Guidelines to design 3D printable parts for Robotis Dynamixel

Ok so you are an awesome guy and you want to design new mechanicals parts for a Poppy creature ?
Here some guidelines to help you start your own project and make your contributions easier.

CAD Software

You can of course use any CAD software you like. If you do not have yet a preferred one, we have few advises:

  • Solidworks because it has been used for the Poppy Humanoid, you have a lot of mechanical parts already done and there is a Robotis Library you can use: https://github.com/poppy-project/Robotis-library
  • OpenSCAD because there is a complete set of tool made by @jgrizou to quickly design any kind of robot:
  • OnShape, because it is as powerful as Solidworks but with a better interface, it works on any platform and it is free. AIt is now my main CAD tool to make my work accessible to everyone.

If you want even more choice, you can explore the review the community is doing:

3D printing Tolerances

3D printing is amazing, we are all agree for that (even the grumpy cat) but the actual precision is still quite low and require adjusted tolerances if you do not want to end up cleaning each interface of your design with a file.

Here I will tell you the dimensions we are using to ensure an optimal mounting given the 3D printing quality constraints.


Dynamixel XL320

For 20 bucks, the Dynamixel XL320 is a quite good actuator and allows for dynamic behavior.

You will find the drawing of this motor here: http://www.robotis.com/view/XL-320/XL-320.pdf and a 3D model (STEP) here: http://www.robotis.com/view/XL-320/XL-320(stp).zip

However, the OLLO patented rivet system made the 3D printing of compatible parts on low cost 3D printer quite challenging… With @jgrizou we explored several dimensions and we eventually find satisfying ones.

FDM 3D printing

I personally use this dimensions

M1.6 screws (XL320’s horn):

  • clearance hole diameter = 2.3 mm
  • counterbore diameter = 4 mm
  • max thickness = 2 mm

Ollo rivet:

  • clearance hole diameter = 4.4 mm
  • counterbore diameter = 6 mm
  • max thickness = 2 mm

Part with U shape:

  • add 0.3mm tolerance on both side.

SLS/SLA 3D printing

With high quality printer, you basically can use the exact dimensions:

M1.6 screws (XL320’s horn):

  • clearance hole diameter = 2 mm
  • counterbore diameter = 4 mm
  • max thickness = 2.2 mm

Ollo rivet:

  • clearance hole diameter = 4 mm
  • counterbore diameter = 5.2 mm
  • max thickness = 2.2 mm

Part with U shape:

  • add 0.1mm tolerance on both side.

Dynamixel MX

Drawings:

Download:

SLS/SLA 3D printing

GIven the high cost of the Dynamixel MX, we mainly used high quality 3D printing.

M2 bolt (MX28 horn):

  • clearance hole diameter = 2.2 mm
  • counterbore diameter = 4.4 mm
  • max thickness = 1.5 mm

M2.5x4 bolt (MX64 horn):

  • clearance hole diameter = 2.7 mm
  • counterbore diameter = 5.3 mm
  • max thickness = 2 mm

M2.5x6 bolt ():

  • clearance hole diameter = 2.7 mm
  • counterbore diameter = 5.3 mm
  • max thickness = 2 mm

U shape:

  • add 0.2mm tolerance on both side.

FDM 3D printing

No data for the moment but you can guess it by adding more tolerance than the ones for SLS printing…

Additional links

All Robotis drawings: http://www.robotis.com/xe/download_en/26324
What is a counterbore: http://en.wikipedia.org/wiki/Counterbore

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