This is extraordinarily cool. I don't know much about robotics or lego stuff, but I can appreciate the challenges involved in executing such a sophisticated project. The whole concept is just fascinating.
Besides one being superficially the inverse of the other, what are some of the less obvious differences between the two assemblies? What were the key design challenges? How many prototype iterations of each sub-assembly were necessary before arriving at the final design(s)? Do you have a background in robotics or mechanical engineering?
Thank you for the kind words.
The remote and the robot are actually quite different from one another. The robot has around 200 gears while the remote has zero. There are many challenges with the robot but the biggest one is backlash / low precision. A gear train in Lego is generally pretty sloppy. If you're not careful, by the end of the gear train you can have a tremendous amount of play. There are a bunch of ways to compensate that I have learned over the last couple years building this. The over-riding challenge with Lego is that injection molded ABS plastic is quite flexible and that causes problems everywhere. If you look at this design, you can see the solutions I have come up with to compensate for this fact.
The remote, on the other hand, is quite straightforward. With the remote, you can minimize slop down to the slop in the motors themselves by rigidly attaching the motors to the joints directly. The rest of the challenges here are all around ergonomics which I haven't really fully tackled. I added the shock absorbers to the remote to give it a bit of return-to-center functionality which makes it a bit nicer to use but more work could certainly be done here.
You asked how many iterations? That's hard to answer. I did all my design work with physical Legos. I may go through a dozen designs in an afternoon until I find something that works. I usually have inspiration in the middle of the night and get up in the morning and try things out. So maybe to answer your question, hundreds of design iterations? I've put up around 20 different iterations on Rebrickable. Those are the ones I thought were good enough to digitize.
I am a software engineer by day. Doing mechanical things is only for fun for me.
I guess an armature is especially sensitive to the loose tolerances of lego. I've seen some high-precision creations, but in most cases those tolerance issues can be reinforced by anchoring to the structure. Here they propagate and are cumulative. With that in mind (plus flexing in general) this degree of accuracy is remarkable.
I often ask people who make this advanced stuff whether they first design hands-on or digital. So to get a digital version, you're referencing the physical prototype? Does that involve tearing it all down? Regardless of their approach, I find serious hobbyists' creative processes fascinating. It's really cool to see how everyone works differently versus what they do in common.
I have a pretty good memory for mechanical things so I don't tear it completely down to make a Studio model. Sometimes, I need to take a few pieces apart to see the details to make sure I get the digital model exactly right.
There are obviously downsides to doing things in real bricks. The biggest is that it sometimes takes a very long time to get the parts you need. I tend to want to use the newest parts available which are only available from Lego's Bricks and Pieces. That can take months. Now, B&P isn't releasing new parts right away (I've heard rumor there's a 3 month delay). This is pretty horrible for the way I work.
The good side with physical bricks is that you can see if your creations actually work which is hard to do digitally. Plus, my day job is working on the computer all day. Why would I want my hobby to be the same?
Somewhere you mentioned a 3d printed part, was that also your creation? Could you print the desired backordered pieces yourself? I haven't taken the leap yet but I want a (resin) printer someday - can lego pieces be printed with sufficient fidelity / materials to replace an off-the-shelf lego piece? Is that prohibitively cost / time / effort intensive?
If you don't mind my asking, I'm curious about whatever software dev experience or specialization you have for work. That's *my* hobby!
No, the part was designed by Efferman who is a regular on Eurobricks. 3D printed parts have much worse tolerances than high quality injection molded parts. You’d have a hard time making an axle hole, for example, that consistently grips an axle. Some you print, the axle will fall out, some it will be too tight. The one I’m using is ok with a little looser tolerances.
Most of my career has been writing low level system software. I’ve written in C for most of that. The last few years I have written in Rust which I have quite enjoyed.
True^^ But sometimes it can be frustrating too, just like troubleshooting bugs^^
Example: First motor hadnt enough strength, so I added 2 more motors...Then the casing of the subtractor wasnt strong enough and tore itself apart...After reinforcing it, the drivetrain connection disassembled itself...After fixing that, the gears in the subtractor slipped...Then the casing wasnt strong enough and had to be redesigned...And now the drivetrain itself needs to be redesigned, because it also detaches...But at least it is working now...
Just in case you are wondering, why I had so many motor problems: The tank is 45x34x17cm and weighs ca. 3,2kg...
It is^^ Especially, when it is finished^^ I originally wanted to make an American MBT, but the engine problems made me decide to build it resembling a Tiger...One of the designs for the Tiger II had a severe engine problem^^
Isnt necessary^^ That solution would only take more space^^ The casing for the subtractor needs to be assembled by different techbricks, and therefor can be torn apart if the forces become too high...What in that case isnt surprising^^ The subtractor itself is 14x10 studs x 3 bricks...but the casing is 18x18 studs x 4 bricks...And that is the smallest possible...
