Front sprocket mid-drive

[ChapinB]

Would you need a freewheel on the crank with a drill? Pedaling with the drill off seems like a real pita, literally.

 

[lnanek]

There's tons of free acoustic bikes laying around on trash days here. Particularly kid's bikes that have been outgrown. If I had to make a jack shaft I'd adopt one, cut off the bottom bracket, and weld it to the target bike. Then you just need to use 2x chainring for a jack shaft.

 

[Auroa]

Brushless motors...Limiting a motor to 500rpm when it wants to spin at 2700

It's never been brushless? And it's never been 2700?

Would you need a freewheel on the crank with a drill?

Freewheel cranks aren't available, I don't think.

 

[ChapinB]

My motor is 120kv. At 6s, it wants to spin ~2700rpm under no load. Although I have it limited to ~1000rpm to avoid getting my shins torn up from a runaway crank. At a 6:1 ratio, my motor would need to be limited to around 500 rpm depending how speedy your legs are. Used as an example.

Freewheel cranks exist. Not terribly common, but they exist.

 

[Auroa]

Freewheel cranks exist. Not terribly common, but they exist.

I'll ask but like, if it's not common in yours how would I know it exists in Egypt?

 

[ChapinB]

I dont know what is available at your location. I have no idea what you can locally source or how ordering from another country, like china, works. But they exist in the world is my point. It is up to you to source them in your location.
A freewheel is not needed with a simple setup like your diagram. The cranks turn with power, but you get used to it quickly. Pedaling with the motor off, the motor resistance is not large. Its easy enough to remove the chain on my setup if I need to.
With a gearbox, like a drill, it might have significant pedaling resistance. Not sure.

 

[Auroa]

A freewheel is not needed with a simple setup like your diagram. The cranks turn with power, but you get used to it quickly. Pedaling with the motor off, the motor resistance is not large. Its easy enough to remove the chain on my setup if I need to.

We're on the same page here, the variable power input (especially with a pot if i get one) can adjust the rate I'd like.
A lot of the issues and viability just have to be proved when I've gotten to it, speaking of; what should I opt for to attach the motor to the frame?

 

[ChapinB]

I used a bike stem - in particular the part that clamps over the handlebars to mount the bars to the stem. Along with a 3d printed part to mount to my downtube. A handlebar is the same diameter as my downtube. I can upload the file if needed.
Others have used bent or machined aluminum, or u-bolts.
Look at FZBob's thread. It shows a handful of methods.

 

[Auroa]

Oh, Ubolt round the stem and then the bracket if I understand correctly?

 

[ChapinB]

Yes. I cannot locate who posted that at the moment for a photo.

 

[wturber]

My motor is 120kv. At 6s, it wants to spin ~2700rpm under no load. Although I have it limited to ~1000rpm to avoid getting my shins torn up from a runaway crank. At a 6:1 ratio, my motor would need to be limited to around 500 rpm depending how speedy your legs are. Used as an example.

Freewheel cranks exist. Not terribly common, but they exist.

Food for thought.

 

[wturber]

Would you need a freewheel on the crank with a drill? Pedaling with the drill off seems like a real pita, literally.

FWIW, there are old Schwinn bikes that had "new" index shifting that had cranksets with a freewheel. That would be one cheap way to get a freewheel on a crank.

 

[ChapinB]

I had one of the schwinn bikes, was a fun novelty, shifting while pedaling backwards or coasting. Cleaned it up and sold it, but wish I kept the crankset in hindsight.

This particular bike was built to be light and low powered. Alternator would ruin that. Iv already got a big piggy ebike for when I want it. But might be a cheap alternative for someone and probably about the right kv too.

 

[lnanek]

If going with a jack shaft, maybe one could be made using a hub from an old abandoned rear wheel. That would have a freewheel integrated.

If using jack shafts to get more reduction, might also be able to skip the chainwheel entirely and go straight to the rear wheel. Say via a cog screwed on where the brake disc usually goes on the left. Feels like the rear hub freewheel would then prevent the motor from turning the pedals and endangering shins.

 

[ChapinB]

If using jack shafts to get more reduction, might also be able to skip the chainwheel entirely and go straight to the rear wheel. Say via a cog screwed on where the brake disc usually goes on the left. Feels like the rear hub freewheel would then prevent the motor from turning the pedals and endangering shins.

A member here did a middrive directly to the rear hub, although I dont know how it worked out. I remember it was belt driven with the motor on the rear stay. Could put a huge rear sprocket on there, getting a good ratio without having a 2nd chain near your legs or a motorized skin kicker.

 

[wturber]

FWIW, I used a white industries freewheel and some adapters to get my front crank to freewheel. While I'm sure a person can get used to it, I just decided I didn't want to deal with a motor driving cranks and pedals where my feet would be.

There is a freewheel on the motor and on the chainrings - so either can power the rear wheel independently of each other or in tandem with each other. This also allows me to use a torque sensing bottom bracket since the chainring freewheel keeps the motor does from applying torque to the BB spindle.

I'm aware that these parts may be either too expensive or hard to source in other parts of the world.

Here's an example of the Schwinn freewheel currently being sold on ebay. Of course, international shipping could be an issue.

https://ebay.io/m/U4iuoQ