Spur gear retro-direct

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Miles   100 GW

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Spur gear retro-direct

Post by Miles » Feb 10 2009 6:17pm

This one is reasonably simple.

-Two different ratio pairs.

-One ratio pair connected by an intermediate idler reverse on its own shaft.

-Over-running clutch bearings needed on all gears except the idler.

The only additional load for either ratio is the bearing drag of the other - only the gears of one ratio will be active for each motor direction.

I haven't drawn it out, yet, but it works in my head :mrgreen:

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Re: Spur gear retro-direct

Post by natem » Feb 10 2009 6:53pm

Ya.

I think your essentially aiming for:

low gear going backwards and then high gear going forwards. (or visa versa). Is that right?

Bicycles in the 1920's or so were able to do this using a single chain and two freewheels on the rear wheel. Some people have modern versions for the novelty of it. Works very effectively and while it feels awkward it is no big deal pedaling backwards in terms of fatigue or whatnot.
http://kentsbike.blogspot.com/2008/11/b ... cycle.html
http://myspace.voo.be/pcoupard/retrodirect_drive/

But I suppose your already well aware of that.

And you want to do that using just gears? Interesting.

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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 10 2009 7:05pm

Hi natem,

Yes, that's it. The motor doesn't care which direction it's going :mrgreen:

I posted a design for a chain or belt drive retro-direct here:
http://www.endless-sphere.com/forums/vi ... 79&start=0

This spur gear one could be quite compact, and with minimal losses from the redundant ratio....

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Re: Spur gear retro-direct

Post by natem » Feb 10 2009 7:10pm

Do they make spur gears (or whatever) with one-way clutches like they do with freewheels?

I think the technical term is 'sprauge clutch'. Because if so then the design should be relatively simple... You have have two sets of gears, one with a even number of gears so the output shaft rotates in the opposite direction of the motor... then a second set of gears with a odd number of gears so the output shaft rotates in the same direction as the motor. Then put the sprauge clutches so that the motor can only drive the output shaft in one direction, then use the direction of the motor to choose which path to output the power through. :)

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Re: Spur gear retro-direct

Post by GGoodrum » Feb 10 2009 7:11pm

You are definitely going to have to draw this up. Between you and Hal, my head has been on the verge of imploding for the last week, or so. :mrgreen:

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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 10 2009 7:13pm

natem wrote:Do they make spur gears (or whatever) with one-way clutches like they do with freewheels?
Not that I know of.

Yes, Sprague clutch is a type of overrunning (or one-way) clutch.

Yes, it could be done with an active intermediate stage, or as I outlined above.

The idler (which is neutral in terms of reduction) would allow a lot of flexibility in specifying the ratios.

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Re: Spur gear retro-direct

Post by Miles » Feb 10 2009 7:26pm

GGoodrum wrote:You are definitely going to have to draw this up. Between you and Hal, my head has been on the verge of imploding for the last week, or so. :mrgreen:
I'll model it tomorrow, Gary.

It's past my bedtime...... :)

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Re: Spur gear retro-direct

Post by natem » Feb 10 2009 8:45pm

Here is my rendition...

background:
(I know that everybody knows this and I know that you are not stupid, but I am just saying it for the sake of clarification and the description. Just so that everybody knows were I am coming from.)
You know how when you spin you pedals in the wrong direction on a bike they just spin? No power is delivered to the rear tire and you don't go anywhere. That is as long as your bike isn't a fixie or has a roller brake. :) Well that works because you have a freewheel or cassette system on your rear wheel that has a racheting system that only allows power to be driven in the right direction. This allows you to coast on your bike without having to pedal all the time.

So, I guess, one manner of rachetting mechanism is the sprage or sprauge or however you want to spell it. Apparently Wikipedia says these things are common in UK engineering and in automatic transmissions. Something like that.


So here is my version... The black circle represents the input shaft. The yellow is the output.

The goal is to spin the yellow shaft in a clockwise direction.

So there are two gears attached to the yellow shaft. One is the Red gear, and the other is the blue. They are not keyed to the shaft, instead they are pressed onto two sprauges. So that they can spin independently and can only apply power to the yellow shaft in a clock-wise rotation.

So on the black input shaft there are two gears, the Blue one and the Red one. These are keyed to the shaft so that they don't rotate independently... they are fixed to the input shaft.

So when the black input shaft rotates counterclock-wise this causes the Small Red gear on the output shaft to rotate clockwise. This causes the sprague to engage and drive the shaft.
At the same time this causes the Blue gear on the output shaft to rotate counterclockwise. This causes the sprauge to not engage on that gear.

So when the black input shaft rotate clockwise this causes the small Red gear to rotate counter-clockwise and thus disengage.
And, finally, when the black input shaft rotates clockwise this causes the Blue gear on the rear output shaft to rotate clockwise, engaging the sprage clutch and driving the yellow ouput.


