Posts made by jgb

I was so emboldened by getting the demo to almost work, after Curbs clued me in, I spent the afternoon creating and testing a near model of the landing gear, that is part of my main model. Frustration Station!

I've attached it here. First, what you see is a rough replica of the Landing Gear model. I've omitted a lot of detail that has no bearing on the problem at hand, and it is not quite to scale. It is also (temporarily) missing several elements that are not important at this time, such as the drag struts and the LG door linkage. Use the layer visibility to see it better. Mainly turn on/off layer 1.5 A/C outer skin which can hide the works, as well as layer 2.0 Documentation.

The main parts are the Drive crank with a servo attached. The crank is fixed to the airplane structure at its lower part and it rotates 180 deg clockwise to push the bogie straight down. Before I add the drag struts, the bogie should simply hang loose from the top part of the crank. I have left out the upper hinge on this demo.

I have servo control of the crank, but when I try to hinge the bogie to it, the crank and the bogie lock up at that upper hinge point. I've tried various combinations of state and grouping; nothing seems to work. I even tried hanging just a simple box off the crank, same results. And other joint types make no difference either.

WTF am I doing wrong?????

jgb

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BMF-LG-demo.skp

Curbs,

Thanks for the trouble shooting on the landing gear demo.
Thanks to your tutorial, I know understand shape and debug far better.

When I looked at your solution, and noted the disconnections still occurring at the far ends of motion, I figured the joints must be OK now, but perhaps an element shape error is the culprit.

So I changed the shape of the connecting rod to CONVEXHULL, and lo, it works properly, with no disconnects, at least on the left side. You are absolutely correct that the door would not be moved past its normal position to the right. I need to figure how to limit that direction of motion within the joints, in particular, the servo.

Now the conn.rod spins on its joints, which is another problem to solve.

Also, I do not think a simple hinge would work on the conn.rod. You will note it is at an angle (blue axis) which was deliberate, so the rods angular relation to the actuator and door does change in 3 dimensions. The hinge has only a single axis of freedom. The only other joint I can try is the "U"joint.

Need some time to play more....

jgb

I played a bit more. I adjusted the servo range to min -90.0 and max 0.0. Now there are no disconnects at either side of servo motion. However, and this is a problem that has been highlighted before, the servos default run start position is 1/2 the motion range, in this case, 45 degrees. I really want it to start at its rightmost or max position, in this particular case. I and others may need some other arbitrary run start position between min and max, so I am not suggesting the run start position be fixed at just min or max.

I tried raising the servo max to +90 and putting a physical static block to prevent motion from 0 to +90, but that only resulted in disconnects if I tried to go from .5 right to 1 in the servo control.

Chris, what we need is a modified servo control joint setting, with a "start" angle input, between the min and max positions. An also nice addition would be to show the actual servo angle in the controller rather than a 0 to 1 position, or a choice if possible of angle or 0-1. That would go a long way to finessing the control of model motions.

Oh, and I changed the left-most ball joint to a "U"joint, and the con.rod spinning has stopped. Assembly motion is what I was looking for, except for the run start position.

jgb

A few weeks back, in the SU/SP forum I committed to writing a basic SP tutorial, to fill the vacuum. I am a rank newbie in SP, and only been using SU a few months, but SP was the "bees knees" to SU. However, I could not master even simple stuff in SP (or what I thought would be simple) so the idea was that as I learned, and with Chris's and others help, I could write a basic in depth tutorial covering all the elements in a consistent manner.

Then Curbs tutorial emerged, and it is better than what I envisoned doing.

I've done tutorials before, but none this complex, and I well know the amount of research and work involved, especially with the quality and level of detail Curbs has presented.

So, my hat is off to Curbs, and I now will refer to his tutorial and make any comments in this forum.

jgb

PS: I just read it again. I have 1 comment...... MORE PLEASE!!!

I took a quick look and I need to study it some more.

However, your solution (chain like link) to the conn.rod may work, but I cannot use it in the context of the model this simple example illustrates.

The "real" model is an aircraft landing gear, where the stationary block is the fuselage, the servo arm is the main actuator lever, the door is part of the landing gear doors, and the conn.rod is the strut. When the actual gear structure (not shown here) moves (via the servo arm), the door will open. So a flexy link cannot be used as I lose positional accuracy and timing in the linkage. There is to be only a single drive motor in the landing gear system.

I've seen far more complex models that seem to work flawlessly using similar constructs, but they are too complex for this SP newbie to figure out. I'll get back to this later in the week, or next.

LilDood

Yes, on the right track. It "almost" works, except for the disconnect at high/low angles.

So what did you do to get this far? What did I forget or do wrong?

I don't have the time today or tomorrow to compare mine to yours, so I would appreciate if you would clue me in.

jgb

Thanks Solo, but I may have bit too deep here. Time will tell.

LilDood, A coupla things. I tried all sorts of combinations of ball joint attachments, nada. I want the doors to be unequal, because I am simplifying a device that I need to set up just like that, and more. An aircraft landing gear. Also, as I asked, can you make it work?

I noticed a drafting problem with the conn.rod. I needed to make the connection ends pointy so it was free to move, and to lift the conn.rod block up off the floor, same reason. Still doesn't work. Attached is ver 1.1.

jgb

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Minor edit to "need help" file.

StarWarsKnower; My bad!

I tried your example in the older version. It works as advertised in SP-2.0b1.
But I would appreciate some info on the settings you used.

jgb

I have been using SU since Jan 08, and I am getting to master it. Long way to go yet.

I discovered SketchyPhysics yesterday, and it is the promise of a dream come true. I've loaded SP-2.0b1 which solved a few problems I had with the older version.

Since most of the tutorials on FaceTube and elsewhere either offer no details on tool selection & configuration, or go too fast to learn anything or go way advanced from start, I will attempt to write a series of basic tutorials as I climb the learning curve. I well know the effort involved, but being retired, I have the time (DON'T tell my wife!! )

The essence of a good tutorial is to also cover basic errors made during initial trials and how to fix them. None of the tutorials I've seen do that. So, I want to create some fairly complex models, but in step-by-step fashion, committing typical errors and fixing them, so the process is better understood. It will be a series of tutorials covering all of SP's functions, I hope. The format is TBD, but I'm leaning toward multi-scene SU files. A video format is too hard to follow, while a native SU format allows student follow-along experimentation.

But I am learning too. I spent hours doing simple stuff, like a hinged door, and I still do not fully understand all the joint settings, etc. But I can hang a door now, when this AM I could not. I've progressed to the point that I made a 3 block object, a post with 2 hinged doors at each end. They both move independently. Then I replaced 1 hinge with a servo, and I can swing it at will. The next step was to connect the free ends of the door with a simple connecting rod, set at an angle, and connected to the doors with ball joints. In this way I should be able to swing the servoed door and drag the other door with it.

But, I cannot! When I hit the go button and move the servo, the servoed door falls off the hinge, and nothing moves. I've attached the file for the more experienced to sleuth out.

I would appreciate if you can explain what is wrong and how you corrected it, rather than simply fix it. The best explanation gets a by-line mention in the tutorial. As I progress, I will use this forum and collaboration for a lot of help.

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Linked doors that won't move.

I d/l'd the example, and it falls apart when I hit GO. I put in a floor as well.
I joined a hinge to a door, now both fall down when touched.
Does a hinge HAVE to have 2 sides to attach? I've seen examples of something rotating freely in space. How is that done?
To me, the example seems incomplete.