RepRap: Blog

One of the most challenging problems associated with experiments on the Feynman Path are the constantly mutating and changing software and electronics requirements. Software is pretty easy to deal with - just use version control. The electronics side of things is much more of a challenge - each experiment has its own specific set of actuators and sensors and supporting these electronically is something of a time and effort consuming roadblock. 

I think I have come up with a reasonably versatile and adaptable solution...

Instead of one large multi-function control board, the electronics have been split up into many smaller modules each of which performs only one function. Since they are so simple, each module (called a Steggo Module) can easily and quickly be manufactured by hand. These modules can then placed side-by-side on an inexpensive racking system and wired up to form whatever experimental apparatus might be required. When the experiment is complete, the modules can be disassembled and re-used later on.

All-in-all it seems to be a pretty versatile system. Have a look at the Steggo Module Video and FPath Experiment 007 writeup for more information. 

Labels: Feynman Path, FPath, Modular Electronics, Nanotechnology, Steggo Modules

# posted by OfItselfSo @ 6:52 AM 0 comments

More and more, as one attempts to move down the Feynman Path it looks as if actuators are the real roadblock.

In retrospect, this should have been obvious if one pays attention to what one "does not see" as opposed to what one "does see". A casual survey soon turns up a dearth of viable millimeter scale actuator designs and yet people have been making millimeter scale devices for over 100 years. Yes, some actuators exist, but far less than one might expect. A quick search on terms like "millimeter scale actuators" soon reveals that many are only "milli" in one dimension – if that.

So what causes the problem? Why the shortage? Well, some of it is probably due to the fact that commonly available machine tools are quite accurate at the millimeter scale. In other words, if you need to move something 0.1 or 0.01 of a millimeter this is easily within capability of macro devices – so why bother creating hard-to-work-with millimeter scale actuators for the purpose.

The other reason is that there seems to be a gap between the scale at which electromagnetics stop working efficiently (centimeters) and electrostatics start working efficiently (microns). Simply put, finding a way to actually actuate anything at the millimeter scale is hard and so it is easier just to ignore the problem and find some other way of doing what you need to do.

Does this mean there is no point to milli-scale actuators? Why not just skip to the micron scale and have done with it? This is essentially what the MEMS people are doing, however, since there is nothing at the scale above them, things like assembly or complex multi-material manufacturing of devices is not practical. Machine tools and repurposed semiconductor fab equipment are suitable for the creation of parts but not really intended for construction, manipulation or operation.

The Feynman Path is intended to address this issue by working down the scales leaving behind a toolkit at each scale able to build and operate the tools and devices below it. Maybe milli-scale actuators really are impractical and a jump right to the micron scale is necessary. Nevertheless, an exploration of the millimeter scale actuation space would seem to be worthwhile - no need to give up on it without putting in some time.

So, having got the closed loop control thing operational, it is time to put that area of exploration to one side and begin work on millimeter scale actuators. I have some ideas…. more in future posts.

Labels: Feynman Path, FPath, millimeter scale actuators, Nanotechnology

# posted by OfItselfSo @ 12:10 PM 0 comments

My first physical step down the Feynman Path is a pantograph.

“What”, you say, “something that stopped being hi-tech in the 1700’s is somehow relevant on a path to Nanotechnology”. Well, no and yes. No, the pantograph is not really an optimal solution – I think flexures such as are being developed for the RepRapMicron are the more promising avenue… and... Yes. I do think machinery at the micro and nano levels will resemble massively parallelized versions of older solutions - maybe not the 1700’s but certainly the 1800’s. I will have more to say on this complexity vs simplicity issue in future blog posts.

Back to the point. My primary interest at the moment is how errors might be removed as big devices build smaller devices. The pantograph is a simple thing built out of LEGO bricks and has a reduction ratio of slightly over 5:1. The goal is to create a really nice, visible circle using closed loop feedback to iron out the errors as extremely inaccurate large scale actuators move the tool head about. The tool head has a barrel and lead scavenged from a mechanical pencil mounted on it to record the path.

The image above shows the pantograph. The macro end is on the left (red arrow) and the toolhead is in the center at the micro end (green arrow). 

Closed loop control was used to drive the macro and micro ends around a circular path. The image on the left shows a typical path taken by the toolhead when the control was applied to the macro end (it is also supposed to be a circle). This forms kind of a baseline case representing the inherent accuracy of the hardware. The image on the right shows the path taken when the control was applied to the micro end of the pantograph.

It is fairly clear from the image on the right that the errors attributable to the pantograph mechanism have been greatly reduced by applying closed loop control to the toolhead. Please see the webpage (FPath_Ex006) and short (8 min) video for more a more complete discussion.

