Subject:
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Re: A better device for tank treads than the adder / subtractor
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Newsgroups:
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lugnet.technic
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Date:
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Fri, 16 Aug 2002 08:25:50 GMT
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Viewed:
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3940 times
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In lugnet.technic, Roy Nelson writes:
> I have a challange for those realy good at using differentials and gears:
>
> The adder / subtractor device is not the ideal device for use in tank
> treads. An ideal device would drive straight forward and back with both
> motors running. It would also be able to turn in place with some
> combination of motors running, (maybe one motor or both motors turning in
> opposite directions). It would be good if it allowed partial skid steering,
> (both treads turning buy one turning faster than the other).
>
> The above condition may be accomplished by motors directly driving the
> treads but with a mechical link to ensure equal turing when both motors are
> powered. The mechanical link would be broken if only one motor were
> powered, or if the motors where powered to drive the treads in opposite
> dirrections.
>
> Anyone have any ideas?
> Roy Nelson
I think most of your problems would be solved by installing a clutch that
links the left and right drive axles. It would be somewhat like the limited
slip differential in the Ferrari brothers book. I perfer using the clutch
gear instead of pulleys like they use; the pulleys introduce a lot of drag.
The clutch consists of an axle, a 24t gear and a 24t clutch gear. The 24t
gear engages the drive gear for the left track and the clutch gear engages
the drive gear for the right track. The two gears are tied together by the
axle. When one track starts to turn faster than the other the clutch steals
some torque from the faster track and suplies it to the slower. It's not
perfect, but it works pretty well and is easy to implement.
If space is tight, or you don't have a clutch gear, you can build a modified
version of the clutch using two axles, two gears (whatever size fits best)
and a length of ribbed hose. The ribbed hose hose and axles form a "Sleeve
Clutch" (if there is such a thing).
I put an image and LDraw file on Brickshelf to show what I am talking about.
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=23480
If you need to go perfectly straight you could create a locking
differential. There are examples of this in the Ferrari book also. You
install a differential where the left shaft turns the same direction as the
left drive shaft, and the right shaft turns the opposite direction of the
right drive shaft. The differential housing is stationary if both drive
shafts spin at the same rate and in the same direction. If the speed or
direction is not the same, the differential housing will turn. Locking the
differential housing locks the left and right drive shafts together. A
third motor attached to the differential housing via gears can provide the
locking mechanism. Lock the motor when you need to go straight, and float
the motor when you need to turn. You could even use the motor to supply
extra power when turning. The only problem is that turning one direction
you speed up, and turning the other direction you slow down.
The put a bitmap showing the framework for the locking differential on
Brickshelf also. All you need to add is the motor.
Dean
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