5 ms·

Interesting project. I wonder how the rigidity holds up over time. Working at a robotics company, the mechanical engineers had to overcome quite some challenge

Interesting project. I wonder how the rigidity holds up over time. Working at a robotics company, the mechanical engineers had to overcome quite some challenges to find a compromise between, precision, speed and repeatability. And that was with a metal frame.

sgnelson 3y ago
I imagine a lot of that will have to do with the 3d printed material used. If you're talking typical FDM style PLA, ABS, the creep on these can be pretty terrible. If you're talking something like carbon fiber reinforced nylon, it's probably a bit better. If you move to something like Markforged's fiber-strand reinforcement it'd get even better. And then there are the SLA/SLS solutions, like Formlabs "rigid" material, which I think would be a very interesting material to try for this. I think at the end of the day, you need to keep in mind this is an educational robot, not an industrial robot. If it can maintain 0.050" of repeatability, that would probably be good enough for a lot of use cases (but of course, that depends on your use case.)
krasin 3y ago
My biggest concern is that they use screws over plastic as fasteners: https://github.com/PCrnjak/PAROL6-Desktop-robot-arm/blob/main/Building%20instructions.pdf https://github.com/PCrnjak/PAROL6-Desktop-robot-arm/blob/mai... Quote from the manual: > Screws are in this example M3 screws and holes are undersized to 2.7-2.8mm that means that when we screw in the screws we are tapping holes in 3D printed parts. > There are multiple benefits to this: > ● Connection is strongest compared to tapping holes with a tap or using brass inserts > ● It is simple and fast > ● No need to prepare the hole, it can be printed undersized > Cons are that you can’t disassemble it a lot of times. In case you feel screws slipping in the hole. Put some super glue in the hole and wait for it to cure. After that re tap the hole.
- invalidator 3y ago
  I've used this technique on several of my projects. The formed threads are strong and reliable. It cuts down assembly steps and BOM. The tight fit means the screws won't back out (like locktite or nylocks). The only downside is they can only be reassembled a few times before they start getting loose, at which point you can either add material (superglue), or just reprint the part. If you have something you want to reassemble frequently, use inserts. If you're putting it together once and intend to use it that way for a long time, threadforming works fine.
  - krasin 3y ago
    > I've used this technique on several of my projects. Did they have any moving parts? Did they experience continuous vibrations and frequent mechanical shocks? For DIY robot arms, fasteners are very often the issue #1, if arms operated more than just for demo purposes.
    - iancmceachern 3y ago
      Just print it and find out. If there is a problem put in heat set threaded inserts. I don't think it'll be a problem though
      - krasin 3y ago
        > If there is a problem put in heat set threaded inserts You would be surprised how many screws will go lose after a a thousand of hours of operation, even in this case.
        iancmceachern 3y ago
        I'm a mechanical engineer, product designer and technical leader that has designed many products, some of which have been implanted in people and are in the Smithsonian, etc. I know screws can come out, that's why they make loctite. What I'm saying to you is to make sure something is an actual problem before saying it is. In this case, the fact that the screws are used as self tapping, the screws themselves create the threads, likely combats this. Like a nylock nut. This isn't what I would do for say, a surgical robotics system, but that's not what this is. If given the choice of having the design as is, or making it more expensive, more difficult to assemble, and less accessible. I'd choose it as it is. There are always tradeoffs. I believe the designer made the right ones here. Before saying they didn't, maybe build one.
        krasin 3y ago
        This is a case, where appeal to authority actually makes sense. Thanks, I accept your point.
- iancmceachern 3y ago
  If you like, you can always slightly modify the parts in CAD before printing or even after printing with a drill bit and then put one of those heat set threaded inserts in with a soldering iron. Not a big deal. Do what you want
PCrnjak 3y ago
I have been abusing it for 8 months straight and too be honest I was trying to break it. Software has a lot of safety features to not hit joint limits, speed limits, ESTOP is operational... Only problem is that robot has no brakes so during power loss it falls. I thought it will be fatal for robot to fall like that but it survived it multiple times. Only parts that brake are esthetics and covers. Also i thought that repetability will suffer under such abuse but it stayed the same. The clip on youtube is after 6 months of a lot of use.
- fudged71 3y ago
  Is a possible solution to the arm “falling” to mount it upside down?
  - PCrnjak 3y ago
    Brakes will be added in later design
- arlcode 3y ago
  Sounds very interesting. Maybe this is a project where I can put the random collection of components to use which lying around in my basement. Not exactly to spec but that's the spirit I think.

