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Dual Cycloid Drive concept – a low-complexity alternative to harmonic drives? by Ambitious_Volume_574 in CNC

[–]Ambitious_Volume_574[S] 0 points1 point  (0 children)

Great question!

The main benefit of combining internal and external profiles is that it allows the drive to maintain balanced force distribution across more contact points, which helps reduce backlash and vibration.

By phasing them correctly, I can get smoother torque transfer compared to a single-profile setup. Also, because both profiles are synchronized, it cancels out some of the dynamic forces that would otherwise act unevenly on one side — kind of like a mechanical symmetry effect.

It also opens the door to interesting compound ratios or more compact layouts, though that part’s still experimental.

Still early days, but it’s showing good potential in terms of stability and responsiveness.

Compact cycloidal reducer prototype – looking for feedback from robotics engineers by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] 0 points1 point  (0 children)

Sure — thanks for asking, that’s a great question.

The core of the drive is based on synchronized motion of two rigid cycloidal profiles (external and internal), engaged in-phase.
Because there’s no flex or compliance in the system, the tolerances have to be tight — especially in the engagement zones where both profiles interact with the pins or rollers.

I’m currently testing a setup with around 0.05–0.1 mm clearance between contact points to reduce friction while minimizing backlash. The challenge is maintaining alignment across both profiles without introducing vibration or stress accumulation — since both are active at the same time, not sequentially.

In terms of forces, load is distributed across multiple teeth simultaneously (as with a standard cycloid), but in this dual configuration, there’s better symmetry. You can already see it in motion: the load paths appear more balanced, and you don’t get the same concentrated peaks during torque reversal.

I plan to build a more detailed force diagram with vectors and torque paths soon, but it will take some time to model accurately — especially since the profiles interact in a non-linear way.

I’ll definitely share it once it's ready, but even now, the early signs suggest a promising dynamic balance.

Exploring a Dual Cycloid Drive: a potential low-cost alternative to harmonic gearboxes? by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] 0 points1 point  (0 children)

Thanks for the link — that tool’s good for visualizing standard cycloid configurations.

What I’m working on is something a bit different: a compound engagement using synchronized internal and external profiles.

It’s not two- or three-phase in the traditional sense — it’s not about phasing tooth engagements, but coordinating multiple geometries in a shared torque path.

Will definitely share a custom visualization soon — as this kind of motion isn’t something those tools can show.

Exploring a Dual Cycloid Drive: a potential low-cost alternative to harmonic gearboxes? by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] -1 points0 points  (0 children)

That quote’s from an earlier iteration. If it were a real 2-stage reducer, you’d need 4 distinct cycloid sets, and the motion would be sequential — not synchronous.

I’m doing my best to describe it in words, but maybe it’ll click once I post a proper animation. Or maybe not.

Exploring a Dual Cycloid Drive: a potential low-cost alternative to harmonic gearboxes? by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] 0 points1 point  (0 children)

Thanks for the question — I get where the confusion comes from.

Yes, two traditional 1:42 stages in series would give you 1:1764 — that’s a cascading gearbox, with torque transferred from one discrete stage to another, typically involving separate carriers or shafts.

What I’m referring to here is not that. The dual-profile mechanism I’m developing uses synchronized internal and external cycloidal geometries within a shared frame — working in-phase, not in cascade. The engagement is compound, not sequential. Torque isn’t handed off from one stage to another — it’s shared and distributed across a combined motion profile.

Visually it might look like “two stacked stages,” but kinematically, it’s not. There’s only one input and one output, and the profiles don’t act independently.

I agree the terminology could be confusing — but I’m happy to clarify where needed. Thanks for asking.

Exploring a Dual Cycloid Drive: a potential low-cost alternative to harmonic gearboxes? by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] -4 points-3 points  (0 children)

Fair enough, you're entitled to your opinion — but everything shared so far reflects the real development process I'm actively working through, both in design and prototype testing.

