Introduction: Automaton Hand

I was given the brief to design and construct an automaton for a university project. It was stipulated that the piece's mechanical parts must be constructed of laser cut acrylic. The model was to be marked on complexity, innovativeness and amount of moving parts. The materials used must be 3mm thick acrylic and the overall size used must be no more than A4 (420 x 297mm).

The brief allowed for ultimate possibilities, I had several ideas but finally decided to try and emulate a human hand. I searched through images and videos online for inspiration and ideas to make initial sketches.

First of all I built a prototype concept from 3mm plywood to confirm the mechanisms worked which can be seen in the video:

Materials used for the initial plywood concept:

Roughly A4 (420 x 297mm) of 3mm thick Plywood
Quantity 35, M3 x 12 mm button head machine screws
Quantity 25, 3mm x 6 mm long button head wood screws
Quantity 35, M3 nylock machine nuts
Quantity 100, M3 washers
Various gears and racks that can be bought from ebay
2 part epoxy resin(shown in the pictures above to glue the plastic racks to lever sliders).

Tools required for plywood concept

Dremel tool with drill bits and cutting disks
Various G-clamps
A vice
Hobby sized band saw
Sand paper (various grades)
Square file
Round file
Engineers rule
Flat Head Screw driver

The sizes used for the fingers and palm were from my own hand. The design was not finalised when I started but it evolved as I built it. Spending lots of time analysing and measuring my hand, I split each finger into parts and joined them with the m3 bolts to act as pivot points to give articulation. This was repeated through each finger which were then attached to the palm section with slots. Again, I simply drew around my hand and took measurements for sizes. The mechanisms that bring the fingers all together were cogs and rack and pinion mechanisms which I found was the best way to transfer actuation throughout the hand. This is a concept model, and even I could not reproduce it again to the same specifications but I learned a lot about gearing, ratios and levers to apply to the final concept model.

After experimenting with the initial plywood concept model I created parts on pro engineer. This software package is not necessary to create the parts or the laser cut file as they are only 2D sketches. I extruded the sketches to 3mm and assembled the parts to test the mechanisms. From the working assembly in pro engineer I created a drawing file with all the individual parts. I could then export it to DXF file format to be laser cut.

Video of working CAD assembly:

Materials for acrylic model

Roughly A4 (420 x 297mm) of 3mm thickacrylic (colour of your choice, transparent works well)
Quantity 35, M3 x 6 mm button head machine screws
Quantity 10, M3 x 6 mm countersunk machine screws
Quantity 2, M3 x 10mm button head machine screws
Quantity 1, M3 x 10mm button head machine screws
Dichloromethane plastic weld
Toothpaste (cutting compound for tapping threads to stop the acrylic shattering)

Tools used

Spirit laser cutter
M3 tap
Small flat file
Allen key (2mm)
Countersink drill bit

Each finger has 3 main parts ordered in size with 3 ligament levers. The 2 pivot bolts on the middle part of each finger are countersunk to give clearance for movement using the countersunk bolts. Clearance holes are cut at 2.8 mm diameter, holes to be tapped were cut at 2.3 mm diameter. Glueing required for each finger rack was done using Dichloromethane which is a solvent plastic weld.

The model is operated from the transparent crank rod handle and can be turned clockwise or anticlockwise. The crank handle operates a gear to the opposable thumb mechanism and also a crank to the pinky cog. The pinky cog drives a rack and pinion that transfers rotational motion to linear motion pushing and pulling the levers extending and moving the finger. This is repeated from the pinky to the index finger.

This was a long frustrating process with many iterations in development of the piece produced but the end result turned out great. Hopefully my efforts are reflected in my mark.

I have posted the DXF file used to cut the parts on the laser cutter. This was the file that was used to cut the parts for my final model. With this anyone should be able to reproduce their own acrylic automaton hand.


Rhadamanthys76 made it!(author)2014-03-29

My friend

Kudos on a beautiful design. I hope you aced the project with max marks

I took the liberty of making a 3D printable version of your model. So basically took your dxf and extruded it into a 3D model. Took me like an entire day to do it since I had to make a bunch of changes to the sketches and I'm a retard with CAD

Just printed it and it came out rather nicely. I made it 5mm thickness so will have to see if I manage to put it together in the end

Attached is a pic and the STL file (still dont know if the 5mm thickness will cause an issue) The STL is the same size as the DXF so your instructions and bolt sizes still apply. In the case of my printer at least, I had to shrink it down so it would fit on the printbed

Anyway I'll keep you posted after putting it together and adjust the STL if needed

Again, excellent design

mid2 made it!(author)2014-05-11

Dear sir, I have used the file to cut it on both 3mm acrylic. The problem is how i can determine rocker for each finger, can you give me rockers length for each finger because their are about 17 rocker so its Very difficult to try each rocker.

thank you anyway

keziajhls made it!(author)2014-01-02

Dear sir, I have used the file to cut it on both 3mm plywood and acrylic. The problem for me seems that the gears can't be turned. As I turn, the screws keep getting tighter and tighter. The gears near the 'fingers' are stuck as well. Do you know what can I do to improve on it? Thanks and much appreciated.

