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[DPRG] Docking connector advice needed

Subject: [DPRG] Docking connector advice needed
From: chris cbrenizer at socket.net
Date: Sat Jan 24 00:08:01 CST 2004

the inductive pick ups sound like the coolest solution.  so the robot would
control its own charging.

that being said,  i've always wanted to come up with a mechanical
latching/docking setup.

NASA should have bunches of stuff on the subject.  this one...
http://www.tsgc.utexas.edu/archive/fulltext/lunar_launch.pdf

shows an interesting idea, a large docking alignment dowel to absorb any
initial velocities(like an overly enthusiastic robot), then a smaller
alignment rod to insure positive contact.

but it seems to me that there should already be a latching design in
existance that would work a little like a robotic hand with fingers that as
they close would draw in the robot.  the force to draw in the robot could
either be provided by the robot itself or the docking station.

the robot might push on levers that force the stations 'fingers' to grasp
the robot.  or the docking station might close the fingers once it senses
the robot is in position.  possibly powered 'screws' that engage into
threaded holes on the robot.  simple small plastic funnels might work as
guides, the 'screws' could have rounded ends to allow smooth operation.  as
well as additional guide rails if needed.

once you can garuntee mechanical contact and alignment, then there would be
any number of options for electrical contacts.

one reason i keep leaning toward this type of solution is the force required
to mate most normal connectors.  even though zero insertion force connectors
are available, i can imagine added benefits to postive mechanical docking
(like drive train testing or cargo loading or unloading or lifting the robot
into a cupboard for storage while it charges, etc).

but even with a low insertion force connector, requiring maybe 5 pounds per
contact, 5 contacts plus ground gets up to 30 pounds or so of force.  even a
small db 9 connector for communications can take tens of pounds of force.

which isn't impossible with a small robot.  but if it's already low on
battery power it seems prudent to allow in the design for the robot to
'limp' to the station, then get help hooking up...

there again, the inductive charging would eliminate that worry...

chris brenizer

----- Original Message -----
>From: "Karim Virani" <karim at compuguru.com>
To: <dprglist at dprg.org>
Sent: Thursday, January 22, 2004 11:09 PM
Subject: [DPRG] Docking connector advice needed


I need some connector advice.  I want to back my robot up to a charging
station.  I haven't found a suitable connector, and I'm pretty sure that
fabricating my own won't offer the reliablity I'm looking for.  I've found
multitudes of connectors that meet some of my needs, but none that meet all.

Leads: qty=5, 6A, 24v.  The circuit requires 5 leads - 2 ground and 3 power.
Mating force: near zero - 1 lb. max
Retention force: 0, or negative - the contact will be maintained by the
robot itself
Durability:  2,500 mating cycles - 3 or more charging cycles per day - 2
year life  :)
Blind Mating: .5" misalignment tolerance - the robot is big, has poor
steering and various inflation levels in it's wheels.  I can build some
extra guides around the connectors to assist with mechanical docking.  These
spring loaded guides will also trigger the power to the chargers - after the
mating is complete.

It's a largish robot, so the connector could be big too - as much as a
couple of inches wide.  If I had to do it myself, I might try for a spring
loaded butt mating between flat copper slugs .25" dia:

robot       charger
side        side
       /   /
|=====/  -/---|
|//]     [////|
|=====\  -\---|
       \   \

I'm not overly worried about exposed leads on the charger side.  The
chargers are intelligent enough to detect a battery type load, and I'll have
an additional keyed guide that the robot needs to trigger before power to
the chargers will flow.

Any and all ideas are welcome.

Thanks,

Karim
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