
Inception Drive: A Compact, Infinitely Variable Transmission for Robotics - mcspecter
https://spectrum.ieee.org/automaton/robotics/robotics-hardware/inception-drive-a-compact-infinitely-variable-transmission-for-robotics
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Animats
This is cute, but the use case in robotics is questionable. A variable ratio
transmission for a robot seems to solve a problem nobody has. Electric motor
control today is able to do that job over a wide torque and speed range. From
drones to electric cars to Diesel-electric locomotives, nobody uses variable-
speed gearboxes much any more. There are many robot gearboxes, but I've never
heard of one with a shifter. Machine Design has ads for robot gearboxes,
including ads from Harmonic Drive, but they're all fixed ratio.

This thing would need a second motor to adjust the speed change, with an
encoder, plus encoders on the input and output ends of the transmission.
Something has to control all that.

If you need sudden bursts of high torque, overload the motor while monitoring
temperature. You can run electric motors far above their continuous rating for
brief periods, and if temperature is monitored, this is safe. That's how
Tesla's "launch mode" works.

Not seeing the use case for this thing in robotics.

~~~
Mithaldu
How do you feel about his claim that this would be good for energy efficiency?

Or the claim that this would allow for easier human-safety by having the
torque, if lowered, not be dependent on logic, but on the actual mechanics,
making it possible to stop the entire system if a failure in the torque-change
motor is detected?

~~~
Animats
_How do you feel about his claim that this would be good for energy
efficiency?_

It's unproven. If you have to haul more mass around, that's worse for energy
efficiency.

 _easier human-safety by having the torque (limited)_

There are mechanical 'fuses' for torque limiting.[1] Having a transmission
that can downshift into a very high torque mode is probably worse for safety.
If torque is directly proportional to motor current, there are lots of
standard safety devices for limiting motor current.

[1] [https://www.mayr.com/en/products/torque-
limiters](https://www.mayr.com/en/products/torque-limiters)

~~~
Mithaldu
Interesting, thanks for expanding. If you don't mind another question:

> a transmission that can downshift into a very high torque mode

I'm missing something here i guess, how is this different from a motor that
can deliver full torque just because the logic chip is driving it at full
power? Is it because the motor wouldn't be able to reach such high torque in
the first place? (Which might be a point in favor of the transmission.)

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bullfightonmars
It almost looks like they combined a CVT and a planetary gear.

For those saying it has too many moving parts, consider the number of parts
found in an 11-speed internally geared hub on a bicycle [1]

I would be really curious to see if this inception drive could be an
alternative to internally geared bike hubs.

[1]
[https://www.sheldonbrown.com/alfine-11.html#details](https://www.sheldonbrown.com/alfine-11.html#details)

~~~
NegativeLatency
That is a gem of a website. Glad it hasn't been ruined.

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ggm
Like a lot of mechanical contrivences, if you come from a world of digital
'machines' you're tempted to say but F R I C T I O N.. The thing is that
clutches, gears, back-chatter, teeth wear, this is all bread-and-butter to
mechanical engineers, this stuff has been well known for years. If these
people have managed to package things into an assembly which is tractable,
repairable, can be scaled, and suits their purpose I say hats (and spare arms,
and feet) off to them.

I suspect if you went to the room of clockwork/gears in Musee des arts et
metiers in paris, you could find much of this there, but the point is, you
might not find all of it, as one composition.

Thats what I love about mecha: its often like rotational lego, you add it in
the right combinations and it does stuff.

(the one which gets me, is the use of diagonally mounted rotators as 'wheels'
which can drive sideways: you see that on some forklifts. Its like michael
jackson moonwalking for machinery...)

~~~
alanbernstein
That is a place I never knew I needed to visit.

~~~
MengerSponge
It's worth an hours-long trip! Make sure you take the Metro; Arts et Metiers
is a gorgeous station.

[http://onesmallwindow.com/the-life/the-coolest-museum-in-
par...](http://onesmallwindow.com/the-life/the-coolest-museum-in-paris-musee-
des-arts-et-metiers/)

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kazinator
This seems like the mechanism can be summarized as working by precession.

The inner pulley wobbles inside the flexible V-belt and is induced into
rotating by precession.

