Electrically actuated mechanical power transmission

This is my first attempt at a solenoid switched rotating shaft. It kinda works. I've been using LEGO to prototype some ideas, with a minimum number of 3d printed parts to integrate the solenoid, etc.

Different gears, better integrated solenoid.

Parallel Manipulator with Closed-Form Forward and Inverse Kinematics

This is my completed model of a Byun & Cho (1997) 6-DOF, 3-PPSP Parallel Manipulator, printed in PLA. In a working machine, steppers would walk the ball-and-socket joints horizontally and vertically. The rectangular sliding joints in the middle are passive, as are the ball-and-socket joints. This was mostly an exercise in reducing the number of bolts I needed - and working around the problems of printing overhangs - and was otherwise straightforward.

Ball and socket joint

While I don't expect this 3d printed ball-and-socket joint to be especially fit for the task, it's been an interesting experience in solving overhang issues without using supports. The top-left picture shows a slide attached to the back of the joint using a clip mechanism. Top-right is the completed clip, and bottom is the completed joint. The hemispheres of the ball (one with rod) are printed separately and bolted together.

XYZ Machine

This is my current project, a three stepper motor XYZ machine. The rods are about 250 mm long and made from aluminium. The flat surfaces are laser cut acrylic and the remaining parts are 3d printed ABS.

So far I have the driver board working for one stepper motor (I'm expecting the other two tomorrow) under control of a Particle Photon, and I've requested a quote for the acrylic parts. I've also purchased the rod, the tube, the bolts to hold it all together (not shown). The design of the other parts appear printable to me.

Laser cut parts ordered. $41 pickup.

Picked up the laser cut parts today (4 Dec) and John soldered the other two sets of stepper motor and driver boards.

Wire cutting 10mm tube and 6.3mm rod using my poor man's lathe.

I found extra-virgin olive oil works better than canola spray :)

Putting it together without the 3d printed parts proved difficult. It was informative though. First redesign:

Included is the cutting tool and holder, and a first pass at a platform. I made the sliders clamp around the acrylic parts as I noticed them bowing. (That didn't work, btw.)

Today I finished the assembly and did some programming. At first I was less than impressed with the mechanics of the sliding motions but I managed to get a simpler slide part to work and it's quite stable while still being stiff. The cutting tool is mounted and seems to cut ABS easily enough.

As you can see from the video, the sliding mechanism is still quite poor. The square being cut is 2500x2500 steps. The top stepper motor isn't connected yet. Third slide design:

I added rollers, which solved the friction problem, while maintaining the stiffness.

I mounted my dremel (a Ryobi rotary tool). Tomorrow, hopefully, I'll wire up the Z-stepper and do some programming.

I got it cutting:

I've experimented with lifting and lowering the cutting tool between every 100th step of the platform. This "pulse" mode seems to produce better results than using the steppers to push the platform into the cutting tool. Either way the results are pretty terrible.

I got my own 3d printer yesterday, the white components are printed with PLA and seem sturdy enough. I'm back to scraping using the tungsten cutting tool. At 1/10th speed I get about 100 micron repeatability. At 1/100th speed I get much better repeatability - perhaps even one micron. So far I'm just drawing a square, and it cuts better in one direction than the other.

This is the result of my hunt for platform stability. The steppers are now 3/4 enclosed (neither open in the direction of travel), bolted onto the frame. The sliders are now externally guided, with rollers that are mounted on bolts. It seems pretty stable, but the X direction (left to right in this picture) is a bit too loose, I think.

This is the final version of the slider - two rollers on top, one on the bottom - centers the stepper rod in the acrylic slots and prevents rotation. The high stiffness makes the repeatability exquisite.

This is probably a terrible idea, but let's see how cheap of a DC motor I can use with an engraving cutter.

As expected, the stiffness of this ZDriller is pretty horrid, which results in very wild cutting. Considering that the bit is not even properly centered on the motor shaft, it's amazing it works at all. 