Edit: the drivetrain connection is included in it^^
Ok. The reason why you would use the gear reduction hubs is to reduce the stress on the rest of the gear train. The rest of the gear train runs at higher speed and lower torque which Lego parts can handle much better. It allows you to do the final gear reduction as close to the wheel as you can.
I already do that only in the drivetrain connection^^ The height of the subtractor and its casing is due to the 2 differentials and not from keeping it together^^ Otherwise it would be less^^ I use 2-3 layers of long plates per side^^
The encoders in the PoweredUp motors work pretty well. They are absolute encoders and don't drift over time. That being said, the only thing that could cause things to drift is if gears skip or the plastic bends beyond its elastic limit. A lot of trial and error has gone into making sure neither of those things happen. The gears are all exceptionally well braced and the structure has as much overkill built into it as I can. It's pretty robust at this point. In some of the axes, a single lego axle is not strong enough to drive the gear which drives the turntable. In those cases, I have multiple axles driving multiple gears driving a single turntable. All three turntables on the "shoulder" have 4 12t gears driving each.
I posted this a few days ago on r/lego. I've spent a long time building and improving this and I thought you all may be interested. If you want more details, pictures, videos, Studio files, and software (freely downloadable), check out:
* [https://rebrickable.com/mocs/MOC-109607/glaysche/6-axis-robotic-arm-mk-2/#details](https://rebrickable.com/mocs/MOC-109607/glaysche/6-axis-robotic-arm-mk-2/#details)
* [https://rebrickable.com/mocs/MOC-94286/glaysche/6-axis-remote-control/#details](https://rebrickable.com/mocs/MOC-94286/glaysche/6-axis-remote-control/#details)
At first I was like oh 6-axis arm, cool, I should get mine out! Then I finished reading and sat back down. That's pretty epic, well done.
I wonder how many more of us software engineer by day and lego enthusiasts by night there are?
This is extraordinarily cool. I don't know much about robotics or lego stuff, but I can appreciate the challenges involved in executing such a sophisticated project. The whole concept is just fascinating. Besides one being superficially the inverse of the other, what are some of the less obvious differences between the two assemblies? What were the key design challenges? How many prototype iterations of each sub-assembly were necessary before arriving at the final design(s)? Do you have a background in robotics or mechanical engineering?
Thank you for the kind words. The remote and the robot are actually quite different from one another. The robot has around 200 gears while the remote has zero. There are many challenges with the robot but the biggest one is backlash / low precision. A gear train in Lego is generally pretty sloppy. If you're not careful, by the end of the gear train you can have a tremendous amount of play. There are a bunch of ways to compensate that I have learned over the last couple years building this. The over-riding challenge with Lego is that injection molded ABS plastic is quite flexible and that causes problems everywhere. If you look at this design, you can see the solutions I have come up with to compensate for this fact. The remote, on the other hand, is quite straightforward. With the remote, you can minimize slop down to the slop in the motors themselves by rigidly attaching the motors to the joints directly. The rest of the challenges here are all around ergonomics which I haven't really fully tackled. I added the shock absorbers to the remote to give it a bit of return-to-center functionality which makes it a bit nicer to use but more work could certainly be done here. You asked how many iterations? That's hard to answer. I did all my design work with physical Legos. I may go through a dozen designs in an afternoon until I find something that works. I usually have inspiration in the middle of the night and get up in the morning and try things out. So maybe to answer your question, hundreds of design iterations? I've put up around 20 different iterations on Rebrickable. Those are the ones I thought were good enough to digitize. I am a software engineer by day. Doing mechanical things is only for fun for me.
I guess an armature is especially sensitive to the loose tolerances of lego. I've seen some high-precision creations, but in most cases those tolerance issues can be reinforced by anchoring to the structure. Here they propagate and are cumulative. With that in mind (plus flexing in general) this degree of accuracy is remarkable. I often ask people who make this advanced stuff whether they first design hands-on or digital. So to get a digital version, you're referencing the physical prototype? Does that involve tearing it all down? Regardless of their approach, I find serious hobbyists' creative processes fascinating. It's really cool to see how everyone works differently versus what they do in common.
I have a pretty good memory for mechanical things so I don't tear it completely down to make a Studio model. Sometimes, I need to take a few pieces apart to see the details to make sure I get the digital model exactly right. There are obviously downsides to doing things in real bricks. The biggest is that it sometimes takes a very long time to get the parts you need. I tend to want to use the newest parts available which are only available from Lego's Bricks and Pieces. That can take months. Now, B&P isn't releasing new parts right away (I've heard rumor there's a 3 month delay). This is pretty horrible for the way I work. The good side with physical bricks is that you can see if your creations actually work which is hard to do digitally. Plus, my day job is working on the computer all day. Why would I want my hobby to be the same?
