Subject:
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A-S -> Adaptive Transmission (long)
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 17 Feb 1999 04:43:20 GMT
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Viewed:
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1200 times
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My own incarnation of the much discussed A-S transmission uses a single
differential and relies upon software to synchronize two independent drives.
I term my gearing and software system an Adaptive Drive, since it
continuously monitors differential rotation between two independent power
trains and coordinates synchronization by adjusting the power applied to one of
the two drives. I have built a tracked vehicle using the drive and the
performance is quite excellent.I would be less than candid if I didn't note
that the finite state machines that control the differential comparitor isn't
quite ready for "prime time", but the mechanical parts work beautifully,so I'll
briefly describe the prototype tracked vehicle and do a separate post when I
have the software bits better behaved.
The tracked vehicle is powered by two independent motors and gear
trains, one for each side. Each gear train is connected to one "output" shaft
of a differential. The gearing is arranged so that the two inputs to the
differential are counter-rotating and operate at the same gear ratio.
Consequently, if both gear trains are in synchrony, the outer housing of the
differential does not rotate. If however, there is a difference in rotation
between the two, the outer housing of the differential rotates, with rate and
direction dependent upon the relative rates and directions of rotation of the
inputs. During normal no-load operation with a final gear reduction of 1/3, the
differential slowly oscillates +/- 10-15 degrees of rotation (those LEGO gears
aren't perfect...). The outer housing is connected through gearing to a LEGO
rotation sensor. I spent quite alot of effort in optimizing the gear trains
and have reached a point where I don't think it can be further simplified, but
I'd love to be proven wrong. There are only three gears between the LEGO motors
and the tracks. By substitution of the primary motor drive gear (and an
appropriate number of 1/3 thickness shim plates between the motor and the
chassis), final gear reduction ratios of 1/9, 2/9 and 1/3 can be achieved with
no other modification to the chassis. There are 8 more gears plus a
differential in the differential comparitor, but these are not under any load,
so they contribute negligibly to friction.
Although I originally developed this system independently, not being a
mechnical engineering type, I was unaware that none of this is new. Primarily
through reading this news group, I have learned otherwise. The concept of
using a single differential in this way was discussed here in a very nice post
by Don Hewitt. I also wish to thank Leo Dorst for his ingenious two
differential design, that got me thinking about this in the first place.
I have developed a set of LDRAW CAD specs that illustrate the design.
I don't have a web page, but would be very willing to email them to someone who
could provide general access.
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