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Reel for lowering a sensor

Posted: Tue Jan 22, 2019 9:01 am
by sdzafovic
I am looking for a small reel that can be hooked up to an Arduino/DC motor combo and used to lower a sensor into water and recover it. The maximum depth would be 10 metres.

All the reels I have seen are much larger and would be massive overkill for my purposes.

Does anyone know of a reel that might be usable for this purpose?

Re: Reel for lowering a sensor

Posted: Tue Jan 22, 2019 11:18 am
by dyarker
size of line and/or cable?

Re: Reel for lowering a sensor

Posted: Tue Jan 22, 2019 1:29 pm
by sdzafovic
1/8" wire rope or something similar.

I wasn't thinking of nylon fishing line, but if there is a nylon product that could serve the same purpose, I'd be happy to use that instead.

Re: Reel for lowering a sensor

Posted: Wed Jan 23, 2019 4:53 am
by dyarker
Lets say 4in diameter spool so we don't bend wire rope too sharply.
4in * 3.141 = 12.5in circumference
10m * 39.37 in per m = 393.7in
393.7in / 12.5 in per turn = 31.5 turns
31.5 turns * 0.125in rope diameter = 4in spool width
'Or -
A 4in diameter spool 2in wide with sides more than 1/4in high.

Now we have a ballpark for size of thing you need.

With weight of sensor plus weight of rope, and gear ratio from
spool to motor the needed torque can be figured.

The torque will let the estimated current be calculated so you can
pick a driver transistor.

I do not know were to find it; but now everyone knows the
approximate size.

Cheers,

Re: Reel for lowering a sensor

Posted: Wed Jan 23, 2019 11:34 am
by Lenp
Without exact information here are some things to consider:
First, reels are often referred to as spools, so that may help in the search.
What about a wire and cable reel, or one from film or recording tape.
A hole saw and some acrylic or PVC sheet and rod can be an easy DIY spool to exactly fit your needs.
Monofilament fishing line is an option as is bulk string for a string trimmer.
Since this is going into water use stainless steel wire rope if possible to avoid rust.
Depending on the weight, insulated stranded wire is amazingly strong and Teflon coated wire wears very well.
Post particulars and I'll rummage through the junk box!

Re: Reel for lowering a sensor

Posted: Fri Feb 15, 2019 4:50 pm
by haklesup
Take a look for "Gear Motor" on ebay or google image search. These will give you the reduction in shaft speed and increase in torque you likely need. There are many voltage, speed and torque ranges so you should be able to find a fit for your application

Most have output to a shaft but you shouldn't have too much problem making a spool to put on it to take up your cord. Whether you can use the motor you have or one that comes with the reduction gear depends on the type of control you want and physical configuration. With a DC motor, you pretty much get one speed either direction, reducing voltage does not only reduce speed, it also reduces torque. Its easier than controlling a stepper though which is what you want if you need precision positioning (lower exactly 9.3 meters for example).

you can probably find more options at robotics component suppliers. They tend to have more stepper and servo solutions but also have permanent magnet DC motor types as well for example https://www.sparkfun.com/categories/31 and they have better tech support for interfacing it to your uController

For stopping and starting or measuring, I suggest you use an optical encoder and put light and dark marks on the cord it can count.

Re: Reel for lowering a sensor

Posted: Fri Feb 15, 2019 9:16 pm
by Lenp
If you use an encoder disk with a reel, remember that the circumference of the layers change as the reel is turned so the measurement would have a growing inaccuracy. To overcome that use a free turning pulley with an encoder disk that has a wrap or two of line on it to make it turn properly as the line is payed out. That should be a pretty accurate measurement.

For a line option, consider string trimmer line. It's durable, cheap, visible and available in different thicknesses and colors!