Tag Archives: invention

How to stop crutches from clicking

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Adjustable-length metal crutches click with each ground contact and lifting, which some people find annoying. The reason for the clicks is that the push button used to adjust the length of the crutch is not snug in its hole, but pushes against the top of its hole when the crutch is pressed against the ground and against the bottom of the hole when the crutch is lifted.

The push button length adjustment system consists of two pipes inside each other, with holes in the outer pipe and a spring-loaded button on the inner one. Pushing the button in allows the pipes to slide relative to each other. When the button is released and pops out into a hole, it locks the pipes together. Similar push button systems are used to adjust the handle length of rolling luggage and the weight stacks of gym equipment.

To silence the clicks, the button should push against the same side of the hole at all times, which can be achieved by adding one spring. The spring should pull the inner pipe of the adjustable part of the crutch in the direction of shortening the crutch, i.e. the same direction as ground contact. Then the button always stays in contact with the same side of its hole instead of alternately hitting the two opposing sides. The reason the spring should pull in the same direction as ground contact is that the upward force on the adjustable inner pipe when the crutch bears the weight of the user is much greater than the downward force of the weight of the inner pipe when the crutch is lifted. Thus it is easier to overcome the downward force using a spring.

A homemade version of the spring is to tie a rubber band under tension to above and below the adjustment button. A bungee cord or bicycle inner tube would work as well.

The length adjustment of the crutch with a spring would be similar to that of an office chair – automatic in one direction, but requiring force in the other. When the button is pushed, the crutch shortens automatically by one hole. To lengthen the crutch, one has to push the button in and then pull the crutch in two opposing directions.

A sewing machine design

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Needle shaped like a helix, positioned horizontally. The needle can be held in place by four rollers around it with axes parallel to the axis of the helix and magnets that prevent the helix from moving forward or back along its axis. Another way is to use two rollers above the helix and a magnet above these. The needle is rotated around the axis of the helix by the rollers, which touch it.
As the helix rotates, the corkscrew motion makes the point of the needle go into and out of cloth like a curved surgical needle. The two-roller setup is convenient if access to the other side of the cloth is restricted, e.g. when sewing the lining of a garment closed.
An advantage over the current sewing machines is the simplicity and the need for only one thread per seam, not two threads, one of which is restricted in length because it is on a bobbin. For long seams, the single-thread design has the advantage of dispensing with the bobbin. Long seams are usually simple (hemming curtains, bedsheets), not zigzag or some fancy design, so the limited seam design options with the helical needle are not a big problem.
The problem is that towards the end of a long seam, a long thread needs to be pulled through the entire seam behind the needle. The friction gets large. The thread is not relatively straight, but in a “spiral binder” seam, which bunches the cloth.