In the initial planing we talked about how the automata in the Archive Project would be driven. We decided against manually turning a crank handle because we were worried about damage caused by over-vigourous cranking, clock work was out for practical reasons leaving electric motors. Some of the twenty models proposed need to be sited away from mains electrics so we plan to use 12v rechargeable batteries as the power source. I’ve sourced a suitable motor that is both powerful and runs quietly. The output shaft is 6mm in diameter and it runs at 145rpm, roughly two and a half turns a second. Pretty innit!?
Now it needs a suitable mount.
Here’s the cradle I’ve come up with, made from 3mm thick laser cut plywood. Notice the segmented segment in the cradle section. The gear box section of the motor sits here, the segments are glued into place and provide a surface to which the motor can be clamped.
The motor fits in the cradle and a gear connects to the output shaft.
The whole thing is clamped together with a jubilee clip allowing the motor to be removed and replaced in necessary.
While I’m prototyping the gears on the wooden automata I need to be able to assemble and disassemble the model so that I can experiment with designs.
I’ve tried all sorts of design variations. Brass axles, grub screws, flanges, perspex joints. Finally I feel like I have settled on a consistent design. I’m using 12mm dowel for the axles and a keyway in the gear’s axle hole to hold the gears in position.
I drill a couple of small holes in the dowel in the place where the gear is being fitted. The holes don’t go all the way through the axle. I then make a curve-topped staple from a short length of 1mm diameter wire.
The staple fits into the two holes, the fact that it is curve-topped ensures that the centre of the staple is raised above the dowel.
The gear then slips onto the shaft with the keyway located over the staple. The staple works to stop the gear rotating out of position. Perfect!
Here’s a sample of the gears in position. Looking good!
My continuing mission to work out a work flow for designing and making wooden automata has borne fruit.
Having made up a prototype box from corrugated card – previous post – I’ve set about dividing up the automata into its various mechanisms.
Firstly, the parallax hills. The two smaller gears (14 and 22 teeth respectively) are fixed onto a single shaft. The two larger gears are where the magic happens. The 37 tooth gear is fixed to a 7mm tube, the 43 tooth gear fits onto a 6mm rod threaded through its centre. The hill profiles are fitted to these coaxial tubes. As the small gear turns, the front hill turns faster than the rear hill producing the illusion of movement.
Next, the legs. I’ve made up the mechanism as a complete unit. This fits inside the box. The legs of the Yellow Earl fit down into the top of the two fingers. As the gear turns the fingers are driven back and forth moving the legs in the process.
The final mechanism is the thought bubble window. As the Yellow Earl trudges onward ever onward towards the North Pole he is haunted by the memories of the various women in his life. In a ‘thought bubble’ window behind his head the pictures flips past showing portraits one after another. The mechanism is driven by a ratchet and pawl.
Mechanisms in hand, I visited Archive this morning to see how everything fits together with Dawn’s splendid puppets.
Dawn has done a fantastic work making her distinctive puppets to match with my mechanisms. The Yellow Earl is no exception. Everything fits together in the prototype form.
Having taken measurements and made sure everything works we’ve arranged to meet up again early next week for final assembly. Exciting stuff!
The automata in the Archive Project use all kinds of different mechanisms to make all kinds of different movements. The one I’m working on at the moment uses a particularly interesting mechanism. There is a little window in the background of the model. Through the window you can see a portrait of a woman. As the mechanism runs I need the picture in the window to change to another portrait, then another, then another… and so on. I need the picture to be stay still for a set amount of time then flip quickly to the next picture as the mechanism runs.
This is the perfect tesk for a Geneva drive.. In my test version I went for an eight step drive.
The mathematics of the parts layout is fairly straightforward. I wrote a blog post about it a while back here. The key centres for an eight step drive are based around a right-angle triangle with a 22.5° angle. The angle is worked out by dividing 360° by eight, for the eight steps, then halving it.
Having designed the parts in Illustrator, I’ve cut out the resulting mechanism from 3mm plywood and used 12mm and 9mm hardwood dowel for the axles. The drive pin is then fitted onto a 26 tooth gear which will be driven direct from the automata mechanism. This prototype works a treat!
Finally! It’s taken me weeks and weeks of experimentation and development but today I finally finished my first laser cut automata for the Archive Project. The Archive, as its name suggests, is Cumbria’s repository of all the county’s historical documents. I’m hoping to supply them with a series of plinth mounted automata to embellish the public areas of the building. The first model is of Mary Chambers, I’ll fill in the historical details in a later post but suffice to say, Mary was transported to Australia for a variety of petty crimes.
At the heart of the model are these three gears They are made up from three layers of 3mm thick laser cut ply cut ont my HPCLaser laser cutter. I’ve opted for quite large teeth with fifteen millimetre pitch. The larger teeth will be stronger and the larger size will hopefully mask any small inaccuracies in cutting and assembly.
Once all the parts were designed and cut I started the process of putting everything together. As is often the case new ideas and things-I -could-do-better-next-time cropped up all the way through the process. The model is designed to be taken apart for maintenance. I’m using brass tubing for axles with the various parts being fixed to the axles using drilled holes and split pins. This will be one of the first things I change for upcoming models. The holes are awkward to align making it difficult to fit the pins. Perhaps a brass collar fitted with a rub screw next time? The gears fit down the inside of the box in their own little section. The centre gear is the driven one. It will be turned via a toothed belt and an electric motor.
The front axle is connected to a small-throw crank. This is used to lift the boat gently up and down. On either end of this axle are the animated waves, again driven by cranks.
The axle at the other end of the boat is geared down with a twenty seven tooth gear. In turn this is connected to this crank. The crank push rod is then threaded up through a hole in the boat base and connected to the ends of the oars by a couple of flexible straps.
With all the parts put together it’s more than gratifying that it worked smoothly, and with just the motion I was aiming for. Phew!
This morning I took the mechanism round to Archive and Dawn H and I fitted the puppets she has made into place. It worked fantastically, the nameless rower really puts his back into the rowing motion and poor Mary rocks back and forth dolefully in the front of the boat. I can’t wait to get started on the next one!