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Hah this thread is perfect. I just finished building my new four axis robot arm design. It’s all open source. Three months ago I started playing with a new plan

Hah this thread is perfect. I just finished building my new four axis robot arm design. It’s all open source. Three months ago I started playing with a new planetary gearbox concept, where the first stage is in the middle with second stages on both sides. The first sun is driven by a shaft that goes through a hole in the second stage sun. The result is a very balanced joint design with parallel outputs. A good configuration for weak materials like plastic. And then the gearboxes and the frame are all integrated together, so this is not something where you assemble a gearbox and bolt it to the frame. The gearbox members and the frame members are unified. I’m very happy with it so far! Video here: https://twitter.com/tlalexander/status/1455320442642714625?s=21 https://twitter.com/tlalexander/status/1455320442642714625?s... It’s open source, CC0 licensed. Please fork the design files here! https://cad.onshape.com/documents/d663661f8c0c34e7a29bbfa6/w/29dc0f544ac7c3325eeb2b5a/e/d7899f39770190df953bd7fd https://cad.onshape.com/documents/d663661f8c0c34e7a29bbfa6/w... EDIT: you may prefer to watch the project and wait to fork it until I have fleshed out a few more things. In that case feel free to star this git repo and I will update it as I make progress. https://github.com/tlalexander/brushless_robot_arm/ https://github.com/tlalexander/brushless_robot_arm/

nielsole 5y ago
Wow awesome. This is one of the most impressive arms I've seen. How much did it cost you to build? About how many newtons can you excert when fully extended? / What weight can you lift? What is your experience with backlash? Definitely considering forking
- TaylorAlexander 5y ago
  Thank you! I had all the parts lying around and I’ve not put together a full BOM to calculate costs. But it’s two odrives and four brushless motors plus maybe $100-150 in bearings from AliExpress, then some screws and a couple kilos of PETG. So maybe $850 if you built it from scratch? I haven’t done testing of its capabilities yet as I just got it working today. Also I am running at 24v but I want to try 48v when I can upgrade my odrive controllers to the 56v version. Not sure about backlash either except joint 3 has bad backlash not due to gearing but from a fixable issue with the way the output connects to the frame. But I am very happy with this design! I think it’s pretty promising.
  - TaylorAlexander 5y ago
    Also it should be noted that with my $850 estimate that is $400 worth of Odrives. For years I have longed for good brushless drives for under $100 per channel and there are some newer ones out there. But basically brushless drivers are a major chunk of the price which I think could be reduced with cheaper custom drivers.
    - quanto 5y ago
      For my previous work years ago, we did custom brushless motor drivers including basic control theory implementations. I was under the impression that the driver designs were fairly standardized/commoditized. Could you explain more on your search of suitable drivers and on why you didn't build your own drivers? Why are these drivers so high in price?
      - TaylorAlexander 5y ago
        I have designed brushless motor drivers in the past. But at the time I was fairly busy and I discovered the VESC 4.12 which is pretty good, but the creator moved to a new design that costs way more and the user community fragmented. The 4.12 designs are still for sale and pretty affordable, but I switched to Odrive due to the very active development community. It seems the price of Odrive has gone up though. I mostly use them at work so I don’t care, but this arm is a personal project and I used a couple odrives I had previously purchased. There’s other new drivers out there that I haven’t tried. And I could take a crack at a new driver again. But really I want someone in China to produce a good design and sell them on AliExpress. Something with open source design files and code, able to handle 2kw power, able to use one or two encoders, etc. You can get a VESC on AliExpress for $75 or an Odrive clone for $95 with two channels. But I guess I feel bad buying an Odrive clone because the newer hardware isn’t open source so they are unauthorized clones, and I know the Odrive team works really hard. I would feel bad showing off my work with Odrive clones. There’s other options out there though and I may want to try them. It’s been a while since I’ve needed new drivers at home but with this project I sure do!
- romanzubenko 5y ago
  In the beginning of the pandemic I've attempted to build a 6 axis arm from this project https://www.anninrobotics.com/ https://www.anninrobotics.com/ Overall great documentation, and the author also sells hardware kits so you don't need to source all gears by yourself.
  - TaylorAlexander 5y ago
    Fun! In my case all the gears are 3D printed so there’s no sourcing issues. Tho those designs are more finished than mine!
fsckboy 5y ago
I count three axes, what am I missing? (considering the "stick" at the top "a finger" and moving down, I see the wrist rotation, the elbow rotation, and a rotation at the shoulder down on the desk)
- TaylorAlexander 5y ago
  So in the video you first see a section of movement using the second and fourth axes. Then after that the arm goes back to zero (sticking straight up) and you see the midsection rotate back and forth without the end section rotating. That’s the other two axes. There are also closer photos here: https://twitter.com/tlalexander/status/1455100498428588036?s=21 https://twitter.com/tlalexander/status/1455100498428588036?s...
  - fsckboy 5y ago
    ah, i see, thx

