2222: Pickle Barrel?
2223: Early American Pizza stand off! 8>) or a cup holder?
2224: Safe opener? Security door entrance device?
2225: Barn door closers?
2226: Joiner for metal or wood?
On 04/21/2011 05:24 AM, Rob H. wrote:
In all seriousness, what a wonderfully goofy idea!!!
Whoever thought this up deserves an award for creativity.
On 4/21/2011 12:22 PM, Rob H. wrote:
Or -- to be jailed for cruelty to records. I can't imagine any
way that this would track properly without exerting enough force on the
stylus so it would rapidly shorten the life of the recording.
And -- what RPM is it set to? It is bound to be wrong
everywhere except at one radius.
And if you put it on backwards, it would play the record
backwards, as in some of the old stories about nasty trick built into
some rock recordings. :-)
When I said:
"In all seriousness, what a wonderfully goofy idea!!!
Whoever thought this up deserves an award for creativity."
I was expressing awe that our society can produce such a product.
I don't want to pick a fight about the explosive subject of combining
the words 'rational' and 'vinyl' in a discussion. (I still have a good
working vinyl system.)
Thinking about how this thing works...
The left and right wheels are separately servoed.
A common speed input goes to each servo.
A tracking signal, derived from the stylus displacement from center, is
a differential input to the servos. This centers the stylus and makes
the thing go in a circle (ok, spiral).
The difference in rotation of the wheels is used to derive a radius
measure, which is used to generate the speed input signal, to make the
speed compensate for the different linear velocity at different radii.
(Or money could be spent on a gyro to get rotation rate.)
All this is done in a fairly-low-volume toy at an amazingly low price.
On 4/22/2011 4:16 AM, George W Frost wrote:
Don't bother buying one on eBay. This video shows how it works and why
it doesn't need all the fancy stuff you thought of:
At about 23 seconds into the video you will see that the stylus is on a
swinging arm so that it can move inward and keep following the record
groove. It looks like the bus runs in a constant radius circle around
the outer part of the LP record at a speeed which "delivers" 33-1/3 RPM.
Does anyone else find it curious that 45 (RPM) is damn close to the
difference between 33-1/3 and 78.26?
78.26 was the "official" speed for 78s, arising from some easy to reach
gear ratio coupled to a synchronous AC motor. (I suppose that was
established before they started driving turntables with those rubber
recorded without electric motors because line frequency was not
considered steady enough. Record players were adjustable because
different producers used different speeds, from 74 to 82 RPM.
In 1925, Bell Systems began making electrical recording equipment. Bell
went with 78 because that's what Victor, the biggest producer, used.
Rubber wheels wouldn't have been precise enough, but a worm gear would
give them 78.26.
The same year, Bell Systems set the 33-1/3 RPM standard for cutting
records to play with movies. Movies soon went to other technology.
45s and consumer 33-1/3s came out after WWII. They were probably chosen
because they are exact factors of synchronous speed and are easier to
remember than 78.26.
Equipment for 50 Hz uses 77.92.
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