[WIP] Mechanical Arm

[Nazgarot]

I found I need something more flexible and stronger than a simple mechanical third hand to help me when I do welding.

The Third Hand I have right now is rather clumsy, somewhat like this but bigger.

The other standard variants are way to flimsy, and of little use for my purposes.

Today I happened upon this, and immediately thought I need to have this! Both for usefulness and because it's cool. Then I thought it was way to expensive, and that I could build one myself. I first thought i could do it from metal, using the one I found as a blueprint for how to make it. Then it hit me it would be much cooler and much more fun to prototype it with Lego. So here I am.

This is what I'm hoping to end up with, and I would much appreciate it if anyone has tips for how to make something like this, or links to other similar projects. The important part for me is that it needs to be strong and stable. I prefer using as few gears as possible in order to reduce backlash. It might be some time before I can start this project for real as I'm about to replace the roof of my house, but I'll try to update here as often as possible.

-ED-

Edited August 17, 2016 by Nazgarot

[Saberwing40k]

I hate to sound like a wet blanket, but a robot arm, made out of Lego parts, would be really useless for welding projects. You've got hot metal, and sparks going all over the place. Not the best place to have a plastic arm you presumably aren't willing to destroy. Even a metal robotic arm would not be good for that purpose, due to the motors probably being fairly weak, and so easy to backdrive. For welding, you're better off making something like this, with wing nuts to lock the joints.

But, I'm not going to talk about that, Let's talk about a nice Lego project. So, have you decided on how you want to control the arm? How many joints do you want? Do you want a gripper? How many motors do you have? If you have an SBrick, and at least 2 servos, you'd be able to make a 4DOF robotic arm, completely under your control, from a smartphone. Another alternative would be to use an NXT or EV3 brick, with their servo motors, although you'd have to program that. Although, in that case you're better off just buying the metal kit, because the EV3 and extra motors would be more than that. Just running the arm through standard PF controls would be very inaccurate, given how you'd be moving it by timing alone. Okay, as a general rule, in robotics, particularly with arms , legs, and humanoid robots, each joint is considered a degree of freedom, or DOF. Human arms, at the most basic, can be considered to have 3DOF, the shoulder, in two axes, and the elbow. So, a basic arm, with gripper, needs four motors, bare minimum. Every joint you add is another motor you need to control. The arm you linked to is actually a 6DOF unit, given that it has a wrist, pivot and rotation, and a gripper.

Here are some units you might like:

Edited August 17, 2016 by Saberwing40k

[JM1971]

Maybe using worm gears to precisely move and lock everything into place, along with some kind of spring loaded pushing force, will have to knock something up in LDD and come back later.

[Nazgarot]

I hate to sound like a wet blanket, but a robot arm, made out of Lego parts, would be really useless for welding projects. You've got hot metal, and sparks going all over the place. Not the best place to have a plastic arm you presumably aren't willing to destroy. Even a metal robotic arm would not be good for that purpose, due to the motors probably being fairly weak, and so easy to backdrive. For welding, you're better off making something like this, with wing nuts to lock the joints.

I think you are missing a part of the point. I need a better third hand (i.e. one that has longer reach, and is easier to place correctly) and making a robotic hand is fun and cool, and will make it a lot easier to do minor adjustments compared to using something with wing nuts or similar. It will mostly be used for welding on electronics, motors etc. Not welding pipes or similar. And the Lego version would only be a prototype to see how I should design it. I often use Lego to prototype things that I make out of metal or wood, to save time on developing solutions. The lego model would mainly be to find the correct numer of joints (DOFs), size and test usefulness.

Strength of motors should not be a problem as a final version in 6061 aircraft grade aluminum would contain servos rather than standard motors. Basically it will be similar to the arm I linked to, but adapted for my purposes.

For the arm I'm thinking it will need 5 or 6 DOFs, and interchangeable tools. The big problem lies in making it easy to control. Lego version would probably use simple PF solutions, but final version might be controlled through an arduino processor on a prototyping board.

Still if the Lego prototype is good enough I might just use it, and if it shows it is very hard to use, or difficult to make accurate enough, I might drop the project altogether.

I was hoping to see some models that others have made to get some ideas, and your videos where helpful. Thanks!

I've also found this, that seems like a very compact solution, and easy to build out with further functions. I might base a first prototype off something similar. If anyone knows of a video of this thing I would be very happy to get a link. It's posted by DLuders, who seems to be Banned from the site for some reason. There was no video in the post, and I can't seem to find any...

-ED-

Edited August 17, 2016 by Nazgarot