Another way to take drive through the normal chainline

Discussions related to motors other than hub motors.
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Another way to take drive through the normal chainline

Postby bobc » Tue Apr 19, 2011 2:55 pm

I'm going to make one of these, it's just too cool not to.....
OK this leads on from a post miles made with a patent for some harmonic "gearboxes".
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The picture is an assembly that replaces the chainring on the cranks; pedal drive enters via the "sun wheel", electric drive via the 2 outer "planet carrier" wheels.
The output ring rests on a triplex chain which sits in the middle.
Why are the planet wheels in pairs? because it's not possible to tension the triplex chain adequately with single planets; - I don't know if anyone has ever done this "binary planet" chain drive harmonic gearbox before... I had to have 3 sets of planets as these are what locate the big output ring.
The harmonic gearbox part gives about 14:1 reduction; with a further large (up to another 15:1) reduction available to an RC motor outrunner, an effective 70rpm cadence on the pedals would be matched by a 70*14*15 rpm motor - that's 15k rpm: the thorny old issue of getting sufficient reduction to the cranks is solved!
The output reacts against the pedals, so this would not be suitable for much over 500W; however as the bike cannot go without pedal pressure, it may meet the EC "pedelec" requirements (?)
I'll get the dxf's to the laser cutters over the next few days - I just have to decide whether to go stainless or mild: - I'm going to have to tap some 3mm holes & don't fancy that in stainless.....
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Re: Another way to take drive through the normal chainline

Postby TylerDurden » Tue Apr 19, 2011 3:10 pm

Neat idea! :D
Have a Nice Day,

TD

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Re: Another way to take drive through the normal chainline

Postby recumpence » Tue Apr 19, 2011 3:14 pm

This is effectively like a differential. Yes, the cranks will try to rotate backward when the motor is running, on this setup. That is a definate problem because if you try to pedal with the motor running, you will be pedalling much harder than when the motor is not running. Also, if the motor is off, much of your pedal energy will be put into back running the electric drive.

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Re: Another way to take drive through the normal chainline

Postby bobc » Tue Apr 19, 2011 3:44 pm

For more powerful setups you could put in a ratchet (one of those spring clutches??) to stop the pedals from turning backwards -
typical of Matt to worry about shoving 4kW into it ;^)
re: the motor turning when you pedal, I was reckoning that the "cogging" torque of a stationary outrunner would be enough to prevent that (coupled with the huge "gearing up" ratio and the somewhat esoteric way a harmonic gearbox works - I was thinking it might be reluctant to back drive, rather like a worm drive; only way to find out is to make one!!!)
I'm interested in opinions regarding legislation with this - does it qualify as a pedelec?
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Re: Another way to take drive through the normal chainline

Postby spinningmagnets » Tue Apr 19, 2011 4:35 pm

This is a really great idea, because I don't have a problem adding a belted single reduction to an RC motor, however it can get exotic if you want a belt and pulleys over 4:1 for the primary reduction, which are affordable off-the-shelf.

There may be some development stumbles along the way, but I feel this has potential, and is definitely worth playing with...
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Re: Another way to take drive through the normal chainline

Postby Miles » Tue Apr 19, 2011 5:03 pm

I'm glad you decided to have a go at this, Bob :D
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Re: Another way to take drive through the normal chainline

Postby recumpence » Tue Apr 19, 2011 5:11 pm

I think it is cool, don't get me wrong. I just wanted to point out something that may not be apparent on initial observation.

There are a few ways to prevent back-running and other issues. They merely add complexity.

I think it is a cool way to mechanically circumvent the pedalec issue. Of course, you do not need to pedal to use it, you merely have to hold the pedals stationary. And, if you use some kind of lockout, to prevent back pedal affect of the motor running, you will eliminate the pedalec affect as well.

Hmm, it is worth a try, though. This kind of thing is impossible to evaluate fully without just building one to test.

