I made these steampunk thumb drives out of Kingston 4GB DataTraveler thumb drives. They’re for sale at USD 25.00 each on etsy.com. The money goes towards buildling the Logical Engine!
I only made five, but if they go quickly, I can make more. Go take a look!
Got bored, so I played around with the book cover template in InDesign. What if Charles Babbage and George Boole had brainstormed together? And what if Babbage ditched decimal representation in favor of binary? And then went on to build the much simpler and cheaper Logical Engine? I think this would make a fun alternate history, one where *I* didn’t have to build the damned thing because Babbage already did it 150 years earlier!
Image of Difference Engine is cc-by-sa by Flickr user Gastev.
Tags: babbage, boole, logical engine
A few months ago I took a trip to see my good friend Dan Reetz in Los Angeles. He took me to Norton Sales in North Hollywood, a surplus store specializing in space program castoffs, and which has an enormous warehouse of same. We spent a happy hour clambering through the mostly unidentifiable technical detritus of the nation’s space program.
I found some welding goggles and mugged for the camera. Thanks to Dan Reetz for the image and the post-shooping. I don’t know what that thing that I’m holding is.
I found a Univac tape used in the Polaris program. There are fun things like this tucked into all sorts of unlikely corners.
Also, an individually-wrapped screw. Your tax dollars at work.
Here are some of the promised drawings, which I drew in SolidWorks, and exported to PDF format. I’ve sent these out to eleven machine shops around the country, asking for quotes.
I tried using emachineshop.com’s CAD program, which promises an instant quote based on your drawing, but for 1400 rods (each of which is a 14.5″ x 1/4″ x 1/8″ steel bar with 36 holes drilled in), the instant quote came back as around a third of a million dollars. Clearly something is wrong, but I’m not in the mood to fight with their program to figure it out.
Anyway, required for the ALU are (click on each part to get the PDF):
- 1242x Rod R16
- 444x Notched 16
- 612x Blank 16
- 280x Drive Bar 16
- 280x Drive Arm
This doesn’t include the helical drive, bearings, springs, or bumps, which I can buy or machine myself.
I found that adding a key to the Acme rod and sliding a chain sprocket on acted as a perfect driver for the module. The key allows the sprocket to slide as the Acme rod moves up and down, and can rotate the rod at the same time. The sprocket can be driven by standard motorcycle chain.
Since that is the final design challenge, I am ready to start getting quotes for parts, but first I have to draft drawings of the parts. I’ll be posting the drawings as I complete them.
Based on the plan in the previous post, I have completed and tested the spiral cam drive. First, I cut to size some aluminum round stock on the lathe, and drilled a 3/4-inch hole through, also on the lathe, for the Acme rod. This became my blank.
Next, I wrote a program to generate GCode to mill the spiral cam out of the blank. I went through several iterations, improving the efficiency each time. It still takes about 20 minutes to mill the spiral cam. And here is the inevitable CNC porn:
I drilled and tapped a hole radially into the cam, drilled a set hole radially into the Acme rod, and attached the cam to the rod. Here’s the installation showing how the bearing rides on the cam surface:
And here are some videos showing the mechanism in action, driving 12 rods. Four of the rods have extra-strength springs so this is the equivalent of 16 rods. The action is incredibly smooth, and doesn’t take much force.
I also tested stringing fishing line between two modules, and that worked perfectly. I still need to work on getting the length of the string just right, since I can’t adjust the spacing between modules for a given string length.
NextFab is closed for two weeks for the winter solstice holidays, and this also ends this phase of investigation. The next phase, to be started in January, is making a cylindrical gear to rotate the drive, and then putting together a single bit slice module. When those tasks are completed, I will have enough proof that I can complete the 16-bit ALU, which means that I can start a Kickstarter project. I hope to complete the bit slice module by the end of February.
Here’s video showing the new drive. It’s sooooo much easier to move. Next will be attaching a bearing to the drive bar, and milling a fusee to push against the bearing. I have high hopes for this design!
Improved 16-rod drive test from Robert Baruch on Vimeo.
Here I put together 14 rods, 4 of them having stronger springs, because I ran out of the weaker springs, so I think this is probably equivalent to 16 rods. This is the maximum that the Logical Engine should use.
16-rod drive test from Robert Baruch on Vimeo.
A lot of force was required, and when I tried to drive the bar using the rotating cylinder drive, the bar wouldn’t move. It would just bend. I also had to replace some of the casing with aluminum parts, because the force was too great for the acrylic to handle.
Looking at the forces, it is clear that there is a lot of extra energy going into friction due to parts twisting:
So on the drive home, I came up with another idea, which looks like this:
Instead of having a complex bar which pushes the rod stops at an angle, I can push the rods straight out, with the only friction being the bar sliding against the rod stops. All other wasted forces go directly into the pivots where they don’t do much harm.
However, I’m still left with the cylinder drive, which has a tendency to push down on the bar. I think I can solve that by cutting a profile into the slope like this:
The bar rests against a flat, not a slope, and the flat is helically wound around the cylinder. This is extremely similar to the point on a screw, or to a fusee, which is a cylinder with varying radius around which is wound a groove for a chain. Fusees were used in clocks to keep the torque going into the clock the same even as the spring winds down, delivering less force.
I might be able to use the lathe at NextFab to cut one:
Due to the geometry, the diameter of the large end needs to be a little over 2.3 inches, and I only have a 1.625 inch steel round. So it’s not likely that I will get the bigger round by this weekend. I will only be practicing fusee cutting this weekend, but hopefully next weekend I’ll get to try the improved drive system.
Here’s the cam drive which sequences the drive bars in the right order.
And here’s a video showing how it works:
Springs will return the drive bars – I had to move the bars myself (and one of them just dropped because of gravity).
Here’s an explanation of how I implemented noise margins for the Logical Engine design. Recall that rods have holes for bumps every 0.3125 inches (5/16″), and that the spacing between rods is 1/2″ vertically and 0.625 (5/8″) horizontally. Also, I am using 1/4″ hex standoffs that have the following measurements:
Here’s a setup which will illustrate noise margins. The logic here is two inverters, but that doesn’t really matter.
The blue bumps are the bit bumps, while the green bumps are the sense bumps. The hexes are aligned so that the pointy end is along the direction of motion.
Here are the measurements of the bottom pair:
The key measurement is the distance between the flat end of the bit bump and the pointy end of the sense bump: 0.0432″. The geometry of the second pair is identical, so the same measurements apply. So if the bit bump on rod #1 were to be slid in front of the sense bump…
Then rod #2 will only be able to move that much, 0.0432″:
And now, if we slide rod #3, since the bit bump on rod #2 isn’t in the way of the sense bump on rod #3, rod #3 can slide the full 0.3125″. Or can it?
Zero clearance! So if the sense bump on rod #2 were just a little thinner, rod #2 will move that much more, and then the sense bump on rod #3 will smack right into the bit bump. You might figure that because the sides are sloped with respect to each other, it’s not such a big deal: rod #2 gets slid back by the force of rod #3.
But that’s not what noise margin is about. The idea is that the bit on rod #2 should stop short of rod #3′s sense bump’s path, so that any noise in the movement will not affect the result.
By making the bit bumps square, we solve this problem:
And so the noise margin for a zero bit is 0.0193″. The noise margin for a one bit is, of course, 0.125″, being half the width of a bit bump.
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