Let's Make Robots!

'Wobble' the delta robot

Err...waves it's 'arms' about

Here is my second robot, a delta robot.

I had no idea what a delta robot was until the other day, when I was browsing through old posts and came across this robot, created many epochs ago in 2009. I thought it was pretty awesome, so decided to make my own (although sadly my version isn't quite as beautifully made!).

The base is made of plexiglass, the rest is metal strip and rod. I used processing to make the mouse interface and picaxe to control the servos. It cost $0 to build because some of the parts I already had, the rest I got a week ago on my 14th birthday.

I will post a video soon - at the moment I am still trying to figure out how to move the mouse and control the camera at the same time (multi-tasking was never my strong point!). Hopefully when I do post the video, you will see why it's called Wobble ;-)

EDIT: Added another arm per servo, and uploaded video.

Pictures below:

The base, before I put the arms on ^

added the arms ^

close up ^

birds eye view ^

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Much better with the "correct" double arm design. I expect the wobbling to be gone now.

Looking closely at your short video still reveals some "issues". Ideally the end effector, the top platform you move around, should be parallel with the base plate all the time. I'm not sure that's the case with your robot. You could try to increase the distance between the arms further, but that would require some even longer screws there. Also it might be a problem with the ball joints not completely tight all the time, especially in outer positions.

Nevertheless great build and progress! Whats up next? Will you learn it to dance Disco or to collect nasty slugs in your garden? Oh yeah, a Disco-Bot, don't think we have such a thing here, yet!

Thanks for your input - I was wondering why the top platform wasn't parallel, and I think you are right in that the joints are not completely tight. Do you think I should fix the ball joints at the top in place so that they can't move at all, or should I just make them slightly tighter?

I have been thinking about turning it upside down and somehow attaching a pen to it, to make a sort of drawing robot :-) But I had better sort out the problem with the end effector first.

 

Your ball joints have to be tight but still free moving. Be aware if arms are hitting something or if you move beyond the limit where the joints can go.

The upper arms, in your case they are lower, the arms attached to the servos, are they flexible? They should not be! The horizontal screws must be horizontal all the times.  If they are kept horizontal, their "partner" at the other end of the dual arms must be as well, horizontal and parallel.

Now, if all three screw pairs are horizontal, the end effector must be horizontal as well.

About the usage. Be aware that the delta robot design is optimal for fast movement in 3D. Less precise than their linear  counterparts but MUCH faster. The speed comes due to the fact that all the moving parts are passive, no need to move a bulky motor around. With greater speed comes , in this design at least, less precession. Attaching a pen to the end effector and make it draw on paper would not be the "right" job for this type of machine. It will only need to work in 2D and my experience with cheap hobby servos  are that they are not precise enough for anything but a jerky drawing. I'd say, give it a try and learn something, but don't be too disappointed if it doesn't work perfectly. (or better that that, prove me wrong..)

How about adding a magnet to the arm and use it to move chess pieces around on the chessboard. You will have to glue a nut on the head of the queen and the rest of her court.

I see, thanks. I like the chess idea, I might try that!

Would having a pair of long arms per servo smooth out the movement, or, would it just adjust the way the head moved (ie instead of pointing the center point of the head would it just move the whole head itself?)?

It would make it more stiff. In Purples current construction you can sorta twist the end effector, no mechanical structure is blocking that. That's why delta robots are usually made with double parallel "lower" arms. Lower being a relative term, in Purples current setup  they are actually on top.

Also with parallel arms you are guaranteed that the end effector is parallel with the base. which again makes everything more stiff.

I am planning to add another arm for each servo as soon as I've purchased some longer screws, so hopefully that will smooth out the movement a bit :-)

thought it might be useful to mention here. You look to be using a bolt straight through your black plastic end connectors. You will likely need to move to a full ball and socket type end, if/when you add the second long rods. Otherwise, 'I believe' (notice the single quotes, I am not at all a guy on top of mechanics) you may have problems moving things as the rod ends won't allow for free movement that will be needed.

Thanks for the advice, but actually I am already using ball and socket type ends - the nuts I am using are a funny shape though, so they do look like bolts from the pictures!

Looks good. Gonna be interesting to see where you take it. Don't complain about your materials, they are still way more high tech than the ones I used here http://letsmakerobots.com/node/27921 (my way of building is: break a stick, hot glue it and compensate for it's crappynes in software)