| Electronics > Projects, Designs, and Technical Stuff |
| Does anyone know of a wire pullstrength sensor ? |
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| Kjelt:
--- Quote from: KL27x on May 15, 2019, 09:03:04 pm ---Sounds like you want a strain gauge. I would consider trying to estimate the relative load, indirectly, by way of motor current consumption. --- End quote --- Thanks for the term also OM222O thanks. I will certainly look into that. The motor current could also be a good parameter, it is 230VAC but with a small current clamp around the phase or something like that it is easy to measure :-+ --- Quote from: Benta on May 15, 2019, 09:33:10 pm ---Far too complicated. Just let the "pulling" tubemotor run and disengage the other (let it run free or lightly braked). --- End quote --- Have to investigate this because I think the Somfy motors brake the shaft when power is off and I never noticed that they can be disengaged. They are usually used for window blinds, you know those heavy aluminium bars, and you don't want to have the whole blinds tumble down if you stop halfway. --- Quote from: soldar on May 15, 2019, 09:57:03 pm ---I do not know the particulars but it sounds like a bad design to begin with. In principle you do not need two motors at all as you can have one rolling up the screen and working against a constant tension provided by weight, spring or whatever. Having to control two motors to achieve the correct tension seems unnecessarily complex IMHO. --- End quote --- At this moment it works with a heavy spring, so heavy that the metal wires can be used to play piano ;) Twice already the past ten years the spring has disengaged, a lot of noise and even damage. So I would like to replace this since it is too heavy for the application. Since I want to go to a new wider screen I am looking for alternatives. But thanks for bringing it up, valid point. |
| soldar:
--- Quote from: Kjelt on May 16, 2019, 08:18:18 am --- At this moment it works with a heavy spring, so heavy that the metal wires can be used to play piano ;) --- End quote --- If the tension is too high then that is a reason to make it lower, it is not a reason to redesign the whole thing from scratch and throw the baby out with the bathwater. Adjusting the spring tension should be fairly easy. The way I see it the motor would have limit switches/sensors at both ends and adequate tension provided by spring or weights or whatever. Keep it simple. If you want to get fancy you can design a system where the tension increases as the shade reaches maximum extension and that keeps it well extended but as soon as it starts to be retracted the tension diminishes and makes the motor work less. IMHO having two motors is the worst solution and is asking for countless problems. ETA: I am attaching some ideas for tension activated switches which I have used in the past. |
| Housedad:
Why couldn't it be done with just current sensors and a microcontroller ? |
| Kjelt:
--- Quote from: brennafullen on May 23, 2019, 08:09:42 pm ---I had a similar problem. --- End quote --- Had? Did you solve it? |
| KL27x:
--- Quote ---Why couldn't it be done with just current sensors and a microcontroller ? --- End quote --- This was my suggestion. Measuring current consumption of the motors. A strain gauge may give you higher precision/resolution? Any way you slice it, you are probably better off with springs in addition to electronics. What I presume is a worm gear motor will hold a high tension, but you should want springs, too. They wouldn't be there to roll up the screen; springs would be there to give a bigger zone of relatively constant tension. Even if you stop a worm gear motor at exactly the right spot, you may end up stretching the screen/wires or whatnot. Then your electronics wind the motor up again, either right then or on the next go around. And you risk cumulative damage to the screen/cables or suboptimal tension. I am imagining relatively short and stiff springs. Limit switches plus spring tension could be just as good, really. |
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