Modelling a Servo Spline

Let's Make Robots Robots
1

I have wanted to design my own servo arms for my robots without the need to attach the servo horns to them. With a 3D printer available I wondered if it was possible to manufacture hubs for the spline on the servo shaft. The problem was to know the geometry of the spline. I am not the only one to be

This is a companion discussion topic for the original entry at https://community.robotshop.com/blog/show/modelling-a-servo-spline
2

Splines

Thanks for posting. I hate it when it works the first time. Sets my expectations too high for the next project.

3

Yes they work!

You are right Staffan a good resolution 3d printer is the key factor here. with Otto DIY i learned couple of interesting observations would like to share using PLA too:

1. The orientation of printing is important, for example with the leg of otto have an orientation facing the bed which unfortunatelly gave me more trouble adjusting the tolerance; needs some supports for the flat part, with the feet did nt have that issue, but is important to clean it a little bit with a knife after printed. At the end put stronger fit (smaller size) for the leg

2. The spline design i did it using a 3d model from GrabCAD and so far works; but seems there are hundreds of manufactures of SG-90 servos that i have found differences in diameter up to 1mm! making it almost impossible to have an average of size and tolerance (some would have strong fit others will be loose, very few actually perfect fit)

3. Found out with the time the teeth start to dissapear and then completely lost attachment, so my recommendation is to have the strongest fit at the begining and then would loose until the perfect match. as you mention at the end.

4. A chamfer at the end help to put the servo hub in; if the tolerance is too tight.

 The 3d model is here you can check the skecth spline quite similar to yours http://www.123dapp.com/123D_Design/OTTO-DIY/5658659

Thanks for the post

4

Noticed the difference

Hello

Thank your for the comment. As you write proper orientation in the printer is important. That is really a “design for production” part one has to consider. I also noticed your second point when I received a new batch of SG-90 servos. The servo spline had a much smaller diameter so my hub had a way too loose fit. In the design where I intend to use these servos I will design limbs where I mount the servo horns instead. I have “killed my darling” in a way but on this design there is room for the horn.

Staffan

5

It backlashed :slight_smile:

You might notice my reply above that my new batch of servos did not work with my design. So now my expectations are back to normal. :slight_smile:

6

indeed they change all the time i think the best approach is to make space for the servo arms they are the ones that usually have same standard size

7

I tried to print splines for sg90 servo using a design on Thingiverse. Sadly the shaft size printed way to small.

Then I came up with an altogether simpler idea - the sg90 comes with servo horns with the correct splines. I snipped the arm off one with some side cutters and then filed off the rough bits with gf’s nail file. I measured the diameter and depth of the little cylindrical part with a micrometer. Then I used CAD software to cut out a cylindrical recess in the 3D printed gear, which I wanted to mount on the servo. I printed the gear and glued the spline containing part in the hole with superglue. It works and fits perfectly.