Hello
For a project I have to measure the length a rope is being pulled out. I have no idea if it is possible to do with an arduino?
I have been searching the internet without succes. I was thinking maybe someone is able to help me with this.
Best regards
Castel
Is it being pulled over a roller or pulley so you can measure the number of rotations of the roller? A simple quadrature encoder will do this easily. US Digital make some really nice absolute encoders that will allow you to measure the rope down to fractions of a millimeter.
If it's being pulled past a window, perhaps the sensor out of an optical mouse can be used?
Look for a wire measuring meter, such as: http://www.ebay.com/itm/Antique-Improved-Wire-Measuring-Machine-device-John-J-Waldman-New-York-Tool-/272054702140.
You can measure wire or rope. Basically a wheel pressed against the rope so it will turn as the rope is pulled. The circumference of the wheel is known. Count the revolutions times the circumference and there is your rope length. You design the rest and the Arduino connection.
Paul
MorganS:
Is it being pulled over a roller or pulley so you can measure the number of rotations of the roller? A simple quadrature encoder will do this easily. US Digital make some really nice absolute encoders that will allow you to measure the rope down to fractions of a millimeter.If it's being pulled past a window, perhaps the sensor out of an optical mouse can be used?
Hello, what do you mean with the US Digital encoder?
Is it possible to use a pulley with a potentiometer?
Put "measure rope arduino" into Google and the first result is
castel:
Hello, what do you mean with the US Digital encoder?Is it possible to use a pulley with a potentiometer?
Is Google broken today? (No, I just checked.)
Probably not. Most potentiometers don't rotate more than 270 degrees. Depending on what you really need, this is unlikely to work for you.
You can get pots that are continuous rotation, but as they rely on part making physical contact with another for resistance, I think you'd wear it out mechanically pretty quick. Encoders are meant to be turned continuously. Another option is a series of magnets around the spinning shaft/perimeter of pulley, and Hall sensors on the fixed frame.
8 magnets on one side, 8 on the other at the gaps of the first side, get 16 pulses per turn of the pulley. No mechanical parts to wear out.
Or a series of dark bands and optical light/dark detectors, could be even finer sensing, and can establish a zero point too.
Thank you for the helpfull answers. I am thinking about using a pulley and "rotary encoder module" to measure the position and rotations of the pulley. The only problem is the attachment of the encoder to the pulley.
Since the pin of the pulley is not turning around I have no idea how to connect it to eachother to measure reliable positioning of the pulley.
Anyone having a solution for this?
Best regards
put a reflective dot on the pulley and count rotations with an ir transmitter
A rotary encoder puts out a series of pulses that your sketch must interpret as the pulley rotation.
I suggested a couple of ways to get pulses from the turning pulley.
dave-in-nj suggested another way to get one pulse per rotation.
Perhaps you are after a shaftless rotary encoder?
CrossRoads:
A rotary encoder puts out a series of pulses that your sketch must interpret as the pulley rotation.
I suggested a couple of ways to get pulses from the turning pulley.
dave-in-nj suggested another way to get one pulse per rotation.
I figured that since the OP could not figure out how to put the shaft of an encoder on the roller, that maybe the mechanics was a bit too much.
http://thedenneys.org/pub/robot/encoders/
about half way down the page he shows a way to use two pickups for either a higher resolution or direction.
I mean you or I might just buy an encoder with a wheel
http://www.aliexpress.com/item/Rotary-encoder-gauge-meters-wheel-with-wheels-encoder-gauge-meters-wheel-set/32227458706.html
dave-in-nj:
put a reflective dot on the pulley and count rotations with an ir transmitter
In this case the accuracy will be too low.
castel:
In this case the accuracy will be too low.
how are we to know ? you have not given us any clue as to what you need. is your project in need of 10 decimal places for a mm ? or do you need to know 'to the inch'
my friend, we have given you lots of ways to do this. each one can work. you have to pick one you like. shooting down ideas without details is of no help to anyone.
what if you put 2 dots ? double the resolution. 4 ? double it again, one at each spoke ? one in between each of those ?
ever hear of a pulley ? add a pulley, 3:1 and your wheel with dots spins 3 times faster, ergo, 3 times the resolution. I am well over 0.001 mm, but now you have to pull the rope really slow so the counter can keep up.
As previous posters have asked - what is the practical application for this, as that may help to drive the possible solutions?
I use this exact scenario to determine how much anchor line I have deployed on my boat when overnighting or fishing offshore, but I use a combination of a rotary encoder on a polyurethane roller and counter of how many milliseconds the anchor windlass motor was engaged in the down direction to do the counting
This gets me within a foot or so with ~500ft of anchor deployed which is more than perfectly acceptable, but I have a desired outcome and a solution to meet it.
//j
dave-in-nj:
how are we to know ? you have not given us any clue as to what you need. is your project in need of 10 decimal places for a mm ? or do you need to know 'to the inch'
my friend, we have given you lots of ways to do this. each one can work. you have to pick one you like. shooting down ideas without details is of no help to anyone.
what if you put 2 dots ? double the resolution. 4 ? double it again, one at each spoke ? one in between each of those ?
ever hear of a pulley ? add a pulley, 3:1 and your wheel with dots spins 3 times faster, ergo, 3 times the resolution. I am well over 0.001 mm, but now you have to pull the rope really slow so the counter can keep up.
I am sorry, I am kind of new to Arduino! I'm not shooting down any ideas at all. Let me explain some more of the practical application:
A rope is being pulled out manualy with a pulley system to move some weights. the rope has a diameter of about 0,5cm. I need to know the amount of cord being pulled out at realtime. (resolution about 0,5). I have allready thinking about measuring the distance the weights move but that's improssible because of practical issues. So I wanted to measure the displacement of the rope by adding a pulley somewhere in the circuit atached to a rotary encoder in order to measure the displacement.
So, I hope you have an idea of the project now. If I use a rotary encoder, the rope has to be pulled out very slowly otherwise the encoder won't measure?
Appreciate your reactions!
If you are afraid of rope slipping on the pulley, use a knurled pulley and take a complete loop of rope around the pulley.
Paul
(resolution about 0,5)
What units? Half a what -- meter, centimeter, milimeter?
If I use a rotary encoder, the rope has to be pulled out very slowly otherwise the encoder won't measure?
Rotary encoders are designed for motorized use and can be very fast. I doubt there is any way a manually pulled rope will turn a pulley too fast. The resolution will determined by the diameter on the pulley with the encoder, and the number of counts per revolution from the encoder. Slippage, as Paul_KD7HB points out will need to be controlled if you wish accurate measurement from pulley turns.
I thing the slippery could be avoided when the weight is heavy enough. Is that correct?
I thing the slippery could be avoided when the weight is heavy enough. Is that correct?
Yes. The amount of the weight, the texture of the rope and pulley, and the friction of the pulley axle , and the maximum acceleration of the pulls. I doubt it will be a problem in practice.