Separation of the inner pulleys controls the effective precession cylinder's
inner diameter, the variation of which is accomodated by flexing of the belt:
how far it is "squeezed off" and displaced from its outer mount.

[https://en.wikipedia.org/wiki/Precession_(mechanical)](https://en.wikipedia.org/wiki/Precession_\(mechanical\))

Note in the precession animation here how the fast spinning green arrow can be
regarded as an input (the wiggle), and the slow spinning of the square-
centered blue wheel as an output: there is a many-to-one reduction here,
effectively forming a transmission.

Not to be confused with:
[https://en.wikipedia.org/wiki/Precession](https://en.wikipedia.org/wiki/Precession)

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jcims
Trying to devise a mechanism like this has consumed many many hours while
mowing the grass in rural Ohio. I'm a bit too much of a perfectionist and
probably would have discarded this idea even though it seems to be perfectly
serviceable for a number of applications. The segmented belt is interesting.

Unfortunately my search has yielded nothing but the same topological(?) traps
over and over again to the point where now I just listen to podcasts and
entertain my wife with seemingly unprovoked laughter as I chase my grass
mulcher around the yard.

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mikepurvis
I don't think the article mentions this, but being able to vary speed like
this leads to some interesting possibilities around centralizing power plants—
for example, being able to do a diff-drive or mecanum/omni platform with just
a single large motor rather than multiple smaller ones.

The responsiveness probably wouldn't be there for this application, but I'm
also curious about whether this could be made to work for a longer range
gas/hybrid quadcopter.

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bittercynic
Maybe the greatest feature is that it can have a very high ratio while
avoiding Harmonic Drive related IP.

~~~
captaindiego
Does anyone know if this Inception Drive will be patented heavily as well? Or
if it will be fairly easy to build products around this sort of design?

~~~
wpennington
Given the work is being completed at SRI, I would assume the tech would be
positioned in a patent or portfolio of some sort. However, this is purely
speculation. Nevertheless, this suspicion is further supported by the fact the
inventor has a history of patenting for commercialization. That's largely the
SOP at SRI and central to their business model.

However, worth noting that just because a patent is filed doesn't mean it (or
all of it) will be allowed. So, wrt your second inquiry -- assuming the tech
was filed on -- whether or not it can be designed around will largely depend
on 1) what was claimed in the patent (e.g., how broad and thorough the claims
are) and 2) what is eventually allowed by the examiner. The latter is largely
a product of the prior art in the space.

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XorNot
How long before you can print the parts for a low strength one off of
thingiverse?

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cjsawyer
Nice design, but I wonder about wear issues. With that many moving parts I
don’t imagine it could be made durable with any cheap material.

~~~
digikata
Especially that main drive belt! It's not a normal belt. It looks like you'd
need a flexible material that would accept making high-aspect, thin teeth.

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PaulHoule
It is hard to believe it is really efficient seeing the description. I have
driven cars with CVT and not been impressed.

~~~
semi-extrinsic
Subaru?

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thebooktocome
I own a '16 Impreza and it really drags at low speeds. It's my only complaint
with the car however, and it is better with higher octane fuel.

~~~
readams
Unless you're getting premature ignition in your cylinders from compression
(knock) the higher octane shouldn't matter.

~~~
chadgeidel
If its a turbo (i assume not?) the car’s ECU will compensate for lower octane.
Source: me when, half asleep, I accidentally half-filled my 03 WRX tank with
87.

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agumonkey
I think I've seen this nested configuration on youtube a while back...

Still nice drive.

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imaginenore
It's clever. But so many moving parts, and doesn't look very sturdy, nor
efficient.

~~~
theoh
There was a device called an electric wheel, a few years ago, which did the
continuously variable thing using a planetary gear (the sun and ring were
driven by separate motors, and drive was taken from the planet carrier.)

[http://web.archive.org/web/20080104094149/http://www.solomon...](http://web.archive.org/web/20080104094149/http://www.solomontechnologies.com:80/wheel.htm)

This design is inherently more compact than that arrangement, and the parts
are simpler. (I think)

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letlambda
This is exactly how the Prius (Gen 1) 'Hybrid Synergy Drive' works.

