Harmonic drive.. Because I need another project...

Thought this would be a neat experiment to see if a minimally printed harmonic drive would work (for some definition of..) Just printing the flex and outside gear.

Some torque wrenches have plastic harmonic drives in the adjusting mechanism to drive the scale round.

Martin C

Nice work Sam. I have been searching for a small, low power ( sub 1Nm) 'zero' backlash gearbox and have been looking into these types of reduction boxes, as well as the cycloid reducers. The latter seem to be easier to machine but not so easy to achieve a few arc-minutes backlash! I built a 3D printer using Polar co-ordinate arms and the interface between my steppers and the arm pivot is only 10:1 . The steppers have a 6400 microstep resolution, so I was hoping it would all work - Does not..Some arm positions result in perceptable print nozzle 'wobble' as the motor step is not small enough. So I need to reduce down another 10:1 or more, and the printer mechanical structure makes it difficult to add such a reduction - hence looking into a small inline strain wave reducer. The cost even for such small ones is not insignificant. Not sure a 'printed' version will be good enough for my application though. Certainly looks good and amazing what the 3D printer has achieved.

The pics below just to show where the reducer would have to fit.

Joe

Edited By Joseph Noci 1 on 28/01/2021 06:06:59

started an actual 4th axis........

and another update...

Interesting stuff Sam.

Is this something you are going to use?

If nothing else it made me look it up on Youtube.

Cheers Michael.

I plan on using at a lightweight 4th axis.. For either the turco or my 440 sized machine.

Thanks for sharing a great project.

Harmonic Drives...

Not sure if it suits what you have in mind, but a contribution on What I Did Today, yesterday reminded me that a Scotch Crank with the crank as the driving rather then driven part, gives a harmonic reciprocating drive.

(A regular crank or eccentric drive does not, due to the connecting-rod's obliquity, and the distortion increases with the shortening of the rod.)

My recollection of this was very roundabout, as the post there was about a steam-engine.

It had reminded me of reading of a Scotch-crank mechanism for calibrating small hydrophones at very low frequency (typically < 10, and indeed < 1, Hz). The hydrostatic head difference given by the vertical stroke immersing the transducer at a sinusoidally-oscillating depth change of only 100mm, is 1000Pa; equivalent to 60dB sound pressure-level in the 1Pa based scale used for measuring sound in water.

roughed out the back of the face plate....

face plate mounted... Need to drill and tap a bunch of holes.. Getting there...

another painful update

more goofing around...

That’s nice !!

MichaelG.