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 )

MfG JRD

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

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------------------------------------- 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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Homosapien had written this in response to

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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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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

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 ) to the industrial PUMA about 1978 (?) 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: 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:

?_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