Making a 3D Printed Harmonic Drive Using a Timing Belt

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A harmonic drive reduces the RPMs of a motor output shaft and increases the torque proportionally. I created a proof-of-concept harmonic drive using 3D printed parts and a small, closed-loop timing belt.

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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.

BenryanALS
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Beautifully simple design, I love the belt idea.

thomasmills
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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!

unionseen
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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.

gordonjones
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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!

kaden
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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👍👍👍

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

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

j.o.
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This is really a good design, Impressive.

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

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

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

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

ekaggrat
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Good job, you are doing fine
Good luck

asgharrezaei
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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).

gsegallis
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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.

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

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

willschmit
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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?

ninehundreddollarluxuryyac
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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.

bogdanluncasu