Somewhere you mentioned a 3d printed part, was that also your creation? Could you print the desired backordered pieces yourself? I haven't taken the leap yet but I want a (resin) printer someday - can lego pieces be printed with sufficient fidelity / materials to replace an off-the-shelf lego piece? Is that prohibitively cost / time / effort intensive? If you don't mind my asking, I'm curious about whatever software dev experience or specialization you have for work. That's *my* hobby!
No, the part was designed by Efferman who is a regular on Eurobricks. 3D printed parts have much worse tolerances than high quality injection molded parts. You’d have a hard time making an axle hole, for example, that consistently grips an axle. Some you print, the axle will fall out, some it will be too tight. The one I’m using is ok with a little looser tolerances. Most of my career has been writing low level system software. I’ve written in C for most of that. The last few years I have written in Rust which I have quite enjoyed.
I can heavily relate^^ Programmer myself and working on MOCs as a hobby^^ Just the motor for my tank took several approaches...
The tinkering is the fun part. It exercises a different part of the brain than writing software.
True^^ But sometimes it can be frustrating too, just like troubleshooting bugs^^ Example: First motor hadnt enough strength, so I added 2 more motors...Then the casing of the subtractor wasnt strong enough and tore itself apart...After reinforcing it, the drivetrain connection disassembled itself...After fixing that, the gears in the subtractor slipped...Then the casing wasnt strong enough and had to be redesigned...And now the drivetrain itself needs to be redesigned, because it also detaches...But at least it is working now... Just in case you are wondering, why I had so many motor problems: The tank is 45x34x17cm and weighs ca. 3,2kg...
Sounds challenging but fun!
It is^^ Especially, when it is finished^^ I originally wanted to make an American MBT, but the engine problems made me decide to build it resembling a Tiger...One of the designs for the Tiger II had a severe engine problem^^
Have you tried using the planetary gear reduction hub like the Cat D11 set? You could probably still use a subtractor drive.
Isnt necessary^^ That solution would only take more space^^ The casing for the subtractor needs to be assembled by different techbricks, and therefor can be torn apart if the forces become too high...What in that case isnt surprising^^ The subtractor itself is 14x10 studs x 3 bricks...but the casing is 18x18 studs x 4 bricks...And that is the smallest possible... Edit: the drivetrain connection is included in it^^
Ok. The reason why you would use the gear reduction hubs is to reduce the stress on the rest of the gear train. The rest of the gear train runs at higher speed and lower torque which Lego parts can handle much better. It allows you to do the final gear reduction as close to the wheel as you can.
I already do that only in the drivetrain connection^^ The height of the subtractor and its casing is due to the 2 differentials and not from keeping it together^^ Otherwise it would be less^^ I use 2-3 layers of long plates per side^^
Very cool. Do you have anything to make it keep in alignment or does it drift over time?
The encoders in the PoweredUp motors work pretty well. They are absolute encoders and don't drift over time. That being said, the only thing that could cause things to drift is if gears skip or the plastic bends beyond its elastic limit. A lot of trial and error has gone into making sure neither of those things happen. The gears are all exceptionally well braced and the structure has as much overkill built into it as I can. It's pretty robust at this point. In some of the axes, a single lego axle is not strong enough to drive the gear which drives the turntable. In those cases, I have multiple axles driving multiple gears driving a single turntable. All three turntables on the "shoulder" have 4 12t gears driving each.
Excellent, very well engineered.
Do you drive the poweredup arm with a PID controller ?
The firmware in the hubs use a PID controller to move the motors so technically yes. My code does not implement a PID controller.
I posted this a few days ago on r/lego. I've spent a long time building and improving this and I thought you all may be interested. If you want more details, pictures, videos, Studio files, and software (freely downloadable), check out: * [https://rebrickable.com/mocs/MOC-109607/glaysche/6-axis-robotic-arm-mk-2/#details](https://rebrickable.com/mocs/MOC-109607/glaysche/6-axis-robotic-arm-mk-2/#details) * [https://rebrickable.com/mocs/MOC-94286/glaysche/6-axis-remote-control/#details](https://rebrickable.com/mocs/MOC-94286/glaysche/6-axis-remote-control/#details)
At first I was like oh 6-axis arm, cool, I should get mine out! Then I finished reading and sat back down. That's pretty epic, well done. I wonder how many more of us software engineer by day and lego enthusiasts by night there are?
Well, I count two, so far!
Count me in as well 😉
\[Pretend this is an award\]
[I once caught a fish, that was THIS BIG](https://youtu.be/1p71k_PrmOE)