawbar pull refers to the force available to move a load through a hitch or drawbar for tracked machines. Both concepts capture the effectiveness of the machine in terms of power transfer to the surface below.

Think of a bulldozer pushing dirt. The strength it pushes with through its tracks represents the drawbar pull. Meanwhile, a pickup truck pulling a trailer's weight through its rear wheels shows rimpull. Both are necessary to understand how well these vehicles can perform their tasks on the job site.

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