Scissors Mechanism
-
Hi,
I'm trying to build a scissors mechanism, but I'm having some problems.
Everything seems to be working fine (rotation around the center hinges) when I have the 4 bars and the 2 center hinges. However, when I add one of the side hinges at the end of the bars, the mechanism doesn't move how it's supposed to...
I wonder if I should also add some sliders moving along the Y axis, or if there's a better way to make the whole thing work.
Thank you in advance,
Andre
-
Hi Andre, It isnt clear from your model just what you are trying to create. Can you tell me what you are trying to make? Do you have a diagram or picture?
Chris
@movingshapes said:
Hi,
I'm trying to build a scissors mechanism, but I'm having some problems.
Everything seems to be working fine (rotation around the center hinges) when I have the 4 bars and the 2 center hinges. However, when I add one of the side hinges at the end of the bars, the mechanism doesn't move how it's supposed to...
I wonder if I should also add some sliders moving along the Y axis, or if there's a better way to make the whole thing work.
Thank you in advance,
Andre
-
Hi Chris,
Thank you for responding and sorry for my delay on the reply. I was doing some "homework" before continuing this thread.
After sending my initial post, I found your "walker7 and studying your model and realizing mechanical linkages are possible on sketchyphysics, I decided to finish my scissors lift model. The model is attached. For convenience I'm attaching your Walker (which is Ted Jansen's legs, which I was also planning to build) model as well. Thank you for sharing it on the warehouse.
So my question now is why my model is not working? I know I could have used less joints, but even with the extra joints I tested (sketchy play) some of the bar "double linkages" and they worked as expected - some of them. It's just the whole system that is not working. I wonder if you could shed some light.
In regards to this model I have also a couple of simple questions:
a - Should I have done any specific grouping or non-grouping for this to work? Is there a specific type of grouping you'd recommend? I didnt make any of the hinges to be part of any group, just as a safety measure (also looking at your Walker model). Can we safely include joints inside deeper levels of grouping and still expect them to behave they way we want? Can nested joints access objects nested inside another hierarchy?
b - I notice the hinge joint representation on the model has a "direction". I tested an "x" linkage with two bars (a real pair of scissors), and was able to make both bars spin on both directions (clock wise and counter clock wise), so it doesn't seem that the hinge has a direction. But could you confirm that please?
I also have some basic questions about sketchyphysics that the docs dont cover. If it's ok with you I was hoping to start posting them here, on subsequent mini-threads, and then we can put the answers together in HOWTO or FAW formats. I could help with that if you'd like. Maybe it's time for a wiki, as I found it hard to dig and put together knowledge from the forums.
Thank you for your time and sharing your work and knowledge,
Andre Philippi
CPhillips Walker model based on Ted Jansen's leg mechanism.
My finished scissors lift mechanism that is not working. yet
-
Sorry I didnt get back to you before now.
What you are trying to build is fairly advanced. I tried to build one a while back and spent a lot of time and it wasn't very good. Its kinda a hard machine to simulate because it is so interconnected.
I would suggest you start with something a bit easier and build up to the scissor lift. First build a single scissor for example. Then try adding the piston. Tweak everything till you get it right and then make the lift.
Off the top of my head I can see a few things wrong with the model.
-Its probably too small. Small things and huge things behave strangly.The joints arent connected right.
-I am not sure how you have the joints connected but it isnt right. You should only need 5 or 6 joints. If you used servo's you could get by without having to have the piston. It would be simpler.
-I am not sure if you made that in real life it would work very well either. The piston is going to have to apply a lot of force to get the lift to start moving.Here is how to make a simple scissor.
-Create 2 long square boxes in a scissor shape
-Create a hinge at the center of the scissor
-Group the hinge with one of the boxes
-Connect the other box to that hinge.Let me know if you have any other questions.
Chris
@movingshapes said:
Hi Chris,
Thank you for responding and sorry for my delay on the reply. I was doing some "homework" before continuing this thread.
After sending my initial post, I found your "walker7 and studying your model and realizing mechanical linkages are possible on sketchyphysics, I decided to finish my scissors lift model. The model is attached. For convenience I'm attaching your Walker (which is Ted Jansen's legs, which I was also planning to build) model as well. Thank you for sharing it on the warehouse.