zoo2boy made it!(author)2013-01-05

can u post a diagram of al the parts i have a prdject n woods at highschool and i want to try this i tried making a hand already but your design is really freaking cool please post part diagram

alasdair.robertson made it!(author)2013-01-06

All the parts are in the picture here(they are in 2d, material 3mm thick)

If you are wanting to recreate it you can just download the dxf file above. It has all the parts to scale in it. It will open with Corel Draw. Hope this helps

zoo2boy made it!(author)2013-03-02

thnk you for the link it turned out better than i expected with the wood i choose it looks sorta mid century robotics thnks again

alasdair.robertson made it!(author)2013-03-03

Do you have any pictures you could post? Id be interested to see how it turned out

zoo2boy made it!(author)2013-03-12

unfortunately i wont be able to post pics until i get it back from an old teacher that wanted to use it as an example for his wood shop class i will asap idk when srry

sSkEzAfNs made it!(author)2012-12-31

if i was to make something like that, i would use a few different sized gears in the fingers, that way they would each mover at different rates. Not drastically different, just a range from, say, 8-12 teeth.

3dfernando made it!(author)2012-12-27

Great job, this is a piece of art! And now i'm left just wondering how artists could make similar or even more complex models in the past without 3D software and CNC cutters!

One question, did I understand wrong or you can't cycle the crank? Looks like it will stumble on the thumb's gear.

Wouldn't it be better if you could cycle the crank handle so you could rotate endlessly just to see the automated hand crawl around? hehe, just a comment, I wouldn't be able to do one tenth of this work!

alasdair.robertson made it!(author)2012-12-29

something went wrong uploading the video but you can still see it working;

alasdair.robertson made it!(author)2012-12-28

Cheers 3dfernando,

Believe it or not, making the plywood concept model took less time than the cad model! I find working with my hands with physical components is a lot easier than visualising it in your head. Although the final product was very much worth enduring the long hours producing it on CAD. Although similar, there is only a few generic parts in there.

I am currently uploading a video of the CAD assembly operating as I didn't get a chance to film the final physical piece. I like your attention to detail, you are right in spotting the thumb gear drive. It doesn't actually turn the whole way round although the drive handle can be turned round continuously.

I made the drive gear for the thumb mechanism full for purely aesthetic reasons. The ratio from the large gears to the small gears is 1:3. This means the large gear driving the thumb mechanism only turns 120 degrees before it returns. With a half or a third of a gear I wouldn't be unable to hollow it out for a spoke effect and would leave quite a lot of empty space on the main palm part.

I have had some excited friends want to make it automated by attaching servos etc to it and make it crawl around. If any one does develop this I will document it and post it.

Tomdf made it!(author)2012-12-28

I'm working on something very similar and I've decided that these servos would be the best choice for what I'm doing. Figured I share, maybe your friends will like em:

Pointy made it!(author)2012-12-28

I really love the design! You should take another look at the spacing on the cutting file.
Parts could be so much more condensed, especially since it's designed to be laser cut.
One would really waste material this way..

Or is this my Dutch DNA speaking...

alasdair.robertson made it!(author)2012-12-28

Thanks for the comment Pointy,

I did manage to cram twice as many parts into the A4 sized piece of material on the first attempt. I knew because of the brittleness of acrylic and the stress that is produced when trying to tap threads that I would need some spare parts! If you look closely in this picture you will see that I had utilised all the space available!

The downside is it took about 45 minutes to cut and the close proximity to complex parts such as the cogs (>10 mm diameter) which had a lot of heat concentration (even with compressed air), caused some parts to warp.

You might not think it would cause too much problem but I had to take into account the laser cut width of 0.2-0.25 and remade all the CAD parts to accommodate for this. Because of so many moving parts, the sum of play between just 4 moving parts (0.25 x 4) is 1 mm, so if you look at just the gear mechanism, which has 20 parts that would be 5 mm play. That 5 mm play would make the finger at the end (index) twitch instead of articulate.

With the second and final cut I spaced the parts out a bit more as It was easier to group/ungroup them in Corel Draw when selecting colours to indicate cutting sequence.

I do agree though, if I was planning to do a job lot of them I would try and cut costs with material by cramming the parts as close together as possible without causing any defects!

Pointy made it!(author)2012-12-28

I see. Spacing on the link you provided looks much better.
But then again, I would not have factored in the distortion by heat.
What machine was it cut on? 45 minutes seems like a long time for a cutting run..

alasdair.robertson made it!(author)2012-12-28

I am not sure about the first machine it was in uni, The technician was not happy though as he was late for his lunch. I just gave him the DXF file and he done the rest so I didn't have much influence on the cut settings but there was 100+ parts.

Second cut was at Maklab, a local Fablab in Glasgow where I set the machines up. It was a 40W Spirit Laser which took alot less time.,d.d2k

Tomdf made it!(author)2012-12-27

That is a work of art! Good Job.

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