Starting gate does not concern to Arduino construction set for adults. Nevertheless, it is impossible to assemble timing system for ski without a mechanical part 🙂 I would like the “mechanic” to be reliable, and easily and quickly installed without taking off the ski gloves. In this note I will share the design of the start gate.
As mentioned in the note “Timing system for Alpine ski based on Arduino. Task formulation”, the starting wicket must mechanically “stick” in the open state. And in my case it is necessary just for reliable operation of the micro limit switch.
The design of the starting gates, which I came across earlier, were not arranged in such a way. The operation was at a small opening angle of the gate. This led to additional nervousness in training, fear of accidentally hitting the gate when you are preparing for the start. In addition, in self-made designs it was difficult to achieve reliable operation.
Sometimes the first gate of the course is installed so that it is necessary to start not perpendicular to the gate twig, but at an angle.
Strangely enough, the “non-sticking” wicket in such cases may simply not work. That why, I want to make it so that the gate always mechanically opens completely, pulling in with a special spring and at the same time the electrival contact is switched securely. Just like a wall light switch. I emphasize that the design of the gate can be very different. I just now want to do just that.
Technical rules FIS (FIS Timing Booklet, ver 2.55, Nov 2017) regulate the trigger angle of the start time and the height of the “twig” (see figure).
It can be seen that the “start on” angle should be at least 10 degrees from the opening of the gate and not more than 30 degrees. That is, the gate with a limit switch, triggered on a full opening, for maintenance of FIS starts is not suitable. In general, it doesn’t really bother me, because the task is timekeeping in amateur trainings 🙂
I did not have suitable materials, so I went to the nearest OBI. I was looking for a fiberglass twig for the “antenna” of the gate (in the garden section, a twig for plant support). Not found.
Then I looked for a pair of different tension springs: one for damping the mounting of the antenna of the gate, the second for constructing a two-position switch. Not found. Also looked up to the pile of wooden blocks that need to be hammered into the snow for fixing the gate, and also did not find it.
So nedded to switch to a backup option: to design a spring opening at 90 degrees mechanism with fixation in extreme positions from the hinges of kitchen cabinets ($1.77 per pair). The antenna is made of 8 mm duralumin tube ($0.77 per meter). For the “chassis” I took T-shaped duralumin profile ($3.92 per meter). The spring for damping the antenna was taken from the broken flex zone for slalom gates. This is a compression spring, and it’s too powerful. But more or less came up.
I have no idea how many openings on the gate these loops from the lockers will work. But it is good that they are easy to replace, they entered the design without any alterations at all.
The internal diameter of the spring turned out to be slightly larger than 8 + 2 mm (+ 2 mm is a transition tube), therefore, in order to choose the backlash, I used heat shrinkage.
The button with a microswitch from the USSR times is securely pressed with a plastic cap from the loop mechanism.
On the “lower floor” of the T-shaped profile placed the wicket mount. This is also a part of a broken hinge from slalom gate – a plastic tube with an outer diameter of 25 mm. On the “chassis” mounted, wall by wall, a box-casing of yellow polypropylene 4 mm thick. This is a kitchen chopping board from a grocery and household hypermarket, price $0.51.
Polypropylene is perfectly welded with an industrial hairdryer. The connection is strong, and easy to weld. It is necessary to warm the joints and press. The process is more like gluing with a thermogun. From the same polypropylene made several corners for mounting two faces on the screws. Yet there is no connector to send a signal to electronic unit (ordered, waiting).
Quite an important question – mounting the gate in the snow. As already mentioned, the wooden bar was not be bought. And, frankly, I do not like the design with a bar. Ready to sacrifice solidity mounting in favor of ease of installation. Going to install on every workout, everything should be simple and ordinary.
The easiest way – the use of broken parts from slalom poles, was rejected. The gate works reliably, but the tube from the pole was too flexible, the whole design at the start is somehow unconvincingly swinging 🙂
The use of a massive duralumin corner was not pleasant either. Firstly, it turned out that it is rather difficult to install a corner exactly to the marked depth, so that the height of the gate would fall into FIS requirements. The corner can “fell” below, and vice versa. Everything is very dependent on snow. Secondly, the corner badly fit to a round hole. Therefore, given that the gate bear a sharp efforts, the corner wobble. Not bad, but unpleasant.
A good was the option with a wood. But not with a bar, but with a handle (handle for a broom, it looks like birch, diameter 26 mm, price $0.69, in grocery and household hypermarkets). The bar needs to be slightly ground (for example, with a file with milled teeth, which is used for a rough point of the ski edges) to a diameter of 25 mm, after which it is placed inside the slalom gate pole and auger.
The auger is tightly twisted in the snow with a key for slalom gates. There were fears that he would twist out. Does not twist out. In general, the design turned out to be “monolithic”. While we can stop at this 🙂
Added in June 2021
I looked closely at the option of manufacturing a start gate based on a rotary limit switch:
There were doubts that the switch would be able to rotate 90+ degrees. In the drawing from the description, it was shown that only 60 degrees. A huge plus of such a limit switch is that it has a spring mechanism for returning the rod to its original position. The concept of the wicket is different, the twig does not stick when open. When a limit switch appeared on Ali Express for a reasonable price, I ordered it ($3.3). So far, it seems that the limit switch fits. The rotation angle turned out to be 90+ degrees.
To unload the mechanism, I ordered from Ali the spring (wire thickness 2 mm, outer diameter 12 mm, length 60 mm, $4.7 per pair). In a local fishing store I bought a fiberglass whip with a diameter at the thick end of 6.8 mm ($0.95).
It turned out like this:
Here are two gates:
Here are collected all the notes on the theme “DIY timing system for skiing with Arduino”.