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:]
After 3 weeks of intense focus and little sleep, here’s the final product. I’ve called him Carl the animatronic but since he’s not really actuated yet, the ‘anim’ part is left out for now.
I think he ended up looking quite silly, but I guess that could be a good thing 🙂
I didn’t manage to add actuators yet, so nothing moves unless you push it. However, I’ve been asked by my University as well as DTU Fablab (Workplace) to continue working on it during the next semester and possibly longer, so there’s a good chance that it’ll start moving. Currently the eyes and eyebrows are made so that they’re able to move by pulling/pushing some strings or rods and it should only be a matter of adding the servos, control and connectors. Not right now though. I’ve finished my 2nd. semester at Uni and it’s exactly how I’d hope it would be. Now celebrations and summer holiday.
For those of you interested, I’ve uploaded the STL parts at thingiverse.com. It’s only the STL’s though, as thingiverse doesn’t seem to accept solidworks files. If anyone should be interested it getting the Solidworks work files and assemblies as well, you can get them below… but don’t expect clean files.
Given that this was a Uni course I had to write an assignment about it as well. It’s not perfect by any means but it’s there as well. Read it if you please and don’t hold back on comments. I’m here to learn!