nielsole 5y ago

Wow awesome. This is one of the most impressive arms I've seen. How much did it cost you to build? About how many newtons can you excert when fully extended? / What weight can you lift? What is your experience with backlash? Definitely considering forking

TaylorAlexander 5y ago
Thank you! I had all the parts lying around and I’ve not put together a full BOM to calculate costs. But it’s two odrives and four brushless motors plus maybe $100-150 in bearings from AliExpress, then some screws and a couple kilos of PETG. So maybe $850 if you built it from scratch? I haven’t done testing of its capabilities yet as I just got it working today. Also I am running at 24v but I want to try 48v when I can upgrade my odrive controllers to the 56v version. Not sure about backlash either except joint 3 has bad backlash not due to gearing but from a fixable issue with the way the output connects to the frame. But I am very happy with this design! I think it’s pretty promising.
- TaylorAlexander 5y ago
  Also it should be noted that with my $850 estimate that is $400 worth of Odrives. For years I have longed for good brushless drives for under $100 per channel and there are some newer ones out there. But basically brushless drivers are a major chunk of the price which I think could be reduced with cheaper custom drivers.
  - quanto 5y ago
    For my previous work years ago, we did custom brushless motor drivers including basic control theory implementations. I was under the impression that the driver designs were fairly standardized/commoditized. Could you explain more on your search of suitable drivers and on why you didn't build your own drivers? Why are these drivers so high in price?
    - TaylorAlexander 5y ago
      I have designed brushless motor drivers in the past. But at the time I was fairly busy and I discovered the VESC 4.12 which is pretty good, but the creator moved to a new design that costs way more and the user community fragmented. The 4.12 designs are still for sale and pretty affordable, but I switched to Odrive due to the very active development community. It seems the price of Odrive has gone up though. I mostly use them at work so I don’t care, but this arm is a personal project and I used a couple odrives I had previously purchased. There’s other new drivers out there that I haven’t tried. And I could take a crack at a new driver again. But really I want someone in China to produce a good design and sell them on AliExpress. Something with open source design files and code, able to handle 2kw power, able to use one or two encoders, etc. You can get a VESC on AliExpress for $75 or an Odrive clone for $95 with two channels. But I guess I feel bad buying an Odrive clone because the newer hardware isn’t open source so they are unauthorized clones, and I know the Odrive team works really hard. I would feel bad showing off my work with Odrive clones. There’s other options out there though and I may want to try them. It’s been a while since I’ve needed new drivers at home but with this project I sure do!
romanzubenko 5y ago
In the beginning of the pandemic I've attempted to build a 6 axis arm from this project https://www.anninrobotics.com/ https://www.anninrobotics.com/ Overall great documentation, and the author also sells hardware kits so you don't need to source all gears by yourself.
- TaylorAlexander 5y ago
  Fun! In my case all the gears are 3D printed so there’s no sourcing issues. Tho those designs are more finished than mine!

fsckboy 5y ago

I count three axes, what am I missing? (considering the "stick" at the top "a finger" and moving down, I see the wrist rotation, the elbow rotation, and a rotation at the shoulder down on the desk)

TaylorAlexander 5y ago
So in the video you first see a section of movement using the second and fourth axes. Then after that the arm goes back to zero (sticking straight up) and you see the midsection rotate back and forth without the end section rotating. That’s the other two axes. There are also closer photos here: https://twitter.com/tlalexander/status/1455100498428588036?s=21 https://twitter.com/tlalexander/status/1455100498428588036?s...
- fsckboy 5y ago
  ah, i see, thx