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A stepper motor with sine/cosine drive and positional feedback can have its dynamic characteristics adjusted to simulate the old flywheel tuning dial drive, with the added bonus that the effect of friction can be cancelled out.
You turn it by hand to change an input variable, such as the frame counter
in a video clip. It would keep spinning at the same speed until you stopped it.
I see it being used as the "shuttle control" for a digital video editing suite, to mention one example.
Coupled with voice recognition, for example:
"Video one" <spin> <grab> <twiddle> <nudge> "Mark, Cut"
"Video two" <spin back; control hits start of video take and stops> <nudge nudge> "Mark" etc . . .
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Absolutely. I'm all for more physical inputs to computers. |
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<aside>I was recently shown a software digital signal processor that simulated all the knobs in a recording studio on screen (you did have to scroll about a bit). The user of the software was really impressed. I wasn't because it was a pain adjusting all those knobs with a mouse.<aside> |
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I think I understand what you're talking about, but I don't suppose someone would mind explaining the first paragraph a little more simply to me would they? |
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st3f: On-screen sliders are usually good. On-screen rotary things are bad at best; some implementations are so bad that who ever came up with them should be forced to sit in a room ... well... come up with something. |
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One useful twist to an on-screen slider is a control which, if the mouse button is pressed, "lock" the mouse pointer in place until the button is released but cause motions of the mouse to affect the control setting. Hard to describe, but really works well. |
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kaz: stepper motors are usually run by switching transistors connecting their windings directly to the supply voltage. This simple scheme would cause them to "step" a small angular distance each time a command was issued to it, hence the name. |
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With sine/cosine drives, the two windings of the motor are driven by sinusoidally varying currents with a 90 degree offset. This requires more electronics but can produce smooth motion. |
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Since the idea is to drive a control which also is manipulated it is necessary for it to feel smooth and free of vibration, hence the drive. |
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When you grab the spinning wheel to slow it down, its position will lag behind the driving voltage. If you speed it up the position will lead. This can be sensed by a position transducer or by sensing the motor currents. With appropriate control the wheel can be made to act as if it had zero friction, ie, to keep on turning at the same speed once it was set in motion. |
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[neelandan]: I don't think kaz was asking for a deeper explanation of the drive electronics. FWIW, I think this could be done just as well, if not better, using a dc motor and a rotary encoder. Maybe add a strain gauge to the shaft (if back-EMF sensing isn't good enough). |
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[kaz]: the idea is that the computer can control the "feel" of the knob by driving the motor, so it's completely software-determined whether it's a light, spinnable knob, a heavy knob, a knob with detents and stops, etc. |
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