I have built a winch for a 4wd, to race with. I would like suggestions on a sensor to detect rope position as it nears the end of the line retrieval. Not at the drum end, as that may vary. Something along the lines of a short piece of trace wire, inserted inside the winch cable, a few meters from the hook end, to turn a light on as it passed by a sensor? Is there something like this? Application would be in water and dirt, 12v power supply. Thank you for any help. Great feed back, thanks. see the winch here.https://www.youtube.com/watch?v=vgx1hc5GikU FYI I want some kind of warning system, for when the hook is attached to the front of the truck, and we are winding the loose rope back onto the drum, and you cannot see how near the rope is to stopping as it pulls tight.
There are several types of sensor you could try.
Tie a knot in the rope. Put a lever operated microswitch next to the rope inlet on the winch.
Wind some iron wire round the rope (assuming it's not steel rope). Perhaps use a sleeve of heatshrink over the top to hold it in place. Then arrange a magnetic circuit with a permanent magnet and a linear Hall effect sensor, such that the output of the sensor changes as the iron changes the reluctance of the magnet path. Use an opamp or comparator to sense the change in Hall output.
Wind some copper wire round the rope, and solder the start to the end to make a shorted turn (assuming it's not a steel rope, but with care it might even be got to work on steel). Use a high frequency oscillator and a search coil close to the rope, to sense the shorted turn. Sense either a drop in level of the search coil, or coupling to another coil.
For both of these schemes, sensitivity and rejection of false triggers will be improved by using a pair of sensors side by side, sharing the same exciter in the middle, and sensing them differentially. Common mode interference and drift will be rejected as the sensors are differential. As the rope comes in, first the outboard sensor will react, then the inboard. Look for this sequential signature.
I assume that reflective sensors would quickly be blinded by mud.
Implementation will depend on type and size of rope.
a sophisticated way would be to add a sleeve to the outside or a(n enlarged) core to the inside to increase the diameter of the rope by say 20%. This should not impact massively on the rope flexibility and may even help to prevent tangles by stiffening it a bit. If strength is not the limiting factor replacing part of the inner core and making the rope thinner may be possible but could compromise the rope safety ratings, might work with some types of woven fibre ropes I expect.
You would then have a second pair of slot rollers behind those that feed the rope onto the drum spring loaded firmly and they will indicate the altered thickness of rope has entered the winch.
If the rope is conductive and sleeved with an insulating tube or braid it may be possible to detect the change in surface conductivity but in mud and such not altogether reliable.
If the rope is non conductive a braided wire sleeve may be electrically detected.
If the rope is non metallic or a non-magnetic stainless steel a ferrous braiding or core could be magnetically detected.
*An inductive metal detector (stud/pipe/conduit finder) should be able to pick up a thinnish ferrous core wire.
Magnetic inserts may be an option (get a bunch of small magnets and insert them into short lengths (say 1 inch/25mm) of tubing and then insert a bunch of these into a heat-shrink tube of the length you want to have your detected end (say 80 inches/2m). This will let you pick up the end of the rope as it passes a magnetometer (3 axis compass sensor might be the best) by generating a field anomaly as each magnet passes. Stronger magnets are better but too strong and they will pick up bits of scrap iron, rust and magnetite. The two layers of plastic should protect the rope structure from too much damage from the magnets. Rubber magnetic sheet (fridge magnet sheet) cut into a ribbon might work but is much weaker and will need more sensitive detection. Placing a string of magnets with coded North-South arrangement at regular intervals (every 2m) could theoretically let your system know which point is passing through along the whole length of the cable.*
The simplest idea I can think of would be to put a small, powerful magnet in the rope. As in open up the strands with a blunt screwdriver, place the magnet, and let the strands close again. They will tighten back up when you put tension on it.
Next, a few Hall sensors along the fairlead. A single one won't work as every winch I've ever had or seen has either a roller fairlead or at least a slot so the cable can be angled side to side or up and down. So you need to make sure the magnet never gets out of range.
Once that's done, the rest of the problem is simply reading the sensors. However, I can't see what problem you're solving. Although it was a long time ago, I have a lot of experience with off-roading and needing winches. I can't think of a single time (except the few times I was alone) that I was retrieving the winch cable and there wasn't someone on the outside of the truck keeping a light tension on it to feed the cable properly and tell me when I was getting close.
if you go the magnet/hall sensor I would go for smaller multiple ones distributed along a length of a meter or so. This allows a certain number of 'dropouts'. also multiple hall sensors along the pipe for the same reason. I think anything within the rope may potentially weaken it if the hard object is pulled over the fairlead under tension or possibly just the tension while winching will squeeze the strands of rope over the magnets.
because you dont need to know the length I would steer away from trying to measure anything but if you were I would have a pinch roller/wheel setup, the error in any spooling compared to 11m/s wind in probably will not matter, your light would trigger at 30m so give 2 seconds for winchman to react and slow the winch in time. With the harsh environment you are operating in I would also go as simple as possible and this solution would involve some electronics, probably arduino(https://forum.arduino.cc/index.php?topic=366220.0) and then you could also have an estimated length display.
Have you though of a simple mechanical solution? http://www.trulineaustralia.com.au/item-details.asp?CategoryID=71&ItemID=201 You would need to make some kind of "remote" wire or shaft linkage
Micro rfid chips/reader would to overkill.