Anyone Running Power THRU the Bottom Bracket?

[CrazyDan]

Having loads yanking from differing angles will cause a twisting force till it equals out (the loads equal out having the same angle). The only way to prevent this is making the forces equal or overpowering the forces till they become negligible.

 

[5-7HEAVEN]

We'll see.

I'm concerned about pulling away from a stop.

 

[Wrench]

Make it a hybrid with an electric front hub

 

[FurryOnTheInside]

We'll see.

I'm concerned about pulling away from a stop.

I do see what you mean. I think.
If you regard the resistance as an insurmountable hill or the moment before the bike is set in motion, then its like being attached to fixed point, like in physics, pulley diagrams, where you'd always draw one end of the rope attached to a fixed point and it'd be assumed that the unbreakable fixed point of attachment actually exists, in a lot of real life situations.
So in the pulling away from a stop scenario you're putting a force through the large sprocket that depends on the radius of that sprocket and not the ratios or the radius of the very small sprocket that provides the force in the opposite direction.

Tbh I'm very not sure about it myself; though I had been working on the assumption that, as the ratios needed are still the same ratios, a more compact chainset all over will lower the torque on sprocket hubs and raise the tension on chains, and vice versa. Larger sprockets all around, with all the ratios kept the same, would raise chain speeds, lower chain tensions, and raise sprocket hub torques.

Confused myself many times.

 

[5-7HEAVEN]

As a teenager, my best car was a 1951 Chevy sedan.
The previous owner had installed a stock 283 V8 engine with an awesome-sounding Corvette cam.
I spent many a night replacing original 6-cylinder transmissions.
I even broke an axle once.
After I sold the car and moved on, it dawned on me that the old Chevy's driveline took a helluva beating and kept on ticking.

If I was more mature, I wouldn't have had to change a single tranny.

And EVERYTHING! broke at a standing stop/start.

I have to respect the 212's torque off the line and at shift points, for the sake of the drivetrain.

And I have to respect its power, or it'll hurt me badly.

 

[5-7HEAVEN]

Years ago, I explored the possibility of running engine power thru the bottom bracket.

I didn't get far, as the fact of two pedal cranks operating independently stymied me.

Now it DOES seem possible.

It's a simple goal, yet complicated as heck.

It's an affordable project.

I'm enjoying the journey tremendously.

Thank you all.
Mahalo for your feedback. It's helped a lot,
and I appreciate it.

LOL, my friend's a sheet metal worker.
He's been very patient, making the chain/belt guards.
There have been many changes to the driveline, in my head.

I told him to hold up, until I finalize the driveline.

 

[FurryOnTheInside]

1k views.

 

[5-7HEAVEN]

Foot pedals turn a 5/8" axle inside a larger, hollow shaft. Both shafts then travel thru the bottom bracket.

Engine torque delivered by a 44t pulley/sprocket spins the large hollow shaft. Power then travels thru the bike's bottom bracket to the other side of the bike. A 24-tooth chainring sprocket bolts onto the same hollow shaft on the right side, and drives the 7-speed freewheel at the rear.

THAT'S the plan.

A simple goal with an extremely complicated assemblage of parts and ideas that were never made to work together.

It strains my brain. I wake up in the middle of the night with a question, or an answer to "What if?!"

I'm enjoying every minute of it!

I wonder how much torsion/ twist the hollow shaft will endure, before it breaks?

The hollow shaft is too thin to machine a keyway onto it

Will the sprockets twist off without keys?

Do I weld both sprockets to the hollow shaft?
Then I can't replace the bottom bracket(BB) bearings.

I wonder how much heat the friction of a shaft spinning within another shaft will create?

Enough to make fire by friction?

Idk.

 

[Chainlube]

I wonder how much heat the friction of a shaft spinning within another shaft will create?

Enough to make fire by friction?

Idk.

You need a bearing between the two parts or it will melt down from friction. The inner (solid shaft) should take all the force from the motor.

 

[CrazyDan]

The inner (solid shaft) should take all the force from the motor.

That wouldn't be possible while still keeping pedals. The motor chain would interfere.