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It's not a bad idea. I had something similar where the string is on a spindle and through the center on a fourth leg is a tension rod to keep up the slack.
The major problem with that design and pretty much every other design is that this robot is going to need to be calibrated. The string will introduce a springy member that will do things like sway, stretch, and so forth.
Also, in some conf
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Lawrence Kincheloe
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Delta Machines
Interesting,
I'm in the NW OKC region and I know that there is an active robotics club in norman OU doing reprap stuff and there is also a oklahoma robotics club that dabbles as well.
It sounds like we need more communication between RepRap/hackerspace/robotics clubs around the area
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Lawrence Kincheloe
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Oklahoma City RepRap User Group
Viktor,
Thanks for the clarifying picture. I had hoped that I was communicating effectively but I'm afraid I came off as rambling.
What you have pictured is what I had hoped to describe above, but I would like to add a few points.
1. By increasing the diameter of the ball sphere, to approximately 1.75 of the diameter of the magnet+housing, you can get a greater range of motion. The trade-off
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Lawrence Kincheloe
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Delta Machines
Ok, so I did some some testing and realized that the parts I wanted don't exist in a cheap commodity form or wouldn't work exactly how I thought they would. What I came up with is this demo setup. The neat thing about the setup is that the plastic cup makes motion very smooth while keeping the ball centered in the magnetic field of the magnet. Without the cup, the ball skips while overcoming stat
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Lawrence Kincheloe
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Delta Machines
Ok, before I get inundated with more stuff. I need to lay out the entraped magnet arrangment I'm kicking around.
The idea is to use a metal bearing with a low coercivity and to use a strong magnet to attach with, such as soft iron or ideally an iron nickel alloy.
Ball joint using a steel ball to entrap a strong magnet between a lubercating cup
The second idea is to encapsulate a strong magnet i
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Lawrence Kincheloe
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Delta Machines
Torsten, what parts are you using for your magnetic joints, and where did you order them from?
I've become disillusioned with trying to model plastic joints with metal rod hinges, and want to see what it would take to use magnetic joints instead. The cost per joint is surprisingly good and I've been wanting to play with designing a halbach magnet array anyways.
Thanks,
Lawrence
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Lawrence Kincheloe
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Delta Machines
Link to thesis.
THESIS REPORT
Ph.D.
A Three Degree of Freedom Parallel Manipulator
with Only Translational Degrees of Freedom
by R. E. Stamper
Advisor: L-W. Tsai
Ph.D. 97-4
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Lawrence Kincheloe
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Delta Machines
reinoud, thanks for the info!
If you can, can you post a link or a copy of the paper you found useful?
Gears are going to be an issue no matter what material they are made with. Personally I am planning on adding a feedback loop with a camera if and when I need the extra precision. Think optical laser mouse.
With regards to the motors, I was thinking of actually counter-balancing the weight
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Lawrence Kincheloe
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Delta Machines
do post some pictures, it might help others avoid the same mistake.
Currently I'm meddling with openSCAD and am mostly happy with the results, just not the compile times. I'll post something this weekend.
Stepper motor wise, I wanted to go with something like this. But they are out of stock now. Instead I went for some geared steppers, that have fewer steps per rotation but hopefully will be m
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Lawrence Kincheloe
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Delta Machines
That looks really good. Do mention what kind of tooling method your going to employ. My first thought is, steppers for cnc lathing would make great contact free machining but couldn't hold up in a traditional lathe setup. Although thats depending on motors and materials.
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Lawrence Kincheloe
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Mechanics
Mmm, yes I'm extremely gpl friendly.
If there is enough interest in collaboration in the early stages then I would be willing to write up everything I have. Otherwise I'll wait until I have a working prototype and know its going to work before bothering. I'm still in the, design phase. That being said, if there is interest in the models I'm doing, then I'll release them early as GPL, with the h
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Lawrence Kincheloe
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Delta Machines
What I'm going for is not necessarily precision, but to further boost the percent of plastic, and hopfully reprapable parts.
Victor, I would be interested in what your thinking for cross hinges, because what I'm thinking of right now is a plastic tetrahedron. as the basis of the universal joint. Where the axis lay on opposite perpendicular edges of the geometry.
What struck me about the delta r
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Lawrence Kincheloe
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Delta Machines
Is anyone else interested in doing a design for a reprapable delta robot structure? I'm currently churning one out, but I could use some help in determining the optimal leg member lengths for the maximum work envelope.
Thanks,
Lawrence
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Lawrence Kincheloe
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Delta Machines
Looking at the google groups pictures, I like the use of hardware parts! I think it would be a great idea to put up plans for a repstrap/mill that takes up less room than the currently advertised repstrap.
I'm actually jumping around projects because I think that we are about to reach a point where we don't need repstraps as much as we need to improve the percent of reprap that is printable. I'
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Lawrence Kincheloe
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RepLab Working Group
Here is the link to the build information. I'm willing to admit that it has a lot of problems, which is why I'm keen on a real community designed successor.
These guys have some great ideas about using pre drilled extruded aluminum for the frame.
And here is some thoughts about using maker beams and grid beams as well.
