Contemplation: How do the tubes grow?

May 30 2013

The telescopic frame is built – 3 x 60cm high segments which are held within a base-drum of the same height. Each of the legs of this structure has teeth marked in the wood ready to cut, but I have held off from doing this task so far. Why? Because its an enormous task and I want to be 100% certain that there isnt an easier way to do this.

There has been an important design evolution recently which is not reflected in any of the machine parts – the substrate will be extruded every hour not every 4 hours. This means the substrate layer will be 1cm tall not 5cm tall, which in turn means that the tower will rise 1cm every hour until it reaches its maximum height of 180cm. This translates roughly to mean that the tower will reach its maximum height of 180cm in 18-21 days (assuming the substrate compresses slightly over time) through 10 extrusions per day (10cm increase / day with an evening rest/dry-time of 14 hours).

 

The Pulley System

The tower currently employs a system of pulleys to rise out from its base and reach its maximum height – with me tightening the cords to achieve this change. It works, but the friction is absurd and quite frankly I dont trust the accuracy of this approach especially not as the idea now is for it to rise in much smaller, more controlled increments of 1cm. If one cord is pulled even slightly tighter than the others, the increase in tension puts the rising segment completely out of alignment and the tower will certainly collapse or have big problems.

So, problem Number 1 to avoid is the possibility of one leg rising faster than the others and problem Number Two is to avoid friction and ensure that each incremental rise is an accurate 1cm.

There seem to be two solutions to this – either use a toothed leg with a synched stepper motor for each leg (9 in total), or use a single motor and a chain-sprocket system (3 in total or only a single 1 if the system is complex enough).

If a roller chain and sprocket system will reduce friction, allow a controlled rise, and bring it all under the control of a single motor then this seems the sensible route to take. Its certainly simpler than having a motor system for each segment leg. Review this decision again playing devil’s advocate.

 


 April 20 2013

There is another problem. How do the tubes grow?

The idea is that substrate is moved up the inside of the tube and deposited at the top in a donut shape. After a few hours – when this new layer has solidified a bit – the extrusion head of the machine rises a couple of inches and the process is repeated. Substrate is pushed up from the base of the tower through a tube, whose walls are made from a ring of wax – a ring of wax inside a ring of substrate. Ring on top of ring – and the tower rises.

This is the idea..

Pneumatic Telescopic Steel Column

But… this process relies on a wax tube taking the pressure of the pumped substrate. It also assumes that wax can be moved in a solid form without blocking any tubes from the base up to the tip where it is melted and shaped. Is this absurd?

The current idea assumes that substrate can be moved from the base to the top without any problems like blockage or bursting, and also that the tower will rise perfectly perpendicular to the ground and not topple over. Are these demands realistic?

Perhaps something needs to be reimagined.

If a telescopic spine structure is concealed underneath the base – along with the tube-fed substrate-reservoir – it could be gradually extended upwards.

Because of its rigidity and water-tightness it would function perfectly as a tube and the substrate could be pumped up through another tube (flexible tube of about 2″ diameter) inside it.

A traditional telescopic tube logically requires each inner segment to have a smaller diameter than its parent segment.

Rings and rods structure

If each segment has the same diameter then a slightly different telescoping mechanism needs to be employed.

Consider rings and rods – where the rods fit into holes around the circumference of the ring.

Cables are tightened and sets of rods are pulled downwards. In this way a motor can be placed at the bottom of the growing tower, cables are tightened by this motor, and the tower of rods and rings will rise.

Peristalsis Pump

 

So, the tower has a hollow telescopic pvc spine running through its middle.

Inside the spine is a tube which reaches from the substrate reservoir to the tip of the tower.

Its length never changes, although the how much it is outstretched depends on how mature the tower is.

Substrate needs to run all the way along it – which means it needs to travel about 220cm. It should not be visible under the platform, so it will be loosely rolled – this will make pumping slightly more tricky.

A peristaltic pump moves the cement-substrate along the tubes.


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