sensing a point on a rope.

mikeweezer · 2006-03-08 21:16

Hello All,

I have a need to know when I have reached a certain point on a wench line. This will send a signal to the Stamp telling the device to shut off. I was thinking of using a magnetic switch that is tripped when a piece of the line, covered with magnetic tape, passes the sensor. Can anyone recommend a specific device?

Thanks,
Mike

Paul Baker · 2006-03-08 21:26

I am concerned that repeated use of the rope and winch system will adversly effect the tape, also flexible magnetic products have a much smaller gauss/volume than rigid magnets. Are you meauring the winch-in limit or the winch-out limit? I'm thinking painting the line and using a color sensor may work, or alternatively using foil tape and IR pair to detect the difference in reflectivity.

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mikeweezer · 2006-03-08 21:30

The color sensing sounds pretty clever. Is there a simple, out of the box solution that will see a specific color and output signal? Good point on the tape...

Thanks
mike

Robert Kubichek · 2006-03-08 21:31

mikeweezer said...
Hello All,

I have a need to know when I have reached a certain point on a wench line. This will send a signal to the Stamp telling the device to shut off. I was thinking of using a magnetic switch that is tripped when a piece of the line, covered with magnetic tape, passes the sensor. Can anyone recommend a specific device?

Thanks,
Mike

I would stay away from anything having to do with magnets, as the winch cable will conduct the magnet force...
If the winch cable will stay reasonably clean, use an optical sensor , or a limit switch thats triggered by a preset "block/ball' thicker than the cable...
Mount the switch on a moveable plate that allows for delay of motor shutdown so you don't stress the cable....
You can also mount an "encoder" disk on the drum and use it to determin play out or in of the cable and gain a greater control of the winch....

Bob N9LVU

mikeweezer · 2006-03-08 21:34

Any suggestions where I could pick something like that up at?

thanks

Paul Baker · 2006-03-08 21:43

Here is a color sensor sold by Parallax: http://www.parallax.com/detail.asp?product_id=30054

There is alot of intended use factors that figure into this project on which method would be best.

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·1+1=10

mikeweezer · 2006-03-08 22:16

I will need to set this up twice, so not sure that I want to pay $80 for each end. I have already beta-tested the device, and would be happy to post an image of the piece, or direcct you to a video... I'll post the piece this afternoon on my site: mweisert.com

PAR · 2006-03-09 00:36

mikeweezer said...
I have a need to know when I have reached a certain point on a wench line. This will send a signal to the Stamp telling the device to shut off. I was thinking of using a magnetic switch that is tripped when a piece of the line, covered with magnetic tape, passes the sensor. Can anyone recommend a specific device?

Metallic "rope" ("line"), or non-metallic?

Thick, or thin?

Any narrow constrictions through which the rope must pass?

Slow or fast travel?

What keeps you from simply observing (by eye) when the (marked) rope passes by and manually turning off the winch?

All these and probably other questions about the apparatus and conditions would possibly affect the kind of solution you'd choose.

PAR

mikeweezer · 2006-03-09 00:45

It is a metallic rope

pretty thin, like airline cable

There are no narrow constricutions

fairly slow

I will have two units operating in 2 seperate locations. I need to be sure they turn off at the right moment. Otherwise it will destroy some of the sensing equipment I have.

The application is a Tug-Of-War machine in which 2 groups of individuals are pulling on winches. I need to know when one of the teams has lost.

thanks, mike

Joe M · 2006-03-09 14:49

You could try to use tape or paint since its metal to mark your point and use an LED to illuminate the wire and a cds photoresistor to detect the mark on the wire. Just an an idea.

-Joe

steve_b · 2006-03-09 15:32

IF you aren't actually winching the line then you can have a bit of reflective tape hanging off and use an IR sensor or a laser and a photocell.

How will you keep the 2 groups pulling along the same line?
In college we would pull and it wouldn't just be back and forth...we'd sometimes end up 90deg from our starting point but with the center of the line still in the 'safe zone'.

