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Strain Wave Reducer (Patreon)

Published:
2021-03-29 08:15:55
Imported:
2026-06
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Content

Here's next week's video, early for Patrons. This one goes out publicly on April 6th.

Not too unhappy with this, although it seems to be a bit too easy to stall the motor compared to the cycloidal drive. I'm pretty sure this type of reducer is higher friction due to having to deform the flex spline - considering the commercial ones are made of metal as well.

Proper tests with an ODrive and comparing this with the Cycloidal drive are coming up next week.

Files

Previews only

Experimental Harmonic Drive Reducer - PREVIEW VERSION

Over the last few weeks I've been investigating 3D printed Cycloid Drives. I thought it was time to take a look at a Strain Wave, or Harmonic Drive reducer. I'm using TPU for the flex-spline in this design, and the rest is PLA. I'm using the same brushless motor and the reducer is a 10:1 ratio to match the cycloidal drive so we can compare them. You can support me on Patreon or buy my Merchandise: *************************** Patreon: https://www.patreon.com/xrobots Merchandise: https://teespring.com/stores/james-bruton *************************** Affiliate links - I will get some money of you use them to sign up or buy something: *************************** Matterhackers 3D printing supplies: http://www.matterhackers.com?aff=7500 Music for your YouTube videos: http://share.epidemicsound.com/xrobots *************************** Other socials: *************************** Instagram: https://www.instagram.com/xrobotsuk Facebook: https://www.facebook.com/xrobotsuk/ Twitter: https://twitter.com/xrobotsuk *************************** CAD and Code for my projects: https://github.com/XRobots Huge thanks to my Patrons, without whom my standard of living would drastically decline. Like, inside out-Farm Foods bag decline. Plus a very special shoutout to Lulzbot, Inc who keep me in LulzBot 3D printers and support me via Patreon. HARDWARE/SOFTWARE Below you can also find a lot of the typical tools, equipment and supplies used in my projects: Filament from: https://www.3dfuel.com/ Lulzbot 3D Printers: http://bit.ly/2Sj6nil Lincoln Electric Welder: https://bit.ly/2Rqhqos CNC Router: https://bit.ly/2QdsNjt Ryobi Tools: http://bit.ly/2RhArcD Axminster Micro Lathe: http://bit.ly/2Sj6eeN 3D Printer Filament: http://bit.ly/2PdcdUu Soldering Iron: http://bit.ly/2DrNWDR Vectric CNC Software: http://bit.ly/2zxpZqv Why not join my community, who are mostly made up of actual geniuses. There’s a Facebook group and everything: https://www.facebook.com/groups/287089964833488/ XROBOTS Former toy designer, current YouTube maker and general robotics, electrical and mechanical engineer, I’m a fan of doing it yourself and innovation by trial and error. My channel is where I share some of my useful and not-so-useful inventions, designs and maker advice. Iron Man is my go-to cosplay, and 3D printing can solve most issues - broken bolts, missing parts, world hunger, you name it. XRobots is the community around my content where you can get in touch, share tips and advice, and more build FAQs, schematics and designs are also available.

Comments

Thomas Messerschmidt

LOL! I know some of what you must go through: design , print, build/video, edit, post, repeat! I do it myself. It’s never easy being a one-man show. Or are you hiding a team of helpers off camera?

Anonymous

Very interesting stuff as ever, keep up the great work

Anonymous

Awesome video! I've been looking for good robot gear mechanisms for a while I'm I'm interested to see where both of these methods go! For the strain wave issues, I would guess that the NinjaFlex is too flexible for the flex spline and the teeth themselves are bending, causing the slipping and maybe even some friction. You could maybe try a more flexible filament like PETG or ABS for the flex spline, or dual-extrude some TPU with PLA teeth so you get the benefit of both materials.

