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Dozer Engine Torque and Horsepower Calculations

  1. Aug 2, 2012 #1
    I have been given a project at work to find the number of dozers needed to push a certain volume of material in a certain amount of time. My issue comes with the actual horsepower of the dozers. We run D10T, D11R, D11R CD, and D11T Cat "track-type tractors". So from what I am thinking, I want to find the horsepower to push one cubic yard of our material, then I can easily find the production and the final result. However, my issue comes from finding the horsepower. I do not want to use the horsepowers or torque given in the specifications from Cat, but need to calculate the horsepower for each dozer in each type of material. All I know is the velocity, force the dozer is exerting on the dirt, volume of the dirt being pushed, material characteristics, and the RPM. Any ideas on how to solve this issue?
  2. jcsd
  3. Aug 2, 2012 #2
    it's called drawbar.
  4. Aug 2, 2012 #3


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    If one D11R Cat can push 45 yards of material with 3330,000 pounds of thrust, how many yards can 5 (five) D11R Cat push. Then you just have to figure out how far they will move the material and in what duration of time. Then double the time to add in the return trip.
    Different materials would have an extra time added also for setup for each load and whatnot.

    Are you attemtping to break it down into a formula :
    HP/yard x # of yard = total HP needed ,
    and then allocate different types and numbers of Cats from the total HP calculated?
    Could work theoretically> I still think there still would have to be a fudge factor in there somewhere for unforseen problems.
    If you are in the industry of earth moving, then experience in presenting bids should already have that information within the company. No one at your company with that knowledge?
  5. Aug 3, 2012 #4
    There is (sort of related) expired information within the company. So this is a brand new study.

    I understand what you said, however, I cannot find a reasonable way to calculate the horsepower for each dozer individually. I realize that Cat does supply horsepower and torque information, but I do not trust their numbers, because according to my last study I found that our dozers move twice as much material as the Cat specs say they can.
  6. Aug 3, 2012 #5
    This is one place where theory and practice don't match well. The reason is that it is extremely hard to model the dynamics of hitting the dirt while moving.
  7. Aug 3, 2012 #6
    What something is rated at and what something can do are two different things. I know full well my axle stands can take more than 2 tons, but if I put three tons on it and get squished, it's my fault.

    Those values are what Cat are willing to bet their reputation on, even though you and they know it'll do more.

    Be a good engineer and use book values, if you feel confident enough reduce it by a factor, do so. Calculating power requirements is really just a meaningless exercise as you are assuming so much.
  8. Aug 3, 2012 #7
    Chris: I understand where you are coming from, but in today’s environment that is rather outdated advice. The reason that fleets are hiring engineers is to do better than the book. I was an engineer for a fleet big enough to employ four and sometimes five engineers for about 25 years. Our reason for employment was to carefully scrutinize every aspect of the business to figure out how to either get more production from the fleet, or to minimize the cost of maintaining and operating it, or to optimize the frequency of equipment replacement. We are also heavily involved in deciding which mix of equipment will have the best ROR. I never take what the OEM publishes as gospel truth. Very little of it is good for any particular fleet operator because they try to make that information either applicable to all users, or the worst user; depending on what their lawyers and bean counters tell them is most appropriate.

    If I push equipment beyond its operational ratings, then I know I will shorten the life and increase repair costs. But I need to know what those costs are and what benefits those costs buy me. After performing that decision analysis, I’ll often go run the piss out of it. A good example is a scallop boat captain I know. I talked to him after he capsized his four million dollar boat because he was hauling too heavy a load. I asked him why he did that. He says that by carrying the extra product, he can make an extra $10,000 per day when the scallops are plentiful, and sometimes much more than that—and he has demonstrated a very excellent ability to put his boat where they are plentiful. He knows that he is increasing the risk of capsizing, but he has mitigated that risk the best he can so that he has only lost two boats in 40 years. So he provides the ability to his crew to make a boat loss survivable and the boat recoverable at minimum costs; and then he runs for it. We do much the same thing in the heavy equipment world.

    These fleets used to get along nicely without any engineers on staff. They don’t keep us on the payroll to simply follow the book. They can do that nicely with less expensive staff. But very often if they have engineers on staff, then the OEM’s will actually work with them to optimize the equipment for their particular unique application. In so doing, the engineers pay for themselves and that is why they still have jobs.
  9. Aug 3, 2012 #8
    Heres a creative way to solve the problem. Instead of trying to calculate the exact horsepower, why not assume a range of horsepowers and estimate how many dozers you will need or how much time the job will take for each case. You can present this information to your boss and he/she should be able to tell you which horsepowers are feasible.
  10. Aug 4, 2012 #9
    Good idea, it's much better than a fag packet calculation where you are assuming absolutely everything.

    You've got to start somewhere. And I'd always pick manufacturers specs over an arbitrarily calculated starting point. Please note I also said. If you feel confident enough reduce it by a factor, do so.

    This type of problem isn't solved from calculation, but by bench marking and experience. For precisely the reason you stated before, theory and practice don't match well.
  11. Aug 4, 2012 #10
    Good point, Chris. I always study the books first. Then I talk with the mechanics and operators. Then I talk with the job planners and check actual records. I might find that some operators always get more work done. So I'll go figure out what they are doing differently. After I develop ideas, I'll bounce them off of everyone. That motivates them to share more information than they did the first time. Then I have a long conversation with the OEM. Then I will set up a change in operation or maintenance and monitor the results. This is where actual meaningful test data is important. Then I'll refine my assumptions and repeat the process.
    Last edited: Aug 4, 2012
  12. Aug 4, 2012 #11
    Here is another example. I have put the same engine model onto three different pieces of equipment. One required 120 HP, another 400, and another 750. This is a common industrial diesel. All applications performed extremely well, even though the manufacture killed the warranty on all but the first. The difference was that in the first, weight was not a concern, but we wanted a 50,000 hr engine life. In the last case, weight was very critical, but if we got 500 hrs out of it then that would be more than enough. The middle case was in between, and we were shooting for 2000 hr life. There is a big difference in a piece of equipment that runs hard 14 hrs per day every day, and a special piece of equipment that might see 2000 hrs in 20 years.
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