Guidelines to design 3D printable parts for Robotis Dynamixel

[Matthieu]

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: GitHub - poppy-project/Robotis-library: Robotis CAD library made with Solidworks
• OpenSCAD because there is a complete set of tool made by @jgrizou to quickly design any kind of robot:

[CFC] Extending the poppy mini family: we need your help!

Help us extend and improve the poppy mini family! Poppy mini creatures are built from XL320 motors from Robotis. Motors are linked together with parametrable frames designed with OpenScad. The resulting robots are controlled using the pypot library, typically running on a Raspberry Pi. These robots aim at being low cost and easy to modify. [image] Currently the poppy mini family includes: poppy-ergo-jr poppy-4dof-arm-mini poppy-multipod-mini poppy-snake-mini poppy-4wheels-mini poppy-dragste…

• 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:

Alternative to Solidworks?

For professional (mechanics and designer), Solidworks is a widely used CAD software. Thus it is a good choice for people in Research labs and Universities. But Poppy has to be easily hackable also by makers/artists. For the moment the accessibility of Solidworks may be a constraint (Windows only + cost). I open a topic to discuss about potential alternatives to the use of Solidworks for the Poppy project. Please share your idea and experience. EDIT: Post only software which can be actually use…

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.

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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.

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Dynamixel MX

Drawings:

• http://www.robotis.com/view/MX-28T/MX-28T.pdf
• http://www.robotis.com/view/MX-64T/MX-64T.pdf
• http://www.robotis.com/view/MX-106T/MX-106T.pdf

Download:

• http://www.robotis.com/view/MX-28T/MX-28T(stp).zip
• http://www.robotis.com/view/MX-64T/MX-64T(stp).zip
• http://www.robotis.com/view/MX-106T/MX-106T(stp).zip

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: Counterbore - Wikipedia