Muscle-triggered dancing crab: Biometrics, hell yeah!

A few days ago I finally received a muscle sensor which I’ve been wanting to buy since forever – this one: https://www.sparkfun.com/products/11776. 4 days seemed like an infinity to wait playing around with it but tonight I finally got the chance.

What I found the most exciting was reliability of the signal. How hard it would be to measure the tension of a muscle and whether I’d need a whole bunch of filters to get anything sensible out of it. I had no idea what to expect when I bought it apart from having seen a few examples of it’s use online.

Turned out that it was really quite easy to control. I added a moving average filter with 10 samples and instantly had a signal I could use to control… in this case a servo with a crab on top.

I applied the electrodes on the flexor pollicis brevis – the muscle that pulls your thump towards your pinky -, set up a few conditions for the signal on the Arduino and BAM! The crab was dancing 🙂
By pushing my thump agains the other fingers, I tense the muscle and depending on the amount of tension I can make it rotate slower or faster. As for the conditions I set up a minimum signal threshold after which it would start moving. Each time It’d go beyond that threshold it would go in one direction, speeding up depending on the tension. When the signal goes below the threshold it reverses direction, so it’d go the other way when I tighten again.
The fact that the crab may seem to follow my hand at certain points, could be a bit misleading as I’m merely playing around and aiming it by tensing/relaxing the muscle accordingly. All motion is muscle-controlled 🙂

Oh, and sorry about the sound. I happened to be listening to Radiohead while recording and now Youtube recognized it and claimed that it was copyrighted, so they offered a way of removing only the song from the video. Didn’t really work, but as long as it keeps my back clear I’m good.

[In case somebody is wondering about the thing attached to the servo, it is a crab made of chestnuts:]

Kindly donated by Rebekka

Kindly donated by Rebekka

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One thought on “Muscle-triggered dancing crab: Biometrics, hell yeah!

  1. Hej Jacob

    Fedt lille projekt 🙂 Jeg lavede selv et exoskelet der skulle reagere på EMG signaler med en studiekammerat i bachelorprojekt på P&K… Vi moddede selv en EKG forstærker til at passe bedre til EMG og lavede boards selv. Hvis de forstærkere du køber er forbandet dyre (grunden til at vi lavede vores egne), så kan jeg godt finde noget dokumentation frem 🙂

    Vi snakkede sammen i FabLab engang sidste semester. Jeg laver en mekanisk fugl i speciale projekt. Ved ikke om det ringer en klokke 🙂
    Anyhow, jeg havde ikke din mail så jeg spammer bare din blog 😛 Jeg har bare nogle spørgsmål omkring STL og andet godt, og tænkte at du var the man til den slags 🙂 Og jeg kan måske også svare på lidt af hvert hvis du skulle have noget at spørge om med mekatronik og deromkring…

    Har du forresten overvejet at bygge en robot til RoboCup på DTU? Du burde kunne banke noget fedt sammen, og lære en del samtidig… Lego mindstorms robot om ikke andet, til at få styr på det grundlæggende…
    http://www.robocup.dtu.dk/
    Jeg savner mere kreative løsninger i konkurrencen 🙂

    Men skriv hvis du er interesseret i at snakke…

    Mvh. Mikkel

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