Another way to take drive through the normal chainline

[Green Machine]

Holy jeebies!!!

Well done bob!

Amazing to see you go from concept, to drawing to working prototype so fast...

Really a beautiful piece.

I cant wait to see how this develops given your not even one month in.

[Whiplash]

Awesome! What keeps it all together when you are standing on the pedals...

[bobc]

Ball bearings fixed on the crank axle Whiplash - they should control positions of planet carrier & therefore outer ring rather better too. I'm pleased with the way the outer ring is solidly located (it floats on the chain loop. Thinking about the size and gearing I've been idly sketching up mk2 - this is just 10:1 reduction & thus much smaller. Now I can hide all the workings inside the toothed belt primary drive pulleys - here's the sketch.

I think this is much more practical: I'll need 6:1 or more reduction via the toothed belts but I don't think that's a problem...

[Miles]

I think this is much more practical: I'll need 6:1 or more reduction via the toothed belts but I don't think that's a problem...

It would make it more attractive if only one other reduction stage was needed. If you can get a 12:1 ratio, it would make that more doable, perhaps?

[spinningmagnets]

On the first page I had a feeling this was more of a theoretical discussion about an obscure option. The video of the prototype not only shows that the concept does work, it also shows how viable this is as a real-world option. This is a great amount of reduction in a very compact package!

[bobc]

Thanks for the generous comments ;^) Miles - I'd say any ratio you want between 10 and 20:1 is pretty easy. Spinningmagnets - what I like is how accessible it is - I made that in a fortnight by walking down to the local laser cutting shop with a pen drive in my pocket with dxf's on it, bearings off the web & an hour or two on my lathe. A spur or planetry gear would need more than one stage to get that degree of reduction and is an expensive technology way outside the scope of the amateur tinkerer. I'm fairly happy with it; I don't think the mk1 is a practical solution;- too much metal flying around too fast... but I think the mk2 will be. And the way the whistling input and wobbly chain motion translates to such a smooth slow output drive is, well it's just cool!

[Solcar]

It's really cool to see this approach actually built. Thanks for the video.

[amberwolf]

I love watching that in operation. I'm tempted to put one on my list of projects to do by hand, so that I can use it as a reduction drive on a treadmill motor for one of the bikes.

[bobc]

New drawings taken to the laser cutters today.
This is what I'm aiming for

There is 10:1 between the timing pulleys and the chainring, with the harmonic stuff all protected inside the timing pulleys. Plan is to clamp an outrunner to the seat stay driving the timing pulleys directly, giving me an overall 70:1 reduction.
Yes I've ordered the big chainring is stainless - should look good ;^)

[Miles]

Can't wait to see this one in action...

[Whiplash]

Now you're talking!

[REdiculous]

That's one of the coolest mechanical things I've ever seen....simple but complex...strange.

[dbaker]

Epic, Bob! I must have one!

[bobc]

New parts for the smaller, neater and less frantic mk2 - I'll assemble this over the next few days & start thinking about installation ;^)

stainless - bling... unfortunately I'll have to do some grinding to fit the 7 speed chain......

[Green Machine]

Unreal Bob...

Can't wait to see the next video....

Really amazing to see you develop this so fast...

[Whiplash]

Yeah, what HE said ^^ Beautiful!

[amberwolf]

New parts for the smaller, neater and less frantic mk2 - I'll assemble this over the next few days & start thinking about installation ;^)

I'd definitely like to see this in action. But am I missing something, or do all the moving parts end up invisible inside the pulley? Seems a shame to hide the wonderful clockwork.


Speaking of clockwork, what are you going to do with the first one?

[bobc]

yeah, the laser cutters really do a quality job.... ;^)
I'm afraid the gubbins will all be out of sight - yes it would be nice to see the mechanics strutting their stuff, but I reckon it's nicer to keep the noise in and the road grit out.....
The original? wall decoration? modernist sculpture? mount on a plinth as a trophy? Might make sense to mount it up as a working demo model ;^)
22/5/11 - I started putting it together - need to get hold of some loctite & do a bit more fettling.......

I'm hopeful I'll be able to get this onto a bike over the next couple of weeks.

[kfong]

Wow just caught wind of this, do you have the cad files to post. I could then modify them and play with my own version. Thinking of milling out a micro version out of g10 just to tinker with. I've worked with harmonic drives before but never seen one done this way.

With this design, is there a problem with chain growth and was the triple chain hard to obtain?

[bzhwindtalker]

Impressive! I'm always surprised by the possibilities of mecanical engeneering!

[bobc]

Sorry guys - this is sitting in a box in the shed waiting for me to get my finger out..... I will get on with it one day, I still think it's a good way to go. Anyone wanting the CAD files, I'll stick them on here. yes triplex 8mm chain was tricky to get hold of ;^)

[liveforphysics]

bobc- This is extremely cool. I don't know how I missed this thread. I didn't expect to see DIY harmonic drives on ebikes, I should have known better by now.

Very impressive! Any guesses about the efficiency?

[neptronix]

So amazingly cool, i love it. It's things like this that make me read the forums every day.

[Solcar]

...

Speaking of clockwork, what are you going to do with the first one?

Clockwork is a great description of it.