Learning with mistakes

A little progress has been made. And a lot have been learnt.

So my fingertips worked… sort of. But the ‘microphones’ were not large enough to close the holes. And rigid plastic is not good, rubber or something else soft is better to cover the holes. I am now using the 1×1 rubber pads used on LEGO Technic tracks (like in the BOOST set):

part 2437

Still not perfect but better.

Also found out that rubber balloons have some non-linear properties. After reaching some internal pressure level, if I keep inflating it the pressure drops drastically. So my idea of using a pressure sensor to regulate air volume is not so easy to achieve. Elastic hysteresis doesn’t help either…

I increased the LEGO air compressor air flow by changing the 2x Power Function ‘L’ motors with ‘XL’ motors and gearing it faster. But still not enough for long tests and still too noisy. So for now I am using a small air pump used on Arduino and other projects. At 5V it’s almost strong enough to ditch the “bag” (the balloon).

This is now the current state of the project:

Tuxie McPython – alfa version
  1. LEGO MINDSTORMS EV3
  2. Wi-Fi Power Plug
  3. Mini air pump
  4. Mindsensors pressure sensor for EV3
  5. Party Balloon
  6. MINDSTORMS EV3 medium motor
  7. LEGO custom air valve
  8. LEGO Powered Up Technic Hub (2x)
  9. Practice chanter
  10. LEGO Powered Up Large Angular motor (8x)

The air pump is powered by a power wall adapter connected to a Wi-Fi Power Plug. The plug state (ON/OFF) is controlled through UDP messages sent from the EV3.

The EV3 also reads the pressure inside the pneumatic circuit with a Mindsensore pressure sensor and tries to keep pressure steady by turning the air pump ON whenever pressure drops bellow a threshold.

The air valve is used only at start, when we need to inflate the balloon. The EV3 medium motor is used to close the valve (squeezing the aquarium air tube between the balloon and the chanter) and when there is enough air in the balloon the valve is opened.

Each Technic Hub is responsible for controlling 4 LEGO fingers with 4 Powered Up Large Angular motors. Probably smaller and faster motors would be better since they have much more strength than needed (if I don’t take care, they bend the “fingers” easily)… but that’s what I have with internal zero reference, it helps coding (but I did I had a problem with two of them, looks like they came with a large offset, near 100º… had to replace them).

The whole setup can now be described as an IoT project. I don’t have everything integrated yet so the EV3 functions are still independent of the Technic Hub functions:

  • the EV3 can be controlled manually and/or with MQTT messages
  • the Technic Hub can be controlled with Jupyter Notebook (using pybricksdev) or with two Chrome browsers running the Pybricks IDE

I have a video of current stage in action – please be warned, terrible noise:

In this video the reed has an elastic ring applied to it (I ordered a bag with the chanter). It does reduce the noise a bit but it also changes the required air pressure to play it so I ended up with a very large balloon… and that also changes the reed’s sound. Will have to make further tests to choose the best balloon size and try to adjust my code for it.

In the meantime, wainting for two orders to arrive:

  • some other practice reeeds to check if that makes any difference in the sound (I feel that my reed sounds like a cracked cane… my coding is bad, my setup is not the best but it does sound odd)
  • a pair of USB adapters for the Technic Hubs, I am tired of replacing batteries

Series Navigation<< Tuxie McPython – a LEGO bagpiper (or at least a noise machine)A whole week improving fingertips >>

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