Re: need advice from lego gurus

Dan, 
If you are okay with it being further forward when it
is raised than when it is lowered, you can use a
rather simple but robust method of raising your
gripper while keeping it parallel to the ground/floor.

I'm afraid I can't whip up a drawing, but I will try
to explain. The top view photo shows that you have the
gripper assembly pivoting around an axle with 40 tooth
gears on it. These have to be replaced.

It looks like the assembly has room for a 8 or 12 hole
beam at the point where it currently has the axle with
the 40t gears. The idea is that you need a long-ish
beam that will be horizontal to the floor mounted on
each side of the gripper assembly.

Mated to this (somewhat) you will need a 12 or 16 hole
beam mounted on the robot chassis on either side of
the gripper assembly. It looks like there is plenty of
room. The beams on the gripper and the beams on the
robot chassis don't have to line up perfectly, though
it would be great if it works out that there is
currently three beam widths of space between the
gripper assembly and the chassis on each side of the
gripper assembly, 6 beam widths total.

Now that you have the two beams on the gripper, and
similar beams on the chassis, you need only to take
four shorter beams, and using two on each side, use
the shorter beams to connect the two beams that you
mounted on the gripper assembly and chassis. The
manner for doing this should leave the gripper
assembly resting in its 'down' position such that if
you manually pick it up, it will move up and forward
while remaining horizontal to the floor/table surface,
leaving your gripper to be fully effective at a larger
range of motion. This is a sort of modified scissor
lift as used in many commercial heavy duty lifing
systems as well as car lifts in auto repair shops.

The mechanism you use now to raise the gripper
assembly can be modified so that its 40t gear is
connected to the scissor lift with a short beam on
both sides of the gripper assembly. This adds weight
to your machine, but gives it a very sturdy and
capable lift mechanisim. If you use worm gears to turn
the 40t lifting gear, it will be slow, but also
capable of greater weights. As the 40t lift gears
turn, the beams attached to them push on the gripper
mounted portion of the scissor lift causing it to move
forward and upward.

This is in fact one of the simplest car lift
mechanisms used for auto repair shops. It can lift a
car using a hydraulic jack that is not much bigger
than required to lift one side to change your tires.
Once raised, it is locked in place and can easily hold
a car up off the ground by several feet for
weeks/months.

Your scissor lift on your robot, if moved by a worm
drive gear, will be able to remain extended for long
periods. Creative use of switches will allow your RCX
to know when to stop motion in both directions.

If you want to increase the weight bearing capacity of
this scissor lift, you can get creative and add a beam
to the 40t lift gears such that they are connected to
a counter balance weight system that extends toward
the rear of your robot chassis, thus rebalancing the
robot in proportion to how much is added to the front
of the robot by a weighty object in the gripper. The
counter balance weight pod/arm extends toward the rear
as your scissor lift/gripper extends forward of the
robot, all with the single motion of your 40t lift
gears. So this adds no electrical or software
requirements to the system and gives you quite a bit
more capacity.

I have a similar mechanism on my robot. I'll apologize
for the poor photography in advance, but you can see
pictures of this to get an idea. Go to www dot
brickshelf dot com and search for a user name of
zappepcs

main photo page
<http://www.brickshelf.com/cgi-bin/gallery.cgi?f=96749>

closeup of counterbalanced arm
<http://www.brickshelf.com/cgi-bin/gallery.cgi?i=919354>

The arm fully extended
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=919353

Anyway, I hope that gives you some ideas

Scott


--- dan miller <[email protected]> wrote:

> I'm thinking about the next version of my one-armed
> robot, Grabot. 
> Presently he looks like this:
> 
> http://www.danbmil.com/lego/DSCN6131.JPG
> 
> what I want to do is have the claw go up and down
> but stay parallel to the
> floor, rather than hoist itself up as in this
> picture.  Does anyone know of
> a technique, used or just conceptual, for doing
> this?  I'll need some sort
> of elevator construction, that can hold quite a bit
> of weight for the arm
> assembly.  Here's a top-level view that shows how
> the arm looks now:
> 
> http://www.danbmil.com/lego/DSCN6128.JPG
> 
> Any thoughts will be greatly appreciated.  I am
> thinking of some sort of
> worm gear + one of those toothed strips, but I can't
> really see how to make
> it work efficiently with a good range of motion.
> 
> thanks in advance, this is a great group
> 
> - dan
> 
> 
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