T-Bot (3axis gantry)

[Mr Jos]

The instructions for my fast moving gantry robot (designed after a T-Bot) are now finished. It uses a surprisingly low amount of items, nearly half of them are chain links.

https://rebrickable.com/mocs/MOC-80519/Mr_Jos/t-bot-gantry-3-axis-superfast-robot/#parts

The end-effector can be changed with other equipment as long as it is not to heavy and to much out of center.

 

The idea about mounting all motors on the fixed frame was nice, but hard to get it working for the last movement as it goes through so many axles.

 

Up to the next project.

Edited June 30, 2021 by Mr Jos

[ord]

Simple, yet effective.

One small improvement I can suggest is to keep the chains perpendicular. Currently they are at an angle that will change with gantry position, which will reduce accuracy. At least I think that's how it works... 

[Mr Jos]

14 hours ago, ord said:

Simple, yet effective.

One small improvement I can suggest is to keep the chains perpendicular. Currently they are at an angle that will change with gantry position, which will reduce accuracy. At least I think that's how it works... 

True, but, it would make the moving part much bigger as the 16T gears have to go wider. Or the 40T gear has to be a 16T aswell, making it 60% slower. Gearing up on the 16T axle would be possible, but also less accurate due to play in the gears (now it's direct drive). The chains do allow some stretching, and it's pretty accurate in both directions. You can see this when moving up/down without sideways, the carrier stays in position.

Now trying to make a H-bot with perpendicular chains, but for now failing, as it tears the carrier in pieces, and Lego is not good for precision guidings (pulling on 1 side and expecting the other side will follow).

[ord]

Fair enough, I guess there are always some trade-offs and sometimes it's best just to keep it simple. 

I feel your pain with trying to make Lego precise. I'm currently building a simple XY plotter and the large links for the main rail are even harder to work with than the small links (imo). 

[Glaysche]

@Mr Jos This is a very clever robot design.  I'm impressed!  I made my own interpretation of it:

 

I made significant changes.  I don't have an EV3 set so I made mine with PoweredUp components.  I used medium Spike Prime motors and a standard control+ hub.  There are no extension cables for PoweredUp motors so I needed to put the hub at the top where the wires will reach.  I tried to make the external frame as rigid as possible using lots of frames, panels (in the top back) and triangles.  I made the horizontal sliding piece out of 7x11 frames instead of 5x7 frames.  This has the downside of reducing the horizontal range of the robot but it made the mechanics simpler and allowed me to use 4 horizontal 32L axles for better stability.  This also allows me to keep the chains mostly parallel  / at right angles which seems nice. Here's a close up of the horizontal slider:

If you look very close behind and to the right of the bottom 28t gear, there is the red 8t sliding gear that transfers power down the right hand vertical 32L axle.  That power is transferred from the red 8t gear you can barely see behind the 24t gear on the right.  The red 8t gear in the middle is jammed against a 2L beam to keep it stationary.  This pairs with a DBG 8t gear jammed against a 1L beam in the bottom module, closeup in the next picture.

The right axle drives the gear rack in and out.  The left axle attempts to keep the bottom module from rotating.  This bottom module is as compact and symmetrical as I could make it.  This was a super fun build and something I hadn't thought of before seeing your post.

[Mr Jos]

Very well done! It's a fun little thing to make and play with, I'm curious to see a video of yours working. Your bigger frames made it much easier to fit in the gears to get the rack moving at the end, but I don't have any of them (yet). Problem with a 5x7 is that nearly any gear inside will touch the edges of the frame, that was the hardest part to design for mine. All other things you did good as well like I did, 8T gear for blocking rotation etc. I did however like the 40T gear on the motors for more speed. 

[Glaysche]

I can probably make a video tomorrow. Right now, the controls are basic through the PoweredUp app with the math thrown in so I can have one vertical and one horizontal slider for x and y that just control the speed.  The in and out axis has a slider for speed as well which is problematic when you run it into the stops.  I’m sure I can come up with something better with more experimentation with the PoweredUp coding blocks.

[Glaysche]

25 minutes ago, Mr Jos said:

Your bigger frames made it much easier to fit in the gears to get the rack moving at the end, but I don't have any of them (yet). Problem with a 5x7 is that nearly any gear inside will touch the edges of the frame,

I have found all the frame sizes incredibly useful for robotic arms.  I ended up buying hundreds of them from Bricks and Pieces in all available colors and sizes. My 6 axis arm uses all sizes extensively. I think my new favorite piece is the 15L beam with alternating holes.  The 11L version should be available in August and hopefully they will produce all the lengths over time.

[Glaysche]

I played around quite a bit with the PoweredUp programming and ended up with this as a basic control:

The top bit does initialization and calibration.  The bottom bit does the controls.

 

Here's a quick video I made.  You even get to see me run the robot into the side.  It still seems pretty quick even with the 24t drive gears.  The rack driving in and out also seems pretty quick.  There seems to be plenty of torque for that axis so I could probably gear it up more but it was tough to fit more gears in.  (Embedding videos doesn't seem to work from Flickr): https://www.flickr.com/photos/188456966@N07/51323492017/in/dateposted-public/

 

One additional note: I made it a bit more robust with better axle support for the horizontal shuttle:

Before this change, there was an 8t gear on a frictionless axle pin that would sometimes slide out of place.  That's now supported from both sides and no longer has the problem.  I also used the red 16t clutch gears with 3L frictionless pins.  This more securely holds the frames together. It seems pretty robust now.

[Mr Jos]

Looking good. The clicking noice I hear in your video, I know where it's from. I've ran multiple times into it, and still don't know why, but these red 16T gears and chains don't like eachother like a normal 16T gear with chains. The clutch gear one makes clicking noices always, that's why I changed mine back to the grey ones.

When jamming it into the side, these axles do like to bend a bit haha, I've had it here multiple times I jammed it to much and chains were flying everywhere through the air. I still think a part of about 12 links is hiding somewhere, but I didn't find it back after picking up pieces of chain all over the floor.

[Glaysche]

Yeah, I think you're right.  It does at least sound better with the gray gears.  I changed mine back, too.  I also added some of my signature lime green accents.  I'd probably call this "done" for now... until I think of something else to change.

 

[Glaysche]

I made a Studio model for it and made it available for free on Rebrickable:

https://rebrickable.com/mocs/MOC-85202/glaysche/gantry-robot-3-degrees-of-freedom/

I made some minor changes from the version pictured above. The holder for the top pulley for the chain is improved.  I made a few minor structural improvements. Here's are some renders:

 

 

[Mr Jos]

There now is a new end-effector for my T-Bot, the gripper is able to take 1,25Long pins up to 3Long pins. The system sorts them by length and color.

Thinking about how I can integrate it in my big setup.

[Jonas]

I like the new type of gripper. It seems to be well suited for small elements.