Novel gear reduction strategies

[Grantmac]

https://youtu.be/AEzJfPi7jzc

[youtube]AEzJfPi7jzc[/youtube]

I was having a late night look at various gear reductions and came across that beauty.
Gears are difficult for a home machinist to produce and any inaccuracy leads to a lot of noise. They also require a rather "clean" environment to run effectively.
Chains are so simple but usually take a lot of stages to make a high enough reduction to run small high RPM motors in their efficiency range.

It's not particularly compact in diameter but if combined with a larger diameter out-runner might still fit between cranks which is really what an ebike needs.

I'm tempted to see if it can be 3D printed to run with belts to give it a try.

 

[TrotterBob]

I'd be interested to see a chain drive or a belt drive version that isnt a pant leg eater.

 

[Grantmac]

It's designed to be run enclosed, although because it has no ring gear the case can be extremely light.

They designed some very compact geared versions which are similar sized to the planetary gearboxes we have now, just higher potential reduction and quieter apparently.

 

[scianiac]

It seems at high speed the vibration could be quite bad in the config shown, maybe 4 chains/belts could be setup to be balanced. This reminds me of an idea I had the other day for how to make a 3D printed harmonic drive. Any real wear gear components 3D printed generally don't last well even if done in something like Carbon Fiber Nylon due to surface imperfections but I was thinking the main strain wave gear could be a thick toothed belt turned inside out, bearings provide the inside shaping/contact points and the outside "gear" path could be made from steel pins inserted into the printed housing since many toothed belts can interface with a round surface quite well. Getting a wide enough and small enough belt may be hard since one side needs to be mounted to a drive block for output.

 

[Grantmac]

At least according to the white papers on their website one of the strong points if this design is lack of vibration. A 4 planet setup would probably be easier to machine in some ways, you might even be able to use 2 chains instead.
But I don't think it would be better balanced.

They actually have a pretty decent video comparing it to a variety of other drives, including harmonic.

Here is another design which uses a chain as a ring gear:
https://www.machinedesign.com/mechanical-motion-systems/article/21837300/roller-chains-and-planetary-gearboxes-yield-accurate-efficient-motion-control

 

[scianiac]

Ah I see, got confused by the video, at first glance it looks like the planet sprockets are eccentric but they are not. Not sure how much torque could be put through a printed version before the planets start going out of alignment from lack of 3D printed stiffness (also the failure mode of many 3D printed gearboxes), but this could be solved by making the drive plates a bit thicker with dual bearings or from metal, they are fairly simple in design. Off the shelf sprockets or pulleys could probably have the offset holes drilled accurately enough with a simple jig. Very interesting.

 

[Grantmac]

Oh I wouldn't try to actually USE a 3D printed version, besides I have a machine shop.

If I could do 4 planets with two chains then the whole thing could be thinner.

Offset holes in the planets should be easy to do. Their white paper says that durability is best if the bearings are in the carriers rather than the planets.