XRobots
>>56586545

I was thinking it was too rubbery and grippy as the teeth mesh, but it's really hard to see what's going on in there ;-)

Pete Mertz

As always, amazing! Tangential question here, do you use a certain method or plugin for generating gears in fusion 360?

XRobots
>>56592614

I generally download the CAD for gears from KHKGears.com, although there are some gear generators in the Fusion360 'store'

Faraz Sayed

I've never heard these being called Strain Weave, Are you sure you didn't mean strain wave (and an extra 'e' had appeared somewhere?) . The video is great and very informative

XRobots
>>56598513

Yeah, that's weird ;-) I'll just update the text and hope that all the people criticising my pronunciation in the comments helps drive engagement on the video ;-)

Scott Cress

Great video James really does a good job of showing the harmonic drive and it's comparison to your last drive. As far as the holding torque for this drive: From what I know about them the "flexible" part of the drive doesn't need to flex as much as the TPU you used. Try making the flexible gear out of a more rigid material like HDPE or another more stiff yet flexible material.

XRobots
>>56619447

I think then the teeth would have to be smaller which would mean tolerances need to be tighter. I tried to make it really chunky so it would be easier overall, which kind of worked, but it isn't ideal. The tolerances on my Cycloidal reduction really aren't that tight and the discs are nice and chunky, but it works anyway, so I guess there's some comparison in that at least.

Scott Cress
>>56619447

I just read Keith's comment above. His materials suggestions are excellent too. The force of the wave generator is supposed to really force the barely flexible material into the receiving gear. When done, yeah it won't be back-drivable but should hold a heavy load with high resistance too.

Scott Cress
>>56619447

One of the factors for the holding power/torque of this drive us the radius of the wave generator is it presses the flexible gear into the receiving gear. The bigger the curve the more teeth are shoved into the receiver, narrow point on the wave only shoves 2-3 teeth into the receiver. More teeth = more torque.

Anonymous

I suggest nylon for the flex-spline. Also only have teeth at the top of the flexspline’s cup, but no teeth elsewhere. You also want a tall cup. You want radial flex but no flex elsewhere in the cup, as it makes it harder to deform if the lower bits are too thick. Your teeth profile also seemed really shallow. Nylon will reduce the friction as will adding some silicone lubricant.

XRobots
>>56643847

Thanks - I left the teeth all the way up so that it could lock into the plate at the top. Probably needs a lot of further optimisations.

Anonymous

I made similar experience with my attempt building a harmonic drive years ago. After several month and about 50 prototypes I abandoned the idea. It seems to be a reason than only one company is building propper one. At the end I got a version that worked somehow and was to some degree backdrivable. They also tend to induce harmonic oscillations under load. At least my where not rotating with constant speed. The cycloidal drive looks much more promising, I even think of building one, even I decided never to touch gearboxes again after the harmonic drive disaster.

XRobots
>>56698963

Yep - I think that will be my conclusion. The Cycloidal Drive is looking like the way forward.

Darius Zaerin
>>56583072

are you still making videos Thomas? i follow you on twitter and see something now and then, but i'm pretty sure i originally found your stuff on youtube, unless i'm getting mixed up. i'd love to keep up with your projects more, you make great things!

Thomas Messerschmidt

Darius, I am still making videos. With James’s permission I will post a link to my “Hello World- Simone” video. James?

XRobots
>>56831070

Yep saw it the other day. Not sure how robust that flexible section is though.

alicetaur

i feel like strain wave would delaminate unless you use PP plastic

Anonymous

Hey James. Are you limited to printing a single material at a time? I've got an e3d toolchanger and been doing some experiments with nylon and TPU composite structures. I think it would be possible to combine the flexible spline and output disk into a single part. Send me a message if you ever want to try out some composite structures.

XRobots
>>57194615

Yes I have dual extruders on the TAZ Pro, I have done similar rigid-flex parts before. Not sure I'm going to further develop this reducer right now though - the Cycloidal Drive is far more useful for my needs.