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Swarm Robotics

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DaveE
(@davee)
Prominent Member
Joined: 2 years ago
Posts: 681
 

Hi @thrandell,

Re: I anticipated the detection area would increase with the duty cycle, but instead it’s more of a bell curve.  Clearly demonstrating my lack of understanding of how PWM and the receiver work.

Sorry, I haven't taken the time to carefully follow your thread, but I assume your experiment producing the bell curve is based on Vishay TSAL6400 LED and TSSP58038 IR receiver (not the Sharp device).

I didn't see much description of your software or hardware, so the following conjectures are also based on guesses ... hence they may be useful or irrelevant ... I'll leave you to judge. 🙄 

A quick scan of the datasheets for Vishay TSAL6400 LED and TSSP58038 IR receiver suggested:

  • LED is just a 'simple LED' ... no electronics built in ... light will directly related to the applied voltage/current
  • IR receiver ... not just a photodiode, but a 'mini-system' with amplifier, band pass filter, etc.

From the data sheet: https://docs.rs-online.com/0aa8/0900766b8118041d.pdf

image

You mention PWM, but not frequency, etc., or what is doing/required for.

The IR receiver includes a bandpass filter centred on 38 kHz ... that is, it is trying to measure the intensity of light which is being modulated at 38 kHz, and rejecting everything else.

As the LED does not contain any circuitry to modulate the light, I guess your PWM frequency is 38kHz, effectively switching the LED light production on and off at 38kHz.

Oversimplistically, I am guessing the 'raw' (internal) signal picked up by the photodiode is a square wave, and that you are changing its mark-space ratio in your test that yields a bell-shaped curve.

The Fourier transform of a square wave with 1:1 mark-space (e.g. see ref https://mathworld.wolfram.com/FourierSeriesSquareWave.html) is the sum of sine waves based on the fundamental square wave frequency and its odd harmonics. From the same reference:

image
image

Hence passing this waveform through a bandpass filter centred on the fundamental frequency, will allow the fundamental frequency sine wave to pass through and attenuate the harmonics .. possibly to the extent that only the fundamental frequency sine wave passes through with a significant ampltitude.

To properly evaluate the effect of changing the mark-space ratio, I suggest an investigation with a Fourier transform software program ... but I will just offer a guess that deviating from 1:1 will reduce the effective amplitude of the fundamental frequency component.

I should emphasise, the last statement is only a guess, but sorry, I don't have the time to do the experiment (or to analyse the maths) suggested. Maybe you would like to look into it and report back?

Best wishes, Dave


   
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robotBuilder
(@robotbuilder)
Noble Member
Joined: 3 years ago
Posts: 1554
 

@davee 

I didn't see much description of your software or hardware, so the following conjectures are also based on guesses ... hence they may be useful or irrelevant ... I'll leave you to judge. 🙄 

Which was the problem I was having not really knowing enough about the setup to guess an answer.

Thank you for making the effort to try and work it out.  It has been a long long time since I last read a little book I once bought explaining op amp theory and practice.

 


   
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THRandell
(@thrandell)
Estimable Member
Joined: 1 year ago
Posts: 117
Topic starter  
Posted by: @zander
Is it April 1 somewhere? Cut their legs off and glued onto others, really?

Ron,

Look what I came across today.  Odometry and insect navigation  Check out figure 4, a cruel experiment to be sure.

 

Tom


   
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Ron
 Ron
(@zander)
Famed Member
Joined: 2 years ago
Posts: 3403
 

@thrandell OUCH!

"Don't tell people how to do things. Tell them what to do and let them surprise you with their results.” - G.S. Patton, Gen. USA
"Never wrestle with a pig....the pig loves it and you end up covered in mud..." anon


   
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THRandell
(@thrandell)
Estimable Member
Joined: 1 year ago
Posts: 117
Topic starter  

Well I finished a second prototype.  This one is smaller with different motors, cheaper sensors, and a different MCU.

IMG 2303

The design grew from trying to fit everything within a 3.25” diameter, the size of the prototype board that holds the sensors

IMG 2167

The MCU is a Raspberry Pi Pico and it sits between the sensors and the top bit that holds 3 small LEDs and a photo transistor

IMG 2300

In the requirements doc I put together for swarm robots (it’s actually more of a wishlist) I have a section for sensing and signaling with these five items:

  1. minimal interference among robots
  2. kin-detection
  3. interference from environmental factors
  4. stigmergic sensing and signaling
  5. generic sensing

 

I’ve been working up a way for the robots to signal each other via the IR emitter and receiver, and the same sensors work well for obstacle detection.  So now my big hurdle is #1 from the list above. It’s been a bit of a mental shift to go from making something in my garage to sitting in front of a laptop experimenting with different ideas to minimize the interference that these two robots cause each other.  Sometimes it turns into a Sumo Match.

IMG 2295
IMG 2294

 

Tom

 


   
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robotBuilder
(@robotbuilder)
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Joined: 3 years ago
Posts: 1554
 

@thrandell 

Apparently I can only react not like anymore 🙂

Your latest look great.  Are you going to share any details of their electronics and software?

Have you seen the reddit Robotics site?  It’s pretty cool.   https://www.reddit.com/r/robotics/

Thanks for the link.  Very interesting to read.

 

 

This post was modified 2 weeks ago by robotBuilder

   
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Will
 Will
(@will)
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Joined: 1 year ago
Posts: 2112
 

Posted by: @robotbuilder

Apparently I can only react not like anymore 🙂

Use the little thumbs up icon on the lower left side, it expands into thumbs up and down which allow you to indicate like or dislike.

 

I was kidnapped by mimes.
They did unspeakable things to me.


   
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