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A simulation project we are on, we have a machine with hydraulics that are powered (They don't just look like they move something, they are the only thing moving/turning/lifting something) - However, the hydraulic extends the same speed no matter what it is pushing. So, say there is a 10 ton object attached to one end of the hydraulic and the other end is attached to a plate on the ground. In real life it takes a few seconds to build up pressure depending on how heavy the object is, but in our project the hydraulics don't care about that. It will lift a 100 ton object the same speed as a 10 ton object.

We have a way to fake the hydraulic pressurizing by reducing the 'drive amount' (how fast or slow the hydraulic extends based on the weight of what its lifting) when we sense that it is touching the ground and that does a relatively decent job but we would like to be able to take other things into account like engine speed, ratios, loads, low and high idle, etc. but we aren't too sure what the most important things are that we need to think about.

Our main question is how to determine the amount of hydraulic pressure (Does it build up to 50% pressure or 100%, etc) is required to lift x amount of weight. The hydraulics on this machine are very powerful and only take a second or two to start lifting about a 50 ton chassis but we dont know how pressurized the hydraulics are when they start lifting. I'm not looking for exact numbers about this type of vehicle but more a general idea of whats required. (if that can even be answered simply)

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Hi Mungyun to Physics SE! At the moment your question does not really have an answer. It is unclear whether you want to simulate a physical system as realistically as possible or what the goal really is. A full simulation of an hydraulic system involves computational fluid dynamics, engine simulations can be approached in various ways, depending on the engine, etc. So maybe you can clarify your question a bit. –  Alexander Apr 4 '12 at 13:53
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The general rule for cross-posting is to pick one site at a time and don't cross-post unless you don't get adequate answers. –  dmckee Apr 4 '12 at 14:15
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Apologies, I thought about that after i already posted but I was told my best bet was to come here for an answer so I did. I deleted my post on the GameDev site to correct for that. –  Mungoid Apr 4 '12 at 14:21
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@Mungyun That is certainly a reasonable course, my comment was mostly for future reference in any case. BTW--I suspect the answer you're going to get will be mostly empirical (i.e. experience shows that pressure build up can be parameterized by $P = P(t,V,p)$ for a given volume and driving power) as there is little point in trying to analyze such a system from basic principles. As such it will depend on there being a user with experience on such systems. –  dmckee Apr 4 '12 at 14:50
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@Mungyun what you did is fine, though its better to flag the post for a moderator to migrate it. That way the gamedev.SE question doesn't become a deadlink--redirects to this question instead. And any existing answers/votes get migrated as well. –  Manishearth Apr 4 '12 at 15:26
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