Some improved stability.

I had an amusing incident where I couldn't get my pliers into a small area to hold a 6mm nut and found myself thinking "if only I had a tool that could reach around this bracket". Well, I have a 3d printer...

In any case, I dropped a complicated design that was three parts bolted together, with superfluous wheels and came up with this single part:

By adjusting the shims between the inverted pyramid and the ZDriller, I was able to find the sweet spot where the dremel bit is held in contact with the motor gear and doesn't have too much friction pushing it into the holder. It makes sense:

Now that I have a stable cutting tool, the rock and roll of the platform is even more obvious, though.

Applied Science Reading

It's a well kept secret that most of applied science is just reading and writing reports. This collection from 1974 is a good example of why writing down the various techniques used in a lab can have long distance effects. Many of the techniques described are still applicable today, and although refined and superseded, they provide valuable insight into how the approaches were developed and how they can be reproduced. Combined with modern micro-controllers, some can be rival more expensive machines. In any case, reading these sorts of works provides valuable motivation and inspiration.

Assorted watch parts

The Ugly Truth Of Aluminium Etching

I did some experiments with Ferric Chloride on 3mm and 1mm aluminium (6063-T5). It's a good thing I did it outside.



This is the same stuff they use for PCB etching, and I've gotten most of the information from there too. I'm hoping to try some photoresist techniques and watching the epoxy melt into an even bigger mess than this. Another idea I have is to continually wash the etching solution away and reapply, automated of course.

In other news, I got another drill today. This time attached to a bit of extruded slotted aluminium and jokingly called a mini-lathe. I don't really think it's gunna be good for much, but it was cheap.

Solenoid-based Gripper

I had this pretty simple concept in mind for a gripper. The idea is to pick up components that have "handles" that have been designed for the gripper, so it doesn't have to be very good. This little prototype seems to work, but it needs a stronger return spring. 12V supply. Turns out superglue is a pretty useful way to join aluminium and steel :)

Floppy wireform

This wire-form model shows the problem of stiffness. The materials have sufficient stiffness but the joints have too many degrees of freedom.

Main wire: 1.57mm galvanised steel.
Binding wire: 0.8mm.
Holes: 3 x 1mm.

The base needs to be bigger, and the platform needs to be smaller.

Laser Engraving

My el-cheapo INSMA 2000mW USB laser engraver came today. I'm hoping to make some masks for chemical etching with it. But first:

and here's what the top of Snoopy's ear looks like under the microscope:

After some experimentation, I found that 4x4 pixels are about the limit of the printing resolution with each pixel being approximately 10 micron. Different materials, laser power and "depth" settings may yield better results. This is sufficient for my purposes.

Jewellery Making

AJS Product Catalogue 2018/2019

Jewellery making is this super-accessible field of alternative manufacturing.

I'm thinking it's a treasure trove of techniques waiting to be automated.

Synthetic jewels and machining them... drool. Watch parts are some of the most well crafted components in the world. Surely we can make more than watches out of them.

Work in progress

I recently started doing some experimentation with alternate manufacturing techniques (commonly called "crafting") with a view to making small components for robotics. Not shown is the 3D printer that I have borrowed from a friend a few times, with which I made this 25-x scale model of a Stewart platform concept that I'm pursing.

The joints on this hexapod manipulator are an interesting form of universal joint called a revolute joint. It's mostly held together with M3 bolts. If you look at the bottom right corner of my messy workbench you'll see an attempt at a much smaller wire form. It's supposed to look at bit like this:

Drilling a 1 mm hole through 1.57 mm wire by hand was a pretty fruitless experiment, but I thought I'd give it a go. As this microscope shot shows, I have a long way to go.

This is, essentially, jewellery making, and I am no jeweller. My second attempt was better:

It looks good, but it's very off-center - in this photo the hole should be further to the bottom-right. Hopefully my mini-lathe will show up this month. It should make this work a lot more precise.