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Re: Another way to take drive through the normal chainline

Postby recumpence » Tue Apr 19, 2011 5:12 pm

bobc wrote:typical of Matt to worry about shoving 4kW into it ;^)


I was thinking 8kw. :wink: :mrgreen:

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Re: Another way to take drive through the normal chainline

Postby Miles » Tue Apr 19, 2011 5:14 pm

:mrgreen:
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Re: Another way to take drive through the normal chainline

Postby bobc » Wed Apr 20, 2011 12:50 pm

And it's started - I just bought a 165mm 48spline 19mm crank axle and enough 8mm triplex chain for 2 systems.
Dammit that's one poorly finished ebike, a pusher trailer with incorrect gearing, and a mountain bike with reversing gearbox half done...
I'm trying to pursuade my mate that his recumbent (which he never uses) needs the binary planet harmonic gearset.......
Somebody stop me from starting any other projects!!!!!
Is there a data store on here where I can put drawings in case anybody else wants to copy the thing? - dxf files for the laser cutters and pdf engineering drawings?
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Re: Another way to take drive through the normal chainline

Postby Miles » Wed Apr 20, 2011 1:02 pm

bobc wrote:Is there a data store on here where I can put drawings in case anybody else wants to copy the thing? - dxf files for the laser cutters and pdf engineering drawings?
Yes: http://www.endless-sphere.com/forums/vi ... =28&t=7832
You'll need to Zip compress the DXFs
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Re: Another way to take drive through the normal chainline

Postby bobc » Wed Apr 20, 2011 1:22 pm

OK it looks like you don't upload the files to this site, you just post hyperlink to the file on (say) your own website(?) - (thanks BTW ;^)
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Re: Another way to take drive through the normal chainline

Postby Miles » Wed Apr 20, 2011 1:25 pm

No, you can upload the files as attachments to a post. That's how they are in that thread.

Thank you for your contribution, Bob!
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Re: Another way to take drive through the normal chainline

Postby mdd0127 » Wed Apr 20, 2011 4:20 pm

I haven't tied it here but on other forums, you can just put ".txt" at the end of your file and it will trick the system into accepting it. People downloading it just have to rename the file and include.dxf at the end to get them to open in their CAD program.

I'm not sure if this messes stuff up or is the best way to do things but I have seen it done on other boards...maybe even here.
Turn it OFF!!!

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Re: Another way to take drive through the normal chainline

Postby Miles » Wed Apr 20, 2011 4:25 pm

mdd0127 wrote:I haven't tied it here but on other forums, you can just put ".txt" at the end of your file and it will trick the system into accepting it.
Yes, that would work too.
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Re: Another way to take drive through the normal chainline

Postby bobc » Thu Apr 21, 2011 7:30 am

OK I just spent £91 on bearings...... I had a couple of minor redesigns to do last night:
1) triplex chain loop must (obviously) have an even number of links.... DOH!!!!
2) means to grip the crank axle shaft considering it is far too hard material for me to drill it....
So [1] means I now have a 78 link loop - gear ratio 13.5:1
2) I will grind a couple of grooves in the axle & pop a 3mm ball bearing in, locating a matching bump in the sun sprocket. The whole will be squeezed on each side by tapered inserts locating the planet carrier sprocket bearings. phew. So there will be a couple of mechanical keys AND a couple of taperlock inserts - should be sufficient I reckon.
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Re: Another way to take drive through the normal chainline

Postby bobc » Tue Apr 26, 2011 6:49 am

And... minutes before dropping the dxf's at the laser cutters, I've decided to change it all....
1) there's no need for triple planet with the binary planet system - I can use 2 and get a better reduction ratio
2) I don't like chains for very high speed work as they throw off all their lubricant....
So redesign (if clearances allow) will have dual binary planets, 76 tooth sun and 80 tooth ring, and a pair of 5mm HTD belts driving it (9mm wide)
I'll put a drawing up tonight ;^)
(note the harmonic chain loop is not moving fast so it should stay lubricated.....)
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Re: Another way to take drive through the normal chainline

