Skid-Steer Problem
Skid-Steer Problem
(OP)
I am new to the industry, thus I have minimal experience with applying fluid power concepts to design applications. The project I have in my hands now is an interesting one, as in I don't think it's even possible to use an efficient solution. If anyone has direct experience with a similar application, any helpful information would be appreciated.
I am working on the drive system for an OEM that builds railroad maintenance equipment. Usually their machines are built for use on railroad tracks. This machine, however, will use two CAT track systems for ground mobility. The GVW empty is 120,000 lb, and full load could be upwards of 250,000 lb, depending on the average density of the iron ore it will be loading and transporting. This means possibly 125,000 lb supported by each set of tracks, assuming even distribution of the weight (not the case, but assume true for sake of simplicity at this point). The largest problem, I think, is the dimensions of this machine. It is roughly the shape of a railcar - long and narrow. To be specific, the dimensions from center to center of the tracks and width are 30 ft x 10 ft. Not the ideal ratio of dims to apply a skid steer.
Two design directions at the moment: steer both sets of tracks with differential flow, or steer one set (front) and fix the other (rear). What I would like to know is how to roughly spec a system like this (pumps, hyd motors, torque specs). I assume something needs to be known about friction coefficients and associated forces on the tracks. Ultimately, can this machine be steered in this way?
I am working on the drive system for an OEM that builds railroad maintenance equipment. Usually their machines are built for use on railroad tracks. This machine, however, will use two CAT track systems for ground mobility. The GVW empty is 120,000 lb, and full load could be upwards of 250,000 lb, depending on the average density of the iron ore it will be loading and transporting. This means possibly 125,000 lb supported by each set of tracks, assuming even distribution of the weight (not the case, but assume true for sake of simplicity at this point). The largest problem, I think, is the dimensions of this machine. It is roughly the shape of a railcar - long and narrow. To be specific, the dimensions from center to center of the tracks and width are 30 ft x 10 ft. Not the ideal ratio of dims to apply a skid steer.
Two design directions at the moment: steer both sets of tracks with differential flow, or steer one set (front) and fix the other (rear). What I would like to know is how to roughly spec a system like this (pumps, hyd motors, torque specs). I assume something needs to be known about friction coefficients and associated forces on the tracks. Ultimately, can this machine be steered in this way?





RE: Skid-Steer Problem
Ted
RE: Skid-Steer Problem
Go to the Brevini website (other gearbox manufacturers are available) and download their catalogue for track drive gearboxes. There are a bunch of equations and tables which you can work through to size the gearbox you will almost certainly need to drive the tracks. Specific questions you will need to ask yourself are: how fast does the thing have to move, what is the steepest hill it has to climb, what sort of ground does it have to traverse.
Just as a rough guess, if you use a closed circuit transmission you could realistically expect a maximum of 70% efficiency (in terms of power) between the flywheel of the engine and the input to the track drive gearboxes. There will be losses in the gearboxes (allow 3% per stage in an epicyclic box). Then you make a further allowance for losses between the big sprocket and the track and even more allowances for power wasted in the track itself and all the loaded rollers that are carrying the weight of the machine. Only then will you start to add on the extra power you need for acceleration, going up hills, the nature of the ground etc.
For the pumps and motors (and brakes and pilot controls): you need to decide how the machine will be controlled - consider where in the world it will be used and choose a technology that is appropriate for the skills/resources available to maintain it. The machine you design for California will be very different from the one you design for Ethiopia. You can reasonably expect that the increasing sophistication brings with it some energy savings/efficiency - you are right to expect a rather inefficient machine.
DOL
RE: Skid-Steer Problem
I appreciate the heads up. I know that I have much research to do. Thank you for the initial thoughts to get me started.
This machine will be used in a railyard in Brazil. The earth it is navigating is relatively compacted and shouldn't exceed a grade of 3 percent. It needs enough maneuverability to pull up parallel to a line of railcars on a set of railroad tracks. I can't imagine a very good turning radius for this machine, making this sort of 'parallel parking' maneuver quite difficult.
Here is a primitive sketch of the scale of the machine:
RE: Skid-Steer Problem
RE: Skid-Steer Problem
You could turn both sets of tracks 90 degrees to parallel park.
Ted
RE: Skid-Steer Problem
RE: Skid-Steer Problem
RE: Skid-Steer Problem
RE: Skid-Steer Problem
Excavators can skid steer while traveling. The excavator upper structure can rotate while traveling.
Ted
RE: Skid-Steer Problem
Ted
RE: Skid-Steer Problem
I know Sauer-Danfoss has application engineers who do nothing but help people design hydraulic circuits, so it would be worth trying to contact them since you mentioned you were looking at our/their products (Sauer-Danfoss Engineer here). That said, I'm sure Bosch-Rexroth, Parker, Eaton, etc... have similar people on hand to help you with your questions as well.
RE: Skid-Steer Problem
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: Skid-Steer Problem
Chris Brunner
Brunner Equipment LLC