Interestingly, both Heinlein and Feynman proposed using pantographs to have large machines make smaller machines. One reason I decided to use a pantograph as my “first device” is to acknowledge their ideas – a kind of homage if you will.  

Labels: Feynman Path, FPath, Nanotechnology, Pantograph, Stigmergic Path Following

# posted by OfItselfSo @ 5:35 PM 2 comments

Well, my initial efforts to build physical things on the next step down on the Feynman Path are proving to be quite frustrating. Turns out hardware is more difficult than software - who knew? Still, no matter, one keeps pressing on.

While the physical side of the project slowly gets its act together I thought I would report on an interesting variation of the “Graphical Stigmergy” technique mentioned in my previous post. This has now manifested itself as Experiment 005.

Basically, this experiment demonstrates an effective method for the 2D filling of an area if you are using inaccurate and imprecise actuators.  I call it Stigmergic Fill and there is a short (8 min) video demonstrating it.

Stigmergic Fill lets reality be its own model and, using it, there is no need for a complicated mechanism to build an internal representation of the system state. Things are what they are and, however an inaccuracy or disruption may have happened, the discrepancy between reality and the ideal is immediately obvious and the control software can take steps to address it.

More and more I’m thinking that control at the micro and nano scales will probably be much less of running through a sequence of “go to this exact point and definitively do that” type operations and much more of a general “this needs to be done, activate events which should cause that to happen” and then monitor things to see what actually did happen.

Unavoidable errors and lack of precision at smaller scales will make perfect control impossible to obtain and it is interesting to try and develop compensatory methods in anticipation of that.

Labels: Feynman Path, FPath, Graphical Stigmergy, Nanotechnology, Stigmergic Fill

# posted by OfItselfSo @ 2:07 PM 0 comments

One of the major problems with the Feynman Path approach is minimizing and correcting the unavoidable errors as large tools make smaller tools. One way forward is to simply accept that the machinery will be imprecise and use a closed loop feedback system to help eliminate those errors. Developing such a control system is the reason why most of the work on the FPath Project has so far been software. 

In Experiment 004 the Walnut software was used to demonstrate a path following and error correction behavior using real time object recognition. A rather crude XY stage was used to move a 5mm red circle along a green path. The green path is entirely virtual and is overlaid on the video stream by software. 

The video documentation for Experiment 004 can be found at the link: https://youtu.be/bCb2k8tKX6k 

If you watch the video you will see that cheap DC motors glued to LEGO bricks are used to move the tool head. Why do this? Surely something of higher quality would be better? Well, yes and no. Yes, the quality of the movement could be improved and it certainly would not be hard to find better alternatives to the gear motors currently in use.  But no, I actually want the poor quality movement. The goal here is not to have accuracy handed to me on a plate but rather to get experience taking inaccurate tools and making the resulting output accurate. This is a simulation of what needs to happen when larger machines make smaller machines and there is no realistic way to improve the accuracy of the parent. Errors must be corrected and it is much easier to get some practice at this while still at the macro scale.

Stigmergy is the use of the environment to coordinate actions. If you watch the video you will get a sense of how Graphical Stigmergy could be a useful part of an error correction system.

Labels: Feynman Path, FPath, Graphical Stigmergy, Nanotechnology, Stigmergic Path Following

# posted by OfItselfSo @ 10:05 AM 2 comments

Hello RepRappers!

You may be interested in the FPath project which is intended to explore the possibilities of the Feynman Path to Nanotechnology. In 1959 the rather well known physicist Richard Feynman gave a talk entitled There's Plenty of Room at the Bottom during which he pretty much invented the idea of nanotechnology and suggested a method of achieving that result. Feynman’s fundamental idea was to use big tools to make small tools which then make even smaller tools and so on until one is able to perform atomically precise fabrication. 

Of course the FPath project is nowhere near the nano scale yet or even at the micron scale that Vik is operating in. FPath is still at the scale of centimeters and working towards building actuators and tools at the millimeter scale. 

There are many issues with the top down approach of the Feynman path. However, there are also problems with the bottom up approach – billions have been spent and we still don’t really have all that much in the way of viable nanotechnology. Maybe the Feynman path is worth a try – after all, it has been given very little attention since the day it was proposed.

Empowering people to create tools would seem to fit right in with the RepRap philosophy and everything is open source.

https://www.OfItselfSo.com/FPath/

Labels: Feynman Path, FPath, Nanotechnology

# posted by OfItselfSo @ 1:13 PM 0 comments