Linear/Cable Pull Rotary Encoder

Hi All,

Can someone point me in the direction of an affordable cable pull rotary encoder?

What I need to do is measure distance travelled by an object (up to three meters or so) via a cable which will be attached to the object. The encoder will be kept stationary.

Something similar to this: http://www.pepperl-fuchs.com/global/en/classid_364.htm?view=productdetails&prodid=69680 would work well, but I expect this is very expensive and supply of an individual unit seems to be a challenge.

Thanks,

John.

What about a jockey pulley that runs on the cable and has a rotary encoder attached to it?

What level of precision do you want? Precision costs.

...R

Thanks, I need to be able to measure to within 5mm or so over a distance of 3000mm. I'm trying to design a device that can be used to measure the distance travelled by a barbell during a range of lifts, from that, the velocity (peak and average) and, since the weight of the bar is known at the time of the lift, the power produced by the lifter can be calculated.

Essentially, I want to replicate the functionality provided by a Tendo unit for a more accessible cost.

A prebuilt cable pull encoder would simplify the construction of the device over a seperate retractor (where would I get one of these?) and wheel system.

I would look for a wireless distance sensor as an alternative.

however, you asked about wired. a string potentiometer is much more common. maybe change your search terms ?

http://www.andymark.com/product-p/am-2674.htm

and by the way, that pepper and fuchs, $1,419.99. USD.

dave-in-nj: and by the way, that pepper and fuchs, $1,419.99. USD.

That would be almost as painful as the barbells.

Doesn't the barbell system already have a pulley. Why not just add a rotary encoder to that. A very simple (but effective) encoder could be made by sticking a piece of paper with black and white stripes on it to the pulley and using a photo-transistor to detect the passage of the stripes.

It would at least be a cheap way of deciding whether there is a need for a more sophisticated and expensive system.

...R

Robin2: That would be almost as painful as the barbells.

Doesn't the barbell system already have a pulley.

...R

The barbells are free weights as opposed to pin load equipment, so no pulley present.

This article provides a bit more detail.

https://orbi.ulg.ac.be/bitstream/2268/103106/1/LPT%20article%20Harris%20et%20al.pdf

It may be that the cable is attached to a person to measure jump performance for example, or a barbell, or other object.

The article mentions a Celesco string potentiometer which does seem more affordable (a couple of hundred dollars rather than thousands). Even with this, plus an arduino and an android tablet for output and processing, it is still vastly cheaper than the $1,600 or so that a Tendo unit costs.

Johnnytheknife: This article provides a bit more detail.

Not for me thanks. I'm the 7 stone weakling in the ads :)

...R

I got some pricing on the Celesco units. Still $500 to $1000. I might need to look at some alternative approach such as fabricating a sensor. I've seen an example where someone repurposed a retractable dog leash.

Johnnytheknife: I got some pricing on the Celesco units. Still $500 to $1000. I might need to look at some alternative approach such as fabricating a sensor. I've seen an example where someone repurposed a retractable dog leash.

makes the link I posted look like a bargain at $50.00

just use an encoder instead of a pot and Bob's your Uncle !

Johnnytheknife: I might need to look at some alternative approach such as fabricating a sensor.

What about a small pulley suspended above the barbell with a light line running from the barbell, over the pulley and a suitable weight on the other end to pull the line when the barbell is lifted. Then put an encoder on the pulley.

...R

Robin2: What about a small pulley suspended above the barbell with a light line running from the barbell, over the pulley and a suitable weight on the other end to pull the line when the barbell is lifted. Then put an encoder on the pulley.

...R

Thanks Robin. The unit needs to remain portable, and support measurement of a range of lifts, so connection really needs to be between the unit on the floor and the barbell (or event the athlete in the case of a jumping movement).

I think what I'll do is try and fabricate something using a retractable dog leash or a similar device. It'd work in a similar manner to the re-purposed badge retractor linked earlier.

I did consider the use of a bar mounted accelerometer, but the technical challenges with that are substantial.