April 4th: Planned to build a Meccanograph with Grandad, to our own design
Here are some examples of other people’s designs:
April 5th: We will need a strong platform on which to assemble the machinery
Here are the main components for the platform’s outer framework:
The platform needs to stand on four feet, near its corners, for stability
The feet will be fixed to the undersides of two girders fixed across the platform, near its shorter edges; here are the two girders and also the components of one of the feet:
and here is one of the assembled feet:
The base of the foot has a rubber tyre which cannot damage whatever surface we place the model on and also cannot slip on that surface.
The wheel with the tyre is at the bottom of an axle (rod) which can freely move a little upwards against the force of a compression spring.
This arrangement ensures that all four feet will always be in contact with the surface even if the platform is not completely level or the surface is not completely smooth.
April 6th: Components for powering the model
This is what the controller and motors look like:
and here you see two different kinds of gear that can be fixed to them – the motor on the left has a worm gear and the motor on the right has a pinion:
These motors run at high speed, and usually we use worm gears to “step down” the speeds of things driven by such motors.
We will want the actions in our model to run at quite low speeds, for example we might want the paper carrier to take a minute, or even several minutes, to make a complete rotation. And we don’t want the pen carrier to move too quickly either. Next weekend we will do some experiments in timing these motors and working out which gear connections to make to step down the speeds to the right extent.
Structure for the paper carrier
As noted in today’s email, it will be the paper carrier that rotates. Basically it is just a turntable and one way to build this is using two large flanged disks such that the rim of the upper one of these “rides” on a ring of flanged wheels fixed around the rim of the lower one:
Above, on the left, is a rough model to show the general principle – it is not yet properly built. Parts will need adjusting and tightening and there will be eight of the flanged wheels on the lower rim, not the four shown here. Above, on the right, is a view of the lower flanged disk with the upper one removed, to show how the flanged wheels are installed. The lower disk will be fixed to the platform and does not rotate. It is the upper disk that rotates and will eventually support the pad to hold the drawing paper. The upper disk will be made to rotate by the central axle seen here, on which will be a gear wheel underneath the lower disk. We will need to work out the right speed of rotation and will probably need to use at least one worm gear arrangement like that seen below on the right.
April 7th: Parts trolley and test rig for measuring timing under load
To make it easier for us to access common parts like screws, washers etc I have put trays of these onto a trolley in my office – see below.
I have also prepared a simple test rig powered by one of the motors that we will use at the weekend to measure rotation timings under varying loads – see below.
The motor has a worm gear driving a 19-tooth pinion. On the same axle as that pinion there is another worm gear driving another 19-tooth pinion on another axle. This second axle therefore rotates 361 (= 19 x 19) times more slowly than the motor’s worm gear. This is a very large stepping-down, but the rotation of the second axle (carrying the red fan wheel) is still rather faster than we would want for the turntable – at least, that is true when the motor is not powering any significant load. We will measure how fast it rotates when loads of varying weight are suspended from the red hook (which is wound up or down by the second axle), so that we will know how much the timing is affected by load for any given setting of the power dial on the controller.
Here’s a little video showing the test rig in action:
April 10th: Test rig for machinery driving the pen carrier
The pen carrier will be an arm holding the pen. That arm will move in various directions over the paper on the turntable.
Part of the machinery for driving the pen carrier involves moving the pen backwards and forwards, and a simple way of achieving this is to convert rotational movement into linear (straight-line) movement using the kind of mechanism shown below.
As the blue disk on the right rotates it drives the silver strip backwards and forwards, in the manner of a piston. The left-hand end of the piston is made to travel always in a straight line above the blue strip, because it “rides” along that strip using a special component called a slide piece.
The blue disk on the right rotates quite slowly. Two worm gears are used to step down its speed. The one fixed to the motor drives a pinion having 19 teeth. The other one drives a larger gear wheel have 95 teeth. Therefore the blue disk rotates 1805 (= 19 x 95) times more slowly that the motor’s primary axle. If the motor was carrying no load at all then it would rotate at 4800 revolutions per minute, so if the blue disk and silver arm had no weight at all then we would expect the blue disk to rotate a little over two and half times (= 4800/1805) every minute. But as it does have some weight, its true rotational speed will be a little slower than that.
The next two images show the two worm gears.
Besides being able to make the pen carrier move backwards and forwards we also want to control the extent of that movement. The blue disk contains several slots (see the image on the right here) into which the right-hand end of the piston can be fitted. Different slots cause the piston to move to different extents.
Finally, we also want to enable the pen’s direction to be altered. The video below shows that the blue strip can be moved from one side to the other to achieve this. We will build a separate mechanism to control this variation in direction.
