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 Robotics / 17505
17504  |  17506
Subject: 
Re: How much can you shrink a dual differential drive?
Newsgroups: 
lugnet.robotics
Date: 
Tue, 12 Mar 2002 16:05:59 GMT
Original-From: 
Jona <jjeffords@ameritech.NOMORESPAMnet>
Viewed: 
1675 times
  
Miguel,

The smallest design for an adder-subtracter I have seen online is by Denis
Cousineau. You can find it at
http://prelude.psy.umontreal.ca/~cousined/lego/1-Varia/adder/adder.html .
However, you should know that his design, and one that he links to have
inspired myself, and a few of my robotics friends to play around with the
adder-subtracter. We have reduced it in size quite a bit, and I think that
if you just play with all of your options, you are sure to find a solution
for your application.

Good luck,

Jona
----- Original Message -----
From: "miguel agullo" <technicpuppy@yahoo.com>
To: <lego-robotics@crynwr.com>
Sent: Tuesday, March 19, 2002 6:40 PM
Subject: How much can you shrink a dual differential drive?


Hi all,

I've got an intriguing little MOC coming up that hopefully will interest
both the technicheads and the robogeeks. It is a tracked vehicle with a
twist, but you'll have to wait to learn all the details ;-)

In the meantime, here is something I could use some help on. For precise
operation, I'm using a dual differential drive as described by the Ferrari
brothers in their book. My setup is farily different from theirs, mostly
because I need to save space. I've uploaded to brickshelf 2 dats and 4 POV
jpegs of how it looks right now. You might want to take a look.

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=13856

(For those of you who, like me 4 months ago, don't know what a double
differential drive does, it's a mechanism that mechanically links 2 motors
to an axle so that one motor rotates both wheels on the ends of the axle • in
the same direction and the other motor rotates them in opposite • directions.
In practice, this means that a vehicle fitted with this drive will go in a
stright line if one of the motors is used or rotate in place if the other • is
activated. If both motors are activated, rotation still occurs.)

So, a couple of things about my design. First, it's meant to be as small • as
possible. Second, the two input axles (yellow and green in the jpegs) • rotate
the output axle (blue) at different speeds - the green one uses a double
bevel 20 tooth gear/24 gear crown combination for reduction, the yellow • one
a 8/24 tooth combination. I have not attached motors to this drive, but
nothing seems to break or even creak when I rotate the axles with my • fingers
in any direction simultaneaously.

Anybody can come up with a more compact design? Can anybody solve the dual
speed issue? I could add studs in width (distance between wheels) and one
stud in height to what already rises above the wheel axle (and maybe • another
stud below). Height is critical, but losing some length is even more so.

OK, I hope you enjoy it and come up with some ideas.

Chao for now!



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