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Thread: Jointed piston and pushrod

  1. #1
    Member
    Registered: May 2002
    Location: Texas

    Jointed piston and pushrod

    Is it possible to make a pushrod move as if it were attached to a crankshaft? In Dromed it seems that we can make jointed objects only turn or slide back and forth. I'm building a steam engine in Anim8or and I can see everything happening except for the motion of the pushrods. I already have the crankshaft made and turning on a base object along with a second piece as the propeller shaft turning as well. The pushrod would be connected to a piston.

  2. #2
    Member
    Registered: May 2006
    Location: Russia
    What about learning construction of two-axle pump (stock model)? Seems it has the similar kind of motion in some joints.
    If it is completely impossible (who knows?), the only possible way is animated texture. I remember the similar one on interface screen of T2X.

  3. #3
    Member
    Registered: May 2002
    Location: Texas
    I looked at the two axle pump last night but the motions were moving at light speed no matter what rate I selected. I might be able to use two joints on a pushrod but have the upper 'arm' above the pushrod transparent.

  4. #4
    Member
    Registered: Mar 2004
    Location: Marlborough,England.
    Don't know if this is any help John...
    http://nautarch.tamu.edu/PROJECTS/denbigh/Engine.htm
    ..it includes an animated gif.

  5. #5
    Member
    Registered: Mar 2004
    Location: Marlborough,England.
    Whoah...just found this on the Blender forum...
    https://youtu.be/5AoDTeW_JYE

    https://blenderartists.org/forum/sho...eam-locomotive
    Hows that??
    Oh and reading further down on page 2 the author has released it for general use...how cool is that?
    http://www.blendswap.com/blends/view/66342
    And also this...http://www.doug56.net/Blender/PDF034.pdf
    Last edited by Ravenhook; 24th Mar 2017 at 19:22.

  6. #6
    Member
    Registered: May 2002
    Location: Texas
    Those look pretty neat, but I was thinking more along the lines of a triple-expansion marine steam engine like this one:

    Triple-Expansion

    Designing the individual pieces is trivial but what I see as a roadblock is the motion the pushrods have to make as they move up and down while having the lower end rotate with the crankshaft.

  7. #7
    Member
    Registered: Sep 2013
    Quote Originally Posted by john9818a View Post
    Designing the individual pieces is trivial but what I see as a roadblock is the motion the pushrods have to make as they move up and down while having the lower end rotate with the crankshaft.
    This might be achievable with a custom engine-shaped NPC using a custom animation.

  8. #8
    Member
    Registered: Aug 2007
    Location: LosAngeles: Between Amusements
    Or just have that part of it inside of a cowling so that you don't see that it isn't exactly right. Let people's imaginations fill in what they can't see.

  9. #9
    Member
    Registered: May 2002
    Location: Texas
    After thinking about it I realized how simple this is. Basically the push rod will be performing two motions at the same time. The push rod basically acts like a pendulum in a clock except that it also moves up and down. So all I need to do is design the push rod with a joint near the top where it would "attach" to a piston and have the push rod move on that joint maybe 175 to 185 degrees, and also have the push rod move up and down in the same amount of distance equal to the horizontal swing range. The joints property would have to be set or timed so that the push rod is half way up/down its travel while at the maximum of 175 or 185 degrees.

    Edit: Ok I have my object set up with a base (redundant geometry), a piston and a push rod. Basically the piston will use one translating axle moving up and down while the push rod acts as a sub object of the piston and swings left to right while pivoting at the piston. The problem I am having now is the math.

    How do I determine the relation between movement in degrees vs the distance traveled in dromed units?

    I can specify a reasonable distance for the push rod to swing back and forth but how do I determine how fast or far the piston has to move up and down so that the bottom of the push rod appears to make a circle?

    Edit #2: I decided to think in reverse so I made the push rods part of the crankshaft. Using joints each push rod moved around with the crankshaft, but I had to make each push rod spin in the opposite rotation to keep it upright. Still not what I wanted but with Thief I don't think it is possible to anchor one end of an object while moving the other end with a joint. I might just have to hide the top part of the push rod & piston.
    Last edited by john9818a; 26th Mar 2017 at 00:48.

  10. #10
    Member
    Registered: May 2002
    Location: Texas
    Through lots of trial and error I finally found an acceptable solution and have everything short of the positions moving naturally. After I release my mission I'll post a write up of how to build/ configure the engine.

  11. #11
    Member
    Registered: May 2006
    Location: Russia
    Congratulations! One more wonder turns possible in DromEd.

  12. #12
    Member
    Registered: May 2002
    Location: Texas
    Thanks Zontik! I read somewhere where Schwaa was only able to two joints in a row but so far I have three on each object. I'm hoping to push it to five.

  13. #13
    Member
    Registered: Aug 2007
    Location: LosAngeles: Between Amusements
    I was only able to get 4 to work. I'm pretty sure that Schwaa did as well.

  14. #14
    Member
    Registered: May 2002
    Location: Texas
    Probably so. In one particular thread he was limited to two. I was happy when I got just one joint to work.

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