April 11th: Building the base and the pen carrier’s rotator
We got the required pieces together and started building the base.
We then built the rotator for the pen carrier and also the sliding carriage carrying it.
April 12th: Building the turntable and getting it working in the correct position
The first thing we did was to record what we achieved yesterday, as shown in the two photos below …
… and in this video:
And now the first stage has been finished, getting the turntable installed and rotating, as Teddy demonstrates in the video below.
April 16th: Installing a 3-speed gearbox to drive the turntable
Last weekend we installed some simple machinery to drive the turntable. It had just one speed.
Since then a 3-speed gearbox has been added. It works by having a sliding input rod carrying gears that can mesh with various gears on an adjacent output rod driving the turntable. This arrangement offers different gear ratios between the two rods. These ratios are 1:1, 2:1 and 3:1. When the control dial is set to 40, the slowest full rotation of the turntable takes about 2 minutes and 45 seconds. The fastest full rotation takes about 55 seconds.
The picture on the right shows some of the gear combinations involved. The output rod (the middle one of the three seen here) has a compression spring on it which prevents it from making minor movements to and fro caused by slight inaccuracies in the gears – the result is that the turntable rotates much more smoothly that it would if the spring were absent.
Below, the picture on the left gives a fuller view of the gearbox. On the left side of that picture two rods are visible. The nearest one is the input rod and it can slide to the left or to the right – sliding it brings different gear combinations into play, to vary the speed of the output rod.
The picture on the right shows the mechanism for producing that sliding action. Near the top, on the right, is a small yellow lever – when it is moved to left or right it causes the gear below it to turn. That gear wheel has underneath it a toothed rack. When the gear wheel turns clockwise or anticlockwise, the rack moves to left or right, pushing or pulling the input rod to left or right.
So, choosing which of our three speeds to use involves only moving that lever to the appropriate position.
Here is a short video to demonstrate the operation of the 3-speed gearbox..
April 17th: Installing the drawing pad and the sliding platform to hold the pen arm controller
The drawing pad has now been fitted to the turntable as seen below on the left. It is made of 9mm thickness fibre board and has a perfectly smooth surface. It has been screwed to the turntable by four hidden screws. A paper square can be attached to it quite firmly using just two elastic bands, as shown here. Because of the thickness of the pad it has been necessary to lower the turntable by half an inch.
As previously discussed, the arm supporting the pen will not only move backward and forwards along its guide rail, it will also be made to sway to left and right to varying extents by the use of another, smaller sliding platform, shown below on the right.
The next step will be to start building the machinery needed to move that smaller platform back and forth, using an automatic reversing mechanism.
Below is a short video discussing today’s progress.
April 18th: Test rig for the automatic reverser mechanism
Teddy ready to begin the day’s work, at right.
Today we have been fitting a toothed rack to our secondary sliding platform. The rack will be driven by a rotating pinion. We want the platform to move to and fro, automatically reversing its direction. So we have today built a test rig to work out how best to make that mechanism using a sliding gear rod, as Teddy demonstrates in the video below.
We will arrange that when the platform reaches one end of its range it will cause the gear rod to slide so as to change the gearing’s rotational direction, so driving the platform back in the reverse direction towards the other end, where the same mechanism will again reverse its direction.
We will need to do several things to get this working properly: (a) we must ensure the toothed rack and its pinion remain fully meshed all the time; (b) we must work out exactly how the platform, on reaching an end position, moves that gear rod; (c) we must ensure that the gear rod never slides out of position except when the platform makes it do so.
April 19th: Pen movement check and preparing the automatic reverser mechanism
Below, at left – Teddy at the start of the working day.
We added a raised area to the secondary platform (below, at right) in order to support the end of the guide rail and also to carry some of the automatic reverser structure.
With the end of the guide rail now carried by the secondary platform we then worked together on a number of tests to check that the pen would in all circumstances stay within the drawing area, whatever the positions of the primary and secondary platforms, of the pen arm and of the turntable rotation. We marked the drawing paper (below, at left) to show where the pen would draw in various cases.
Teddy then dismantled yesterday’s test rig so that we could begin installing the real reverser mechanism. We got as far as building some of the framework to support this, as shown below, at right – Teddy put together almost of all that framework once Grandad had figured out what was needed.
There is still quite a lot of work to do to get the reverser mechanism fully installed and operational – that work will probably take another weekend.
May 16th: Preparing the mechanism for moving the secondary platform (the pen guide carriage)
May 16th (evening): Preparing a disruptor mechanism for the pen guide carriage
During the rest of the day we installed a structure to support a way of disrupting the normal rotary-to-linear motion in a systematic and variable manner, to add yet further variety to our patterns. The video below says more about this.
