Speed Synchronizing 1

[WADMW]

I'm hoping to combine the power from two cycling machines to generate a single output.
What do you think is the best way to combine two shafts, in line (coaxial) or parallel, rotating at two different speeds to get a single output? Will a power split device do the work for you, or is there any other mechanism to achieve this?

 

[zeusfaber]

The classic approach is probably to back-drive a differential.

A.

 

[WADMW]

Is it possible to back drive a differential? You'll have to change the whole configuration in order to do so right?

 

[RolMec]

You could try a three shaft / twin drive configuration of a planetary gear.

RSVP

 

[WADMW]

Yeah, thats a power split device...

 

[RolMec]

Actually, I had sthg like this in mind:

http://www.finnoygear.no/en/en_tomotor.html

or this:

http://www.industry.siemens.com/dri...le-output-marine-gearboxes/Pages/Default.aspx

or this:

http://www.allengears.com/html/Flender-Graffenstaden-twin-input-single-output-reverse-engineered.php

or then even this, a parallel shaft spur gear solution:

http://www.eisenbeiss-industrial-gear.com/industrial-gearing-solutions/twin-drive-gear-system/

...as you don't mention torque or power requirements...
disclaimer: no relation to either one of these comp.


RSVP

 

[3DDave]

RolMec - he's been asking about joining the efforts of bicycles, so maybe 2hp peak, 1/4 hp per bike on a typical long duration, highest-output.

Having to explain how a differential works makes the rest of this effort seem impossible to accomplish.

 

[RolMec]

@ 3DDave: thank you for ;-)backdriving an erring "notnativespeaker", I just couldn't realize that cycling machine would mean bicycle.
;-) if I read "machine", then in my mind there's always at least 500 pounds of iron involved in further cogitation..
I do hope that your second remark does not imply another verbal stumbling or meaninglessness from my part. If so, pls. accept my apology.

However, on the topic:
For a bicycle (or two bicycle inputs), it is as mentioned in my first post: one may use a twin input planetary gearbox. It's done e.g. for e-bikes to combine pedaling power and electric drive, you could have a look at the Swissbee of Dolphin E-bikes.
To backdrive a differential will not work (for long), as the (even if very small) differences in the input speeds cannot equalize if both shafts are rigidly driven.

RSVP

 

[WADMW]

I was actually referring to a cycling machine and not a bicycle.

 

[itsmoked]

You aught to describe -in a LOT more detail- to this international forum as to what YOU call a cycling machine because I'm pretty sure each and every reader of this thread is imagining something different.

What are the speeds?
What's the approximate HP
What kind of differential speed?
What are you expecting to do with the combined power?




Keith Cress
kcress -

http://www.flaminsystems.com

 

[3DDave]

Since three previous questions were specifically about bicycles and this was another about cycling machines, the difference wasn't clear.

Google cleared it up for me.

https://www.google.com/search?q=cycling+machine&ie=utf-8&oe=utf-8

Of course, if what Google found is what you meant than that's basically a bicycle.

Ask better questions, get better answers.

 

[gruntguru]

"To backdrive a differential will not work (for long), as the (even if very small) differences in the input speeds cannot equalize if both shafts are rigidly driven.
I may be misunderstanding what you are saying here but I believe back-driving a differential is exactly the machine required to sum the power from two shafts. The disadvantage is the two inputs must always have matched torque (or a fixed torque ratio to each other). For this reason alone an electrical summer (two generators) is a better option.

As I said in the other thread, if this is a case of adding the power from two pedaling humans, the best way to do it is give each human a derailleur and cassette to regulate their own pedaling speed.


je suis charlie

 

[zeusfaber]

Ouch. I've woken up this morning with a systems engineering head on (might be a hangover instead - too early to tell). Largely inspired by Gruntguru's last post.

The OP's requirement is to combine power from two shafts rotating at different speeds to get a single output (assume this is on a third shaft, although not actually stated).

What isn't specified yet (and needs to be) is how the whole system - and especially the load - reacts to changes in load and input.

Cyclists deliver a very unsteady torque (when the cranks are vertical, there's no bodyweight involved - it's limited to what you can react through the toe-straps and the handlebar). They prefer to control their power output by varying torque (how hard they push each time) - though can only do so within a narrow band of speeds.

Loads can be roughly divided into constant speed (if you try to drive them harder, they initially react back a much greater torque) or constant torque (drive them harder and they just go much faster for much the same torque).

Cyclists are used to working against constant speed loads. Constant torque (like riding on a stand against a brake with no flywheel) is really uncomfortable.

We've been looking at two fundamental classes of power combiner.

Common input speed. These are mechanisms where the two inputs run at the same speed, but the way the load torque is shared between them can vary - for example the two shafts physically welded together (like in a pedalo) or multiple chain drives converging on the same shaft (like on a Tandem - the combining shaft needn't always be the output shaft). Gruntguru's suggestion of giving each cyclist a set of gears to allow them to match to the common input speed is a variant on this theme. These mechanisms load-share relatively well when driving constant speed loads, but magnify the problems with constant torque loads (how many times have you had the tops of your feet clouted by the pedals on a side-by-side pedalo?)

Common input torque. Mechanisms in this class allow the input speeds to vary independently, but both will see the same proportion of the load torque all the time. Examples are the varying arrangements of planetary gears (including differentials) and dc motor generator links. These mechanisms load-share better with a constant torque load. Load balancing against a constant speed load takes cognitive effort.

There's one more distinction - input synchronism. On a tandem, both sets of pedals are at TDC at the same time, so the riders are producing peak torque at the same time. With independent gearing or if you're feeding into a common torque system, that won't be the case and you need to introduce flywheels (and consider the impact of those on the load) if you want the riders not to interfere with each other. Interestingly, with a common input torque combiner, the effect on Rider A when Rider B stands on the pedals is the exact opposite of what you get with a common input speed combiner.

So which mechanism is best? It depends...

A.