How it works
- Eight arms of 2020 V-slot spread out from a plywood hub disc, making a wheel about 93 cm across. Each arm carries one guitar string, 330 mm long, from a tuner near the hub to a bridge at its tip. The tuner, the bridge and the string heights are Lapless Steel’s, so the string elements share their hardware.
- The wheel turns on a 10 mm axle in two bearings on top of a V-slot post, clockwise as you face it. A stepper turns it through a 4 to 1 toothed belt.
- One turn is one bar. Each arm is a step. As it passes the bottom, a pick on a servo catches its string and plucks it. At 120 beats a minute in eighth notes, the wheel turns once every two seconds.
- It keeps time by counting. The ESP32 counts the stepper’s steps, so it always knows which arm is at the pick, and it runs the wheel so each arm arrives on its beat. A reed switch on the post closes once a turn as a magnet behind arm 1 goes by, which keeps the count true.
- Rests come from the pick. For a rest, the servo swings the pick forward, clear of the strings, and that arm goes by in silence. The wheel never stops, so the pattern can change from one bar to the next.
- A felt pad just before the pick quiets each string as it comes round. A note rings for nearly a whole turn, and a rest is a true silence.
- Only sound leaves the wheel. Each arm has a small magnetic pickup. They’re wired together to a jack in the printed hub cap, on the axle’s line, and a wireless guitar sender plugged into it carries the sound to the console. Nothing on the wheel needs power from the stand.
- An ESP32 on the stand drives the stepper and the servo, and listens to Control like every other element.
The strings
We started with A minor 7, two octaves of it, rising one step at a time round the wheel. Each string is an electric guitar single, on 330 mm between the tuner post and the saddle. The pulls are worked out for nickel-wound and plain steel strings and are close for any brand. Whatever you tune, keep each string between about 60 and 90 N.
| Arm | Note | String | Pull |
|---|---|---|---|
| 1 | E3 | .046 wound | 81 N |
| 2 | A3 | .036 wound | 90 N |
| 3 | C4 | .028 wound | 78 N |
| 4 | E4 | .020 plain | 75 N |
| 5 | G4 | .017 plain | 77 N |
| 6 | A4 | .015 plain | 75 N |
| 7 | C5 | .013 plain | 80 N |
| 8 | E5 | .010 plain | 75 N |
Notes
- This is a first design, drawn but not yet built. The 3D model and the files show the version we started with. Bought parts vary, so check your tuners, bridges, pickups and pillow blocks against the numbers in the CAD script before drilling.
- The arms’ tips pass at about 1.5 m/s. Keep hands, hair and cables clear while it turns, and press the stop button before reaching in; the wheel coasts for a few seconds after.
- Costs in the ingredients are rough estimates for budgeting, not checked prices.
- Firmware comes with the broadcast control system. For a first test, any stepper and servo example sketch will do.
References
- A Leslie speaker throws sound around a room from a rotating horn. With acoustic arms, this wheel would move its sound around the room in a similar way.
