I have a general question about mounting a sprocket

[seanreit]

I see a picture like the one attached, and for the life of me, I have no idea how the sprocket is attached to the wheel, does anyone know of a thread that discusses this in great detail? Please don't come back and say "welded", I want to know the process, and I don't know how to weld, so I'm going to need to be able to tell a welder how and where I want it attached.

My goal here is to be able to take a kids bike with 16" wheels and get a sprocket welded to the front wheel like in this picture.

Also, where do I get a sprocket like the one in the picture?

Thanks,

 

[spinningmagnets]

Several ways, check the links below for some ideas. The sprocket looks like its from TNC, but by adapting a disc-adapter that accepts chainrings, you can easily and cheaply change the tooth-count in the future. If you make a disc-adapter from a skillet bottom, make sure the skillet is the type that has a flat machined surface (some are slightly rounded).

If you decide to make a disc-adapter, hog out the central hole in roughly the center (keep enlarging the hole until the disc sits flat against the freewheel). Set the freewheel over the hole and draw where the teeth are. Drill at least 3 holes through the disc so that bolts can sit in the valleys of the sprocket teeth.

Once you have reached that point, put the entire assembly back in the forks (bike upside-down), and while resting the side of a felt marker against the forks to steady it, apply the tip of the marker to the disc to mark a circle that is perfectly concentric with the axle. The diameter that it should be marked at, depends on the Bolt-Circle-Diameter (BCD) of the chainring you want to use.

To start with, grab a free one that is the biggest ring on the pedal-axle of a trash-day road bike. About a 47-tooth is fairly common. (perhaps carry a cordless drill in your car to remove chainring?)

http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=7192&start=15#p178174

http://tncscooters.com/partsdb.php?type=ES

http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=9855&start=0

 

[John in CR]

Why weld or go to all the trouble of adapting to a small sprocket freewhee? Right side sprocket is easy because the direction of forward force screws a threaded freewheel on. That means you can use a cheap rear hub ready for a threaded freewheel. Then you use a freewheel ready for a bolt-on sprocket like this for $7 http://tncscooters.com/product.php?sku=203170. TNC also has the #25 sprockets and chain that you'll need. If you're looking for heavy duty and higher power handling with serviceability and long life, then track down the equivalent of the above in a White Industries freewheel which will set you back about $80.

 

[seanreit]

I'm imagining the front wheel of a bike such as this one: http://austin.craigslist.org/bik/1887452008.html

with a sprocket mounted to the side, do you know of any threads in that direction?

I don't want to go with any of the hub motors because I already have decided to go with a treadmill motor.

 

[seanreit]

Or this, :http://austin.craigslist.org/bik/1891060242.html

using the front wheel and fork only, mounted to a tubular frame as a single wheel pusher

 

[spinningmagnets]

Without some type of freewheel in the drive-line somewhere, the motor will cause a very strong drag on the bike when there is no power applied to it.

Even if you plan to apply power all the time, the ability to coast on a downhill will save some battery power. Plus, the occasional dead battery means you will have a very hard pedal-job to get home. Best of luck on whatever you choose...

 

[seanreit]

Without some type of freewheel in the drive-line somewhere, the motor will cause a very strong drag on the bike when there is no power applied to it.

Even if you plan to apply power all the time, the ability to coast on a downhill will save some battery power. Plus, the occasional dead battery means you will have a very hard pedal-job to get home. Best of luck on whatever you choose...

Ah, so glad you mentioned that, had not even considered that. Obviously I need to rethink what I want. I desperately want to use recycled parts to the extent I can, and I know I can get treadmill motors for next to nothing in Austin, cause they are constantly being given away in the free section of craigslist. I was thinking a child's bike would be the best idea, but I don't think their back wheels are free wheel.

 

[John in CR]

Recycled parts are fine. The hubs on the rear wheels have threads that the freewheel screws onto. You probably need a bigger sprocket than is on a typical freewheel, so you need the $7 freewheel I linked before. The other option is to open up the hole in the center of the sprocket to fit over the used freewheel. You can then either use bolts to attach the larger sprocket to teeth of the freewheel, or tack weld it.

It depends on how much of a reduction you need from the motor to the wheel sprocket. It's typically a big reduction which creates the need to use the smaller #25 chain, so you can use a small sprocket at the motor, since very small drive sprockets for bike chain don't exist. With the #25 chain, 9-10-11 or 12 tooth drive sprockets are cheap and available, as are 60 on up to 90+ tooth wheel sprockets that will bolt directly to the freewheel I linked above. If you can do you own metal working then anything is possible, but if you have to pay for it, then some of the cheap solutions for pocket bikes and scooters have it worked out for you that will be cheaper and easier in the long run.

 

[seanreit]

Thanks john, can you recommend a site that sells a sprocket that bolts to the free wheel you linked to? For use with the 25 chain? And will that site also sell a sprocket for the treadmill motor?

 

[amberwolf]

I was thinking a child's bike would be the best idea, but I don't think their back wheels are free wheel.

Some (perhaps many) do freewheel, with coaster brakes. They usually have a 16T-18T sprocket already on the right side, which you can use to bolt the other sprocket to (perhaps directly without an adapter, if it has the right hole-spacing).

Also, you could relace a regular bike's hub into a child's bike's rim, using the spokes from that rim, if the hubs are the same flange diameter and width (and same number of holes).

 

[spinningmagnets]

Lift the rear of the bike and attempt to spin the rear tire in both directions, if the chain doesn't move in one of the directions it has a freewheel.