Pasithea

Speaking of you, where have you been lately?

I was in Canada, eh! But now I'm back, I have the newest episode of Dr. Who also, just aired in the UK, two days ago.

Anyway, you could try haxoring the motors, or driving the reels with another set entirely. The pinch roller by the head is what is responsible for maintaining constant tape speed. The take-up reel just has to keep the tape from spewing out into a big pile.

Now that I think about it some more... physics-wise. A circular hoop rotating around its center, has moment of inertia I=kmr² (For a solid disk you need to do a volumetric integral, or I could just look it up... I=½MR²) And we're moving at a constant linear velocity v... If we consider this to be a 1-D case, then L=mvr. The radius will be somewhere between [0,7.5] inches...

The two motors to be concerned about are the pinch rollers by the head, and the take-up. (One at constant linear velocity, and the other at constant angular velocity. (I think))

The pinch rollers need:

1. To have enough friction to pull the tape through


2. The tape needs the tensile strength to not break when transferring the force from the rollers into rotating the spool


3. The lead out (?) spool will require the most torque at the beginning (R=7.5") and will rotate at the slowest. Speeding up as R drops to 0, and the necessary torque will go down to 0 too. It should be free to spin on its own (no motor, ideally frictionless), while playing.

So, the dangerous part will be from the start of the tape, until you only have as much tape left as the player would normally hold. On every tape deck I've ever played with, the pinch rollers had a lot of torque. Enough to pull your fingers through, or snap a tape if it got stuck.

The take up spool only needs:

1. Maintain enough tension on the tape, so that it doesn't fall out of the recorder, or fold back over onto the pinch rollers. (I hate it when that happens -- mostly due to a sticky pinch roller.)


2. The reel... <thinking...> v=ωr ... will spin fast, and then slow down as more tape is wound. Also the amount of torque will go up, but as long as you're not accelerating from rest, there should already be enough angular momentum built up.

I believe that most reel-to-reel decks are designed to have the take up motor just spin as fast as possible, and they are held back by the tape slowly feeding out from between the pinch rollers. If you just put a full reel on the take up, and hit play, does it spin around really fast?

So... in conclusion, I think your tape deck will be ok, but you need to worry about breaking or stretching your tape out. (Always a problem with tape.) (And I didn't have to do any math, yay.)