Optical sensor for measuring kite cord.

Community Projects
1

I am trying to design an auto pilot for flying four line kites and I need a way to spool and unspool measured amounts of line/cord. I was thinking of passing the lines through an aluminum block about 75mm long that has 4 holes drilled in it–one for each of the 4 lines–with some sort of optical sensor aimed at each of the 4 lines. The lines would have marks every 25mm.

I am having trouble finding the optical sensor. I looked at the gesture sensor and it is nice that it can detect the direction of motion but it looks like its “read” time is pretty slow–likely too slow for 1mm wide marks zipping by at 25mm increments.

Any suggestions for a higher speed sensor for counting in either direction? (Line being reeled in or fed out).

Thank you in advance for any help.

2

Look up “string potentiometer” or “string encoder” for real-world suggestions.

3

Each line would probably need its own LED illuminator and a photodiode with focussing optics.

It would take a fair bit of careful engineering and experimental refinement to end up with a reliable system.

4

lyndon:
Look up “string potentiometer” or “string encoder” for real-world suggestions.

I don’t think this one is an option because (as I understand it) it would require each line of the kite to have an additional metal wire. Not practical for kites that are especially weight sensitive–not to mention the whole lightning strike potential.

This has turned out to be surprisingly difficult.

5

Make a box that sits on the ground that has an optical encoder and a counter. Wrap the kite string around the encoder shaft. As the string moves in or out, the encoder pulses and the counter will tell you how far away the kite is. That’s a simple string encoder!!!

BoxGods:

lyndon:
Look up “string potentiometer” or “string encoder” for real-world suggestions.

I don’t think this one is an option because (as I understand it) it would require each line of the kite to have an additional metal wire. Not practical for kites that are especially weight sensitive–not to mention the whole lightning strike potential.

This has turned out to be surprisingly difficult.

6

lyndon:
Make a box that sits on the ground that has an optical encoder and a counter. Wrap the kite string around the encoder shaft. As the string moves in or out, the encoder pulses and the counter will tell you how far away the kite is. That’s a simple string encoder!!!

BoxGods:

lyndon:
Look up “string potentiometer” or “string encoder” for real-world suggestions.

I don’t think this one is an option because (as I understand it) it would require each line of the kite to have an additional metal wire. Not practical for kites that are especially weight sensitive–not to mention the whole lightning strike potential.

This has turned out to be surprisingly difficult.

Not sure how I would take the strain off the encoder shaft (these kites pull really hard) or prevent slipping but worth investigating for sure. Thanks for the information.

7

BoxGods:
[Not sure how I would take the strain off the encoder shaft (these kites pull really hard) or prevent slipping but worth investigating for sure. Thanks for the information.

Mount it on bearings!