Chanter is mounted on aluminum block along with electromagnetic coils that open and close sound holes using rubber pads at the end of lightweight plastic tubes.
The McBlare air compressor. Electric motor (not visible) drives eccentric (center) through a gearbox. Eccentric drives two air pump cylinders (right and left) in opposition.
Garth Zeglin with McBlare shortly before its debut at the Robotics Institute’s Twenty-Fifth Annivesary. Bagpipes are mounted on a display board that conceals the pump and additional electronics.
... uses a custom-built air compressor. A 1/16 HP, 115VAC electric motor drives a gearbox that reduces the speed to about 250 rpm. Two 76 mm ( 3”) diameter air pump cylinders, salvaged from compressors for inflatable rafts, are driven in opposition so that they deliver about 500 pump strokes per minute. (See Figure 2.) The radius of the crank arm driving the cylinders is adjustable from 15 mm to 51 mm (0.6” to 2.0”); we found that the smallest radius provides adequate air flow, calculated to be 0.034 cubic meters per minute (1.2 cubic feet per minute). 1 A small air storage tank sits between the pump and the bagpipes. The bagpipes are connected with a rubber hose that slips over the same tube that a human performer would blow into. By blowing in air more-or-less continuously, we can achieve a fairly steady pressure without squeezing the bag. (Earlier designs called for a mechanical “squeezer” but at 7 kPa (1 psi), a squeezer in contact with many square inches would have to be very powerful, adding significantly to McBlare’s weight and complexity.) Pressure regulation is very simple at present. First, the stroke length of the pump cylinders is adjustable to set the flow rate just above what is needed by the bagpipes. Second, a relief valve, which is simply a weighted plug, vents high pressure (around 10 kPa or 1.5 psi) to prevent over-pressure and avoid damaging the bagpipes. A second bleed valve can be adjusted to release air and lower the pressure. The chanter requires “fingers” to open and close sound holes. Analysis of video indicates that bagpipers can play sequences of notes at rates up to around 25 notes per second. Human players can also uncover sound holes slowly, partially, using either an up-down motion or a sideways motion. The design for McBlare restricts “fingers” to up-and-down motion normal to the chanter surface. Fortunately, this is appropriate for traditional playing. The actuators operate faster than human muscles, allowing McBlare to exceed the speed of human pipers. McBlare’s “fingers” are modified electro-mechanical relays. (See Figure 3.) Small coils pull down a metal plate, which is spring loaded to return. Lightweight plastic tubes extend the metal plate about 3 cm, ending in small rubber circles designed to seal the sound hole. The length of travel at the sound hole is about 2.5 mm, and the actuators can switch to open or closed position in about 20 ms. The magnet coils consume about 1 Watt each, enough to keep the mechanism warm, but not enough to require any special cooling. The magnet mechanism has the beneficial characteristic that the finger force is maximum (around 100 gf) with the magnet closed, the point at which finger force is needed for sealing the tone hole. The whole “hand” assembly is designed to fit a standard chanter, but the individual finger units can be adjusted laterally (along the length of the chanter) and vertically. The lateral adjustment accommodates variations in hole spacing. The vertical adjustment is critical so that the magnet closure point corresponds to the point of finger closure. The actuator current is controlled by a current driver IC, which is in turn controlled by a microcontroller. The microcontroller receives MIDI, decodes MIDI note-on messages to obtain pitch, and then uses a table-lookup to determine the correct fingering for that pitch. MIDI notes outside of the bagpipe range are transposed up or down in octaves to fall inside the bagpipe range. The chanter control works extremely well. The speed allows for authentic-sounding grace notes and some very exciting computer-generated sequences. In its original configuration (see Figure 4), McBlare included a small Yamaha hardware MIDI sequencer so that it could play traditional tunes that we found on the web in the form of standard MIDI files. We also developed a small laptop- based program to allow users to select and play a tune or to record and play a melody from a MIDI keyboard. A further option can automatically ornament the recorded ...
Modifié par Gabpipes, 26 oct. 2018 - 22:09.
