[MINDSTORMS] Delta Robot - Updated

[thebricky]

Hi Friends,

Here is my Delta Robot. I will improve this model a little more and turn it upside down. My intention is to use it as a basic plotter, that can plott something like square, circle or triangle.

I wanted to add photos  but couldn't it. I guess, I don't have enough space. Before that i could only upload one photo.

 

[whitepen]

That looks cool!

[Mr Jos]

You can upload your photos to Flickr, and then post them here.

[Jurss]

Interesting thing. Really needs to be put to some job. 

[gyenesvi]

That's a cool mechanism, is something like that used in real life? Does it keep the platform horizontal, or just approximately? What's the function of the rubber bands? Are they for stability?

[Mr Jos]

7 hours ago, gyenesvi said:

That's a cool mechanism, is something like that used in real life? Does it keep the platform horizontal, or just approximately? What's the function of the rubber bands? Are they for stability?

Normally they are used upside down, then they can be used to pick items from a moving conveyor belt, and for example place them in cardboard boxes. Or just for turning pieces in the correct direction. In real life they move really fast.

 

 

Edited April 10, 2022 by Mr Jos

[Heppu]

Parallel delta robots are indeed cool! Especially the kinematic equations are real funky compared to conventional serial arms.

I made my own a few years back with a suction cup attatchment. Seeing you use tow balls in the joints makes me want to revisit that design and redo the joints with proper geometry.

[thebricky]

12 hours ago, Mr Jos said:

Normally they are used upside down, then they can be used to pick items from a moving conveyor belt, and for example place them in cardboard boxes. Or just for turning pieces in the correct direction. In real life they move really fast.

 

 

 

Thanks, you explained well. They move really fast in real life, it is not possible to reach these speeds with lego motors. I think this tool can something print. To program in python, I'll have to deal with some kinematics equations. I'll try.

19 hours ago, gyenesvi said:

That's a cool mechanism, is something like that used in real life? Does it keep the platform horizontal, or just approximately? What's the function of the rubber bands? Are they for stability?

Yes, rubber makes the arms more stable. I used it for the arms to resist of motor movement. There were sudden movements without the rubber that I didn't want.

[thebricky]

12 hours ago, Heppu said:

Parallel delta robots are indeed cool! Especially the kinematic equations are real funky compared to conventional serial arms.

I made my own a few years back with a suction cup attatchment. Seeing you use tow balls in the joints makes me want to revisit that design and redo the joints with proper geometry.

I have looked at your model, you did a really great job. It's also great that it removes things and puts them somewhere else. Your model is bigger than mine, tow ball joints may not be enough to hold the whole structure together.

I want to ask something. I have seen you use a vacuum to lift  pieces?  Which parts did you use to produce vacuum.

[Heppu]

18 hours ago, thebricky said:

I want to ask something. I have seen you use a vacuum to lift  pieces?  Which parts did you use to produce vacuum.

The vacuum itself in my robot is created by actuating regular large Lego pneumatic cylinder. The suction cup is not Lego but an industrial vacuum suction cup taped to the end of a Lego pneumatic hose.

For kinematics you might find this github page useful: delta kinematics

[thebricky]

Hi Friends, 

Some improvements on my Delta Robot.

I have turned this model upside down with the help of three main columns and added a pneumatic cylinder. The air hose attached to  cylinder holds the part with the vacuum produced by the cylinder and the arms can take beams from one place and put it in another place.

Issues:

The biggest problem I've experienced is moving the motors in opposite directions simultaneously. To give an example, while I rotate Motor-A 360 degrees clockwise, I want to simultaneously rotate Motor-B 180 degrees clockwise and then 180 degrees counterclockwise. They must start and stop at the same time. I still can't solve this problem

 

 

 

 

 

 

 

 

 

 

 

 

 

[Heppu]

I like where this is going so far! Super solid looking base.

Using so many gears will intoduce play into the drivetrain. You'll lose some accuracy in getting exact end effector position if that is a concern to you. Also, with a larger suction surface your setup could easily lift much heavier pieces. 

8 hours ago, thebricky said:

Issues:

The biggest problem I've experienced is moving the motors in opposite directions simultaneously. To give an example, while I rotate Motor-A 360 degrees clockwise, I want to simultaneously rotate Motor-B 180 degrees clockwise and then 180 degrees counterclockwise. They must start and stop at the same time. I still can't solve this problem

Is this an motor/hub problem or a code problem? I assume it's code since you can move all 3 motors simutaniously no problem. Then I guess its a matter of just coding a simple trajectory generator. Do you have IK and FK equations in order? If so, for each movement between 2 points, scale each motors speed by: (angle to travel / biggest angle to travel). This way each motor will take the same time to rotate their desired angle. For longer movements instead of going from A to B, my trajectery generator generates enough "in-between points" such that for each movement between 2 points, each motor has to rotate in only 1 direction.

Hope that helps.

[Mr Jos]

Great illustration movie and machine.

About the gears I also wanted to remark that you now use 8T 4 times in a row followed by a 40T. This gives more backlash than using 8T-24T-40T. You should be able to easily swap out those 3 middle 8T by a single 24T. It will remain at the same 5:1 gearing and rotation direction.

For the multiple direction movements followed after another, you will need to program some Kinematics indeed. Make it calculate the desired speed for every motor with a certain amount of angle to move, to end at the same time. To get this moving forwards and backwards with a motor in 1 move (to go in a line or something) you will need to have a positioning system (XYZ) and use Forward Kinematics (FK) to calculate the current position. And then Inverse Kinematics (IK) to calculate the next coördinates for each motor. Then constantly blast the motor angle + speed to each motor. This is what happens in my 6axis robot aswell, to have it move straight lines. It will need to lean backwards, and return forward, with me only giving 1 set of XYZ coördinates.

It will not be super simple to program, but as it's only 3 axis it should be ok to do with some thinking work.