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

mikeweezer · 2006-03-09 16:36

I actually have 2 machines. When you pull on the 1 winch, the other winch retracts in. The pulling data is sent via TCP/IP. The winches are encased in a large steel enclosure that is bolted down, which keeps people from moving...

steve_b · 2006-03-09 16:57

Hmmm....well, if you're keep the pivot point locked down....you could look at reflective tape on the wire somewhat easily.

Also, you could work with an encoder....

Or, you could tie a piece of rope from a 3position switch to the center of the rope.· IF one teams pulls the winning distance, the bit of rope will pull the switch to that corresponding position and give something to indicate by.

A neat thing to do would be to have a roller over the top of the rope that is pushing down with a given force.· Have a force sensor measure the force pushing back from the tightening rope and you could see how much force each team is pulling with.

IF neither team wins within a set time, have an electronic cable cutter fire and send them both on their arses....hee hee!!

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

mikeweezer · 2006-03-09 17:03

Funny you should say that... I am thinking about building in a device that will pop the clutch and make the line go loose... Here's a video if you want to see what I am talking about...

http://mweisert.com/media/ttofwar.mp4

Thanks for you suggestions!

mike

steve_b · 2006-03-09 17:11

What do you play mp4's with?

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

mikeweezer · 2006-03-09 17:13

The new version of QuickTime will play it.

Richard D. · 2006-03-14 05:13

One could perhaps use a friction drive wheel off the geared drum you have. That in-turn drives an Optical encoder that should work easy enough and pretty cost effective I would think. And way cool idea I liked the video.

Rich

Washer Medic · 2006-03-14 05:38

How about magnets on the drum use a hull effect sensor to count revolutions of the drum

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There's nothing a good wack with a hammer won't fix

Darn I let the white smoke out again

mikeweezer · 2006-03-14 06:24

Can you guys point me to a URL???

Thanks,
Mike

Richard D. · 2006-03-14 07:54

Here is one [noparse]:http:[/noparse]//www.parallax.com/detail.asp?product_id=605-00005
and I have asked about mixing a optical reader from vex for use with a Bs2 in post.
And I think I read something once one of Myke Predko's books on how to make said items.

Rich

mikeweezer · 2006-03-14 08:00

Potential issue....

Since the motor is constantly changing direction, how will the counter know if it should count up or down?

thanks

Richard D. · 2006-03-14 08:38

http://www.swiss.ai.mit.edu/~pmitros/encoder/

Check this site it sould help some

Rich

mediaprefect · 2006-03-23 04:55

Mike,

How about doing something like the way they put limit switches on some winches or chain motors? Just bolt a drilled solid ball, perhaps 2" diameter polyethylene or nylon with a set screw into the wire rope. Place this a foot ot two closer to the winch than the strain guage after running the rope through a 1" ID opening plate tube or ring activating a simple limit switch (microswitch) via a flexible coupling (to allow for a bit of overtravel without damage).

If you wanted to get crazy with the money you saved using a cheap microswitch later, the ball could be a hollow cylinder containing a battery and circuitry to condition, digitize and transmit the strain guage output via RF modem to the winch control CPU. In fact, you could hide the strain guage in the cylinder too.
This lack of wires and invisible sensor would make it more robust for a public venue and even more mysterious as to how it works.

If you electrically isolate the winch from the frame and ground, you might be able to use the wire rope to carry the RF back to the receiver using very low power. I believe this isolated cable method is used on one of the 4 cables used to suspend Skycam.

Rick B

mikeweezer · 2006-03-23 05:01

Can you send me some links to the devices you are thinking of so I can look? Thanks for the suggestion!

Mike

steve_b · 2006-03-23 13:25

mediaprefect said...
Mike,

If you electrically isolate the winch from the frame and ground, you might be able to use the wire rope to carry the RF back to the receiver using very low power. I believe this isolated cable method is used on one of the 4 cables used to suspend Skycam.

Rick B

Might the human bodies holding on to the chain couple the RF to ground?

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·

Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

sensing a point on a rope.

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