Making a 3D Printed Harmonic Drive Using a Timing Belt 

The original 1955 design is genius but I have to say this is equally impressive. You need to pay closer attention to the elliptical geometry so that 30% of the teeth are always engaged. As has been suggested a larger set of bearings in the wave generator will improve things.

Non back driveable is a drawback for arms that you would like to teach via manual positioning. Life is full of compromises . I like the belt as spline idea!

Beautifully simple design, I love the belt idea.

From what I've seen and understand, the flex spline (the timing belt here) is actually physically attached to the output housing in an actual harmonic drive. It's like a bell shape with teeth on the outer rim, with the entire bell flexing. In your design they are separate. Essentially you've created an interesting variation of a harmonic drive with a floating internal flexure. Try using PET to print the output housing as a single unit. This should give you the rigidity to achieve the calculated output torque. I'm gonna try it myself, this is a nifty print.

This is brilliant. I guess it can end to be pretty silent with a rubber belt.

PLEASE keep this project up! I will be entering the harmonic drive realm shortly and I would love a current community online to collaborate with or at least study what their doing. Great work and great video!

Cool project, but a couple of things... Your gear ratio is actually 25:1, not 26:1. (it's (50-52)/50 wrt the motor rotation) In a typical harmonic drive, the flex gear would be the output stage. You actually have a split-ring gear harmonic drive which is a little different. In the case of a split ring gear, the tooth count of the flex gear is actually irrelevant - it is the ratio of the output ring gear to the stator ring gear tooth count that determines the gear ratio. You didn't state it, but your output ring gear appears to have 50 teeth, which is why you get a 25:1 reduciton. If you kept the 52 and 50 tooth ring gears but changed the flex belt to, say, 48 teeth, you would still observe a 25:1 reduction. And if your output ring gear had 52 teeth, it would not rotate at all (regardless of flex belt tooth count, though the flex belt will still rotate).

Consider this: buy two belts (one with 2 more teeth), turn it inside out, and crazy glue it to a 3d printed cylinder...

Wow, awesome work Levi..thanks for sharing. I have been looking at planetary gears which are expensive. This is a very good alternative. Thanks bro👍👍👍

just use a bigger diameter bearing...to have better gear torsion! this will improve your torque!

You're a genius. I'm gonna make a harmonic decelerator.

These are great, didn't know they existed, thank you

I don't understand why the output ring gear doesn't allow the belt's teeth to "walk" past its teeth, like it happens with the stationary ring gear.

does the top lid have the same number of teeth as the bottom or 2 less like the belt?

This is really a good design, Impressive.

It looks like it could be a fully functional design with only a couple of simple modifications that you already intend to implement. It’s a very elegant feat of mechanical engineering. This is just a small semantic nitpick, but can we call these devices strain wave gears? It’s much more descriptive and It’s already a widely used term.

Wishing you good luck for your future projects. Excellent explanation.

Timing belt! You need to know why there is little backlash and long usage life time of it when it is under normal use. The tension force acts on it is along the length of the belt and it is counter-acted or withstood by the fibre strands inside. In yours application, it didn't use any of this benefits, instead it just uses a couples of rubber tooth to hold the two internal ring gears together. Flexible rubber creates backlash when they are under the torsional force, and belt will break apart after a long time high loading usage.

I think it might help if you used larger diameter bearings to press against the belt, so as to get more teeth to engage. That should reduce the chance of slippage and also make it run smoother.

The belt is less of a good idea because it deforms in a non elastic way consuming energy and reducing the efficiency. Another issue with the belt is that it introduces backlash.This part should be made of a rigid elastic material. Just print it and it will be much better.

Belt is better suited to the flexing a flexible splined cup sees. Is this a two stage gearbox? It looks like the belt should add a second reduction when coupling to the output. What is the reason you didn't continue with this instead of going on to cycloidal gears?

great project, thanks for sharing!

Pb with the nema is that it has no torque at high speed. So definitely either you should consider another motor. Nevertheless great job with this harmonic drive : very inspiring

Good video, thanks for posting it. Although it’s definitely simpler to make this drive with a rubber belt, ideally the three components would be made from the same material to reduce wear, ideally something with low friction coefficient. The shape of the teeth should also be revolute, that will increase the force of the alignment. I will cut one out of HDPE on my CNC, the design is definitely CNC-able and I find that HDPE or nylon could be the ideal materials for a cost-effective build.

That's an excellent idea!.

How many teeth does the top part have? From my understanding of harmonic drives bottom part should have 52 teeth. Belt and top part should be one unit, so I don't see the point of having bearing to push against that.

Ingenious!

Nice. Thanks for posting the video.

Can you please post a link for the small timing belt you used for this demo?

I had previously thought planetary gears were king. I now know better.

why does the top rotate, isn't it just a (more or less) mirror of the stationary piece attached to the motor?

You said it is easy to make, cheap and doesn't require tight tolerances... well industrial grade harmonic drive is just the opposite of it, since it uses elliptical bearing which is very hard to make one with decent quality, good harmonic drives have price tag of 700 USD and up.Nice video though. Just curious, why did you abandoned the harmonic drive project and focused on the cycloidal drives? cheers

Good job , you are doing fine Good luck

Really awesome, have you made any new versions of this, that can be used for robot arm

Haven't you change the bearings yet? Did larger bearings solve the vibration and torque problem? I want to use it as a functional part in my telescope mount. Can you make a video of how to design it in Fusion 360, like the one you did for cycloidal gearbox? I don't know how to design an internal gear to pairing the HTD belt.

Great! What is the number of teeth on the upper part?

Great vedio ,thank you for sharing

Use a cam nut (eccentric bearing) as one of the rotor bearings.

Wait... Was this only a test?

Is it possible to use triangular centre hub with 6 total bearings? 🤔

gear ratio calculation: flex spline teeth = 50; circular ring teeth = 52. Ratio = (Flex spline teeth) / [(circular ring teeth) - (flex spline teeth)] Ratio = (50) / (52 - 50) = 25 how did you get 26?

Harmonic drive vs cycloidal drive which better for robotic arm

Use a power transmission belt. See if that makes a difference. Timing belts slip too easy

Would TPU work to print the belt? I bet it would

Cool man! Have you made any further progress? I'm thinking of making some, and i really like that you used standard timing belt.

did you make the robotic arm with it

Greatt!!!! Want to see more

Nice job!!! Any link to gcode for the parts printed or any model to share?

Main usage of a harmonic drive is not gear reduction, it is to reduce back slash

Awesome! Wish I could give 10 likes

Hi Levi I really need your helps about this design. Has its torque improved after the bearings have been replaced? How much is its practical reduction ratio? Does the friction between the belt and teeth cause the belt to wear out?

how many teeth in the top gear there mate?

Hi, Can you share us where you purchase that timing bell?

clever...... how do people have such awesome smart ideas ?

Nice work! Is it possible to share the CAD files?

Wait... It's 50:52:50? Why would you get any output at all?

wow. 0.9 degree motor...

You're better off if you can make an elliptical greased mechanism rather than the bar you have in there.

who else was thinking about the girl from Harry Potter!

Why deteriorate your channel with a half assed project?

this is wrong.... you are not putting the correct number of teeth