So input rotating clockwise == high gear.
Input rotating counterclockwise == low gear.

:D

edit:

I guess the common spelling is 'sprag'. Here is a example of a 'sprag clutch' or 'backstop' in the form of a roller bearing:
http://www.vxb.com/page/bearings/PROD/Kit8181
Attachments
gears.png
gears.png (17.14 KiB) Viewed 3973 times

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Re: Spur gear retro-direct

Post by TylerDurden » Feb 10 2009 11:26pm

Yes, methinks the only difference in what Miles proposes and what Natem proposes is Miles' concept has overrunning clutches on the input shaft: that adds more parts, but reduces friction losses from running the inactive gearset.
Have a Nice Day,

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Re: Spur gear retro-direct

Post by John in CR » Feb 11 2009 2:52am

Natem,

How does odd or even number of teeth have an effect? Also, something seems amiss, re CW or CCW, and/or yellow looks like the input to me or else red gear is overdrive. Don't we want reduction?

John

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HAL9000v2.0   10 kW

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Re: Spur gear retro-direct

Post by HAL9000v2.0 » Feb 11 2009 3:11am

Miles wrote:... intermediate idler reverse on its own shaft...
You are talking about chains and sprockets?
This one you should draw :? :?:

IF gears THEN ok.

The only problem I see is transfering torque over bearing housing without milling the key.

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HAL9000v2.0   10 kW

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Re: Spur gear retro-direct

Post by HAL9000v2.0 » Feb 11 2009 3:22am

But there is a solution...
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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 4:17am

HAL9000v2.0 wrote:
Miles wrote:... intermediate idler reverse on its own shaft...
You are talking about chains and sprockets?
This one you should draw :? :?:

IF gears THEN ok.

The only problem I see is transfering torque over bearing housing without milling the key.
Yes, spur gears, Hal.

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Re: Spur gear retro-direct

Post by HAL9000v2.0 » Feb 11 2009 4:25am

It can be made quite compact. But still you have to have some primary reduction or you want to go on some large pulley/sprocket on wheel?

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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 4:37am

natem wrote: So here is my version...
Yes, that's more or less what I described.

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 4:38am

HAL9000v2.0 wrote:It can be made quite compact. But still you have to have some primary reduction or you want to go on some large pulley/sprocket on wheel?
Yes, I envisaged this as second stage.

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Re: Spur gear retro-direct

Post by HAL9000v2.0 » Feb 11 2009 4:48am

Now I understand, basicy it is a simmilar idea like mine but you put three gears instead of two pulleys and a belt.
If the primary drive is also gears it will be like small gear box. :lol:

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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 5:01am

HAL9000v2.0 wrote:Now I understand, basicy it is a simmilar idea like mine but you put three gears instead of two pulleys and a belt.
If the primary drive is also gears it will be like small gear box. :lol:
Yes :mrgreen:

Gears are too noisy for primary, though, IMO....

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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 6:42am

For ratio differences up to about 50%, you would use an idler (passive) gear as intermediary on the second ratio.

For greater ratio differences, the intermediate shaft of the second ratio could be active and have an input and output gear on it.

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Re: Spur gear retro-direct

Post by natem » Feb 11 2009 12:12pm

Miles wrote:
natem wrote: So here is my version...
Yes, that's more or less what I described.
Ya. I made my version just trying to figure out your concept. So it's definitely a variation on your idea. :)

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 12:38pm

It's not really my idea, I'm sure just about every permutation of these has been done in the past, anyway :)

eg: http://www.endless-sphere.com/forums/vi ... 30&start=4

and HAL's is a similar design: http://www.endless-sphere.com/forums/vi ... a&start=67

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Re: Spur gear retro-direct

Post by natem » Feb 11 2009 1:05pm

This is a very cool idea and I think it's actually very do-able...

If you take the simpliest design, how much do you suppose would it cost to build?

Hundred dollars in machine shop, 30-40 bucks for the backstop/sprag bearings, 50 dollars for the big spur gears, 20 dollars average cost for the smaller gears, then you have the output shaft and it's bearings and then the external sprocket that would make up the final drive ratio to the wheel.

Probably ~300-400 dollars for a one-off build. Does that sound about right? This is a mostly uneducated guess.

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 2:21pm

This is a schematic for a version with an active intermediate stage.

Green is input shaft. Blue is output shaft.

Overrunning clutches on input and output gear pairs.

Gears sizes are only illustrative
Attachments
Spur gear retro-direct 2.jpg

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Miles   100 GW

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Re: Spur gear retro-direct

Post by Miles » Feb 11 2009 2:28pm

3d PDF - Click on image to activate model:
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Re: Spur gear retro-direct

Post by HAL9000v2.0 » Feb 11 2009 3:45pm

Nice one. These two small gears ca actually be one wider gear. Big ratio difference can be achived with this one...


Now it will be nice to open a new topic and to ask admin to put all of the types in it so we can further discuss on pros and contras...

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