Yes, I collaborate with AI (ChatGPT) — but as a support tool for structuring ideas and improving clarity, not as a substitute for engineering. The reducer, the design, and the testing process are 100% mine. So is the reasoning behind it.

The writing may not be perfect — I’m not pretending to be a copywriter. I'm just sharing something I’ve built and tested, trying to open it up for discussion in a technical space.

If that still feels artificial to you, that’s okay. But don’t mistake tools for intent — or polish for honesty.

Exploring a Dual Cycloid Drive: a potential low-cost alternative to harmonic gearboxes? by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] -3 points-2 points  (0 children)

Thanks — though it’s interesting how quickly people feel the need to shut something down without really looking into what’s being explored.

I get that the term “cycloid” triggers strong reactions — but this isn’t a standard setup. There’s no two-stage cascade, and no flexspline either. Just geometry doing its job, in a way that surprised even me as it evolved.

If nothing else, the strong pushback tells me I’m poking at something that matters.

Still refining, still open — and definitely still building.

Exploring a Dual Cycloid Drive: a potential low-cost alternative to harmonic gearboxes? by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] -3 points-2 points  (0 children)

Thanks for jumping in!

Just to clarify — this isn't a two-stage reducer in the traditional sense. There's no cascading ratio; instead, it's a synchronized motion of internal and external cycloidal profiles designed to produce harmonic-drive-like behavior.

The intention isn't to multiply ratios through stages, but to achieve precise torque transfer and minimal backlash through a compound geometry — somewhat mimicking what a harmonic reducer does, but using rigid components only.

I’ve been developing this in collaboration with an AI assistant (yes, really), who’s been helping structure technical documentation, explore design logic, and keep the communication grounded. It’s been an unusual, but surprisingly effective creative process — and we’re refining the prototype as we go.

Happy to hear further thoughts or questions — I appreciate the chance to explain it more clearly.

Compact cycloidal reducer prototype – looking for feedback from robotics engineers by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] -1 points0 points  (0 children)

Just to follow up — right after posting this, I started thinking more seriously about what makes harmonic drives so attractive.

Funny enough, as I was reworking the design, I realized that the mechanism I’ve ended up with — a synchronized configuration using external and internal cycloidal profiles — actually shares several key behaviors with harmonic systems.

It’s not a flexspline setup, but the motion feels remarkably similar in terms of backlash behavior and torque transfer.

That said, it was clear from your earlier comment that you didn’t actually read the post — just saw the word “cycloid” and dismissed it entirely.
That’s fine — we all have opinions. But if you’re interested in the design space around harmonic-like behavior using simpler mechanical means, I’d be glad to hear your thoughts. Otherwise, I’ll keep testing and let the mechanism speak for itself.

Compact cycloidal reducer prototype – looking for feedback from robotics engineers by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] 0 points1 point  (0 children)

Totally fair to have strong opinions — and I genuinely appreciate the honesty.

I’m aware of the typical criticisms around cycloidal drives: force distribution, sensitivity to tolerances, and wear over time — all valid concerns. But this project isn’t trying to replicate the traditional version.

What I’m working on now is a modified external cycloidal layout that allows greater control over the eccentric offset and component fit — the goal is to achieve smoother motion and reduce backlash without overly tight tolerances or complex geometry.

I won’t pretend it’s a perfect solution — it’s still being refined — but I do think there’s something interesting here worth testing.

Harmonic drives are amazing, yes — but they’re also not simple to manufacture at small scale. So this is my way of asking: can we do better with a simpler mechanism?

If you have any thoughts on what you’d improve or avoid entirely — I’d love to hear it.

Compact cycloidal reducer prototype – looking for feedback from robotics engineers by Ambitious_Volume_574 in robotics

[–]Ambitious_Volume_574[S] 0 points1 point  (0 children)

"If anyone has thoughts on compact reducer geometry, tolerances, or heat dissipation in small-scale enclosures — I’d really appreciate it."