Mechanics and Construction > Mechanics and Construction

Ideas about connecting servo to threaded rod.

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waltr:
That is a good idea and a good DIY solution.
Lots of ways to attach a flange (disk) to the end of the rod. Brass is readily available, not too expensive and fairly easy to work with. Instead of drilling a tapping just braze or silver solder a piece of brass sheet (~0.025tk) to the end of the rod. Then file to a shape that matches the servo horn and drill holes to couple to the horn.
A flange on the end of the threaded rod would not be hard to couple to the servo. You may want to consider some rubber washer or grommet between the two to allow for slight misalignment between the servo and rod like a universal coupling.

jwatte:
That washer idea sounds reasonable!

If plastic is good enough, you can also just melt some plastic straight onto the output spline, and then flatten/drill it as appropriate. Jamming InstaMorph/ShapeLock against threads/pinions actually works pretty well ;^)

Using the existing horns and epoxying or screwing something to the shaft you're driving is also doable. There's nothing wrong with Epoxy, as long as the load is not too high.

I'd probably try the InstaMorph first, then the epoxy, and if that doesn't work, the washer.

How small is the pinion of the servo? Could you center drill a hole into the shaft, and then use a reamer or something to shape the mating part of the servo spline inside that hole, and get a direct coupler?

Inigo Montoya:
The hole in the centre of the servo spline is 1/16"  The horn comes with a screw that can mate the horn to the spline permanently.  I picked up some washers that fit, and will be trying the washer/screw trick, or washer/screw/epoxy method if that fails.  I will post the results.

jwatte:
When suggesting center drilling, I was suggesting doing it in the 1/4" shaft you're attaching, not the spline/servo shaft :-)

Inigo Montoya:
First, I bought some washers wide enough to accommodate the futaba servo arm, with an inner diameter slightly smaller than the threaded rod.  I tapped the centre of the washer so the threaded rod could screw into it for strength.  I drilled 2 holes in the washer to mate with the servo spline.  I epoxied the washer to the end of the threaded rod, with a nut epoxied in place for added strength and stability.  Then, it was easy to screw on the servo arm!  For pocket change and some hard work, I was able to avoid buying eight $12 couplers.  Attached are some photos of my work.

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