May 24-25th: Revising the drive to the platform carriers and making interchangeable gearboxes
Several changes were made to the mechanism for driving the platform carriers.
The first issue to tackle was the need for these carriers to move in synchrony, not necessarily with the same speeds but with speeds that were rationally related to one another, for otherwise their combined movements would result in chaotic drawing patterns. Rather than being driven by separate motors we arranged for a single motor to drive both of them. Teddy discusses this in the first video below.
However, we also wanted the gearing between the two motors to be flexible (so that, for example, one would move three times faster than the other). We therefore began building interchangeable gearboxes that could be easily inserted between the motor and one of the two carriers, enabling them to behave differently but still with some degree of synchrony. This step was taken in order to widen the variety of patterns. Teddy discusses the gearboxes in the second video below.
May 26th – June 24th: Further refinements and bringing into operation
We were not able to work jointly on the meccanograph during the next month owing to holidays and other matters, so Grandad worked alone on making various improvements. The first step was to acquire some new motors because the existing ones ran at about 2000 RPM, requiring a lot of gearing to step them down to the kind of speeds we needed. This gearing created quite a lot of noise and took up valuable space in the framework. Some new motors were therefore purchased, having very low RPM and far greater power, despite being smaller. They were also much quieter. The photo below on the left shows a new 20 RPM motor driving the platform carriers. The photo in the middle shows one of the gearboxes – in this instance the simplest one, establishing a 1:1 ratio between the input from the motor (via the lower left pinion) and the output to the right-hand platform carrier (via the lower-right pinion).
There was further work to be done regarding synchronisation. Up to now the left-hand carrier platform had onboard a separate motor used to drive the rotator (which it also carried), and that motor’s speed bore no stable relationship to the new motor driving the carriers. Somehow the rotator had to be driven by the same motor that was driving the carriers, to be in synchrony with them. Achieving this was perhaps the greatest challenge in the entire project: how to supply a continuous drive to a carrier that is moving back and forth to a variable extent in a variable section of its track. After much experiment an arrangement was chosen that proved to be totally robust and reliable. The first step was to carry the power from the latter motor to a universal coupling, seen below on the right. The shaft seen on the far right of that picture comes from that same new motor that was now driving the two carriers. The shaft on the far left of the picture, emerging from the universal coupling, goes to the undercarriage of the rotator’s carrier and can be oriented in a wide directional range (thanks to the ingenuity of the coupling) while continuously turning.
In the left-hand picture below the lowest shaft is that emerging from the universal coupling. It enters a small undercarriage suspended below the rotator’s carrier and has on it a long pinion which engages with a second long pinion above it. The latter pinion drives a small contrate gear. When the carrier moves back and forth along its track, the shaft from the universal coupling swings with it and, in doing so, moves horizontally within the undercarriage structure, but the continuous drive is maintained because the two pinions slide along each other while turning.
The middle picture shows the entire structure of the rotator carrier. The shaft bearing the small contrate at the bottom extends right up through the exact middle of the carrier platform and drives the disruptor disc, which is fixed to that shaft. The rotator (having the large ring) is free on that shaft but is itself driven by an auxilliary gear feed from the disruptor. The disruptor rotates three times faster than the rotator. It was designed this way so that it could apply its effect on the pen three times while the pen was being advanced or retracted by the rotator, yielding patterns more interesting than otherwise. The picture on the right shows the upper structure of the disruptor disk, on which variably-positioned pins disturb the bar that is driving the pen arm (visible in the picture’s top-left corner).
With the carriers and rotator now all driven synchronously there were just two main matters remaining. The old 2000 RPM motor driving the turntable was replaced by a new and smaller 80 RPM motor, enabling a lot of step-down gearing to be eliminated. The pen guide was fully constructed and sliders built upon it to support the pen holder, driven by the pen arm. The pen arm is of variable length, enabling the drawing to be located nearer to or further from the paper’s centre. The pen holder – seen in the picture below – employs a conveniently large metal washer of just the right size to squeeze in one of the chosen pens. These are gel pens called Frixion Clickers and they have excellent flow characteristics. It takes perhaps half a minute to instal a pen in the holder at just the right height above the paper to ensure that good contact is maintained during the drawing operation.
It was time to test the machine for the first time, on 24 June. Below are two examples of its output.
June 28th: Exploring the machine’s capabilities
We spent a happy day together experimenting with the many settings on the meccanograph to see what could be produced. At present we do not have a very clear idea of how particular combinations of settings affect the patterns generated. Every time time the machine is operated after a small change we get a new surprise. Below are some of the patterns we made today together with a video in which Teddy talks about the machine.
No doubt we shall produce many more pretty patterns together in the times ahead.
