Subject:
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using adder/subtractor as a transmission
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 23 Feb 1999 03:04:15 GMT
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Viewed:
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953 times
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I was thinking about automatic transmissions the other day and it occured to me
that you could use the much talked about Adder-Subtractor setup to give you up
to three speeds. Using the worm screw idea that has been mentioned, you could
control the speeds. The idea is to feed the input in on of the axial shafts
and then get the output out the other. If you "add" you can go faster, if you
"subtract" you can go slower, and if you do nothing, you'll basically get 1:1
output. With this technique, you could use just one differential too. I'll
attempt an ascii-art diagram here. I haven't had any chance to play with the
design as I don't have any legos at university. (I'll get some soon, I think.
;)
.
| | _
| | | |
| ( )|=|========|-| <--- this gear must be set to subtract
____|_/ / / / /______| | |____|_| motion, giving a low gear
|/ / / / / | |-| \/ | |
| ( )|======|=|-|] [|-|============ output
| | |-|____|_|
| | |_|
| |
.
The spring will hold the worm gear against the left side, sending power into
the 8-tooth gear, through a set of 45 degree bevel gears to transfer the right
down the main input shaft. When the torque rises, the worm will tend to move
right along its shaft, until it makes contact with the other 8-tooth gear.
When that gear begins to turn, it will send power down the subtractor shaft,
which is set to subtract motion from the output shaft. We must ensure we are
turning it the right way and that we have a gear ratio that will slow the
output shaft, but not make it stop completely or turn backwards. Looking at
the design, I realize it may actually stop the output shaft the way it is drawn
now. Thus we'd need to gear it down somehow. When torque decreases, the
spring on the worm will push it left, taking away the subtraction, and let us
go full speed again.
The main problem I see is that the subtractor shaft will turn by itself when
it's not connected. Unless this can be solved, or proven to not be a problem
then the design may not work at all.
Any ideas, anyone?
cheers,
Michael
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