sgnelson 3y ago

I imagine a lot of that will have to do with the 3d printed material used. If you're talking typical FDM style PLA, ABS, the creep on these can be pretty terrible. If you're talking something like carbon fiber reinforced nylon, it's probably a bit better. If you move to something like Markforged's fiber-strand reinforcement it'd get even better. And then there are the SLA/SLS solutions, like Formlabs "rigid" material, which I think would be a very interesting material to try for this. I think at the end of the day, you need to keep in mind this is an educational robot, not an industrial robot. If it can maintain 0.050" of repeatability, that would probably be good enough for a lot of use cases (but of course, that depends on your use case.)

krasin 3y ago

My biggest concern is that they use screws over plastic as fasteners: https://github.com/PCrnjak/PAROL6-Desktop-robot-arm/blob/main/Building%20instructions.pdf https://github.com/PCrnjak/PAROL6-Desktop-robot-arm/blob/mai... Quote from the manual: > Screws are in this example M3 screws and holes are undersized to 2.7-2.8mm that means that when we screw in the screws we are tapping holes in 3D printed parts. > There are multiple benefits to this: > ● Connection is strongest compared to tapping holes with a tap or using brass inserts > ● It is simple and fast > ● No need to prepare the hole, it can be printed undersized > Cons are that you can’t disassemble it a lot of times. In case you feel screws slipping in the hole. Put some super glue in the hole and wait for it to cure. After that re tap the hole.

invalidator 3y ago
I've used this technique on several of my projects. The formed threads are strong and reliable. It cuts down assembly steps and BOM. The tight fit means the screws won't back out (like locktite or nylocks). The only downside is they can only be reassembled a few times before they start getting loose, at which point you can either add material (superglue), or just reprint the part. If you have something you want to reassemble frequently, use inserts. If you're putting it together once and intend to use it that way for a long time, threadforming works fine.
- krasin 3y ago
  > I've used this technique on several of my projects. Did they have any moving parts? Did they experience continuous vibrations and frequent mechanical shocks? For DIY robot arms, fasteners are very often the issue #1, if arms operated more than just for demo purposes.
  - iancmceachern 3y ago
    Just print it and find out. If there is a problem put in heat set threaded inserts. I don't think it'll be a problem though
    - krasin 3y ago
      > If there is a problem put in heat set threaded inserts You would be surprised how many screws will go lose after a a thousand of hours of operation, even in this case.
      - iancmceachern 3y ago
        I'm a mechanical engineer, product designer and technical leader that has designed many products, some of which have been implanted in people and are in the Smithsonian, etc. I know screws can come out, that's why they make loctite. What I'm saying to you is to make sure something is an actual problem before saying it is. In this case, the fact that the screws are used as self tapping, the screws themselves create the threads, likely combats this. Like a nylock nut. This isn't what I would do for say, a surgical robotics system, but that's not what this is. If given the choice of having the design as is, or making it more expensive, more difficult to assemble, and less accessible. I'd choose it as it is. There are always tradeoffs. I believe the designer made the right ones here. Before saying they didn't, maybe build one.
        krasin 3y ago
        This is a case, where appeal to authority actually makes sense. Thanks, I accept your point.
iancmceachern 3y ago
If you like, you can always slightly modify the parts in CAD before printing or even after printing with a drill bit and then put one of those heat set threaded inserts in with a soldering iron. Not a big deal. Do what you want

PCrnjak 3y ago

I have been abusing it for 8 months straight and too be honest I was trying to break it. Software has a lot of safety features to not hit joint limits, speed limits, ESTOP is operational... Only problem is that robot has no brakes so during power loss it falls. I thought it will be fatal for robot to fall like that but it survived it multiple times. Only parts that brake are esthetics and covers. Also i thought that repetability will suffer under such abuse but it stayed the same. The clip on youtube is after 6 months of a lot of use.

fudged71 3y ago
Is a possible solution to the arm “falling” to mount it upside down?
- PCrnjak 3y ago
  Brakes will be added in later design
arlcode 3y ago
Sounds very interesting. Maybe this is a project where I can put the random collection of components to use which lying around in my basement. Not exactly to spec but that's the spirit I think.