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Demotech News
Demotech is involved with the development of a pully to lift water from this well, to be constructed out of rubber from a car tire and wood. In The Gambia (a very similar and nearby region) locally made metal pullies are for sale.
Please report to us anything still wrong through the forum page linked to "Constructing this website".
The frameless setup also makes it possibe to change the whole layout without changing anything of the content, the actual information. So the present "skin" will certainly not be the last one!
The lift worked well with the glider out of a strip tin plus a set of rolers at the bottom. Next was he construction of the shelve that has to carry the projector. The outcome is a box that turns inside the middle space of the lift. This box is stiff, can hinge upwards between the gliders of the lift and when folded, can store some stuff that the user wants to keep with the drawing table when not used. Rollers to center the lift between the legs of the table proved superfluous, when this function was carried out by two strips of sheet metal attached to the inside lowerpart of the legs. The foldable footframe has been replaced by two simple stands, holding the legs apart. This does not impair the stability.
Demotech's target is to design a comparable system that is smaller in size. It should be manufactured locally in 3th World conditions for use in urbanized areas. Presently we work on three components: The caddy-like roling set for transporting the bucket, the lid and a docking station to faciliate easy connection to- and separation from the fluid duct to a suewerage pipe and the pipe for forced ventilation.
Some fight today on how the lift should be designed. This lift, a sliding platform supports the slide projector. So it should be able to move it up and down with a fluent motion, no sticking, no shocks, no chance for the projector to fall off. Three options: 1 Two sets gliders, top and down. The lift is a sledge-like construction, that has to carry the projector. It has gliders that got a sheet metal (tin) cover. This cover made it possible to slide over obstructions, such as the clamping strips and roughness in the boards. The big problem is the reinforcement of braking. This is caused by the balance in their mutual points of contacts between pressure in the guide and the weight of the sledge carrying the projector. Blocking occurs if friction can not be reduced by rolling or smoother materials. As this was the case, I stopped further development of this option. 2 Two sets of rollers, one set up and one set down. This functioned perfectly. However it was a hell of a job to construct it and to line out the rollers. I have folded and nailed little bits of sheet metal strips on the wooded sledge. I got the feeling that this constuction should not become as complicated as this. So over to option three. 3 A sheet metal cover up and rollers down. "Up" has space restrictions. Anything attached has to pass the hinge between the fore and the behind legs of the table stand. "Down" has ample space, as it is at the front. Plenty space as well in width as in height, eventually to be translated in diameter of the rollers. Technically complicated it the relation between friction, the leverage of the load on the sledge, and the pull of the cords of the lift. However there is more. The construction has to defey these complications and be clear and a guide for understanding of how the system works. Now at the end of the day, the choise is for three. Tomorrow this option should be worked out and tested.
Lately we worked again on the Projection Drawing Table. This drawing table is a Demotech design made some twenty years ago. Somehow we liked it, as it properly functioned. But we were not fully satisfied, as this design had complex details, not easy to make. Our visit to The Gambia gave a new impuls. A technical school could use it very well. We experienced the ease and precision with which students worked wood into thin smooth battens. We liked to use such battens in a re-design of the drawing table. Also we drew inspiration from a visit to a revalidation clinic in Mexico. People in wheelchairs could also use the drawing table when certain modifications could be realized. Now we have the new prototype ready to test: very compact when folded, the A2-table top with glass center easy to adjust in angle and height, a lift for the slide projector ajustable in height with a rotating handle ... Very light, as only 13 mm thick battens have been used. Yet stable, because of the use of a box-like structure, standing up against tortion. This tortion box is combined with bearings for the winch. No screws or hinges are used. All fastenings can be made out of tin or wire, to be copied without cost. And while sitting in an easy (wheel) chair, you can place the table top in a comfortable position over your lap. Now the first new prototype is complete, it is easy to find further simplifications. These are on our programm for the next days.
The cross wires for the DemoSticks have been re-designed. Main advantage: the method of constuction is now almost identical to the DemoCamp-units. In effect, Demosticks are now a scaled down version of the DemoCamp-units. Specially the handling of the cross wires became better, as they can't get tangled up anymore. |
