3 ms·

How much power does it need? Could the winding mechanism provide the required power? Got to look up some specs on the maximum torque provided by the winding mec

How much power does it need? Could the winding mechanism provide the required power? Got to look up some specs on the maximum torque provided by the winding mechanism and the turning speed.

squarefoot 4y ago
The capstan is where the maximum torque is, although the very slow rotation would need some gears in order to extract some power from a small dynamo; the tape rolls torque is very limited on purpose to barely keep the tape in tension without breaking it, and they would be unusable for this purpose. Also it wouldn't be easy to keep something in contact with the capstan to extract its energy, since the capstan/pinch-roller pair has been designed to work with tape, not pulleys or gears. The hardest problem is hence mechanical; a repurposed small stepper motor could work great as generator, and the electronics involved beyond the standard Lithium charging chip would be minimal. But adding the necessary gearbox to this device would likely raise significantly the cost of production, which is probably the reason we didn't see it yet.
- planede 4y ago
  That makes sense. I agree that this is probably not cost-effective, but it could still be fun as a hobby project. > Also it wouldn't be easy to keep something in contact with the capstan to extract its energy, since the capstan/pinch-roller pair has been designed to work with tape, not pulleys or gears. The force could be extracted using a tape/ribbon similar to a real cassette tape, but one that loops around internal pulleys with a tensioner. It would be probably not cost effective, but I would still be curious of the maximal power draw you could get from the capstan. I suppose we know the tape speed (2.4 cm/s according to Wikipedia), but we also need the maximal force the capstan can excess on the tape. I wonder if there are some specifications for maximal friction forces within a cassette tape to be conforming, so we can get a good guess at this. 2.4 cm/s translates to 41.7 mN / mW (millinewton per milliwatt). This is not counting for losses for converting the mechanical energy. edit: The force requires seems to be excessive. The lowest power draw I can imagine is ~0.1W for a BL device like this (probably generous), and then we would need 4N pulling force on the tape for that (still not counting losses), which is a lot. Anyway, this was a fun exercise.

How much power does it need? Could the winding mechanism provide the required power? Got to look up some specs on the maximum torque provided by the winding mechanism and the turning speed.

squarefoot 4y ago

The capstan is where the maximum torque is, although the very slow rotation would need some gears in order to extract some power from a small dynamo; the tape rolls torque is very limited on purpose to barely keep the tape in tension without breaking it, and they would be unusable for this purpose. Also it wouldn't be easy to keep something in contact with the capstan to extract its energy, since the capstan/pinch-roller pair has been designed to work with tape, not pulleys or gears. The hardest problem is hence mechanical; a repurposed small stepper motor could work great as generator, and the electronics involved beyond the standard Lithium charging chip would be minimal. But adding the necessary gearbox to this device would likely raise significantly the cost of production, which is probably the reason we didn't see it yet.

planede 4y ago
That makes sense. I agree that this is probably not cost-effective, but it could still be fun as a hobby project. > Also it wouldn't be easy to keep something in contact with the capstan to extract its energy, since the capstan/pinch-roller pair has been designed to work with tape, not pulleys or gears. The force could be extracted using a tape/ribbon similar to a real cassette tape, but one that loops around internal pulleys with a tensioner. It would be probably not cost effective, but I would still be curious of the maximal power draw you could get from the capstan. I suppose we know the tape speed (2.4 cm/s according to Wikipedia), but we also need the maximal force the capstan can excess on the tape. I wonder if there are some specifications for maximal friction forces within a cassette tape to be conforming, so we can get a good guess at this. 2.4 cm/s translates to 41.7 mN / mW (millinewton per milliwatt). This is not counting for losses for converting the mechanical energy. edit: The force requires seems to be excessive. The lowest power draw I can imagine is ~0.1W for a BL device like this (probably generous), and then we would need 4N pulling force on the tape for that (still not counting losses), which is a lot. Anyway, this was a fun exercise.