If I could do it all over again, I would have purchased a lot of stock
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Lawrence Kincheloe
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RepLab Working Group
I'm afraid I'm about to kill the conversation, so to get back on topic.
It sounds like you really want to add a router drill to the RepRap, since it would satisfy the majority of your requirements. I think its an excellent idea, but I think you'll have to use something more rigid than the RepRap, which is why I'm struggling to find non-contact methods of manufacturing.
There are already some g
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Lawrence Kincheloe
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RepLab Working Group
I agree that there will be many different paths to take.
One goal I have is I want desperately to work with metals in a safe fashion. Most methods of direct or indirect heating create fumes. My current idea is to use an electrolyte of potassium hydroxide to act as the medium, use a thin wire of epoxy coated magnet wire as the tool head attached to a Cartesian robot. after that I'm thinking of h
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Lawrence Kincheloe
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RepLab Working Group
I'll have to come back and edit this later but I think this is a good discussion, because there is a balance between being able to do everything and being over specialized. Its also important to recognize what your trying to achieve.
I'll make two points first off, having a machine that can fabricate in a particular manor, dictates the form and function of the objects it makes.
We could desi
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Lawrence Kincheloe
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RepLab Working Group
Depending on what part of the world your in, you can source it from several places. My current favorite is usplastics.com
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Lawrence Kincheloe
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RepLab Working Group
Portability and ease of transport are a serious consideration. You can't cheaply ship or source parts for a machine that weighs more than you do and thats why I want to do a design that moves away from where most cnc machines are right now. Thats also why I'm going to push for non-contact machining methods, because they reduce the need for dampening machine chatter.
Also, consider that no matte
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Lawrence Kincheloe
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RepLab Working Group
Thats interesting and its close to the direction I want to head although I'm thinking of something slightly different.
Because of its increased size I would look at designs that can be folded when not in use, or can have dual purposes. A 5' by 5' table is a bit awkward to deal with unless you have a dedicated shop.
Furthermore, I believe that focusing on non-contact machining methods could dr
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Lawrence Kincheloe
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RepLab Working Group
holy crap, I reinvented this technique a few years ago using a variable power supply and a battery powered dremel powered by the power supply. Plastic feed rod was used as the tool tip and speed was controlled by the voltage. It was extremely handy for working with plastics and safe enough to leave in the hands of inexperienced computer science students who I wouldn't want near a torch based plas
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Lawrence Kincheloe
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Plastic Extruder Working Group
O man, I like the elegance of your aluminum angle bracket center punch method.
Once you have one of these machines have you tried to use it to make more perforated aluminum angle brackets? Your close to having a replicating subtractive cnc machine there.
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Lawrence Kincheloe
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CNC Routers, Mills, and Hybrid RepRapping
There are some links on google about using fluidics as a backup flight control system, but nothing with details. Most of the comments come from a discussion I had a while back with a friend of mine who is an aerospace engineer. He was talking about non-linear dynamics and fluid flows with regards to aircraft control systems.
The link to trueSpace looks interesting. I've honestly not found a cad
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Lawrence Kincheloe
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Plastic Extruder Working Group
I'm curious, because I just had a silly idea involving ball screws. Ball screws are really neat, low friction, low backlash linear motion devices.
What if you printed a plastic ball screw assembly, filled it with steel ball bearings and printed the threaded ball screw rod? My first thought was, thats silly, it would bend like crazy, but what if you stiffened it with a cheap normal threaded rod?
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Lawrence Kincheloe
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Mechanics
I have a question. Are you going to do all the development "in house" or do you have a website where you are developing this stuff?
I'm interested in the robotic arm idea because I have a similar goal and the pick-and-place stuff is prime.
I think someone needs to build a website that has better tools for these sorts of projects because its not easy to collaborate and make contributions at th
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Lawrence Kincheloe
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General
I'm currently running an experiment using something weird called geopolymers. Basically it appears to be alumina-silicates mixed with some other stuff to give it particular properties and then mix in a alkaline base. It works similarly to concrete, but from what I understand the concentrated base dissolves and distributes the aluminum and silicone into a gel matrix and then when its heated a bit,
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Lawrence Kincheloe
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General
I'm familiar with the concrete filled steel tube idea, but not the aluminum square tube one. Do you have some documentation or a link as to why exactly they do this? I'm already aware that it dampens vibrations, but I'm more curious about example machines and possibly data on how well it works.
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Lawrence Kincheloe
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General
I actually have an interesting idea about how to do this. The first time I came up with the idea, it involved using a huge electro-negative potential and a microwave gun to excite an air plasma where the electrode gets eroded as feed stock and big magnetic coils push the plasma stream around.
Then I learned about plasma cutters, which skip all the messy microwave parts and just use a spark gap
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Lawrence Kincheloe
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Plastic Extruder Working Group
I actually am interested in something similar. I once looked down the rabbit hole into fluidic logic, which was popular a while ago but digital logic marched all over the idea. Now its only used in fighter jets because its resistant to EMP attacks.
The idea of embedding logic into the form of an object is gorgeous. It also means that it would be possible to actually "print your own circuit".
P
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Lawrence Kincheloe
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Plastic Extruder Working Group
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