Postby Miles » Tue Apr 26, 2011 6:54 am

bobc wrote:................., I've decided to change it all....
I usually do that just after I've ordered the stock.... :)
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Re: Another way to take drive through the normal chainline

Postby bobc » Tue Apr 26, 2011 2:14 pm

OK here's the revised assembly - now with toothed belt drive...
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The weird cutouts in the planet carriers are so I can grip it in my 3jaw chuck
Unfortunately the belt drive starts to make it a bit wide, but I should be able to make it work.... (I hope).
I'll get the order into the laser cutters tomorrow ;^)
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Re: Another way to take drive through the normal chainline

Postby Miles » Tue Apr 26, 2011 2:27 pm

8)
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Re: Another way to take drive through the normal chainline

Postby bobc » Sat Apr 30, 2011 4:19 pm

Progress - a full set of bearings arrived today; I got the crank axle the other day & have made & rivetted the triplex chain loop.
The dxf files are at the laser cutters (should get the parts next week).
I went for stainless for the sun and ring gears, mild steel for the others: I'll get them zinc plate/gold passivated after machining for a bit of bling...
An unexpected expense was the cranks - cheapest I could find was £69 a pair - OUCH
Because this reacts back through the pedals, I'm going for a smaller motor/ESC setup (I had earmarked a rather large motor for it - but it actually lends itself more as a "performance improver" than an out and out electric bike drive) I think I've persuaded my mate Rich to be the guinea pig with his recumbent... watch this space ;^)
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Re: Another way to take drive through the normal chainline

Postby Whiplash » Sat Apr 30, 2011 10:33 pm

Awesome! So what kind of ratio can you get with this? I am anxious to see the finished product!
Power is a fascinating thing, the more you have, the more you want, but the real power is having the restraint not to use it all at once...............Um...Yeah..

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Re: Another way to take drive through the normal chainline

Postby bobc » Sun May 01, 2011 6:03 pm

Hi Whiplash,
the present design is 19:1 down from the toothed pulleys to the big ring; it should be possible to get a further 10:1 or so from the motor. The pedals are geared down by 5% to the big ring, but that is a big ring with 62 teeth. So as a bike it is probably geared slightly higher because of the big ring. I should get the lasered parts on Wednesday; I do have some other bits to make on the lathe - I'll make a start tomorrow ;^)
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Re: Another way to take drive through the normal chainline

Postby Whiplash » Mon May 02, 2011 10:19 pm

Interesting! So what about pedal cadence? Will it be really high or low due to this setup? What about freewheeling? Will you need to pedal or can you coast while the motor is running?
Power is a fascinating thing, the more you have, the more you want, but the real power is having the restraint not to use it all at once...............Um...Yeah..

The harder you work.....The luckier you get!!

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Re: Another way to take drive through the normal chainline

Postby bobc » Tue May 03, 2011 8:16 am

The pedal cadence/gearing is an interesting compromise requirement. At the moment I'm thinking that the motor should supply only enough torque that can be comfortably held by the cyclist, so more motor power will be translated to higher speed (electrical) in a given gear. Gearing for the human is pretty much unchanged. The user can pedal at whatever cadence they want - their input is added to the electric motor input, by way of adding directly to the speed.
If the cyclist allows it, the electric motor will power the pedals backwards rather than the bike forwards.... Opportunity to fall over while frantically backpedalling, or repeatedly bash your shins.....
BTW I just got a very nice set of lasered parts for 40 notes - I forsee an evening on the lathe...... Oh and I've reduced the width overall by 6mm now I've looked at the real thing rather than the CAD model: - you can't beat hardware....
Stop press - I put the wrong number of teeth on the sun gear. Pillock. Replacement should be ready this week....I'll replace the downloaded drawings (eventually....)
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