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Ideas about connecting servo to threaded rod.

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Inigo Montoya:
I have a Tower Pro SG90 micro servo modified for continuous rotation, and I need it to rotate a 1/4" threaded rod.  (Shown in photo.)  I need the servo to be removable, so it will have to be friction-fit to the (Futaba) servo arm, which is ok.  My first thought was to super-glue the servo arm to the threaded rod, and then trim the ends off.  Before I go about doing this, I was wondering if anyone had a more elegant way of solving this mechanical problem?  How do the pros usually connect servos/motors to rotating rods?

There are are all kinds of shaft couplers. You can find them anywhere from McMaster-Carr to SDP-SI to Amazon/SmallParts.
The main problem you might see would be that the output spline of the hobby servo is not a common type for commercially available couplings.

Typical linear actuators mount the motor parallel to the rod and use pinion gears instead; they do not mount the motor in-line.

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Inigo Montoya:
Why thanks guys, I did find the perfect solution on one of the websites.  Sadly, the price of the coupler is 4x the price of the servo, and I'm going to need either 8 or ideally 16 of these...  The couplers will cost more than the rest of my robot combined.  If I have to I'll do it, but I'm going to have to hunt for a DIY solution first.  I'm going to try the epoxy method first before saving up for those.  I'll post the results of my epoxy experimentation here.  I wish I had a 3D printer, as plastic would probably do for these tiny servos.  Any suggestions on a DIY method other than epoxy and prayer?  :-)

Inigo Montoya:
I was thinking...  if I get a small flat piece of metal, such as a washer with a 1/4" inner diameter, and buy myself a tap & die set, I could thread the tip of the rod into the washer, and then braze the two together.  Then, I could drill tiny holes that would then fit the screw holes of the servo arm...  I'm beginning to think this could be a good semi-pro DIY solution.  What do you expert robo-dudes think?


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