Another way to take drive through the normal chainline

Stuff arrived in the week; I've started assembly. So far so good, it all goes together, the triplex chain is tight, heres a photo. I got some seamless (DOM) tube to make the planet carrier bearing supports and some 6mm plate to make the tapered inserts; I forsee some more lathing sunday afternoon (kinks)
harmgbparts.jpg
 
Looking great! Very anxious to see it in motion!
 
OK I've done a short demonstration video; only one side is on and none of the locating bearings and it's all new and stiff, so it's a bit clunky but you can see the unfeasably large reduction ratio (!). It will be a while before the target bike is ready unfortunately.
[youtube]35JrvpcKKTo[/youtube]
My impressions from doing the test on the lathe are that it will all be rather too "busy" if I'm looking to get output speeds up to 100rpm. I reckon I should probably halve the reduction ratio from 20:1 down to 10:1 - this will make all the gubbins 1/2 size and they will run at 1/2 the revs. And put a greater proportion fo the "gearing down" in the primary timing belt between the motor and the gearbox/chainring. I'll get this one going first though ;^)
 
Awesome! What keeps it all together when you are standing on the pedals...
 
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.
chainset2.jpg

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...
 
bobc said:
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...
Click to expand...
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?
 
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!
 
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!
 
It's really cool to see this approach actually built. :D Thanks for the video.
 
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. :)
 
New drawings taken to the laser cutters today.
This is what I'm aiming for
chainset22.jpg

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 ;^)
 
Now you're talking!
 
New parts for the smaller, neater and less frantic mk2 - I'll assemble this over the next few days & start thinking about installation ;^)
nuharmparts.jpg

stainless - bling... unfortunately I'll have to do some grinding to fit the 7 speed chain......
 
Yeah, what HE said ^^ Beautiful!
 
bobc said:
New parts for the smaller, neater and less frantic mk2 - I'll assemble this over the next few days & start thinking about installation ;^)
Click to expand...
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?
 
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.......
harmmk2.jpg

I'm hopeful I'll be able to get this onto a bike over the next couple of weeks.
 
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?
 
You must log in or register to reply here.

Similar threads

A
best Bafang Mid Drive option for off-road trike? No human power input
Replies
8
Views
2,822
Bullfrog
B
district9prawn
Neu 8057 6kW left hand drive hardtail with vesc and encoder
2 3 4
Replies
79
Views
23,370
Sattva Ram
S
M
drone pancake motor low reduction mid drive with regen
Replies
16
Views
5,824
Voltron
V
gman1971
How to achieve a reliable high power mid drive.
Replies
4
Views
1,896
motomoto
motomoto
A
100W Mid Drive? - Am I an idiot and other questions
Replies
19
Views
3,290
abecrizer
A
Back
Top