[MOC] EV3 Catching a Ball in Mid-Air

[pe668]

Bravo! Great robot model

[Xadhoom]

This is an amazing robot!

You said that despite the robust construction, the arms aren't stiff enough. Do you refer to the beams or to the articulations? If it's the second case, have you thought using some more robust parts than pins, like the small technic turntables?

[Aswin]

This is an impressive robot in every aspect!

You mentioned the sloppy EV3 motors. In my experience the NXT motors are a bit less sloppy. Probably because the internal gear train is shorter.

[lcvisser]

It's not clear to me how to use the plugin. Instead, I wrote up a post describing the trajectory estimation in more detail: http://www.dsharlet....d-observations/

Please let me know if any of it is unclear! However, I have to warn you, that without some background in some of these topics (non-linear optimization, computer vision/camera geometry) it might be difficult to understand, I didn't attempt to explain the math that isn't specific to this problem.

Great, that was very informative! You're approach is simple yet effective. Plus I learned a new algorithm, so that's good

[dsharlet]

This is an amazing robot!

You said that despite the robust construction, the arms aren't stiff enough. Do you refer to the beams or to the articulations? If it's the second case, have you thought using some more robust parts than pins, like the small technic turntables?

It's really both.

The articulations are problematic because they depend on axle-bushing clutch power for stiffness, which is terrible. They also depend on the rigidity of the non-friction pins in the dimensions other than the rotation axis, which is pretty bad. The small technic turntables are new to me, I didn't know about that part! I'm not sure it would be useful in this case, but it very well might be. Two of the 3 joints on each arm are basically universal joints, which are tough to build rigidly and compactly.

The other rigidity problem is that the precision of a delta robot depends on maintaining parallelograms for the "forearm" sections of the arms. It's difficult to build reinforcements to maintain this because the arms need to be able to squeeze together, so you can't build anything in between the arms to hold them together. Even adding just an axle between the two beams of the parallelogram limits the range of motion fairly significantly, and more importantly, means that the delta robot controller needs to be aware of these limits, which complicates the kinematics greatly.

I've since built better joints for a delta robot for another project, but haven't rebuilt the catcher robot arms with these ideas yet.

This is an impressive robot in every aspect!

You mentioned the sloppy EV3 motors. In my experience the NXT motors are a bit less sloppy. Probably because the internal gear train is shorter.

Interesting! I don't own the NXT motors, thanks for the pointer! All of my projects tend to rely on precise controllers/positioning, so the EV3 motor slop has always been annoying. I believe the NXT motors are compatible with the EV3 brick... I might buy one and try it out.

[Angeli]

Amazing! Great skills

[Boxerlego]

@dsharlet So recently I saw a self learning Japanese Robot practice and learn how to catch a ball in a cup as seen in the picture below.  It was said that after a 99 failed tries at catching the ball in the cup the robot catches the ball on the 100th time and then proceeds to catch the ball every time with no miss after all the failed tries. Not bad for a self learning robot. Now the big question is Would it be possible for a Lego robot to do the same.

Edited September 29, 2016 by Boxerlego

[1980-Something-Space-Guy]

On 9/29/2016 at 8:13 AM, Boxerlego said:

@dsharlet So recently I saw a self learning Japanese Robot practice and learn how to catch a ball in a cup as seen in the picture below.  It was said that after a 99 failed tries at catching the ball in the cup the robot catches the ball on the 100th time and then proceeds to catch the ball every time with no miss after all the failed tries. Not bad for a self learning robot. Now the big question is Would it be possible for a Lego robot to do the same.

It always fails during the first 99 tries, and then it always succeeds? That seems a little too regular to me. Hmmm.

[Boxerlego]

43 minutes ago, BrickHat said:

It always fails during the first 99 tries, and then it always succeeds? That seems a little too regular to me. Hmmm.

That seems to be the idea to say the least. After some searching I was able to find an older Robot doing the same thing as the Japaneses Robot I saw. The big difference with the Japanese Robot is that it was able to hold the ball and the string game with its Robotic hand instead of just a robot arm directly connected up to a cup and string like so with the robot below. 

 

 

Edited September 30, 2016 by Boxerlego