So my question now is why my model is not working? I know I could have used less joints, but even with the extra joints I tested (sketchy play) some of the bar "double linkages" and they worked as expected - some of them. It's just the whole system that is not working. I wonder if you could shed some light.
In regards to this model I have also a couple of simple questions:
a - Should I have done any specific grouping or non-grouping for this to work? Is there a specific type of grouping you'd recommend? I didnt make any of the hinges to be part of any group, just as a safety measure (also looking at your Walker model). Can we safely include joints inside deeper levels of grouping and still expect them to behave they way we want? Can nested joints access objects nested inside another hierarchy?
b - I notice the hinge joint representation on the model has a "direction". I tested an "x" linkage with two bars (a real pair of scissors), and was able to make both bars spin on both directions (clock wise and counter clock wise), so it doesn't seem that the hinge has a direction. But could you confirm that please?
I also have some basic questions about sketchyphysics that the docs dont cover. If it's ok with you I was hoping to start posting them here, on subsequent mini-threads, and then we can put the answers together in HOWTO or FAW formats. I could help with that if you'd like. Maybe it's time for a wiki, as I found it hard to dig and put together knowledge from the forums.
Thank you for your time and sharing your work and knowledge,
Andre Philippi
-
Hello Andre and Chris,
I am most interested how this thread turns out as I too wish to model some 'mechanical linkages' driven by a hydraulic ram, but my mechanisms are basic compared to Andre's Scissor Lift.
There are a few open issues here which I have attempted to isolate.
A. Model Size
I can empathise with models being 'small' because I have been using a 1:1 scale in my models and the SketchyPhysics2 joints come out huge. For background, I currently have a 30 mm diameter steel shaft in shear for a slow moving ram, and given the scaling issues raised in previous threads, and the above comment by Chris, I will now make my models 10x bigger.
I just tried that and already the behaviour is already much smoother, thanks.
B. Grouping and Joint Direction
I too am struggling with Andre's questions a & b of Fri Feb 22, 2008 9:16 pm, and it is a real breakthrough for me when I appreciate another one of the deeper issues involved here.
C. Documentation
I too have been reading the threads looking for detail, and I can offer to contribute some time within a WWW team environment to generate some documentation if that helps.
Q. Is such a team already up for SketchyPhysics2 ?
Summary
I reckon SketchyPhysics2 is an exciting plugin for an already awesome tool, and Chris, I am most grateful for the time and effort you and your team have put into it. I just wish I was in a position to offer material support, but who knows what will happen .....
Now to follow Chris's instructions to make a simple scissor.
Regards, AL.
-
I have managed to create a scissor mechanism for a reach type forklift, i had to work from one end towards the other but i managed to get it to work, i grouped the joint on the fly really but i had to continually thing ahead about how the next part would connect to it and what i would have to do. In the attached file the control "Extension" controls the scissor mechanism, i'm now going to see if i can make yours work.
-
@lildood said:
I have managed to create a scissor mechanism for a reach type forklift, i had to work from one end towards the other but i managed to get it to work, i grouped the joint on the fly really but i had to continually thing ahead about how the next part would connect to it and what i would have to do. In the attached file the control "Extension" controls the scissor mechanism, i'm now going to see if i can make yours work.
Thats a nice model LilDood.
-
@al paton said:
Hello Andre and Chris,
C. Documentation
I too have been reading the threads looking for detail, and I can offer to contribute some time within a WWW team environment to generate some documentation if that helps.
Q. Is such a team already up for SketchyPhysics2 ?
Regards, AL.No. No documentation team. But I really would like some help in that area. Sadly documentation isn't among my talents. If anyone would like to help I would greatly appreciate it. Tutorials, videos, howto's whatever. Send me a PM and we can discuss specifics. At the very least I can give you a login to change the Wiki on the home page.
Thanks
Chris -
I don't get how you made the scissor mechanism, I couldn't find any link between the 'X' shaped bits. There is no axis and no link between them, it makes no sense. But it is amazing, I just don't get how you did it.
-
Can i just ask: Who that is directed at? (StarWarsKnower)
-
@starwarsknower said:
I don't get how you made the scissor mechanism, I couldn't find any link between the 'X' shaped bits. There is no axis and no link between them, it makes no sense. But it is amazing, I just don't get how you did it.
LilDoods model has some hidden joints. Turn on "show hidden geometry".
Advertisement