Robotic Arm 7DOF

There are ( always and on almost anything ) books:
   Rivin "Mechanical Design of Robots" McGrawHill 1988
( although didn´t find that an easy read, but i am an EE )

 > I want to use electrical actuators and gears,
 > preferably at a low cost and light weight.
There are several old, "educational" robots like
   Microbot / Teachmover
   Scorbot
   Sekuria ( only here in Germany )
Often they turn up reasonably cheap at ebay.
It would be probably worthwhile to have a look how
they have done it.

MfG  JRD

Homosapien had written this in response to
http://www.www.roboticscommunity.com/robotics/Re-Robotic-Arm-7DOF-28429-.htm
 :


-------------------------------------
Rafael Deliano wrote:


Thank you for your reply.

Will I be able to find mechanical designs on the robotic arm in the book
mentioned?


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Its not an easy read, but at least its focused on the mechanical stuff,
not too much literature ( apart from conference proceedings ) on that.
Victor Scheinman
http://en.wikipedia.org/wiki/Victor_Scheinman
liked it, wrote a glowing review about it in some journal. So i got it.
Note that the experimental Stanford Arm ( which perhaps got some ideas
from the older Unimates )
http://images.google.de/images?q=Stanford+Arm&oe=utf-8&rls=org.mozilla:de:official&client=firefox-a&um=1&ie=UTF-8&sa=N&hl=de&tab=wi
evolved to the industrial PUMA about 1978 (?)
http://images.google.de/images?hl=de&client=firefox-a&rls=org.mozilla%3Ade%3Aofficial&um=1&sa=1&q=Unimate+Puma&btnG=Suche
That one is electrical and was explicitly specified to be
"almost the same as a human arm".
That size hasn´t been commercially too successfull. People are cheaper,
faster, better. There have been some later simple small systems
like the old red Mitsubishi Movemaster from the 80ies:
http://srt-aut.mv.fh-duesseldorf.de/handhabung/index.php/Mitsubishi_RM-501
These are not experimental/educational but have/had applications
in industry and are still somewhat expensive if found at ebay.

The big stuff is often hydraulic:
http://business.shop.ebay.com/Robotics-/50924/i.html?_armrs=1&_mdo=Business-Industrial&_mspp=&_pcatsB892%2C92074%2C12576
http://business.shop.ebay.de/Roboter-/40517/i.html?_npmv=3

Another good book would be:
   Lhote "Robot components and Systems" Kogan 1984
That covers electrical/pneumatic/hydraulic motors
and has some chapter "transmission systems" on the mechanical
side.

MfG  JRD

Homosapien wrote:


You don't state what you want the arm to do.  If it is just to position
something within free space, you might get away with open loop stepper
motors, but if you want to push on things in a controlled way, you'll need
encoders on each joint to track where it is.  I would think harmonic drives
should be small enough and cheap enough to do for the gear reducer.

You also need smaller motors as you move towards the wrist, although you
still need good torque at the end to hold up your payload at maximum
offset.

So, at a minimum, you need seven varying-sized joints, probably with stepper
or DC motors, brakes, encoders, gearboxes, motor controllers and joining
structure.  Robotics Research makes a cool looking robot using roll and
pitch joints only.  The 7 jointed manipulator on space station has joints
in a roll-yaw-pitch-pitch-pitch-yaw-roll sequence, but that configuration
was largely driven by the need to fold the whole thing up into a small
space for launch.

You also need a bunch of good sensors if you want to feel your environment,
and a good computer to act as overall controller that can handle 7-joint
inverse kinematics.  Oh, and a good gripper, which is the whole reason for
moving those joints around.  

If you can accept a little slop in the motion, you could keep the motors in
the base and use cables to transmit motion to the joints, making the arm
lighter and reducing the required torque for the shoulder joints.

Google around for some plans for a small plywood robot, I remember seeing
something like that.  I think it had just 5 or 6 joints, however.

You might just be cheaper off looking through the surplus equipment sites
for a used model.  What you want to do has been done many times before, so
there's no need to reinvent the wheel, unless it's for self-education.

Mike Ross

Homosapien had written this in response to
http://www.www.roboticscommunity.com/robotics/Re-Robotic-Arm-7DOF-28430-.htm
 :



THANK YOU for your reply. I still have a lot to learn :( I'm only
beginning this course and it's already giving me a headache!

I have some ideas of what my arm can do. At the moment, I'm just looking
into some designs that anyone can help me with? I googled the plywood
robot but nothing came up, just mostly plywood!








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